Magical Mount Fuji

The story begins with Japan’s iconic volcano. Mount Fuji has become the poster child of volcanism – it is what every volcano strives to be. This is the most climbed mountain in the world. The spring-time view of Mount Fuji framed by cherry blossom is the very emblem of Japan. The reflection of Fuji is printed on the backside of the 1000-yen bank note. Wedding ceremonies are held at the temple at its summit. The summit is Japan’s highest point. How did such a perfect volcano form?

Mount Fuji is where the Pacific goes to die. The western half of Japan is continental by origin, at one time part of the Asia. The eastern half is younger, with volcanic arcs adding new land and expanding the nation towards the sea. Out in the ocean is the subduction zone where the oceanic plate sinks into a trench and dives below the land. Behind Japan, the Sea of Japan has opened. It has left Japan as an island fighting trench warfare with the ocean, while protecting the continent behind it. The conflict involves earthquakes and volcanoes, whilst the multitude of hot springs are signs of the heat of the battle. This post is about a four-way battle for the heart of Japan, centred around its very own Lonely Mountain with the Five Lakes.

Mount Fuji

As the crow flies, it is 100 km from the centre of Tokyo to Mount Fuji. Driving to the slopes will take you 2 hours (do be aware that the access roads can be closed to private cars during the busy season), or you can take public transport. There are four main trails up the mountain. Each trail is divided into ten stations. The road or bus will take you as far as the 5th station, and the main climb is from there to the top. The summit, at 3776 meter, is the 10th station. The climb is on well-trodden paths and is of only moderate difficulty. For ease of access, there are separate paths for the ascent and the descent. The altitude is considerable, though, and you will find yourself short of oxygen.

The trails can be busy: a quarter of a million people climb it each year – this number has been counted at the 8th station. But the climbing season is short , and all those people are packed into the short period from July to early September. It is very much a community crowd activity, part of Japan’s social fabric. (However, until 150 years ago women were forbidden from climbing the mountain.) During the peak of the holidays, mid August, expect walking traffic jams. If you feel tempted to go for the quiet time outside of the climbing season, don’t. There will be snow and high winds, and the mountain huts (and the trails themselves) are closed. Only the climbing season is snow free. The climb up takes anywhere from 5 to 8 hours, also depending on which trail you take. The walk around the summit crater to the actual summit takes an hour. The return is 4 to 6 hours. To be on the summit at sunrise (4:30 am) requires booking a sleeping place in a hut. In fact, this is recommended for any trip to the summit. Remember to carry money (nothing is free (or cheap), including the emergency oxygen). Wooden walking sticks can be purchased at the 5th station: they make good memorabilia afterwards.

One of the famous 36 views of Mount Fuji, by Hokusai

Fuji’s fame comes both from its location in Japan’s heartland and from its near-perfect shape. Hokusai’s 36 views of Mount Fuji are an excellent example of how Japan’s art is dominated by the beauty of this volcano. But beauty requires maintenance. Mount St Helens used to have the reputation of being the Fuji of America. How different it looks now, after the destructive eruption. But soon, probably within centuries, it will rebuild its cone, resurface its flanks, and re-enter the volcano beauty contest, the ultimate Miss World. Ragged volcanoes are a sign of erosion, when erosion wins out and flank collapses leave holes that do longer get filled. Age builds character but not beauty: a symmetric mountain is a sign of youthful activity. Fuji clearly must be a regular eruptor, an applicant of frequent volcanic make-up. Indeed, it has had two major eruptions in written history.

There are hidden surprises in this familiar volcano. Fuji is actually a conglomerate of five volcanoes, three of which can be recognized in the landscape. On the northern slope, 7 km from Fuji, there are outcroppings of an older volcano, called Komitake. Underneath Komitake lies a still older volcano, buried by Komitake, called Sen-Komitake (meaning ‘before Komitake’). The extinct Ashitake volcano, 20 km southeast of Fuji, forms a deeply eroded but recognizable hump in the landscape. (This is a distant member of the Fuji family and perhaps is not directly connected.) Ashitake (ojiisan) is the oldest, and was active around 400,000 years ago. Sen-Komitake started erupting around 270,000 years ago. It ended with a series of explosive eruptions 160,000 years ago. After this self destruction, the new Komitake grew until is ceased erupting about 100,000 years ago. Now another volcano took over, Ko-Fuji. This new volcano had an explosive flank collapse about 18,000 years ago. Following that collapse, modern Fuji (called Shin-Fuji) arose just west of the old summit and eventually buried its predecessor.

The next surprise is that this perfectly symmetric volcano actually has a severe case of acne. The flanks are covered with 100 parasitic cones and craters. Beauty rarely survives a look with a magnifying glass.

The final surprise lies in the magma. Eruptions in and around Mount Fuji have mainly produced tholeitic basalt. Basalt is not common in Japan, and there is clearly something different about Fuji. Ashitake was andesitic, a common lava type of Japan. But each of the later volcanoes of Fuji started with effusive basaltic eruptions, over time evolving towards explosive andesite/dacite eruptions after which the reset button was pressed and a new volcano took over with basaltic output.

The current volcano, Shin-Fuji, started with voluminous basaltic eruptions between 17,000 and 8,000 years ago. After a quiet interlude with less activity, a mix of large explosive (pyroclastic) and effusive eruptions took place between 5,500 and 3,500 years ago, both from the summit and the flanks. By the end of this phase, the mountain had reached its current height. 2,900 years ago there was a major flank collapse with a land slide volume of 1 km3. It is not known whether this was volcanic or was triggered by an earthquake. Now a series of summit eruptions followed, the last one of which was 2,200 years ago. Since that time, Fuji has been less active, with two major eruptions and 8 small eruptions, all on the flanks.

The two major eruptions of the past 2000 years were a large effusive eruption in 864 and a plinian explosion in December 1707. The 1707 eruption was triggered by an earthquake, not just any earthquake, but this was the Great Hoei earthquake. It had an estimated magnitude of M8.6 and came only a few years after the ‘minor’ M8.2 Genroku earthquake on 31 December 1703. These huge earthquakes are another aspect of Japan, and they can apparently affect Fuji’s magma chambers.

The 1707 eruption came 7 weeks after the major earthquake. Volcanic rumblings had started already in February 1704, suggesting the first trigger was the 1703 Genroku earthquake. Mount Fuji is thought to have two main magma chambers, a dacitic one at 8 km depth and a basaltic chamber at 20 km. Models suggest that the deeper chamber was affected by the quakes, and that after the first event magma may have risen from there to the shallower chamber. This pressurised the upper chamber and after the second jolt it exploded. Between 16 December 1797 and 1 January 1708, there were three main explosions. Together they amounted to a VEI-5 eruption of about 1.6 km3 of ash and tephra. The ejecta covered a wide area which included modern Tokyo, severely affecting the local agriculture. The eruption left three considerable dents in Fuji’s flank, at altitudes of 2100 to 3000 m. The largest of the craters is 1 km across. The eruption produced no lava, but magma accumulation under the surface created a notable bump which nowadays is called Mount Hoei. (Hoei is the name of the era from 1704 to 1711. Genroku is the name of the preceding era.)

An atmospheric non-eruption at Mount Fuji

The other major historical eruption started in June 864. This was a mainly effusive eruption which produced about 1.4 km3 of lava. It erupted at lower altitude on the northwestern flank, from a 6-km long fissure. The eruption lasted two years. The lava buried an existing lake, and the interaction with the lake water formed some pillow lava and a phreatic explosion. The area is now deeply forested and is in part inaccessible due to the terrain and the trees!

The smaller eruptions were also flank events, in some cases on both the northern and southern flank simultaneously. Eruptions in the years 800 and 1083 were mainly explosive. Eruptions in 937 and 1033 produced significant lava flows, with lengths of 17 km and 7 km.

The average eruption rate of Shin-Fuji over its existence amounts to 5 km3 of magma per 1000 years. It may already be in a declining phase. The older eruptions were mainly effusive whilst explosive eruptions are a more recent phenomenon. The rate is very much higher than that of other volcanoes of the Japan arc. There is something about Fuji.

A repeat of the 1707 Hoei eruption has the potential to cause major disruption. If the ash were to be blown towards Tokyo, after two weeks a few centimeters of ash would have fallen in the city area. If it rained, this would be enough to make roads impassable for all but four-wheel drive vehicles, stop trains from running and close the airports. Power outages are likely even at 0.3cm of ash and rain and mobile phone masts may also cease to work. Food supplies would be disrupted. This is a worst case scenario, and a two-week event would give time to keep on top of the ash. We have seen the impact of ash in the La Palma and Etna eruptions, but never in a city on the scale of Tokyo.

At the moment there are no indications of any imminent eruption. But Fuji is active. There is a steady rate of low-frequency earthquakes, located a few km northeast of the summit, at a depth of 15 km. This is suggested to be a dike that is receiving new magma, plausibly from the main magma chamber at 20 km. This is probably normal activity for Mount Fuji and does not presage an eruption. Shallower magma intrusions are likely to cause notable earthquake activity, as was the case in 1704. Any resumption of eruptions is therefore likely to give us years of warning. The quarter of a million annual visitors are safe from the magma. Just be cautious with the weather.

There is something about Fuji. The picture shows three volcanoes in the region: Fuki, Izu-Oshima and Miyakejima. This figure is taken from Aoki et al, 2019, Earth-Science Reviews, 194, 264. The first two volcanoes are elliptical in shape while the third one is round. The ellipticity indicates that Fuji and Izu-Oshima are affected by the local stress in the rocks. They are children of plate tectonics. Mount Fuji is also unusual in showing evidence that its eruptions can be triggered by earthquakes. To really understand the mountain, we need to look at its faults. And Japan has an abundance of those.

Faults of Japan

Japan is riddled with over 2000 active faults. The two most significant in-land faults are the Itoigawa-Shizuoka line, which runs north-south across the country just west of Tokyo and the Median Tectonic line which follows the axis of Japan from Tokyo southwards. The latter is a strike-slip fault. The destructive 1995 Kobe earthquake happened on a side shoot of this fault. Mount Fuji is located around 50 km from the intersection of two main faults, although it is not associated directly with either.

The most important fault lines of Japan. Itoigawa-Shizuoka tectonic line; Tanakura tectonic line; Median tectonic line. Source: Bor-ming Jahn, Masako Usuki, Tadashi Usuki and Sun-Lin Chung. American Journal of Science February 2014, 314, 704-750

The faults are related to the battling plates. Did I mention the four-way battle for the heart of Japan? That was the simple version. The picture below gives the actual situation. Japan is sitting on two separate plates. The northern half of Japan belongs to the Okhotsk plate, a mini-plate which also contains Kamchatka and the Kuril Islands. At one time the Okhotsk plate was thought to be part of the North American plate. Now it is seen as a remnant of the extinct Kula plate, one of the plates of the Pacific ocean. This remnant carried an ancient oceanic flood basalt and this helped it to avoid subduction. The southwestern half of the Japan belongs to the Amur plate, a break-away part of the Eurasian plate which runs from Lake Baikal to Japan. On the eastern side of Japan is the old Pacific plate, and to the south is the younger Philippine Sea Plate. Finally, between the Philippine plate and the Yangtze plate (part of Eurasia) is a microplate called the Okinawa plate. It owns the tip of Okinawa, the southernmost of the main islands of Japan. So Japan lies on three plates, and borders two more. No wonder it is so earthquake prone. (In fact one sliver of Japan, the Izu peninsula, sits on the Philippine plate, so that makes Japan worth four plates. Of all the continents, only Eurasia has more.) It really is the Battle of the Five Plates. And it is centred on the Lonely Mountain. Mount Fuji.

(The precise location of the boundary between the Okhotsk and Amur plates remains under discussion. GPS measurements indicate that the two move independently and should be considered as separate plates but it is not easy to trace the precise line of separation.)

I have left out one more detail. Honshu, Japan’s main island, originally started out as a double. It split off from Eurasia as two separate fragments, one on the Okhotsk plate and one on the Amur plate. Only later did the two meet and join forces. The suture of the two runs near the Itoigawa-Shizuoka tectonic line. The rocks on either side are very different, with granite half a billion year old on the southwest side and young sediment on the north side.

In between the Itoigawa-Shizokua and the Takankura tectonic lines lies the Fossa Magna: the central valley stretching from the Pacific to the Sea of Japan. This is a wide area which includes the Kanto plain of Tokyo. It contains up to 6 km depth of sediment from the sea which separated the two halves of Japan. The Fossa Magna is known as the rift valley of Japan.

Fossa magna: the rift valley of Japan

Most of the major earthquakes of Japan come from the two main subduction zones, which form two deep trenches along the east (Pacific) coast. The Japan Trench is where the Pacific plate dives down underneath the Okhotsk plate. This trench follows the Japanese coast (at some distance) until Tokyo: south of Tokyo the trench bends further away from the land. From here on, the Nankai Trough takes over: it comes from the subduction of the Philippine plate, and it follows the coast rather closer to land than the Pacific plate did. There is a short boundary between the Pacific and Philippine plate which is called the Sagami Trough: it runs east-west, southeast of Tokyo.

