The White Mountain, Úytaahkoo or Mount Shasta

Starting today, we begin to reproduce some of the more popular posts originally published on the old site. But don’t worry! We will continue to produce new posts as and when something of interest crops up!

Fig 1. Sunrise at Mount Shasta with the satellite cone Shastina to the left (Wikimedia Commons)

Sunrise at Mount Shasta with the satellite cone Shastina to the left (Wikimedia Commons)

Volcanic activity in North America is surprisingly infrequent. In spite of there being no less than 255 volcanoes or volcanic features such as maars or volcanic fields listed for California (20), Oregon (65), Washington (21) and British Columbia (149), situated on or adjacent to the Cascades Range and above the subduction zone where the last dregs of the Farallon Plate is disappearing beneath the main continent and the Juan de Fuca plate knocking on the door, there have only been some 20 eruptions or periods of eruptive activity over the past 1,000 years. This is a surprisingly low number for the Ring of Fire and if we compare with Alaska, Japan, the Philippines or Indonesia, we can only surmise that the entire Cascadian Arc with its associated volcanic fields is in a quiescent phase.

Located at the southern end of the Cascade Range in Siskiyou County, California, the 4,322 metres high (14,179 ft) Mount Shasta is ranked as the second highest peak of the Cascade Range after Mount Rainier. It rises 2,994 metres (9,822 ft) above the surrounding landscape and has an estimated volume in excess of 350 km3 (85 cubic miles) which makes it the largest of all Cascade volcanoes, ahead of the similarly sized Mount Adams and the imposing Mount Rainier which towers above Seattle. It is mainly composed of silicic andesite to dacite.

Shasta, Shastina and in the foreground, Black Butte, tiny in comparison in spite of rising more than 600 m above the surrounding landscape itself. (

Shasta, Shastina and in the foreground, Black Butte, tiny in comparison in spite of rising more than 600 m above the surrounding landscape itself. (

Mount Shasta is composed of four overlapping cones, five if you count the destroyed cone of ancestral Shasta, which together form the main peak Shasta and the satellite cone Shastina. At 3,760 metres (12,330 ft), Shastina would rank fourth of the Cascade peaks if it were recognised as a separate mountain. Nearby is a 9,500 year old dacite lava dome associated with Mount Shasta, Black Butte. In it’s own right, it could be considered to be a large mountain as it rises more than 600 metres above the plains to the NNW of Shasta, even if it is dwarfed into insignificance by Shasta and Shastina in the background.

Mount Shasta often experiences strange weather phenomena. Here, Shasta is hidden by lenticular clouds whereas the cone of Shastina is clearly visible. Visible also in the foreground is the remains of the absolutely massive debris avalanche dated to between 300 and 380 kA that resulted from the collapse and total destruction of the ancestral cone. (

Mount Shasta often experiences strange weather phenomena. Here, Shasta is hidden by lenticular clouds whereas the cone of Shastina is clearly visible. Visible also in the foreground is the remains of the absolutely massive debris avalanche dated to between 300 and 380 kA that resulted from the collapse and total destruction of the ancestral cone. (

Before we move on to have a look of the geological history of Shasta, it is worth noticing that because of the meteorological conditions, quite often a difference of 60C or more between the valley to the north and the mountain peak, Mount Shasta is often accompanied by strange cloud formations. Is it surprising then, located in California as she is, that she is a favourite with UFO-ologists with claims such as the one that there is a portal located on Mount Shasta from which alien spacecraft appear periodically…

The landscape left by the gigantic flank collapse and subsequent debris avalanche dated to between 300 and 380 kA. The peaks of Shasta and Shastina tower above the landscape and to the right Black Butte right at the foothills of Shasta is clearly visible. (John Scurlock,

The landscape left by the gigantic flank collapse and subsequent debris avalanche dated to between 300 and 380 kA. The peaks of Shasta and Shastina tower above the landscape and to the right Black Butte right at the foothills of Shasta is clearly visible. (John Scurlock,

Even if there is evidence of much earlier volcanism in the area, activity at Mount Shasta is thought to have begun about 590,000 years ago and is divided into four distinct periods. The first cycle, which lasted about a quarter of a million years, saw the building of the ancestral cone from mainly andesitic lavas and ended with its destruction somewhere between 300 and 380 thousand years ago. The cone of ancestral Shasta was almost completely destroyed by a sector collapse of truly epic proportions. The total volume of the collapsed sector is estimated at 45 km3 and covers an area of about 675 square kilometres with a maximum extent of 49 kilometres to the north. Some of the “boulders” carried down by the avalanche still protrude more than 100 metres above the avalanche deposit floor… As a comparison, the debris avalanche from the 1980 sector collapse of Mount St Helens had a total volume of about 2.5 km3 and reached 23 km down a river valley. There is no evidence of contemporary volcanic activity, thus the cause of the avalanche remains unknown.