Source: wikipedia

Earthquakes

Japan is famous for its earthquakes. 20% of the world’s largest earthquakes (magnitude 6 or higher) occur in the country. The 2011 Tohoku earthquake is well remembered: it left 20,000 dead and 360 billion dollars of damage. Surviving the earthquake itself was only half the story: the devastation came from the tsunami afterwards. The Great Kanto earthquake of 1 September 1923 (next year this will be a century ago) with magnitude M7.9 destroyed more than half of all buildings in Tokyo and caused the death of 105,000 people, mostly from the fires after the quake. The M6.9 Kobe earthquake of 1995 hit in an unexpected place, killed 6,000 people and caused immense damage. The Great Hoei and Genroku earthquakes of 1703 and 1707 were already mentioned. In 1792, a comparably small earthquake (small for Japan, which suffers an M7 on average once a year and an M8 once a decade) with magnitude M6.4 caused a flank collapse of Mount Unzen, an active volcano. The landslide swept up a tsunami that killed 15,000 people. In 1891, an M8 struck Gifu, in-land. Nothing was left standing in the city. And there are many more historical examples of major earthquakes, often accompanied by towering tsunamis.

All of the plate boundaries can produce major earthquakes. The 2011 Tohoku earthquake ruptured much of the Japan Trench. (What actually fails in such a megathrust earthquake is the contact layer between the subducting plate and the overlying plate. The two lock, the subducting plate pulls the overlying plate with it and in the process pushes it forward. When the lock fails, the overlying plate shoots back in a large quake.) The Japan Trench tends to fail in single, huge events, perhaps 500-1000 years apart, as it did in 2011. But in between there are plenty of smaller (M7 or M8) events as well. The 1707 megathrust earthquake ruptured 700 km of the Nankai Trough south of Edo (near Tokyo). The M8 earthquakes in 1944 and 1946 too were on this fault. The Nankai Trough often fails in doublets, producing two major earthquakes every 100-150 years. The 1703 Genroku earthquake ruptured a large section of the Sagami Trough. The 1923 Great Kanto earthquake also was on the Sagami Trough, but closer to Tokyo.

And the other side of Japan is not safe either. An M7.6 earthquake in 1833, possibly originating on the boundary between the Amur and Okhotsk plates, hit the northwest coast of Japan with a large tsunami. The M7.7 Hokkaido earthquake in 1993 also came from this region. And as mentioned, there are also large earthquakes on the other faults, especially the Median Tectonic Line. Japan has shaky foundations.

Plates of Tokyo

Let’s have a closer look at the Tokyo and Mount Fuji region. The plate boundaries are complex here, and the precise location is not always known, especially on land. The dashed lines drawn below indicate such uncertain locations. The arrows show the approximate directions of the plate motions. Tokyo and the Tokyo Bay are on the Okhotsk Plate. But the Philippine Sea Plate is not far away, and underneath the Pacific Plate is heading for Tokyo.

The Philippine and Pacific plate are both subducting. You may imagine some competition here, about who can subduct better. The Pacific plate is older and colder and therefore is the densest. The Philippine plate is younger and warmer and is not as dense. Thus, the order of priority is set: the Pacific plate subducts under the Philippine plate which subducts under the Amur plate. There is a layer cake under southern Japan, where the Amur, Philippine and Pacific plate are stacked. The situation further north is easier as the Pacific plate subducts directly under the Okhotsk plate, meaning there is one less layer to worry about.

If we focus a bit more on the Tokyo, area, we find more complications. There is a large bend in the Philippine plate, creating an extension into the area of the Izu peninsula, between Suruga and Sagami Bay. This is the result of a volcanic arc, a line of volcanic islands stretching into the Philippine Sea called the Izu-Bonin arc. As the plates moved, this arc collided with Japan. Volcanic islands do not subduct willingly: instead they tend to join the land they collide with. The arc also brought a larger volcanic block with it which became the Izu peninsula. This is how Japan grows.

The Izu peninsula, land that was plastered unto Honshu, contains several eroded (extinct) volcanoes. Hot springs also tell of a volcanic history. It is a mountainous land with a spectacular coast line. If climbing Mount Fuji was a step too far, a visit to the Izu peninsula may help you regain your sense of wonder and your breath. And the volcanoes here are much lower, thanks to age and erosion. (The area is also full of golf courses, if that is a sport you enjoy and can afford. The old calderas should make for an easy hole-in-one. Not to be attempted during an eruption.)

The Izu peninsula

Remember the layer cake? It is slightly more complex than I said. Underneath Okhotsk you should only find the Pacific Plate layer. But the Okhotsk Plate is itself moving southwestward – not fast, but measurable. So it is overrunning places where the Philippine plate used to be, with the Pacific plate underneath it. Because of that overshoot, the Philippine/Pacific layer cake does extend underneath the Okhotsk plate. In addition, as recent as 3 million years ago the Philippine Sea Plate was moving north, before it changed to northwest, so this added to the complex layering. Below the surface, the Philippine Plate extends further than you might expect.

The double layering has been detected underneath the metropolitan area of Tokyo. The subducting Pacific plate here lies at a depth of 80-90 km. But there is also a transition zone at 20 km depth, and this is thought to be the top of the Philippine Sea Plate. It becomes even shallower further south, and lies at around 10 km deep underneath the entrance to Tokyo Bay. Follow this 10 km contour, and you’ll find that both the location of the 1923 and 1703 earthquakes are on this line. These were shallow megathrust earthquakes close to Tokyo. The location and depth explains the damage they did.

It provides a warning. An exact repeat of the 1923 earthquake may be a century or more away, as the quake has resolved the stress here in the only way it could. But further east the boundary may have remained locked for 300 years. The Tohoku 2011 earthquake which ruptured the boundary between the Pacific and Okhotsk plates left the Philippine plate untouched and therefore also did not resolve the stress here. A large earthquake in Tokyo in the next 30 years is far from certain, but the danger should not be neglected. The probability of an earthquake causing ground shaking larger than 0.9g in the Tokyo metropolitan area within the next 30 years has been estimated at around 30%.

Fuji and the Arc

Close to the Izu peninsula stands another volcano, one that is often ignored. Mount Hakone is famous for its large and scenic crater lake, but is perhaps best known for its beautiful views of Mount Fuji. The caldera is 10 km wide (the lake is located along part of the caldera wall). It overlaps with a second one, almost as large. Twice, a large stratovolcano blew up here; the last time this happened was 50,000 years ago. Since that time, smaller cones have grown inside the caldera. The last eruption of one of these cones was 3000 years ago. There are traces of a few smaller, phreatic explosions. That was dramatically confirmed in 2015 when there was such a phreatic eruption. Luckily, this eruption gave sufficient warning and the site had been closed to tourism.

Fuji, from Hakone

In its time, Hakone produced lava ranging from rhyolitic to basaltic, the entire suite of possibilities. The mountain may not have been much smaller than Fuji is now, produced a similar (but not identical) range of lava, and it is only 30 km away. It seems to be a member of the Fuji family. However, it is the black sheep of the family as it twice explosively self-destructed. The other family members have had large eruptions and flank collapses, but they have avoided VEI-7 type explosions.

Hakone lies along the line of the accreting Izu volcanic arc and seems to belong to it. It also lies close to Mount Fuji. Does this indicate that there could be a relation between the volcanism of Fuji and that of the approaching arc? The behaviour of Mount Fuji is a result of many things: this is an extraordinary complex region. But Fuji is clearly affected by the accretion of the Izu arc. First, the ellipticity of the mountain is along the direction of the Izu arc, and is the same as that of Izu-Oshima, the largest and closest island of the Izu chain of volcanoes, located in Sagami Bay. Second, the lava composition points at a relation to the Izu-Bonin arc. The arc shows a mix of tholeitic basalts and rhyolite, very different from the andesite of northern Japan. Mount Hakone shows a similar range. Fuji shares the basalt but it is not documented as having produced rhyolite: instead it provides us with occasional dacite and andesite. You could see Mount Fuji as a mix of Izu-Bonin arc and more traditional Japanese volcanoes while the intermediate Mount Hakone is more similar to the Izu-Bonin volcanism.

The source of the Izu-Bonin magmas is the melt of the subducting Pacific plate, with added melt from the Philippine plate crust. For Mount Fuji, it has been suggested that most of the magma also originates from the Pacific plate, but moves through the overlying layer of the Philippine plate without this adding much to the melt. This forms the magma chamber at 20 km. From there the magma moves up to the 8-km reservoir where it evolves to the dacite/andesite composition – if given enough time.

A look at the maps above shows that it is not so clear which plate Mount Fuji is on! It does not help that the volcano family has obliterated all surface rocks. At depth Fuji belongs to the Philippine plate but all three plates put in bids for this real estate at the surface. (They may have missed their chance. Some 20 years ago the government returned the title to the summit and surrounding area to the original owners. It is now private land.) Mount Fuji is located not far from the triple point between these plates. However, triple points are not normally the location of major volcanoes unless they are caused by a hot spot – which Fuji is not.

The precise location with respect to the triple point is probably not too important. The main aspect is that it is at the end of the accreting volcanic island arc and that is mixing behaviour from the arc and from other Japan volcanoes.

The volcano of Izu-Oshima. Pretty, but no Fuji

The high magma production rate, 100 times that of other Japanese volcanoes on Honshu, is not so easily explained. Izu-Oshima, roughly 100 km away, is the nearest frequently erupting volcano on the Izu-Bonin arc. It erupts every 30-40 years, and has a subsidiary volcano just below sea level which also has left deposits on the neighbouring islands. But it’s eruption volume is dwarfed by Fuji. In between lies Hakone but this erupts rather little, apart from the occasional VEI-7. Otherwise the region in between Izu-Oshima and Fuji lacks active volcanism. Either Mount Fuji is collecting magma from a large area, or it has a separate cause of melt.

The melt may be affected by the Fossa Magna in which it is located. This has the appearance of a rift valley, where the low stress allows for easy magma melt and accumulation. Imagine a volcanic arc entering a rift zone! And perhaps from this mix of cultures, Mount Fuji grew and became the unexpected icon of Japan. Japan is not known for encouraging cultural melt, but volcanoes make their own rules.

One can speculate further. Three million years ago, the Philippine plate changed direction from north to northwest. Before that time it would not have affected the region of Mount Fuji. Perhaps the plate has only recently reached this region, pushing down the Pacific plate in the process. Could this have triggered the melt and initiated the volcanism, 400,000 years ago?

There is much we don’t know about Mount Fuji. On the outside: it is the most beautiful, recognizable and touristic volcano on Earth. On the inside, it remains a bit of a mystery. Eruptions are rare enough that we are likely never to see one in our life time. But they are not that rare, with perhaps a 10% chance in the next 30 years, and when it does erupt there may be impacts as far as Tokyo.

But that is not the main message. Mount Fuji is a tectonic sign post where five of the most important faults of Japan come together. Only the Japan Trench keeps its distance. Fuji is not just a poster child for volcanoes. It stands as a reminder of the other powers of nature to which few nations are as exposed as Japan. The reverence for Mount Fuji shows a deep respect for powers we cannot control.

Albert, 1 September 2022

Sources

  • Climbing Mount Fuji: https://www.japan-guide.com/e/e6901.html
  • Yosuki Aoki et al., Recent progress of geophysical and geological studies of Mt. Fuji Volcano, Japan. Earth-Science Reviews, Volume 194, July 2019, Pages 264-282
  • Yanagisawa, H. and Goto, K. Source model of the 1703 Genroku Kanto earthquake tsunami based on historical documents and numerical simulations: modeling of an offshore fault along the Sagami Trough. Earth Planets Space 69, 136 (2017)
  • Christine Chesley et al., The 1707 Mw8.7 Hoei earthquake triggered the largest historical eruption of Mt. Fuji. Geophysical Research Letters, 39, L24309 (2012)
  • Earthquake source fault beneath Tokyo. Hiroshi Sato et al, Science, 309, 463 (2005)
  • Kazutake Mannen et al., Chronology of the 2015 eruption of Hakone volcano, Japan, Earth, Planets and Space, 70, 68 (2018)
  • Ioan McIntosh et al, Past eruptions of a newly discovered active, shallow, silicic submarine volcano near Tokyo Bay, Japan. Geology (2022)
  • Fossa Magna http://ggstar.net/earth/190615-fossamagna/
  • 330 thoughts on “Magical Mount Fuji

    1. Beautiful and very instructive about plate tectonics, thank you. One small thing:
      “The current volcano, Shin-Fuji, started with voluminous basaltic eruptions between 17,00 and 8,000 years ago.” 1,700 or 17.000? (7th paragraph, a little under the diagram)

      I keep wondering whether Tokyo today would be constructed in this area. Like most major cities in bad positions it was constructed before Plate Tectonics came up as a science.

      You forgot one of my darlings, strong contender for beauty, here the shadow seen from la Gomera:

      • Thanks, there was indeed a zero missing. Amazing how much damage a zero can do.

        Teide is beautiful. But I felt that the minute cone on top seemed misplaced and might work against it in the Miss World competition

    2. I knew Fuji was a bit strange compositionally compared to most of the other volcanoes in the general area, but not this weird. Looks like it has a very similar lifecycle as Etna, beginning as a shield that evolves into a stratovolcano, and eventually evolved magma in small amounts (relatively). Also like Etna it has done this several times over a long time period, with very high activity at the peak if the stage.