Shasta’s peaks: SR – Sargents Ridge 250kA, MH – Misery Hill 130 kA, Sh – Shastina 9.5 kA. The current summit, the Hotlum cone is younger than Shastina. (

Shasta’s peaks: SR – Sargents Ridge 250kA, MH – Misery Hill 130 kA, Sh – Shastina 9.5 kA. The current summit, the Hotlum cone is younger than Shastina. (

After the sector collapse that destroyed ancestral Shasta, there seems to have been a hiatus of between 50 to 130 thousand years after which the oldest of the four cones that make up modern Shasta, the Sargents Ridge cone, began to grow less than a quarter of a million years ago. Today, what remains of this cone which has undergone two periods of glaciation is visble on the south side of the mountain. What today is the main edifice of Shasta, the Misery Hill cone began to grow about 130,000 years ago and has suffered one period of glaciation. The final two cones are both Holocene. The truly massive satellite cone Shastina was formed over a period of merely 300 years between 9,700 and 9,400 years ago while the present summit, the Hotlum cone is younger even if it may overlap Shastina in age. A small craterlike depression in the summit dome contains several small groups of fumaroles and an acidic hot spring. The extrusion of these domes was accompanied by pyroclastic flows which extended more than 10 kilometres south and 5 kilometres north of the domes.

“Mount Shastina”. As is clearly visible from this picture, Shastina is a highly impressive volcano in its own right. Notable is that it grew in an incredibly short period of time, 300 years, just under 10,000 years ago. (

“Mount Shastina”. As is clearly visible from this picture, Shastina is a highly impressive volcano in its own right. Notable is that it grew in an incredibly short period of time, 300 years, just under 10,000 years ago. (

Shastina is a stratovolcano composed of silicic andesite flows and dacite plugs and has a topographic prominence of over 137 metres (450 ft) as measured from the saddle that connects it with Shasta. This easily exceeds the typical mountaineering standard (91 metres or 300 ft) for a peak to qualify as an independent summit, yet for some peculiar reason, this is not applied. As Shastina towers at 2432 metres (7979 ft) above the surrounding landscape, I personally feel that Shastina is hard done by. In comparison, Vesuvius is no more than a 1,281-metre midget of a volcano.

The impressive dacite lava dome complex Black Butte as seen from Interstate 5. Anyone fancy a ride? (

The impressive dacite lava dome complex Black Butte as seen from Interstate 5. Anyone fancy a ride? (

The final major feature of the Shasta complex is the parasitic dacite cone complex that makes up the 600 metres high Black Butte, 13 km northwest of Shasta. It was formed right at the end of the period of activity that created Shastina and the Hotlum Cone some 9½ thousand years ago.

Over the last 10,000 years, Shasta has erupted on average once every 800 years. The most recent eruption at the Hotlum cone, the present summit of Shasta proper, may have occurred as late as 1786 A.D. The eruptions appear to have been small, something that cannot be said for the eruptive period of c. 9,500 years ago – andesitic lava flows, dacitic lava dome extrusions accompanied by large pyroclastic flows that reached up to 20 km from the volcano and formed the current summit complex, the massive Shastina as well as Black Butte.





Suggested further reading:


Shasta geology –

Shasta volcanic hazards –

Black Butte –

62 thoughts on “The White Mountain, Úytaahkoo or Mount Shasta

  1. Henrik:

    Wow, now THAT is what I call “Service.” Your response time rivals that of cops depicted in Hollywood movies! LOL


  2. Beautiful imposing volcano!

    I have some replies to the last post.

    Karen: Regarding Katla earthquake before the 1918 eruption, it could have been a M4.5-5, since nowadays M3.5 are barely felt in the vicinity of Katla.

    Henrik: variations of ice thickness of Katla seem too small to account for its seasonal behavior. Like arjanemm, I reckon it must be the summer melt water. But to spice things up, why then does Hekla also shows a seasonal pattern in their eruptions almost always falling in the first half of the year, especially around early spring. While other volcanoes like Grimsvotn, Askja or Krisuvik show no seasonal pattern at all.

    Jamie: those Hekla sudden movements can be a sign of sudden inflation (due to magma influx), or just sudden plate movements (Hekla sits in Hreppar microplate), which often correlates to nothing happening. Anywhere the area is also “due” to a large earthquake eventually. But interestingly, something seems to be happening. There has been two quakes at Hekla yesterday, first a deep quake to the southwest, then a shallow microquake.

    Usually a Hekla eruption would be proceeded first by 1) streams and watertable changes (in days before the eruption – and perhaps the earliest warning sign for an eruption), as well as 2) possible microquakes in the area (but these can also occur without an eruption). Then, 3) smell of sulfur could be felt across the area and animals show weird behavior in hours before the eruption (these are two clear signs of a impending eruption). 4) About 2hours to 30min before, a string of a few M2-3 earthquakes should start at the same time as 5) sharp movements in the borewells at Burfell (

    These last two things only occur before an eruption. As far as I know, GPS changes have not been seen before the previous eruptions.

    • The Hekla stations showing GPS movements to south/southeast are:
      NORS (shows also deflation)
      Fedgar, FEDG (shows also strong deflation)
      hestalda, HESA (seems to show a bit inflation)

      a bit of north movement in MSJK
      Haukadalur, ISAK and GLER shows no changes
      And at Katla, no GPS changes are seen.

      These seem to indicate in my opinion more of a Hreppar movement, or otherwise they behave the opposite that would happen if magma would push upwards at Hekla (or alternatively Hekla magma is migrating somewhere else eastwards or southwards)

      I have seen over the years changes like this, even across Iceland, without anything special happening. I can´t remember last time they did happen, but I have noticed them here in the blog.

    • The only problem I see with 3) is the same as the Forest Paradox [tree falls in the forest with no one around – does it make a sound?] If there is no one around to smell the sulfur or to take note of any strange animal behavior, what good is it as an indicator. From what I can tell and what I have gleaned from this site and others is that the area around Hekla is not exactly populated to any large degree. This is largely due to the highly unpredictable nature of Hekla eruptions (typically almost no warning prior to an eruption).

      And, water table and stream changes are not uncommon in any hydrologic system, especially during season changes. Any precursive eruption-driven change that coincides with a seasonal one could be masked.

      …and I don’t know where I am going with this. Well, other than — I oh-so want to visit Iceland, but just not Hekla. She seems to act like a stick of dynamite that has sat in the sun too long. I would be afraid that I may sneeze too hard around her and set her off! 🙂

    • Re “seasonal behaviour”: I agree that Kalta seems to show it, but Bardarbunga (like Grimsvotn) doesn’t. That does seem puzzling, but Askja and Krysivik aren’t glaciated so in comparison they seem less so – presuming, that is, that Katla’s behaviour is associated with its being under a glacier.

      Re Hekla and Verbosely Laconic’s comments: the nearest farm is about 10 kms away (on a distinct hill), iirc. Would animals at this distance pick up precursor signs?

      • That’s kinda my point. What some would look for as precursors to an eruption may be missed due to the sheer isolation of Hekla. And, as far as tourists are concerned, the very nature of a tourist implies that they do not know what is “normal” or “abnormal” behavior in a local ecosystem. Even if they suspect something, they are less likely to tell or even be believed if they do say something.

    • In the literature, the summer earthquake activity in Katla is attributed in part to large ice blocks falling off the escarpment.

      Ice flow may be more important than ice melt. The summer melt presumably lets water collect below the ice cap, lubricating the flow and speeding up the glacier. This reduces the weight of the ice cap by much more than the amount of melt. The eruptions in late summer may than be triggered by the lower pressure, if the magma is already close to the surface.

      • That’s a tremendous explanation. Your two short paras have brought much illumination to my mind – thank you.

        And so, because Bardarbunga (and Grimsvotn, in a different way) don’t have steep glacial escarpments to anything like to the same degree as Katla, we don’t get seasonal earthquakes nearly as much in them.

  3. Marvelous mountain. Why the low activity of the Cascades? Is it the slowness of the subducting plate? Slow rate of melt? Or difficulty of the melt to get to the surface?