      Volume of Fuji is supposed to be well over 1000 km3, which is enormous for a volcano that isnt powered by a plume. I wonder if it is actually the biggest terrestrial volcano, it is certainly the biggest volcano in its general part of the world and way bigger than a standard arc volcano.

      • Kilimanjaro, Mount Kenya are enormous as well .. but they are rift + plume volcanoes ( But can also have the title as largest land continetal volcanoes )

        Yes Fuji is spectacular and is pretty much the same stuff as Pavlof, Klyuchevskaya Sopka, Shishaldin, Mayon, and other steep mafic basalt and basaltic andesite cones. Fuji is a very young cone … so must have been hyperactive earlier in holocene.

        Fuji Probaly resembled them earlier when it was hyperactive building its cone: it probaly had an open conduit like villaricca and perhaps even lava lakes and huge paroxymal fountains. Its an overgrown lava fountain cone I guess

        Fuji is pretty much the real Orodruin when it erupts .. huge plinian lava fountains glowing hot and mean ashclouds and ligthing flashes as well closer to Mordor you cannot get. Some Fujiian eruptions must have been like large versions of Villaricca 2015 With countless souch events building up that steep cone.

        • Kilimanjaro and the other huge volcanoes in Africa are much older though, only Meru is active today, and they all grow slowly. Fuji is old, but it looks like most of the modern contour of the mountain is young if the 17’000 years date is a reference. It does make it quite spooky, that such a formerly active volcano now goes through long dormacies, it could well be preparing for a caldera collapse. It does look a lot like how Tambora was before it blew up, and Tambora was also a mostly mafic stratovolcano, 1815 was trachyandesite with low crystals, which is a low viscosity magma.

          • A millennium ago, Indonesia had two mountains over 4km. Now it has none (not counting New Guinea), and instead it has two impressive craters. The most dangerous time is when a very large volcano re-activates. Fuji is very active and therefore not in this group – its main danger would be a flank collapse. For Indonesia, its highest mountain is now Kerinci. I just mention it. Actually, Rinjani remains the second highest even after it blew up. If you look at tall volcanoes with little activity, Sumbing is top of the list.

            • Height is only 10.289 feet though.
              Tambora is said to have boasted more than 13,000 feet before collapsing.

            • I’ve spent a good amount of time looking at Tambora in Google Earth, and honestly the massive size of even the extant edifice is mind boggling. Absolute unit of a mountain.

              Would’ve loved to see it in all its glory.

        • Yes rather creepy its been hyperactive earlier in holocene and now its rather silent

          Perhaps We are waiting for the true Mount Doom ..
          a change to lower supply pretty much always means change to more evolved magmas

          • More the point I was thinking is the supply hasnt changed just that the path to the surface is no longer simply an open pipe, so it gets stuck in the crust and accumulates instead of erupting often. I dont think it is evolving more, the Hoei eruption was only highly evolved at the beginning first few hours, afterwards it was andesite and then basalt, so seems to have been mostly the result of a basaltic intrusion pushing some evolved stuff out which blew up. That being said the basaltic and andesitic stage was still violent, it would have been impressive at night, a massive fountain, showering the mountain with glowing tephra.

          • Little reminder:
            “By 2010, the Global Volcanism Program of the Smithsonian Institution had cataloged the assignment of a VEI for 7,742 volcanic eruptions that occurred during the Holocene (the last 11,700 years) which account for about 75% of the total known eruptions during the Holocene. Of these 7,742 eruptions, about 49% have a VEI of 2 or less, and 90% have a VEI of 3 or less.

            About 40 VEI 8 in the past 132 ma it says, and 10 VEI 7 in the past 11.700 years.
            https://en.wikipedia.org/wiki/Volcanic_explosivity_index

            The bigger the rarer (This wisdom I learned on VC first). So, considering Tambora, Krakatau, Novarupta, Pinatubo, Samalas and the South Americans we might not see any Mount Doom in our life time. Might though. You never know. Statistics is not linear.

            • 10 VEI 7’s in 11,000 years is a bit low. I would have expected twice that number. But most VEI 7’s will close to the border line and the uncertainty on the size can be significant

            • The numbers look more interesting when you include VEI 6.8+ events in with VEI 7’s, as a high end 6 for practical purposes is very similar to a low end 7.

              Also, if we still can’t place the eruption that occurred in 1808/9, it doesn’t fill me with confidence that we aren’t missing several such large events from the earlier Holocene. Not all spikes on the ice cores are accounted for, yes? And some large eruptions probably weren’t major climate disruptors, though at that size I would assume more often than not they are.

      • I wonder what would be the largest continental volcano.

        Estimates for Fuji’s volume seem to be of about 400-500 km3. It’s big but far from being the biggest continental volcano.

        The largest active continental volcano is possibly Kilimanjaro at 4800 km3, ten times more voluminous than Fuji. Other large volcanic edifices include Mount Ararat at 1150 km3, and Mount Cameroon at 1300 km3. Toba has probably ejected over 2800 km3 DRE. And volcanic fields can also erupt a lot, Harrat Rahat and Harrat Khaybar volcanic fields in Arabia both have an estimated ~2000 km3 of lava flows.

        As for arc volcanoes the Kliuchevskoi Group has ~5000 km3. Most of which seems to be made up by Ushovsky, with an important contribution from Kliuchevskoi and Tolbachik. And Shiveluch has ~1000 km3.

        • Do remember how young Fuji is. It hasn’t had time (or the magma supply) to build a Kilimanjaro.

        • The modern cone is a holocene product

          It can have a much larger supply than Kilimanjaro at current as .. Kilimanjaro grew very slowly on a very slow moving crust

          • We don’t know how high the supply to Kilimanjaro may have been at times in the past though. Most well studied volcanoes have show to have highly variable supply. I bet there were times when it frequently erupted from its summit with episodic paroxysmal fountaining and lava overflows, much like Ol Doinyo Lengai does today.

        • It seems to me that Fuji and also Teide are unique in collapsing into their calderas before they reach 4000 m/12000 feet which is why they are both sitting on multiple predecessors.
          Kilimanjaro seems to work differently and is also much higher.

      • Sorry, link doesn’t work. I need to figure out the new way with imgur.

      • I might be biased but I always thought the sillouette of Mauna Loa looks phenomenal, its not a perfect cone but the sheer size and magnitude. I only saw it in darkness but even then it was unmistakable.

        The caldera at Kilauea also is impressive, it is much bigger in real life than any picture makes it appear. I think stopping at perfect cones for this contest is too narrow a view 🙂

        • RE:The caldera at Kilauea also is impressive, it is much bigger in real life…

          I’ll second that, from many of the viewpoints that were accessible back in 2003 when I was there. Regret not having the opportunity to view the fully collapsed Halemau’mau’ before the lave lake evolved anew.

          • I dont know what it would have looked like before 2018, but I ecpect today the view is more impressive. At night it really does look just like the expectation of a volcano being a great chasm filled with lava. And it is still very deep, when I was there the lake was still far below, even though it has filled in over half way vertically.

            I do find it quite worrysome that no-one in authority has considered the reality of that crater filling up yet. It will be 1 km3 of lava that is in a liquid state sitting at high elevation… Nyiragongo is doing eruptions after filling only about 1/10 as much and those are very extensive in spite of the small volume of lava erupted. The 2018 lake was of similar dimension and turned out to be hiding enough magma to do an eruption as big as Holuhraun that took even HVO by surprise. If the present lake gets as high as the 2018 elevation (2025 apparently) then it could drain out 1 km3 of lava in but a few hours, and unlike 2018 there would be no build up it would be a lava flood from the start…

            • RE:”I do find it quite worry some that no-one in authority has considered the reality of that crater filling up yet.” Does call to mind 1924. There’s also a photo of an 80ft arcade in the wall of Halemau’mau’, exposed when the lava lake dropped, which is said to have been the runout to the SWRZ in 1922. How do you envision a breakout from the collapsed crater.

            • That feature you are talking about was actually from 1919-1920, to feed Mauna Iki, and exposed in 1921. But yes something similar to that could occur now or at least when the lake is hig henough. Maun Iki was not the first eruption in that style either, the eruption in 1868 was similar although small, and the kealaalea flows that date from possibly the earliest 19th century erupted the same way as Mauna Iki beinglava shields with no pyroclastics that welled out of cracks in the ground. 1823 eruption was very similar to the event I imagine occurring in the near future, that eruption was a total drainout of an even bigger lake, it might have been over 1 km3 of which the vast majority ended up below the waves. Or the eruption was relatively small and most of it went into an ERZ intrusion…
              In 1969 lava from Mauna Ulu filled in Alae crater, which then drained out of a dike, and that dike was entirely created by pressure within the lake inside the crater, it was completely separate from the fissure that Mauna Ulu started from. it might have been related to fissures from a different eruption earlier in that year, however, but in any case deep lava lakes need not necessarily have a vent under them in order to break out or form intrusions.

              The alternative is an eruption from the ERZ that sees the lava lake withdraw into the vent, in which case it will nto completely empty the crater but leave it filled to the level of the lowest vent, which is not necessarily the one that is most visible. This is what happened in 1840, an ERZ intrusion and eruption that saw the lake, which would have been much like the one we see now, withdraw into its feeder vent and leaving the caldera empty.

              It is also not impssible that this could be accompanied by a major earthquake. the 2018 quake didnt see any slip of the area next to the SWRZ, it only moved the south flank between Mauna Ulu and a bit east of Pu’u O’o. During the great 1868 quake the lava lake at Kilauea, which was largely crusted before, was seen to suddenly overturn before it rapidly drained out with the low pressure, in the process there was powerful fountaining from the cracked perimeter of the lake, as well as from a fissure near Kilauea Iki. So a strong quake near Kilauea now (or from Mauna Loa waking up) could make for a show, but also turn dangerous if it drains out in the wrong direction.

              I would imagine the sequence of events at play here would resemble the eruptions from Nyiragongo a great deal, except bigger.

        • Beauty is in the eye of the beholder! And Mauna Loa is phenomenal, and so large it is actually hard to see

          • Right I seen Mauna Loa many times as well in person haves to be Earths most spectacular volcanic edifice

      • My vote also goes to Kliuchevskoi. It combines beauty with a monstrous size, being arguably the tallest stratovolcano in the world after Kilimanjaro.

        • Yes pretty much a Mount Doom in symmetry

          But Shishaldin is probaly even more perfect 😍 its so perfect that it looks almost like a cartoon comedy

          • Yes, most basaltic stratovolcanoes are beautifully symmetric and smooth.

            Silicic stratovolcanoes instead tend to have thick flows and domes bulging out from the slopes, scars from collapses, and deep ravines eroded into the loose ash.

            One other very beautiful basaltic stratovolcano is Villarica:

            Plus Chile has some other symmetrical mafic stratovolcanoes near Villarica, like Llaima, Antuco, or Osorno.

            • Interesting how the southern Andes has got such different volcanism from that further north. The volcanoes in Equador and Columbia, as well as northern Chile and Peru, those are all generally silicic, there are no basaltic volcanoes. Southern Chile however is very bimodal, with lots of rhyolite and many basaltic stratovolcanoes. The rhyolite also much less viscous too, at least in some cases, it looks like the volcanoes here are alot hotter and the crust thinner. Villarrica at times looks like a giant version of Pu’u O’o, doing massive hawaiian-type fountains.

            • Yes that is interesting.

              The Southern Andes also has many small calderas which frequently collapse. Some of these calderas have produced mafic ignimbrites, like those of Llaima and Villarrica caldera-forming eruptions. Although the northern end of the southern Andes does host large calderas (Calabozos, Laguna del Maule, Caldera Diamante).

              The Central Andes generally has giant silicic calderas which seldom collapse. And lavas are generally more viscous than in the Southern Andes. Possibly some of the most viscous lavas of the world are in the Central Andes, there being many flows of crystal rich dacite or rhyodacite which have very high viscosity.

              There is however one big exception in the Central Andes. There is one young basaltic or basaltic andesite stratovolcano, known as el Peinado. There are also extensive fields of basaltic volcanism near el Peinado, and to the west and north of it. The low viscosity and primitive nature of lava in that area is curious and contrasts strongly with other Central Andes volcanoes.

            • There is this memorable video of Villarrica doing dome spectacular fountaining/subplinian eruption back in 2015:

            • The big silicic domes and volcanoes in the Andes are basically granite that has surfaced in a partly molten state, which would make sense given the Andes is a batholith, these are just a few places where that batholith is able to escape.

              I guess if there is mafic magma then that area must not have an active batholith, basalt encountering rhyolite magma is like hot water and cold oil, the water is fluid but cant rise through. Only thing is rhyolite has a higher heat capacity than basalt so only in extreme situations can it be heated up enough to be fluid and crystal poor, and even then it is still sticky compared to basalt. Silicic calderas I think can be considered functionally extinct if basalt erupts within the caldera boundary, at least extinct in the way that further large events are very unlikely.

            • The stickiness comes from the crystals and they come from the minerals that solidified during the cooling. If you solidify the whole chamber, and now remelt it at a low temperature, you get a pure rhyolite magma without crystals. That can and does flow easily. When you find the long rhyolite flows, that is probably how they formed.

    3. Albert thanks for the Fiji article- one of my favourite volcanoes it is.Now need to read it! Whilst here love to see an article on Kadova volcano in PNG-very difficult to get information and close up pictures of this rare volcanic eruption Wondering if it has grown in height and size etc etc.