    • When I was reading up for the Cascade volcanoes for this series of articles, I got the impression that the Cascades has had several periods of activity separated by long periods of quiescence and that the latest period was about 10,000 years ago with the great eruption of Mount Mazama at 7.7 kA BP coming at the tail end. If you look at New Zealand and the great eruptions, there are similar bouts of high activity but is a valid hypothesis or just happenstance?

      • I could see this being related to periodic extensional tectonics. It’s said that the large Italian calderas flare up intermittently when extensional activity starts to occur. Given that extensional tectonic activity does not seem to be regular in these areas, it could make sense that some of these flareups align with region-wide periods of extension, and the slow periods align with periods with very little extension.

        • There was a flareup of activity in central Oregon between Three Sisters and Mount Jefferson about 1500 years ago, and there were several eruptions in Arizona and Utah (these are Basin and Range volcanoes) about 1,000 years ago, those areas have been completely silent since then so it would appear that was a period of increased extension. There was fairly regular activity in the Cascades between 1781 and 1917, with no more than 20 years between eruptions. Now we appear to be in a very quiet period, there was no activity at all between the end of the Lassen Peak eruption in 1917 and the unrest at Mount Baker in 1975, that’s 58 years of total silence. The renewed activity at St. Helens doesn’t seem to have started a new period of increased activity. Maybe this will change when the Cascadia megathrust quake finally happens, but that’s impossible to say.

          • One thing to keep in mind regarding Cascadia is that there simply aren’t that many volcanoes there since the region is much smaller than many other volcanic arcs. If you were to compare the cascades to a similar sized region in central Japan or Indonesia, I would wager that the activity level wouldn’t actually be all that different.

            As for megathrust quakes, they may have some effect on volcanoes, but given the recurrance interval of around 300-400 or so years, it’s worth noting that this is fairly frequent in terms of volcanic periodicity. If volcanoes reacted heavily to megathrusts, we would see more volcanoes that erupt somewhat regularly every 300-400 years, but this is not the case.

          • Regular most of the time, though there have been 1,000 year gaps between such quakes in Cascadia. I was thinking more of a single isolated event after the megathrust quake, like Puyehue Cordon-Caulle in 1960- breaking the lull in eruptions- (after the Valdivia quake) rather than an arc-wide uptick in activity (I would be more concerned about landslides than eruptions though). The last Cascadia quake (1700) roughly corresponds with the most recent Glacier Peak eruption which *could* be related, similarly there’s a theory that a major quake could’ve influenced the unusual event of two VEI5 eruptions in 2 years at St. Helens 500 years ago- note the first blast was just short of VEI6, the second was a bit larger than 1980.

            On a side note, St Helens has had two VEI6 blasts in its history, the second occurred in around 1800 BCE and deposited 15km3. Considering this occurred after a 6,000 year dormancy, could this make St Helens a candidate for a Mazama-sized event at some point in the future if it has another long term dormant period?

            Interesting point about number of eruptions compared to “size” of a volcanic arc. For example, Kamchatka has about twice the number of major volcanoes than the cascades, but probably about five times the number of eruptions (in recorded history at least). That’s probably down to factors such as subduction angle and rate, as well as crustal thickness.

      • i really like this resource for the cascades:

        2007 paper, over 100 pages. Has maps of all quaternary volcanic features in the cascades. As a local this is fascinating, because unlike iceland much of the land here is hidden in forest. Most people here think we only have 5 ‘volcanoes’ in Washington, not thinking of what features were active before the major stratocones, but it’s fun to see just which ‘hills’ we have here were formed from an eruption.

        • Thanks! You officially ruined my entire afternoon at work today. LOL

    • The Cascadia subduction angle is also quite low, which means the rate of melting is relatively low. In comparison, under Kamchatka the subduction angle is steep= more melting= more activity.

      I recently read a paper discussing the reasons for the stark contrast in eruptive behaviour between Mt St Helens and Mt Adams, even though they’re only 35 miles apart; it seems St Helens is to the west of the main arc of the Cascades, meaning the subducting plate is closer to the surface (almost directly on top of the subducting slab). This would appear to be a major factor in the production of more silicic magma, with a higher influx rate. which is likely why St Helens is so much more active and explosive than the other Cascade stratovolcanoes, and why Mount Adams is comparatively very quiet and has a lack of significant explosive activity. The paper also seems to suggest that as the NA plate continues to override the Juan de Fuca plate, the more easterly volcanoes could start to become more explosive.

      • Going solely off of memory here, but Gorda, Juan de Fuca, and Explorer plates are remnants of the Farallon Plate, correct? Farallon can still be “seen” in seismic reflections largely west of the Rockies and [here is where it gets really fuzzy] has broken into two larger fragments buttressed up against the roots of the Rockies. It was this melt that contributed to the Valles Caldera, Wheeler, & other historically eruptive centers in Colorado and northern New Mexico (distinct from the Rio Grande Rift Zone to the south and the Jellystone Hotspot to its north.) I also recall reading somewhere that Long Valley was attributed to it as well, but of this I am not certain.

        Anyway, this aside and more to the point of my comment, since the CSZ has such a slow and shallow plunge, where to the east could one expect a future resurgence of activity – if any? With the Farallon still somewhat intact, is it possible that it could be pushed by the JdF or Gorda beyond the foundation of the Rockies into the Bread Basket of Kansas, Oklahoma, and/or the Dakotas recreating some Wheelers or Valles there? Just the phreatomagmatic interactions with the expansive aquifer located under the Mississippi/Missouri River watershed alone would be spectacular (and devastating).

        Or, are we more likely to see a subducted plate pile-up and any subsequent resurgent melt remain west of the Rockies? Could that then connect with the RGRZ and unzip North America from Mexico to the Jellystone Hotspot?

        • Valles and Long Valley are likely products of basin and range extension, which is loosely related to the Farralon.

          One aspect of shallow slabs is that they seem to occasionally detach, which results in large flareups of activity as it leaves a big gap in the mantle when they sink, leading to hot upwelling of melt and depressurization. Two of the most active volcanic regions in the world right now are believed to be experiencing this phenomenon (Central Kamchatka Depression, and the Kagoshima Graben).

          When the Farralon plate finished subducting, the whole plate seemed to detach, which resulted in a large ignimbrite flareup around 20-35 miliion years back in North America. We’ll all be long gone, but I wouldn’t be surprised for a similar phenomenon to occur when the Juan De Fuca and Gorda Plate finish subducting beneath cascadia.

          • Something that “scares” me is the Explorer Plate (Girabaldi Zone) and the Siverthrone Caldera region of BC Canada. Isolated, unmonitored, and a big banger. It has been a while since anything of note has happened there. Nothing happening or just quietly building up to something….?

          • The VOGRIPA project, which lists all known VEI4+ eruptions in the Quaternary, only lists the 410 BCE eruption of Mount Meager for Canada. Unfortunately, very little is known about Canadian volcanoes; we don’t even have a definitive list of which ones are potentially active (or extinct for that matter). It is rather difficult to get to the more northerly volcanoes, including Silverthrone.

            Since there have been very few eruptions in the past few thousand years, and only one known major explosion, volcanoes seem to be very low down on the list of threats in Canada. That is concerning, especially when the Canadian government has absolutely no proper monitoring or even a plan in case of eruption- they will only react when something happens- NOT a good idea!

            They should at least be monitoring Mounts Meager, Garibaldi and Cayley since they are really close to significant population centres; Garibaldi is known to be very unstable, and there are river valleys leading from it which go right through settlements! It’s a disaster waiting to happen, but sadly I don’t think anything will be done about it.

            I’m not aware of anything of note to date, but who knows when the next Canadian volcano will erupt, and importantly, how- I have absolutely no idea what Silverthrone is capable of doing. Let’s hope we don’t have an undetected major eruption up there when there are planes in the air!

          • I had heard that Garibaldi Lake is a hazard that could outburst and take out a lot of towns on its way to Vancouver and [potentially] the Sound. Being reactive is a rather lazy and negligent strategy, no?

          • Exactly. But of course no thinks something like that will happen to them in their lifetime. Someone always gets proven wrong eventually.

      • Another aspect of subduction angle worth mentioning is that steeper subduction often increases back-arc rifting and extensional patterns. If any of this extension occurs near the Benioff Zone of 100-200 km depth, you often get greatly heightened volcanism.

        • Can they train wreck (like a zig-zag line, only vertically – accordian-like)? Would that not cause the lower portions of the detached plate to melt – and quickly – thus producing some rather evolved magmas in quantity all along the arc. Then all you need is a megathrust to jostle the arc basement and … bang!

    • There have been a lot of M5 quakes there over the past months, and related eruptions (hard to confirm in this region of perpetual cloud and few people). It is a subduction zone so presumably this is related. The depth seems to be set at default at the moment but I would guess it is indeed shallow.