      • Well yes – I had to look this up though – Fiji has indeed volcanoes.
        Never mind, happens to me too, esp. on my smartphone.

    4. This is really a tremendous piece, Albert. Thank you.

      The way you tie specific volcanoes comprehensively to their geologic surroundings is among the best science writing I’ve seen anywhere on the internet.

      • VolcanoCafe is gifted with a lot of brilliant contributors and commentators who share tons of insights and knowledge, but you Albert really posses a Sagan-esque quality in the way you write.

        It’s thoroughly appreciated and a large part of why this place has me completely addicted.

    5. Part continental crust eh? Sort of like the Palawan shard that has Mindoro at one end as it encounters the Philippine mobile Belt area.

      (Sleeper Fish article)

    6. I like the layered cake.
      It seems to be an extraordinarily complex region. The funny thing is that it is moving away from Eurasia whereas on the other side of the Pacific oceans island arcs have moved in like here (Sierra Nevada):
      https://link.springer.com/chapter/10.1007/978-94-011-1614-5_12
      Same thing in South America.

      So it is easy to speculate that a new ocean is opening up west of Japan between the Sea of Japan and Lake Baikal which, in 200 ma or more will replace the then enormously shrunk Pacific Ocean with Japan being the eastern border. It is well possible that this part of Asia is the birthplace of a new ocean. In a scenario like this The US is not the “New World” any more, but the “Old World”, geologically at least.

      If I ever go there I won’t climb Fuji, but Hakone instead, if possible. I like Izu Peninsula. And a beauty like Fuji is probably better admired from the right distance and angle.

      A similarity to El Teide (Las Canadas IV) is the ongoing construction on older collapsed calderas.
      Many million years from now, following this rule, Aniakchak may win the beauty contest.

    7. corr. on the other side of the Pacific Ocean island arcs have moved in

    8. Who doesn’t like layer cake?
      The idea of the rift valley fueling/storing magma reminds me of the bit between Mount Fako and Mount Oku, where rumbling earthquakes seem to happen before magma is transported.

      Nice article! Like many I have a canvas frame of the beautiful Fuji on one of my walls.

    9. A fascinating and enjoyable article, Albert. My thanks for the time and work done!

    10. Concerning Sumbing mentioned by Albert above and twin Sundoro in Central Java I consider this pic from the ISS quite nice:

      • Fuji by NASA: More snow. Snowy mountains win beauty contests:

    11. Great article, Albert! Especially about a place that I know a little bit about.
      Late in the last century, I took employ with a Japanese company based in Fukuyama…and became aware of the Tokai Earthquake warning system that was in place at the time (but has now been largely abandoned as a national program).
      This now well-overdue earthquake (M8-8.3 expected) will rupture a large segment of the Itoigawa-Shizuoka line…primarily near Shizuoka and possibly extending towards Mt. Fuji. Given your piece mentions a possible interplay between earthquakes and impacts to one (or both) of Mt. Fuji’s magma chambers, is there any reason not to think that a Tokai earthquake could also activate Mt. Fuji?
      Note that after learning of this impending disaster, for the last several decades I have been (and still) monitor the area on a near-daily basis…and based solely on my observations, the area around the Itoigawa-Shizuoka line has become somewhat more active in the last 6 mos. or so…and IMHO, the area near Shizuoka may be starting to show signs that some unlocking is going on? With heightened activity occurring in the normally active Tokyo area (which some believe is resulting in part from stress transfer from the 2011 Tohoku megathrust event), I can envision how Mt. Fuji is being subjected to several sources of stress that could eventually lead to a future eruption more in the near term rather than an prolonged extension of it’s current repose period.

      • “IMHO, the area near Shizuoka may be starting to show signs that some unlocking is going on.”

        You cannot legitimatrly claim that without significant evidence. No one has managed to yet find any way of predicting an earthquake before it happens. Statistical forecasts of likelihood can be made but that’s it.

        • In no way am I predicting the Tokai earthquake is imminent.
          But historical data does show that major earthquakes along the Japan trench (such of the devastating 2011 Tohoku megathrust) are often preceded by strong foreshocks.
          While not on the same scale, a similar pattern was present along with the Loma Prieta earthquake that had several M5’s in the days and weeks prior to the main shock.
          But granted, a Tokai quake is not expected on the Japan Trench (though possible), but rather along the Itoigawa-Shizuoka line where the tectonic makeup is different.
          Also, the Japanese geologists have long suspected that would be some precursor signals such pre-shocks and possibly some signs of vertical displacement, but because of the unreliability of these “signals” as far as specific timing and the potential economic impact of a wrong forecast, all that’s left now of the Tokai-alert program is to watch and wait.

    12. There are quite a few volcanoes I discovered years back that fit the profile of young-ish looking but very large volcanoes without any notable activity in thousands of years.

      Quite a few are in central America, Aleutians, and Kamchatka. Some examples are kronotsky in Kamchatka, or agua in central America.

      • Agua I think is not a risk, it is another satellite of Amatitlan, which already is erupting at Pacaya. Fuego is possibly also a satellite but that might be too far, in any case also very active. I guess eventually Pacaya will fall silent too and maybe another stratovolcano will form in the area, Pacaya as we know it today (Mackenney cone) is only a couple thousand years old at most, and the actual visible erupting cone is 1100 years old, although volcanism has happened there intermittently for a lot longer.

        A more scary one to me is Popocatepetl. It is very active and far from an unknown danger but it is also enormous, probably as big as pre-1815 Tambora, and alot steeper. I only bring this up, but still…

    13. With all the pushing, shoving and diving in this area, most notably from the vast and stubborn Australia plate to the south, there is one theory that the whole Indonesia/Philippine/New Guinea basin might arise one day as a new Himalaya. Just a theory. The best climbing season is yet to be determined.

      • It already is, that is why Timor exists 🙂

        Probably in the next 20 million years or so the area will transform into a chaotic terrain of tall mountains with deep ocean basins inbetween, possibly even landlocked. A few of the deep basins like the are actually deeper than average abyssal plain so it could be soem real extremes.

        I would also expect there to be a large number of volcanoes given the long history of subduction under the area and chaotic jumble of plates in the collision zone, that is one way it will differ greatly from the Himalayas.

        • There are still some volcanoes on Timor though aren’t there? At least mud volcanoes.
          Tends to happen in those sorts of settings.

    14. FWIW, Sacramento (capital of California in the normally hot central Valley) just set it’s all-time high temperature at 115F (46C)…and tomorrow may be even hotter. Throughout the entire state, records are being shattered by the dozens. ATTM, our power grid is approaching max draw, with some power failures already being reported (but not due to the entire grid failing, just to be clear).
      By next weekend, remnants from now TS Kay is expected to ride up the west coast of Mexico and California bringing a good chance of thunderstorms…and here in the northern part of the state, a chance of dry lightning.
      If this scenario were to come down as feared, we would be looking at record hot and dry conditions that brought our already parched forests to beyond-critical fire stage followed by a dry lightning outbreak. The potential consequences to virtually the entire state could have a ripple effect world wide, especially for food prices and the smoke from dozens of fires that could encircle the planet.
      While I’m hoping for the best, this upcoming week is looking very dire for the 6th largest economy in the world.

        • Sold our apartment in PV in December after many lovely seasons. The hillside on which the complex is built was experiencing a slope failure and in the process of being re-enforce. The town still looked hammered after the last hurricane and one of the bridges servicing a major road not yet repaired. Just hope this storm doesn’t make matters worse. Our son still in possession of his unit in the same complex.

        • KAY is now a hurricane and expected to strengthen to possible major CAT3 strength which would rake the entire Baja Peninsula as it treks northward along the coast.
          While the storm is expected to weaken as it moves north of Central Baja over cooler waters,
          the remnant moisture will get pulled northward over a good portion of California…which could promote a widespread outbreak of mostly high-based thunderstorms. With dry and hot air near the surface, fire ignitions would be a near certainty from C-G lightning strikes.

    15. Venusian volcanoes are off the scale compared to Earths volcanoes: some venusian summit calderas with scale bars. I guess because Venus does not have tectonics it cant vent it heat as easly as Earth does: leading to larger eruptions and larger induvidual volcanoes. Any of these volcanoes If they where on Earth woud be problematic If it erupted. Infact most venusian volcanic features like Mars are off the scale compared to Earth. Holuhraun, Leilani are tiny compared to these venusian volcanic structures.

        • Jesper’s enthusiasm will run high after those new Venus-missions have started. Mine too, btw. The mysterious fate of a planet.

        • What do you think, Albert, about Mount Liamuiga (Mount Misery!) on St. Kitts, not as a beauty contender, but rather a havoc contender? Maybe a little piece one day could be interesting.
          “The peak is topped by a 0.6 miles (1 km) wide summit crater, which contained a shallow crater lake until 1959. As of 2006, the crater lake had re-formed.The last verified eruptions from the volcano were about 1,800 years ago, while reports of possible eruptions in 1692 and 1843 are considered uncertain.”
          https://www.summitpost.org/mount-liamuiga/633354

      • Pavlof, Villaricca, Shishaldin and Klyuchevskaya Sopka beats Fuji in Perfect ness 🙂

        Anyway I Hopes Kilaūea develops into a Venusian Rouge volcano .. as it already haves an insane potential

        • This guy (Pierre Markuse, found on wikimedia commons) has great sat images, among them one of Klyuchevskaya Sopka, but the following is a sandstorm approaching the Canary Islands:

      • The largest Venusian volcano is probaly Theia Mons and thats a few 1000 kilometers wide. Venusian shields may not have the growth rate of Hawaiian shields.. but they are capable of eruptions that are in – comparabely larger

      • And some Venusian calderas are apparently 100 s of km wide!
        But coud be a tectonic feature rather than magma drainage: But looks volcanic

        • 400 km wide caldera .. thats insane .. luckly we dont have souch basaltic volcanoes on Earth lol

        • I think that Venusian coronae overlie huge magma chambers, layered intrusions, similar to Earth’s Bushveld Complex. The largest corona is Artemis Corona with a width of 2600 km! The reason why I think this, is that coronae are usually surrounded by giant cone sheet intrusion swarms, and you usually get these around magma chambers due to the stresses they induce from inflation and overpressure.

          Artemis Corona is also at the centre of a system of radial dikes and concentric ridges that extends over nearly half of the planet:

          However I don’t think these giant magma chambers caldera collapsed too often. Or if they collapsed it was probably more of a regional sagging than a deep hole. The top of volcanoes is often flat or rarely they are depressed, however I think this was due to lava lakes, often tens of kilometres wide that existed at their summit, and sometimes emptied. You don’t see calderas like those of Martian volcanoes which are kilometres deep and very obvious to identify.

          As for the eruption of Venusian volcanoes, it probably all took place around 450 million years ago. Because the distribution of impact craters across the surface of Venus is homogeneous. If there were surfaces of different ages then the impact craters would have different densities. The density instead shows a general age of 450 million years for the entire surface. I personally have closely inspected much of Venus surface in Google Earth with a kmz and in Google Maps. I haven’t seen any crater that was clearly overlain by a lava flow or cut by a fault. Some craters have also produced secondary lava flows due to the rock they melted during the impact, and these lava flows are bright white in the radar. This is unlike primary lava flows from the vast majority of the volcanoes that are usually darkened to the radar by dust, and thus presumably predate the impact craters.

          What I speculate happened, is that, about 450 million years ago, Venus released a huge amount of magma that had built up for a long time, probably hundreds of millions of years. Shield volcanoes erupted all over the planet at very high rates, producing giant dikes and lava flows that are similar in scale to those of Large Igneous Provinces on Earth. The entire surface was covered in lava thick enough to cover any large pre-existing elevated areas, and for shield volcanoes to grow on top of each other in many places. The whole surface of the planet contracted making the ubiquitously present wrinkle ridges. And the crust was densely intruded by dikes which faulted the surface. Ash soon buried the lava flows under a layer of dust. The last volcanoes to erupt were Sapas Mons, Maat Mons, Theia Mons, Ozza Mons, Tepev Mons, and a couple of others, which are not dust covered.

          However I think it is highly likely that volcanic and tectonic activity died out at the end of the episode, and that for the past 450 million years Venus has been dormant. If there has been any volcanism it must have been minimal and has not affected any of the ~1000 impact craters that Venus has. But I think its most likely entirely dead, building up magma for its next flooding episode.

          Mars is the same, volcanism is also episodic. About 100-200 million years ago there was an episode that affected five shield volcanoes, and covered much of Tharsis in lava. Following this episode there were two eruptions from the Elysium Rise. But otherwise Mars is dormant.

          • We have detected volcanic activity at Venus in the past decades. It is not entirely dead

          • We tend to find a comparison on Earth:
            “I think that Venusian coronae overlie huge magma chambers, layered intrusions, similar to Earth’s Bushveld Complex. ”
            When I first saw Venus’ Artemis with that rim and meteorite sites and traces of volcanism South Africa came to my mind as well.
            Who knows – if the Earth were not in the habitable zone and had the pressure of Venus’ atmosphere South Africa might look similar?
            Just nobody to watch in this case 😉

            Nobody really knows what Artemis is. Maybe it is really old, from the beginning of the planets.It is certainly intriguing.