  4. Is this unusual for the South Atlantic:

    Magnitude Mw 7.4
    Date time 2016-08-19 07:32:23.0 UTC
    Location 55.33 S ; 31.97 W
    Depth 10 km

    • There haven’t been many larger quakes lately (or volcanic eruptions for that matter), perhaps there’s excess pressure to be released. Not that I’m saying there’s some kind of global earthquake pattern/predictability, but perhaps there’s more chance of larger quakes after a bit of a lull. That is until we start seeing a lot of unrest prior to the next M9 quake (like in the days prior to 2011)!

    • Friday
      19.08.2016 16:00:01 63.662 -19.166 2.0 km 3.5 99.0 4.8 km ENE of Goðabunga
      19.08.2016 15:58:56 63.653 -19.173 1.7 km 2.4 99.0 4.1 km ENE of Goðabunga

      • And there was this deep quake there:
        19.08.2016 15:28:04 63.641 -19.118 16.3 km 0.8 99.0 6.5 km E of Goðabunga

  5. There are some similarities between the Iceland and and Switzerland:
    The two countries does not belong to EU and both have mountains with glaciers.
    There are also some differences:
    – Iceland successfully operates geothermal energy
    – In Switzerland (Basel), operation caused some earthquakes and several milions of damage.
    -in iceland there are icequake; as far as I know, there is no such icequakes (or not too much) in Switzerland (see SED network – ETH)


    • Icequakes are nothing compared to earthquakes and in my opinion they are very rarely detected in IMO network.

      But they are very easy to experience. Just go to the edge of Vatnajokull, especially in summertime, and stay there for a while, like an hour or two. In soon, you should hear and feel a big rumble, similar to a thunder, and that is the glacier moving. Because the outlet glaciers from the ice caps in Iceland are pretty steep downwards, like a giant ice fall. In Switzerland the glaciers are tiny in comparison! And mostly without a significant slope.

      Icequakes just move ice and they strenght is under magnitude 0.1.
      Earthquakes are very different, much more power and they relate to movement of a tectonic fault and of rock.

      Sometimes earthquakes can be caused by magma pushing the surrounding bedrock, like the deep quake of Katla today.

      • Err, well… I don’t know about total volume or surface area, but my reasonably well-informed guess (I’ve mountaineered in both countries) would be that Switzerland has a greater surface area of steep icefalls. And whereas there are some very substantial icefalls on the S side of Vatnajokull, I think you’d be waiting quite a long time to see or hear much on most of the rest of it.

        And just in terms of the surface area of glaciers, that of those that radiate from the Konkordiaplatz is pretty big. (?Second largest after Vatnajokull – but perhaps I am imagining that.)

        • While I would disagree. I have been in Konkordiaplatz and it´s tiny compared to Iceland ice caps, and I guess even comparing its outlet glaciers and ice falls.

          Konkordiaplatz is 2 km long, Vatnajokull has plenty of outlet glaciers over its 8,100km2 area. And Vatnajokull is not the only ice cap. Langjokull has also pretty impressive outlet glaciers over a steep angle. And then there is Hofsjokull, Eyjafjallajökull or Þórisjökull, this one with really steep outlet glaciers.

          I have felt many icequakes while across several of these ice caps in Iceland. There is simply no comparison, compared to Switzerland. Switzerland is nice country with glaciers, but Iceland is just a giant leap in terms of experience! And Greenland makes Iceland tiny by comparison.

          By the way, I love both the Alps and Iceland. Both occupied big parts of my life. I have been 3 years living in Austria, and 5 years living in Iceland. I can´t get tired of mountains and snow! But snowstorms in the Alps are a “walk in the park” compared to the ones I experienced in Iceland 😉

  6. Does anyone know about the state of the interior plumbing of Mount Jefferson? From what I can gather, there hasn’t been an eruption of the main cone in 15,000 years, certainly it’s highly eroded. In the Holocene, there have only been a few eruptions from cinder cones a few miles away from the mountain. There seems to be some confusion about whether Mount Jefferson proper should be considered active. Does it have a (somewhat) intact system, or is the main cone extinct? If it’s the latter, then all future activity should be like that of the Holocene so far.

  7. Hekla and Katla both restless today.

    Katla with a M3.5 but 30min before, a deep quake.

    Another magma movement at the depth. Plus the typical shallow summertime earthquake activity. Which one causes which?

    But I think the deep quake (magma movement) might have caused the M3.5 today, because it just followed 30min later.

    HEKLA also had two deep earthquakes today, and its the third eq within 48 hours. This is highly unusual, but it already happened back in 2013.

    So far borehole strain is normal.

    Graphic shows clearly the M7.5 in south atlantic today at 9 local time, and then the M3.5 at Katla around 4pm.

    But let´s remember that GPS signals in 3 Hekla stations are showing sudden strange movements, as pointed in the last post. Both these earthquakes and the GPS signals are a sign of something happening in the region.

  8. A M4.1 earthquake occurred today west from Portugal. It´s the fourth earthquake above M3 within a month, along a fault capable of producing earthquakes up to 6 or even 7 perhaps. Last earthquake was a 5.7 in 1962, but larger earthquakes happened in centuries before. (this is unrelated to the fault, further southwest, that caused the 1755 great Lisbon earthquake, with M9 and a large tsunami across Europe)

    • I calculated M8.4 for the Lisbon earthquake. Huge and devastating, but not M9. Yesterday’s quake seems to be at the edge of the continental shelf. There are some faults in the area, or it could be a sub-sea landslide?

      • You´re right Albert.
        Lisbon earthquake was somewhere between 8.4 and 8.8, most sources agree that it probably did not reach M9. But the tsunami was likely very big. I think most estimates fall around M8.7 and 8.8 but I guess we can´t be entirely sure of the magnitude.

        This small quake now, occurred along a well known fault, capable of producing quakes to at least M6 but unrelated to the 1755 quake.

  9. Isostatic rebound surely must be implicated in the high activity at shasta 9000bp.

    • Not necessarily, Rob. At least not causal although exacerbating is not unlikely.

  10. OK, thanks, Irpsit. Time for dust and ashes on my part if I was correctly interpreted as making a point about the total surface area of glaciers: (see Table 1).

    But I wonder whether I might have left myself open to misinterpretation. My principal point was about the surface area of steep icefalls rather than of ice caps or outlet glaciers: it’s the former that generate serac falls that would register on seismomographs, isn’t it? And that was the query raised by fxs, I think.

    Walking across or near to the edge of Vatnajokull from Vonaskard to the Skafta (roughly 2.5 day’s walking), we never heard or felt anything, and the reason for that would be that there aren’t any icefalls. The kind of comparison I had in mind was between that and the number (and height) of icefalls you get in just one section of the Swiss alps, say the Oberland between the Wetterhorn and the Jungfrau. (Hence my point about the southern perimeter of Vatnajokull.)

    And thats what leaves me sharing fxs’s puzzle, as to why icequakes seem (pace your point) to register in Iceland but not in Switzerland.

      • Nice article. I certainly underestimate my count of steep outlet glaciers. In this article I already remember two of those steep ice calls over the western side of Myrdalsjokull. I forgot and I have even been hiking near there a handful of times! Hiking across there gives you a scary feeling of what looks like to be in a Katla ash desert, scattered with volcanic bombs around, and the rivers have very large flood plains, and ocasional lava fields (from unknown Holocene eruptions – yes, other lava eruptions than Edlgja, and on Katla´s west side) It is hell there when Katla erupts.

    • Hey Am57,

      Its a nice article the one you posted.
      I am surprised and impressed by the total area in the Alps, with about one fourth of that present in Iceland! There is certainly a wide area of permanent snow in the Alps, and perhaps that adds to the 3059 km2. But it is very scattered, and glacier recession is widespread.

      Certainly that adds up to your argument that with such a scattered area, the number of ice falls could be certainly bigger, though they would be usually small sized compared to those in Iceland, which are quite massive. For instance the well known the ice falls of the outlet glaciers near the national park at Skaftafell, but there are many others for example in the outlet glaciers at Langjokull or the other smaller ice caps around Langjokull.

      As snow/ice cover in the Alps is very wide and scattered area, I am not confident enough to say whether the total area of ice falls in Iceland is really larger than the area of ice falls, even if small, in the Alps.

      Being small sized I think it makes them very weak to be able to generate noticeable ice quakes! I never heard of any in the Alps, but certainly in Iceland. And yes, they only seem to occur in steep ice falls as you pointed. I never heard of ice falls across the flat plateau of most Icelandic ice falls. But certainly that massive volume of ice (of generally 400m thickness) certainly exerts great force over the outlet glaciers which come flowing downwards into the lowlands. In the Alps, there is less of these steep ice falls as far as I know.