        • Looks like Venus is another example of a world of Mega Intrusions

        • Tepev Mons has some of the most well preserved volcanic features among Venusian volcanoes, many of which are otherwise buried under thick layers of dust/ash, or deformed by wrinkle ridges, dikes and such.

          Below is the Magellan view of Tepev Mons, and also the same view interpreted. The top of the volcano is dark coloured, to the radar this means a smooth surface, maybe pahoehoe lava texture. It also seems topographically flat. Looking closely you can distinguish cliffs that bound the summit platform to the south and north, and which face outward. It is an elevated plateau. The upper slopes of the volcano around the plateau display a terraced lava flow morphology, similar to the 1614 lava flow of Etna, or the summit overflows of Mauna Loa, but in a larger scale. Jesper you will probably know how these terraced flows form. In long-lived sustained effusions of lava.

          The structure of the volcano is like a huge perched lava lake atop a shield formed from sustained overflows. There is hardly any other explanation I can think of for the structure. The lava lake must have been 30-40 km wide! Although knowing about Io this may not seem so impressive.

          North of the summit there is a giant cone sheet intrusion (giant for the Earth, normal for Venus). Lava erupting at extremely high rates excavated the rock around the fissure, probably through a combination of thermal erosion and wall collapse. There are two large lava channels which issue from different segments of the conduit and head northwards to be eventually buried under younger flows of neighbouring Otafuku Tholi (outside the view). This was a vigorous eruption. With a ~70 km long fissure and torrents of turbulent lava that thermally eroded canyons into the slopes of the volcano.

          • Yes very impressive stuff
            Infact all solar system volcanic features Dwarfs earthly ones .. probaly because the other bodies does not release their heat in small scale eruptions by tectonics

            But a Super Earth class exoplanet woud be very intresting probaly insanely volcanic by sheer internal heating with 6 to 10 Earth masses: but we dont have souch a world in our solar system

            • Plate tectonics create tensional stresses that help dike intrusions happen all the time.

              Other planets like Mars or Venus I think may have cycles of planet-wide dilatation and contraction, as they do through their cyclic magma flooding.

    16. Only a passing mention but there was a mag 3+ quake at Fagradalsfjall just recently, as well as some aftershocks. It isnt a new intrusion but right on the rift still, I dont expect a long wait before we get some more lava 🙂

    17. This is my strogest contender for the beauty contest, and it wasn’t turned into wallpaper. It is more pure, more untouched by business:

      Some activity around Fuji we would call “kitschig” over here.

      • Shishaldin beats Lengai instantly and Villaricca and Klyuchevskaya Sopka beats it as well in perfectness

        • Some landscape or water near a volcano doesn’t hurt too much, so Villarica yes. What makes Albert’s article so nice is also the musings about landscape and Izu Peninsula. So you have naked stratos and stratos with ornaments.

    18. Now you need to sign up for ARCGIS to view the maps at the IGEPN, which doesn’t make any sense, Why should anyone have to sign in just to view some basic maps that are only useful for simple or incomplete information? I also find it interesting that there is no longer any complete monthly reports on deformation or even seismic activity. As they themselves have stated magma is only 1-2 km below the surface so you’d figure that they’d be working as hard as possible to make sure the public understands what’s going on.
      Magma is quickly building at shallow levels, deformation is STILL accelerating, tremor is becoming more and more constant. there are 2 large calderas bigger than the Tambora caldera to the east that are still part of the same system! How is anyone supposed to take these guy seriously when they can’t even show the most basic of information about an increasingly dangerous volcano?,

    19. Very nice piece on Fuji and its layered past. A shame about the photoshopped multiple lenticular clouds though; the original photo is still impressive.

      • Yes, you are right. It had been on my list to check but that list is always longer than time allows! I have replaced it with the original. There are photos of multiple lenticular clouds but nothing like that. Thanks

    20. What I consider interesting is the fact that the old Emperors and Empresses kept away from the trouble spot and had their residences and capitals in changing places roughly around Kyoto, for a longer period in Nara.

      Edo (old name of Tokyo) was given to a minor local clan for achievements in wars and was also the home of the secluded and peace keeping shogunate. This changed with the arrival of Commodore Matthew C. Perry in the middle of the 19th century. Edo became Tokyo and capital. Foreign goods came in, inflation started to rise, and their were upheavals in the population. Tokyo grew anyway, even with profound knowledge on the unhappiness of the location. Henrik has mused about that with a decidedly cynical note.

      Wikipedia says that Matthew C. Perry opened Japan to the West. That’s also how it can be expressed. The last Shogun might have had different thoughts about it.

      Maybe I’m unfair, but I would call it Slave City considering how they live there, the majority. And I believe that Henrik was right with his cynisism. Still one of my favorite pieces:
      https://www.volcanocafe.org/the-new-decade-volcano-program-no-1-ioto-japan/

      If anybody is interested in the age of the Pacific plate (older in the north than in the south east of Japan) Albert’s link to his own piece about the Pacific Ocean (above the plate graph) is helpful. Phantastic maps with age of Pacific Ocean floor. The M before the numbers means plus 120 000 years.

    21. Hoei eruption must have looked like pure armageddon 800 million cubic meters rather quickly ..: at night a ligthing filled orange column going up into a dark cauliflower sky : ) Looking rather like Calbuco But rather hotter ”pillar of hell” Infact I do love basaltic plinian eruptions..

      Hoei woud be something that Sauron woud like alot

      Althrough still nothing compared to Masayas Ticuantepe basalt plinian phase

      • Fujis cone covered by glowing pyroclasts.. tumbling down .. and bad visibilty in the arera, quite a sight, and specialy when it comes from a cone
        Had it came from the summit crater then it woud be a Mega Villaricca .. but collapsing the summit as well

        Hoei was an intense eruption

        • The first day plinian eruption that created the first crater was dacitic and I think what did most of the damage, it was the second big eruption that was as you describe. The greyish black ash downwind is still visible, it only goes a few km away from the vents, so this second stage really might have been an actual gigantic fountain not a plinian eruption, probably very closely resembling those that happened on Izu Oshima in 1986, which was a fissure a lot like Hoei.

        • There is a spatter rim on the Hoei s crater floor so yes was a Mega fountain that quickly died down ( the basalt phase )

    22. A comprehensive paper on the 2021 Nyiragongo eruption. I was impressed by the depiction of the dike geometry.

      • Looks like it was a complete fluke that an eruption didnt break out within Goma, if the magma had any gas there is no doubt it would have, only a couple hundred meters deep. It did in 2002.

        Looks like these lava lake breakout eruptions really do occur out of the blue, the only precursor being overpressure that can also result in much less hazardous activity or nothing at all. I remember when Pu’u O’o broke out in 2011, lava flooding down the west side of the cone up to 3 km away in under an hour, with no obvious sign until it began. Same for that big breakout that happened at the end of the Geldingadalir eruption last year, no warning at all.

        We can only hope Kilauea drains out southwest, and doesnt do what it did in 1840…

      • What is fascinating is that the dike cuts down into the ground as it propagates southward. It starts above sea level but eventually reaches down to 10-12 km below sea level:

        I’ve seen a lot of Kilauea dikes go deeper as they grow in seismic data, those of the Seismic SWRZ in 1974 and 1981 for example. The Fagradalsfjall December 2021 dike also did a slight descent as it grew. The most extreme case from Kilauea is the dike of the Kamoamoa eruption in 2011 which started basically as ground level in the crater of Pu’u’o’o but eventually grew down to depths of 2-3 km below sea level, something seen in InSAR data, and also, with some knowledge of how dikes make earthquakes can be seen in the seismic data..

        There is an incorrect paradigm that dikes are a means from magma to rise vertically towards the surface. I’ve seen plenty of evidence that dikes are rather passively filling space in the crust. They can grow downward and are often non-eruptive. Eruption only happens in cases that pressure is high enough to allow eruption, which is often more than is needed to make a dike. A sustained long-lived eruption probably requires even more pressure that a short-lived one, as I’ve learned from Kilauea. And most eruptive activity on Earth, as well as possibly other bodies in the Solar System, happens from already established conduits rather than new dikes. Like with stratovolcanoes.

        • Is that diagram showing the modelled dike itself or is it showing the area of dilation? If it is the latter then the area that is within the curve, the lower left, might also be full of magma in the deeper system and wouldnt have been affected by brittle rifting. Not to day that the dike didnt grow down but that it might not be that simple. I have read that for the Kamoamoa dike it was actually fed by Napau and maybe Makaopuhi as well, not only the conduit to Pu’u O’o, which makes some sense as the eruption was quite intense with strong fountaining and a passive draining of Pu’u O’o would likely be degassed and I doubt have enough magma to erupt that way at all, let alone to refill after only a few weeks and begin erupting again.

          • The diagram shows the modelled dike opening. Dike opening and dilation is the same though, there is no dike that doesn’t induce dilation. But, yes, it is meant to be a dike.

            The Kamoamoa dike propagated uprift from Pu’u’o’o do the most obvious feeder point was Pu’u’o’o, and it is outside the Makaopuhi swarm. Other lateral eruptions from Pu’u’o’o have also featured curtains of fire, like the birth of Kupaianaha or 1997. It is summit magma being channelized through the Pu’u’o’o conduit.

            • Kupaianaha was much lower foutnaining though, the initial stage was strong but then up until that point Pu’u O’o was a lava geyser so maybe makes sense it was under a lot of pressure, the fissure that actually did become kupaianaha I saw was much less intense and began more passively a day after the episode began.
              1997 dike came from an intrusion that began uprift, sources saying at either Makaopuhi or Napau, but none say it was directly from Pu’u O’o and the collapse there was a visible result of the whole magma system depressurizing to feed the dike. The best map I saw of the 2011 intrusion has it deriving magma from all 3 of these places, the dike was a sort of curved shape that is actually even visible in surface faulting – there are non-eruptive faults west of the vents on the floor of Napau.


              Picture is from https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/jgrb.50108

              For dikes that are fed with degassed magma though, it would seem logical that the angle would be down, the normal effect of buoyancy would not apply so much.

    23. Nice addition maybe to Albert’s piece about the circulation of water, in, on and around Mount Fuji with pictures from Fuji, the lakes, some data of the lakes and pictures of waterfalls, done by a scientist (Geology) from Nepal. Can be downloaded as PDF:
      researchgate.net/publication/283834888_Hydrogeological_Features_of_Mount_Fuji_and_the_Surrounding_Area_Central_Japan_An_Overview

      by Danda Adhikari
      Tribhuvan University
      Abstract different source:
      https://www.nepjol.info/index.php/JIST/article/view/13834

    24. All the talk of the scale of volcanism on other planets, maybe the maximum scale of volcanism doesnt quite compare but there is one thing that cant be changed, that the mega volcanoes of mars and Venus are deep asleep and ours are wide awake 🙂

      Opening stage of the last eruption of Craters of the Moon as viewed from the northern summit of Big Southern Butte about 40 km away. 13 km long fissure that erupted between 1 and 3 km3 of hot trachyandesite lava in maybe only a few days, before long term shield building began, it was like a hybrid of Hekla and Laki. This place is expected to erupt again in the next few centuries 🙂

      • and ours are wide awake —–
        Not awake enough I’d say
        A little more activity could be nice

        • We just got spoiled last year, having 3 volcanoes that were recorded so well. Now nly one of those is ongoing continuously (Kilauea) and it may not be very interesting until it drains out or overflows, both events not immediate.

          But we did also just have the first VEI 6 in 30 years, and confirmation that some of the more extreme claims for eruptionsof this scale are actually far from impossible. I think that fact cant be understated enough. it will likely be decades before an eruption of larger volume takes place, and it might be over a century before one of comparable intensity happens.

          • I’m noticing a lot of places holding to the VEI 5 classification for HTHH. I know there’s always debate and uncertainty, but I thought there were pretty decisive measurements made supporting a VEI 6 level eruption.

            It’s interesting that Smithsonian has it at a 5 as well. Though I notice they tend toward conservative estimates for many large events.

          • Plus Soufriere St. Vincent. If you count from March 2021 (Fagra) to Jan 2022 (HTHH) you basically get five spectacular ones in ten months, not bad.

            • Don’t forget Taal – was that late 2020? Was a VEI4.
              Fukutuka-Okanoba in 2021 was also registered as a VEI4

            • Taal was a 3, and actually not even a big 3, about half the way to a 4. But more significant in that it has set off an ongoing episode, which in the past has often lead to a major event.

      • Better to live on a Super Earth type
        8’Earth masses woud be good that only yeilds 1,3 G .. big words are not as dense and puts you further from the core

        Super Earths are probably worlds of Hyperactive Tectonics If they are in habitable zone .. with their deeper mantles and much hotter interiors

        I imagine a world with lots of broken up small protocontinents and Island arcs and hotspot chains and land rises close to plate boundaries

        Having huge oceans are of good help of absorbing cO2 from over active volcanoes

        Or it coud all be a volcanic mess because of massive internal heating

        • I think it might be impossible to have a ‘habitable’ planet that also has hyperactive volcanism. Earth did have volcanism like that and it was a hellish place, with a dense atmosphere and probably almost no land. Venus was probably exactly the same, but because it was closer to the Sun it was never able to cool down so its early oceans evaporated.

          Exoplanets are so variable there is probably at least somewhere that actually does exist where a habitable environment coesizts with volcanism more intense than our own. But given that many of the LIPs we have had coincide with mass extinctions it seems thsi is not a good bet to take.

          Really, a planet that is that hot might just have a surface temperature too high to allow oceans without a dense atmosphere for billions of years, regardless of its location relative to its star or even if it has one at all. Carbon planets are probably hell planets almost universally, their silicon/titanium carbide mantles would react with water or another oxygen source that is always present (they are not free of oxygen, just have less of it than they do carbon) and turn the mantles into a rigid lattice of mostly diamond. So now you have an iron-diamond planet, and diamond is the best thermal conductor of any bulk solid… Basically the heat of the core is directly transferred to the crust, whic hmight still be largely silicate, and so you end up with a planet that stays as hot as its formation for billions of years….

          There is also the slight problem that many, maybe even most, super earths are probably going to be mini-neptunes or water planets unless they are in close proximity to a star. As soon as a planet can hold onto H2 with its gravity, it can become a gas giant. A supermassive terrestrial planet would have to be created as a stripped core of a gas giant to stay naked.

        • I imagine a world with a 50-km deep ocean, only sea life and volcanoes producing pillow lava only. Or one with an atmosphere ten times more dense than Venus. Conditions on Earth are no indication what other planets may look like. Even the other ‘terrestrial’ planets in our solar system are nothing like Earth. So it seems dangerous to expect something ‘a bit different from Earth’.

          • LoL dont forget sheet lavas.. not all submarine flows are pillows ”pillow lava” is really only submarine pahoehoe

            Faster submarine flows can flow just like it does on land in fast moving channels and currents

      • Superhabitable Super Earth Alien planets? Yes maybe

        A Rocky Planet somewhat larger than Earth coud be ideal for life, If it orbits a somewhat smaller sun that lives longer. ( 3 Earth masses and a K class orange dwarf sun that last 10 times longer than our sun )

        Gravity wont be crushing either..
        3 Earth masses gives almost No diffrence in gravity.
        You needs 10 Earth masses for
        2X Earth gravity. So large Super Earths will haves a supprisingly earthlike gravity.

        A somewhat larger planet will be ideal for keeping Plate Tectonics active, beacuse of a hotter interior than Earths, The interior retains more heat from formation, and more radioactive decay in a larger planet. Plate Tectonics is crucial in recycling Carbon Dioxide and Minerals. On somewhat larger Super Earths 2 to 3 Earth masses .. Tectonics maybe very lively with a thinner litosphere under more stress. Moderate sized Super Earths may have very fast tectonics indeed, forming an oceanic planet with a chaos of microcontinents, and mountain ranges and volcanoes everywhere. Icelands and New Zeelands everywhere on souch planet. Chaos Tectonics maybe in Big oceans

        Tectonics is crucial for keeping the CO2 levels so biosphere can photosyntesis and breathe.
        On Super Earths plenty of volcanic outgassing and as well as fast subduction may keep the CO2 more steady than Earths and avoid snowball events and climate disasters. Tectonics is the planets CO2 thermostat. Moderatly sized Super Earth class planets maybe ideal at this recycling with their larger mass.

        Our Super Earth will also have a very powerful magnetic field, with core temperatures of over 11 000 C the entire core maybe liquid, and combined with the large planets fast spinn, You will have a very very powerful magnetic field.
        Thats very useful protection when orbiting orange dwarf stars that can flare often. Souch a magnetic field coud be much stronger than Earths. The core will be liquid for much longer than Earths too due to the planets greater mass.

        A somewhat denser atmosphere than Earths will also be very useful on these planets. Denser Atmosphere allows you to orbit further out in the habitable zone, denser atmosphere also evens out the temperatures, keeping the poles warmer and as well as helping the winters to get less severe. With more air pressure You gets supercharged creatures with oxygen and CO2, and needs less in PPM than Earth to keep the climate stable. Denser air also warms on its own, less temperature diffrence between Equator and poles, and poles maybe Ice Free.
        There will also be less deserts and more humidity, and rainfall.

        With a denser atmosphere the planet can be placed further out in the habitable zone to balance the greenhouse effect

        A somewhat smaller Star than Earths sun sounds ideal too: it lives longer

        But as Chad say .. there is a huge vaierty of exoplanets

        • That sounds great. Many exo-planets have been found, but invariably with one of two problems:

          1- Not in habitable zone.
          2- Central star red dwarf.

          With problem 2 the question arises whether there has once been life, even more intelligent life. So time plays the biggest role. It is not very probable that we finde a planet similar to Earth during our life span as a species. So, one day the question might pop up (or has already) how and where to leave enough information in space.

          • The info question seems important to me. How to leave sensitive info without the Tw- and FB-blabla, I don’t mean Tw here though, but senseless political fighting. So, how to leave s.th. sensible for any future civilization, science possibly. And in space of course as this location will leave nihil when the sun gets really hot. And not just trash, but info. So far, we have some trash out there. It would shine a bad light on us.

            What happened here, 4,5 billion years ago, can happen elsewhere, for a while at least. And the question is of course, whether there is any possibility whatsoever that is has happened before. ???

            Hard to find out because of the distance. The nearest Red Dwarf to the sun is Proxima Centauri, just walking distance 😉 .

            • The most important information is just a sign that we exist (or have existed). Anything else is just gossip. There are a variety of ways to do this. Start walking probably not: it would take 850 million years to get there. (And that is without stopping for lunch.) Many people have thought about how to do this. Gauss proposed making mathematical shaped clearing in forests. The most effective proposal involves self-replicating mini-probes that can send out signals. How to make those last a billion years (and not evolve into something different in the process) might present a bit of a challenge. Science loves a challenge. Engineers hate them.

            • 850 million years without lunch, that made me laugh. Forests might be gone. So s.th. in rocks? Cratons!!! ? And on Mars for sure.

        • The ideal Star is an Orange Dwarf .. something rather kind of like the sun .. But they live for much longer than the sun will do

          • The very smallest Red Dwarfs have only 1/10 000 th of the Suns luminosity and you dont get anything earthlike with that

            The ideal is something between the sun and a red dwarf

            A Star that somewhat smaller than our sun is ideal

            Althrough VC bar is better for This discussing

            • — The ideal is something between the sun and a red dwarf
              A Star that somewhat smaller than our sun is ideal

              As far as I know nothing like that was ever seen so far. Correct me if wrong.
              This James Webb device is a great achievement though.

              Art and more:

            • They are one of the most common stars Orange Dwarfs

              Search Wikipedia

          • They are called K class main sequence stars are are very common

            • “However, there is growing evidence that K-type dwarf stars emit dangerously high energy radiation levels….”
              “This prolonged radiation saturation period may be sterilising, destroying the atmospheres of, or at least delaying the emergence of life for, Earth-like planets orbiting inside the habitable zones around K-type dwarf stars.”
              https://en.wikipedia.org/wiki/K-type_main-sequence_star

              Nothing is ever perfect.

    25. It l9oks like quales are picking up again on Reykjanes, not a new intrusion but this activity did happen quite clearly before previous intrusions.

      Is it reasonable to expect future intrusions at least at Fagradalsfjall and Keilir will get more quiet as the stress is released and crust heats up? The recent intrusion was already much faster than the first intrusion last year, even though still very noisy.

      Will be interesting if magma fills the rift eruptions might happen more often or last longer.

      • We’re now officially booked for Iceland, leaving October 23rd and returning November 6th. Too much to ask for some fresh lava?

        We’re heading to the site either way; should be a fun hike.

        I really wanted to check out some of the Laki lava down by the Skaftar river where it spills into the coastline, but observing the fissure vents properly would be rather difficult especially at the time of year we go. I haven’t looked that deeply at the travel but I believe it would require an F road, which will be closed.

      • Know of any cool volcanic features to check out that would be accessible this time of year? Our prior trips occurred before I really caught the volcanology bug.

        We’re also planning to travel to the field / valley at the base of Hekla (not too close though!) to get some nice photos of it. I’ve seen Snaefellsjokull and stood on top of Langjokull on prior trips, and I’ve seen Eyjafjallajökull and Myrdalsjokull from fairly close locations.

        We’re going to drive all the way up to the north and stay near Akureyri for four nights. Hoping to check out volcanic Lake Myvatn and some of the places in that area. Askja of course being much too far inland to get to. But anything else along the coast or near enough without requiring an F road would be doable.

        • Jealous. Eldfell comes to mind as a good and accessible place (is there a ferry?) to see the effect of that eruption. Askja would be fantastic but possibly too late in the year and would require an organised tour (don’t need to risk your own car). There are sights close to Reykjavik and at Laki, the cemetery where Steingrimsson is buried might still be there. (I don’t think the church of the fire mass still exists.) Days will be short and the weather appalling, I expect! Perhaps you’ll get to see the northern lights. Actual live lava might be less likely. Perhaps Grimsvotn will give it a go.

          • Vestmannaeyjar has been on the list since our last trip, now with an even more intriguing reason to visit. Thanks!

            And we actually haven’t done much on the Reykjanes peninsula; previous trips we always sort of spread our wings and went off to other corners of the island. So I think, especially as we plan to do the Fagradalsfjall hike, we should check out some of the other volcanic systems on Reykjanes that I’ve been reading about in the comments here for quite a while now =).

            The Laki tip sounds very interesting, I’ll be sure to look into it (I remember learning about Steingrimsson in one of their new touristy volcano museums that was still rather fun and informative).

            Honestly I think early Icelandic winter is a wonderful time to go. In most cases the temperature is above 0C, but much of the higher elevations will begin to form their beautiful white cloaks. In 2019 we had a lovely mild snowstorm for two days that coated everything in a few inches of powder without making travel too difficult. I’m from the northeast US, and in my decade + of having a (brace for it) 100km each way commute to work for a job that’d be open in the actual apocalypse (volcanic or otherwise), I’ve driven through my fair share of serious coastal blizzards.

            With that said, Icelandic windstorms are fearsome and dangerous, but I’m rather accustomed to driving through snow and ice. Just hoping for a stretch of decent weather on our long trek up to Akureyri (where the climate is much closer to ‘polar’), but we’ve built in a couple extra days to our itinerary for any weather related adjustments.

            I’ll be sure to share some pictures, I recently picked up a new DSLR for this trip replacing my 15 year old model that otherwise served me very well.

        • If you’re anyway going close to Hekla I can recommend a stop in Fluðir to take a relaxing bath at Gamla Laugin (Secret Lagoon). It’s an old geothermal bath surrounded by natural hot springs. They even have their own little Geysir right next to the pool.

    26. guess my favorite geological era? Hadean…
      as Albert sourely coud figure out.. early and middle hadean perfect for me

      • Shhhhhh lol yeeeeees!!!

        Theia Merger is probaly the sugar topping for me 😃😜🔥💥

        An insane sight really .. and perhaps the Earth was mostly vaporized forming a huge hot cloud Held togther by gravity or .. A mostly vaporized Earth with rocky vapour – liquid mantle with No sharp transition.

        That woud have been an insane sight
        But perhaps not much to see
        Earth was so hot because of energy of accreation ..Thats perhaps looked like Looking into the sun

      • IO is very addictive as well for me
        : ) Hopes Juno gets there soon

        • Sept 29. But don’t expect too much. There will only be a few images and the best one will be of a patch the night side. The main instruments are not optimized for the moons

      • Is this an eruption or an intrusion do we think?

        To my untrained and very visual eye the earthquakes the last week or so have looked quite similar to those at Rekjyanes. It would make sense that is an active phase as triggers that it is the whole MAR that shifts, so why not at Tjörnes too?

        It’s under the sea so evidence might be less obvious, but is there any info on fires in the area?

        • It is a common event for this area. The fault produces swarms like this every few years. Of course one day it will lead to an eruption – magma in Iceland is always looking for a way up. But very few of the swarms in this area lead to an eruption. You may have to wait a few centuries, and it will still erupt out of view under water

        • Seems to be on the Grímsey Oblique Rift, part of the TFZ which links the Northern Volcanic Zone part of the MAR to the Kolbeinsey Ridge. There has been historic submarine volcanic activity further south along the GOR near Manareyjar Island and to the north on the Kolbeinsey Ridge.

        • Looks like a tectonic mainshock-aftershock sequence.

        • You know, Jesper, when you post these beautiful images with the imagination of an ideal sun and an ideal world you forget time.
          That’s what Hollywood did regularly like in ET or in Independance Day. Only George Lucas was aware of the timmescale: “A long time ago in a galaxy far, far away….” This made me shudder and watch the first six, the Lucas films. Intelligent guy.

          In space there are two entities totally different from our thinking and phantasy: Room and Space. I can see it in Geology already. You get another timescale. You’s say to somebody who asks when the volcano (Thera) on Santorini erupted: “Oh, not so long ago”, and laymen stare at you in disbelief. For the “not so long ago”.

          Most people are used to a time scale between their grand-parents and their estimated death.

      • Waiting to see what Vatnajökull or Myrdalsjökull do to keep up. 😉

        • I’m keeping my eyes on Grimsvötn. It shouldn’t be long now.

          A short reminder: Note how the current swarm at Grimsey causes false detections over a wide area, just like the recent swarms at Reykjanes. During a swarm like this, one should only look at those quakes that are marked with a black outline on the map. Any dot or star with a light grey outline has not yet been manually verified and should be regarded as noise until reviewed. If something looks interesting or out of place, check the nearest drumplots. Any real earthquake of decent size will leave a noticeable waveform in the plot.

          • Will probably be very sudden, like the start of Kilaueas recent eruptions. There will be lots of quakes but the whole thing will happen within a few hours.

            Not sure we should expect anything massive though, 2011 was a very big eruption for the central volcano, if it erupts there again most likely it will be rather smaller. If it forms a dike and ruft though things might be different. No Laki #2 though, not for a long time, several millennia most likely. There is Bardarbunga for that 🙂

            • Unless it’s recharged and ready to go Saskunarvatn Part Deux: Electric Boogaloo.

              Kidding. Mostly.

            • Kidding aside, doesn’t Grimsvotn have a massive magma chamber(s)? What prevents it from having even larger eruptions? Did Laki drain the majority of what it had in reserve? It’s interesting to me after learning about Saskunarvatn which was basically a VEI 7 over 500ish years right?

              Did it lose its capacity to hold that much in reserve since, did the volcano fundamentally change, or is there something else going on?

              Sorry, I genuinely have so many questions and I decided a bit ago to just go for it and ask away on here. You all are so knowledgeable and I’m insatiably curious.

            • @Ryan

              Grimsvötn is a complex volcano. Roughly every 10 years, one of the shallow magma chambers erupts. Their volume is limited. But there is a large reservoir of magma underneath Vatnajökull (fed by the hot spot) and from time to time a large rifting event occurs. In that case the magma from Grimsvötn is drained into the rift. In combination with decompression melt, magma from the large reservoir can enter the rift and then you’ll have a Laki style event.

              The Laki eruption has pretty much relieved the stress in that area for a very long time.

            • Grimsvotn has a sizable chamber but nowhere close to a VEI 7 today, there is maybe 20 km3 that could collapse. That does assume there is somewhere for it to actually collapse into though. Grimsvotn fissure swarm has only erupted 3 or 4 times in the Holocene, and Laki was the biggest of these by a large degree, and very recently. Same as for Katla, it had erupted from fissures outside of its caldera only 3 times and Eldgja was by far the biggest, and only time it was a true rifting event within the Holocene. Basically erupting in this way is highly atypical for both Grimsvotn and Katla, so having Laki and Eldgja relatively close and within the past 1000 years is already a crazy lineup, to expect a repeat of either in any immediate future is very small odds.

              Bardarbunga on the other hand, large eruptions in that direction used to be a regular occurence before Eldgja, every 250-300 years or so. There has only been one Veidivotn eruption in the last 1000 years though, so maybe the next one could have a bit of a kick. Same could apply to the Hekla area, Hekla itself has been very active, while Vatnafjoll to its east has been asleep. Vatnafjoll apparently is capable of Laki-scale events, I dont know where that comes from as maps recently released dont show anything particularly extreme. Still, the area used to erupt regularly every couple centuries and has not done so now for over a millennium.
              These areas are where I would be looking for bigger eruptions in the future.
              But I think if you want a lava flood of massive size and extreme intensity in the next 100 years, in my opinion Iceland is not the most likely, Hawaii is. And slightly longer term, the bext eruption from Craters of the Moon.

            • All major eruptions are atypical. That makes them so hard to predict

            • Appreciate all the responses. All understood, and regarding Bardarbunga and Veidivotn that’s very interesting. Perhaps that’s the next larger scale event in some decades to centuries from now. I always found the explosive component of Veidivotn fascinating in and of itself.

              Albert: You always impart such meaningful shifts in perspective. You I’m sure are a captivating lecturer.

            • I think Veidivotn is usually effusive, just that the last two eruptions there happened through a lake. There are many effusive vents from 1477 that are north of the explosive craters and they look exactly like the lava at Holuhraun, and are compositionally identical.

              I guess the question is if the water present there now is enough to pose a hazard. Rivers likely dont, as Holuhraun erupted in a riverbed too. My guess is the next eruption will be effusive mostly, unless it erupts into þorisvatn. Also probably isnt going to be a disaster, more a year of fissure eruptions ranging from small up to Holuhraun sized, although higher intensity. Might also be rhyolite if the rift goes into Torfajokull and a dike forms from there.

            • Hawaii 2021 erupted up through a lake without going boom. The water simply boiled away.

              It seems that to get phreatomagmatic explosions, the water must be confined: open pots on the stove don’t explode, but pressure cookers and boilers can. Lava under water won’t do it, but lava over water can. 2018 made littoral cones from small explosions from water that became trapped under the lava and then boiled. The supercritical water under Hunga Tonga was confined, until because of the eruption removing some overburden pressure, it wasn’t.

              Veidivotn didn’t explode merely because it came up through lakes along part of its length. Either a considerable volume of water somehow was trapped and heated until a pressure failure occurred, e.g. an aquifer under an impermeable lid, or the dyke passed through, and remobilized, some older magma buried in the region, leftovers from a previous event that had had time to fractionate. Perhaps some of that Torfajokull rhyolite you mentioned.

            • Good point, and Hawaii did it twice, once in the crater lake and once during the 2018 eruption when it overran a large lake. In both cases there was evaporation but no explosion. And in both cases, the lava came into the lake through a surface flow. Phreatic explosions require that the lava come up from underneath and heats the ground water underneath the lake

            • I dont think that is what happened in 1477, it was a VEI 6 by tepgra volume but not comparable in intensity to a caldera formation like Pinatubo or Hunga Tonga Hunga Ha’apai. Think of Surtsey, except now give it a high eruption rate. It is a lava fountain through water.

              Kilauea in 2020 has a key difference, it didnt erupt into the lake but from afissure on the wall of the crater above it. Evidently the water table was not extensive. If the fissure did erupt in the lake though there wrobably would have been strong interaction if probably for only a short time.

              One can see that the craters of Veidivotn and Vatnaoldur are not explosion craters for the most part but tuff cones, which is indicative of surtseyan activity. Most of the craters also later filled with lava, some overflowed. The rhyolite was localised, and mostly effusive, and an explosive initial stage is well located to only the far southwest end, all the rest of the eruption was tholeiite basalt. There is an offset in the fissure line at the southwest end, the rhyolite and some more mafic vents near Landmannalaugar were probably a separate intrusion coming from Torfajokull, while the main crater row erupted along a dike from Bardarbunga. Holuhraun showed that dikes dont intrude into other volcanoes really, and Torfajokull is not dead even if past its peak. Rifts are just failures in the crust, zones of rapid extension. It is not any rule about how they fill, and a rift can go through more than one volcano.

              I will make a map of all this when I have time. It is quite interesting.

            • Kilauea 1960 is a good example of groundwater causing explosive activity.
              By the way, IMO now (finally!) officially considers Fagradalsfjall to be separate from Krysuvik.

            • That is really what I imagine Veidivotn looking like but on a larger scale.

              The 1477 eruption would have lasted a long time, Laki was 8 months, Holuhraun was 6 months, Askja was over 1 year, these rifts are long lived events. The 1477 sulfate peak starts at the beginning of the year and doesnt really go back down until after the start of 1478, so the rift might have been at least a year.
              The areas where the eruptions are effusive also dont show evidence of a scale of eruption that was larger than Holuhraun, so probably the event was similar magnitude but just lasted longer. 10 km3 of tephra is 3 km3 of magma, plus another maybe 0.5 km3 of lava that did erupt as lava in the craters, which is a little over twice the volume of lava erupted to make Holuhraun. So a duration of a bit over a year makes sense actually. My assumption though is that there was probably many separate eruptions, some small and at least one was very big, probably much of the volume in a relatively short time. The eruptions at Torfajokull might have happened before the big eruption at Veidivotn.

              There actually looks to have been two major eruptions during the rifting event. The first, which I think was probably the February eruption, extends across 12 km of the rift, and is all explosive tuff cones that are filled later with lava. The second is actually mostly effusive but has a large tuff cone at the southwest end that it shares with the previous fissure. The eruptions that happened near Torfajokull are also interesting, the rhyolite was entirely effusive, but one of the basalt vents is within an explosion crater. I think that these vents were erupted from a dike that came from Torfajokull locally, which probably happened after the February eruption given the flows are not blanketed in tephra.

              What actually surprises me is that technically this eruption is not historical, it was never seen at all really, and not documented. I am sure its ash was noticed, but no record exists that details a location, like happened for the eruptions of Hekla which is really not all that far away.

            • Veidivotn was a winter eruption, starting in Autumn 1476 and lasting until April 1477, dated from the ice cores. It produced 3.5 km3 tephra, or 1.5km3 of rock/magma. Your value of 10km3 tephra seems a tad high.

            • The 10 km3 number is just from what I have heard generally, mostly on here. Never seen any actual official source on it, actually there is very little information on the area at all.

              It looks like the eruption was very similar in both duration and volume to Holuhraun then, though much more variable in intensity, the February eruption peak was maybe of a similar intensity to what Laki reached but not for a long time. In this case then it might also be a long time before there is another eruption from Bardarbunga in any scale, Holuhraun was a big eruption.

              Hamarinn volcano southwest of Bardarbunga might be able to feed a big rift to the southwest. Otherwise I think if there is going to be another big effusive eruption it is probably going to be from the Hekla area, either Hekla itself or Vatnafjoll.

            • We wrote a short bit of text about it in https://www.volcanocafe.org/volcanoes-of-the-north-the-fire-in-the-ice/ As you say, nothing was written about it at the time. No one noticed it./ Icelanders perhaps mainly stay indoors in winter. This area is not directly visible from the coast: some hill climbing is needed. It is a bit surprising though that so much ash was not noticed. I am open to suggestions for explanations.

            • From the conversations herein, additional research on the event, and a translation of the name ‘Holurhaun’ [pit Lava], I don’t see the connection. Any thoughts?

            • I am surprised. If anyone can find a source for this classification I would be interested. It seemed unlikely that a VEI-6 upwind from Europe could have been missed.

              And yes, it is always best to be cautious in assigning numbers

            • GVP VEI classifications are not the best, they are often guesses or based on poor estimates when proper data is lacking.

    27. Taal just produced another small phreatomagmatic burst, and with a large portion of the volcano inflating once again, now would seem like a good time to raise the alert up from 1 to a 2 or 3 but that’s not what’s happening for reasons I am not aware of. While it is possible that Taal will keep chugging out these smaller eruptions, it’s also possible that Taal will produce a larger eruption. So let’s be safe instead of sorry

      • Just read a recent paper on Taal and it seems that the (roughly) 0.53km3 eruption and the 0.64km3 southwest dike barely made a dent, it began immediate recharge 3 weeks after the 2020 eruption. Seems quite clear that there’s an area of partial melt some 18km down that fed the dike via the smaller chamber under (east) of the central island. It also states that aside from the dike (which became vertical rather sharply), fissures were noticed in the north part of the larger caldera afterwards.

        They also theorise that the constant degassing can trigger an eruption through pressure imbalance, by depressurising and deflating the central island – which would then cause rapid magma ascent and rapid inflation.

        There is another caldera in Batangas Bay to the southwest and I do wonder about the interaction between the two – clearly if the dike became rather vertical as it headed southwest it hit a barrier of sorts – we’ve seen this before in Iceland.

        Clearly there is not enough pressure yet…but that pressure is building. There shouldn’t be anyone on that central island or the entire left hand side of the caldera, in my personal opinion.

        • Could you give the link? My interest is peaked! Phivolcs doesn’t seem to be worried about Taal for some reason

        • The 2020 eruption was not 0.58 km3, that was the volume of the dike. The eruption was probably only 0.03 km3, it was well under the volume needed for a VEI 4 rating anyway. The fissures outside of Volcano Island also were seen in 1911, probably more of a tectonic feature, Taal lacks the elevation needed for its intrusions to erupt.

          High SO2 also is maybe not surprising given Taal is saturated with water that will dissolve the gas and transport it to the surface very effectively. It is basically like having an open conduit except instead of a lava lake it is all hydrothermal. In this scenario it might actually be more dangerous if the SO2 levels drop off, as that means the circulation of water has stopped and could be building pressure. It seems likely that there is a steady supply of magma right now so this situation could be a new normal.

          • Not sure which is the article Andy mentions. But the numbers seem to come from here:

            https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021GL092803

            0.531 km3 is the modelled volume of magma reservoir deflation, and 0.643 km3 is the modelled volume of the lateral dike intrusion. The difference in the values is probably either due to magma expanding when making the dike, or due to some error because the methods are not perfect. This same article puts the Taal eruption as 0.032 km3, but do not mention the method used.

            A more recent article came up measuring the ash thickness and base surge deposits. They give a range of estimates, that with the base surges included, amount to 0.076-0.109 km3. So it was somewhere between a VEI 3 and 4. This value I think is more definitive than from the older article.

            https://link.springer.com/article/10.1007/s00445-022-01534-y

            Something interesting is that the 2020 erupted tephra is andesitic. Much more evolved than the basalts of the 1965-1977 Tabaro eruptions. It is also more evolved than any other samples on Taal. Although one should note that the geochemical sampling of Taal volcanic products is very sparse.

    28. Just occurring to me: Isn’t this a classical Triple Junction (Okhotsk, Amurian and Philippine plates) near or even under Mount Fuji?
      Is this situation comparable at all to the Azores (American, African, European) or Galápagos (Nazca, Cocos, Pacific)? Or, maybe better, to the Kamchatka-Aleutian Triple Junction?

          • Don’t really know what you are talking about. Thanks for the link to Carl’s piece, will read that.
            I put all the links up there, do not know the site, found it by googling the Triple Junction up there and think they used the same source: Google Sat. The text in Carl’s piece is be Karen Z.

            Basically it is like Owls to Athens. You think you found a nice addition, But VC has had it already.

            • VH is a good site. It originated from VC which is probably why you see similarities.

        • Baikal rift appears to extend much further west, I could be wrong but Lake Balkash and Zaysan appear to be the western extent of this platelet. I’m not sure the southwest portion of the Amur plate is as readily defined, because there’s been a few flood basalts in that region and the cratons seem to have welded together, in retrospect of the Indian Plate collision and several Chinese orogenies.

          I think in the future the rift will extend as far as Pakistan and eventually create a new ocean.

            • Read it again, beautiful. So you think Tethys might make a renaissance:

              Albert 23/10/2016 at 10:34
              Perhaps but there is an alternative. The Baikal rift turn east at the north end of Lake Baikal, and west at the southern end. It could also re-open the Tethys ocean but a bit further north than the original, effectively along part of the Silk Road. –

              I believe that this idea is beautiful.

      • That is mentioned in the post. Triple points can form at hot spots, which are the ones you mention. In the case of Fuji the triple point (an area rather than a point) seems largely unrelated to the volcano

        • The piece I linked said about the same you did: That the main disturbance might be the Okhotsk Plate. You wrote:
          “This remnant carried an ancient oceanic flood basalt and this helped it to avoid subduction.”
          Very interesting I’d say. Same thing further south in the western Pacific Ocean. Resistance to annihilation? So, maybe a small part of the Pacific Ocean will survive for good.
          The Queen will be laid to rest on Sunday, 18th Sept. after a ten day procedure.

          • Definitely, under NZ at the moment with regards the Chatham Rise and Hikurangi, it is struggling to subduct and may grind to a halt. Also with the Philippines/Benham Rise.

    29. And the UK reaches the end of an era today with the death of Elizabeth II

    30. North East of Pahala, it was reviewed

      2022-09-08 12:04:03
      Earthquake
      Magnitude:4.2M
      Depth:20.4mi

    31. Hopefully one of these pics of one of the major fires (Mosquito) now raging in California gets posted. The pyroCb is being compared to a volcanic plume…and no wonder.
      At this time, it is not clear if moisture from Hurricane Kay will trigger any rainfall this far north (Truckee-Tahoe) region.


    32. While still somewhat fresh on the topic of the largest continental volcano, check out Marsabit in Africa (north of Kilamanjaro, east of the rift).

      Just doing some quick Google earth work shows that it’s around 150km wide along the rift, and the lava flows extend perpendicular to the rift approximately 100km. Given, no clue how deep this goes, but that’s gotta be up there for the largest based on the expanse it covers alone.

      For more explosive volcanoes, I would say some of the Tibesti mountains in the Sahara would be good candidates. Tarson Voon is approximately 60km across just for the main cone edifice, while the fissure row it’s a part of is much longer. Then there is also likely a good amount of ejecta that was blown away as ash during ignimbrite eruptions.

      • Tarso Voon is indeed very large, flows cover an area roughly 360 x 330 miles.

      • Wikipedia says Emi Koussi has 2500 km3. The complex of Yirrige and Tousside seems also similarly voluminous. So Tibesti has some big volcanoes.

        I do wonder about Harrat Ash Shaam in Arabia, the largest of the Arabian volcanic fields. Harrat Ash Shaam covers 45000 km2. It almost surely the largest active volcanic field of primitive basaltic-basanitic lavas in the world. I have not seen any volume estimate doing a quick search, but if it had an average thickness of 100 meters, which I think could be reasonable, even conservative maybe, that would already be 4500 km3. But the thickness is very variable and hard to know exactly.

    33. Tjornes is currently quite extraordinary; multiple EQs per minute. I’ve never dealt with anything remotely resembling that. We would consider more than 20 EQs per 8 hour shift to be ‘getting busy’!

      • Looks like it is catching up with the Reykjanes Peninsula. Note activity on the Peninsula quietened down when TFZ picked up.

    34. near basel (switzerland) and nuclear plant fessenheim (france) , EQ Mulhouse magnitude 4.7 2022-09-10 17:58
      (volcanocafe: the basel earthquake)

    35. The earthquake rate at Mauna Loa has steadily increased since July, and the summit shows inflation and contraction -the combination suggests that the magma is not quite located underneath the summit but a bit to the side.

    36. Albert, attempt of a suggestion to this:
      “Icelanders perhaps mainly stay indoors in winter. This area is not directly visible from the coast: some hill climbing is needed. It is a bit surprising though that so much ash was not noticed. I am open to suggestions for explanations.”

      Attempt:
      While the exact number of deaths from the Black Death is unknown, it is clear that the plague caused a demographic shock, and that the population did not recover to pre-pandemic levels until the 17th century.
      https://en.wikipedia.org/wiki/Black_Death_in_Norway

      Next to no trade or only little trade for more than a century, very small population between 30.000 and 50.000 (estimate), all living near today’s Reykjavik, different issues, didn’t care for some volcano in the north.

      Didn’t have an issue with the Black Death themselves it seems or is believed, But I am sceptical about this. Anyway, if the population was small they had enough food in the south amd didn’t go up there. Ships see volcanoes, but there might not have been many ships from Europe at the time. Besides ships would go there in summer and not in autumn.
      So nobody was there. This was after the Greenland settlements had been given up. So, those places in the north were possibly dead. The Little Ice Age might have had an onset already, dates for the start vary, and in the north it might have started already between 1300 and 1400. That would have given them enough trouble. Ash would be the least.

      • The 15th century is actually not a bad time for Iceland. Their fish were in high demand in Europe. The eruption was in the south of Iceland, not the north, but in a sparsely populated region. The highlands where the eruption happened was not occupied, but the southern coast was. But I think there were no good harbours there so perhaps people had moved to places where they could fish. There was an eruption in Katla around this time which also is not documented but did produce a thick ash layer to the west.

        The older Iceland eruptions are documented mainly in the annals, which were largely church-based. They ceased between around 1430 and 1500, and perhaps too few other people were literate. Oral traditions can miss out a lot and cannot replace written reports.

        I have found a reference to one historical document which mentions thick ashfall in 1477. I’ll see whether I can dig it out

        • Seems from what I can find the only eruptions that were actually witnessed back in the early historic period were those that happened on Reykjanes. There was also Hellmundahraun, near Langjokull, where the lava was seen but the eruption location wasnt directly. Eldgja was probably also witnessed. Outside of that though not much.

          The first eruption with a definite record might have been the 1000 AD eruption near Blafjoll. The first eruption though where there is no doubt on the dates though is probably Hekla in 1104. Hekla got blamed for most eruptions in Iceland back then too, so wouldnt surprise me if the 1477 eruption did too.

          • We have fairly detailed descriptions of Hekla’s eruptions in the 14th century, from the annals. They were observed and in some cases, hard to miss. ‘Coming up of fire in Mount Hekla’ ‘darkness far and wide’ ”from nine o’clock in the morning to mid afternoon men could not see’ ‘ash was ankledeep’. It is those reports from annals which largely cease after 1420 or so.

            • Next attempt of an explanation: Wrong volcano, by now changed to Veiðivötn–Bárðarbunga:
              “Thórarinsson (1958) associated tephra layer “a” with an observed tephra-fall in the Eyjafjörður area, northern Iceland (Fig. 1), which was subsequently reported in a votive letter written on 11 March 1477 CE. Based on this a historical date of early 1477 CE, most likely February, can be ascribed to the Veiðivötn–Bárðarbunga eruption, and it is henceforth referred to as V1477”.
              https://cp.copernicus.org/articles/17/565/2021/

              So, maybe you were thinking of this above mentioned votive letter.

            • Yes, that was the one. It fits very well with the dates from the ice record.

    37. Specialists comment by IMO, google translated.
      https://www.vedur.is/#syn=skjalftar

      “”Written by geoscientist on duty Sep 12 02:04
      Earthquake activity at Grímsey increased again around midnight after activity had decreased yesterday. Over 6,000 earthquakes have been recorded since the storm began. The largest earthquake of the series was measured at 04:01 on September 8, and it turned out to be 4.9 in magnitude. The biggest earthquakes of the series have been felt in many parts of North Iceland. The last time there was a similar storm in the area was in February 2018.””

      Seems the swarm has a tectonic nature only. Low Hz measurements stay in the usual range.

      Plot beneath shows checked quakes. The swarm occurs in alternately parts of the Grimsey Oblique Rift.
      Credits graph IMO

      The 4.9 triggered the swarm, I think.

      Illustration (taken from Structures and Styles of Deformation in Rift, Ridge, Transform Zone, Oblique Rift and a Microplate Offshore/Onshore North Iceland, Khodayar and Björnsson) shows the complexity of deformation zones in part of the rift.

      https://www.researchgate.net/publication/327341348_Structures_and_Styles_of_Deformation_in_Rift_Ridge_Transform_Zone_Oblique_Rift_and_a_Microplate_OffshoreOnshore_North_Iceland

    38. Given some of the comments regarding deveIopments at Taal, I envision a script written and setting down the conversations of this august body monitoring the the events around Mount Vesuvius beginning in January of 79 AD.

      • Its sort of an arbitrary difference, they are all rifts that open and rarely in the same place. Only Hengill stands out, as a central volcano formed. But nowdays it looks like it is dead, as all recent eruptions there have been basalt fissure eruptions and there is no caldera to suggest an active shallow chamber.

        Reykjanes is a weird place as it is geologically the youngest part of Iceland but also very old for a still active area. There are parts that are over a million years old sitting immediately adjacent to active vents. At the same time it is growing out to sea. I saw some speculation the Vestmanneyjar islands are evolving to replace Reykjanes as the new MAR, but this seems very far fetched. Reykjanes connects directly to the SISZ, which goes up to Hekla. Hekla does rift, it seems that area might be the far end of the Veidivotn rift in a tectonic sense. Katla however almost never rifts, abd Grimsvotn is underdeveloped compared to Bardarbunga, it is only because Laki and Eldgja happened recebtly, both were statistically exceptional events. Reykjanes in this case still seems the place the ridge will always surface at least for the next few million years.

        • The rift has moved before. Somewhere between 7 and 5.5Ma, the rift moved from Snaefellsnes to Reykjanes. At that time, the Borgarfjörður seismic area played a similar role as the SISZ does today.

          • Well yes, but point I am making is that there is not really any evidence that the Reykjanes section is declining now or that volcanism south of Katla is rifting and growing out to sea, actually despite its cyclic eruptions Reykjanes is one of the most active parts of the country. The rest of the western rift, up to Langjokull, probably is declining in favor of the rift that is where Laki and Veidivotn are, but the southwest Vatnajokull rift (‘dead zone’) stops north of Katla, and its furthest extent is at Hekla, next to the SISZ. Veidivotn is also the most active section, and trends more or less directly towards Hekla after which there is only transform movement until volcanism resumes again at Reykjanes.

            It is a wild shot, but I find it interesting that Hekla erupted in 1104 which was within the height of the last cycle at Reykjanes, and it is on the other end of the SISZ which trends directly into the Reykjanes fault. More frequent ctivity at Hekla after this I think would have been due to wider tectonics associated with the massive rifting from Eldgja and then later Laki, well outside of the normal zone of rifting. That is also probably why Vatnafjoll has been asleep, although there is so little data on that volcano I dont know if 1200 years is actually anything unusual. But having Hekla erupt within the same time with a plausible tectonic interaction sounds like an area of interest. At least some of the other early Hekla eruptions also took place during Reykjanes cycles too, not all but more than would seem completely coincidental.

            • The 1104 eruption was not actually in 1104. The Hekla eruptions show no relation to Reykjanes activity, nor would you expect this. Think of it in terms of rifting. There are two main rifting zones, the eastern and western ones, both ending at the southern termination in a large central volcano (Hengill and Katla). The eastern zone takes up most of the rifting but that has’t always been the case. Further south the western zone ends and the rifting is taking up by the Reykjanes fault, a combination of a rift and a transform. This greatly reduces the rifting left over for the eastern volcanic zone, but not quite to zero. So you still get some dikes and some eruptions – more obvious when this area was still above water, but less than further north because of the higher stress (less rifting) and cooler mantle. The rift zones change over time. Hoffsjokul shows a time when there was a rift zone between the current east and west zones. The northern volcanic zone has also moved location over time. Predicting how it will change in the future is risky. Predicting that it will change is fairly safe.

            • Still, it will be along time before Reykjanes is inactive, probably at least a million years before that happens and a new rift zone forms properly south of Katla and Eyjafjallajokull. From what I can find and is known currently, Eldgja was the first time Katla connected to the rift zone in the Holocene, and probably in much longer. There was another large lava flood from it about 7000 years ago but this was from radial dikes that were all on the slopes of the volcano.

        • It will move down to Katla – Bardarbunga line in the future

          Reykjanes Ridge will jump towards westman Islands – Grimsvötn line and connect to Askja

          With more decompression melting under Katla .. she may turn Thoelitic as well

    Comments are closed.