      I could give you a rough count of these steep ice falls in Iceland: near the Skaftafell park, there are several steep outlet glaciers coming out from the Vatnajokull ice cap, only in its south limit (to the other sides, the ice cap has no steep edges). There are at least 8 steep outlet glaciers around the Oraefajokull volcano, and a very large sloping area around the large outlet glacier near Jokulsarlon. Further east you have at least 5 more steep outlet glaciers, until Hofn.

      There is 1 steep glacier (or 2) in the northern part of Eyjafjallajokull. Solheimarjokull in Myrdalsjokull is another one, I am not sure about the eastern outlet glaciers of Myrdalsjokull but I think they are not steep.

      In Langjokull there are two steep large outlet glaciers over its southeast edge. Around the Langjokull ice caps, there are 3 small ice caps, these have around 10 or so extremely steep outlet glaciers.

      Then, most of other ice caps in Iceland do not have steep outlet glaciers. In total, I count 25 medium sized outlet glaciers having ice falls, and two large area of steep sloping ice. It shouldn´t be that difficult to estimate this area.

      My experience in Icelandic ice caps is still limited. I have hiked only to the edges of Langjokull, Hofsjokull, Torfajokull, Myrdalsjokull and Vatnajokull, and atop crossing Eyjafjallajokull, Snaefellsjokull and Oraefajokull. Your experience across Vatnajokull was certainly amazing I guess!

      • In the light of the article Albert posted, and this one I am beginning to think that icefalls might be a bit of a red herring. Icequakes in Katla and on (note: a relatively flat area of) the Rhonegletscher seem to be basal rather than to do with serac fall (ie blocks of ice falling in steep icefall zones).

        This helps make sense of the presumed size of the falling blocks cited in the article Albert mentions: 100m x 50m x 1m is huge on any reckoning of the size of a serac fall. (Not only in Europe, including Iceland, but also in the Himalaya – think of the size of the seracs that make access to the Western Cwm of the Khumbu glacier on Everest so difficult.) It also helps explain why in Albert’s article, there is a citation of an article about glacial calving into the sea, which would produce iceblocks of the relevant size.

        So we seem to have an answer to fxs’s original question: there is seismicity associated with ice movements in Switzerland, but it is less well studied because the Swiss don’t have (or need) anything like as sophisticated a mechanism for plotting it as Iceland has. One can get a sense of the size of the Swiss icefalls (eg in the area I mentioned above) from this superb online resource – Swiss maps are works of artistic genius!

        As to Iceland’s icefalls – I was only citing examples for comparison: I agree, there are some very substantial icefalls in Iceland, especially on the southern edge of Vatnajokull. (This is a very helpful resource: And Yes, the trek we did was pretty amazing: from Nyidalur to Langisjor via Vonaskard and the Tungnaa, from there to Eldgja, Strutslaug, and across to the Laugarvegur, then to Skogar. So we certainly saw and/or traversed a few of Iceland’s glaciers. Been there 5 times now, but wish I could do what you did and actually live there!

          • Sometimes I read in volcanocafé earthquakes magnitude 0.5 / 1.0 / 1.5 /…. 3.0 at depth 0.1km matched icequake. I dont’t know if it’s true or not. Perhaps it is hard to exactly define the depth in case of shallow earthquakes (5 kilometers deep or less). So what ist the meaning oft the depth 01km? Is it a generic value reflecting the uncertainty in the calculation? (like the negative depth in Switzerland). What IMO says about that and the uncertainties?

            I don’t know if the swiss seismological network is a sophisticated one or not (see – or if we need one or not. However it seems to me an earthquake destroyed the city of Basel (Switzerland) October 18, 1356. Near Sierre in canton Valais an earthquake magnitude 6.1 killed 4 people in 1946 .

            SED give us seismic events that were classified as explosions by the analysts (usually quarry-blasts). No word about icequake. But who cares? Sometimes, like in the rest of the world, a part of a glacier may collapse. This is what happened in 1961 and caused the death of 88 people in Mattmark (hydroelectric dam). In addition (maybe?) the presence of multiple dams (in area with moderate earthquake activity) contribute to the interest of a seismological network.

            Of course (hopfully) no comparison with Japan and Iceland.

          • A greater threat in Switzerland are mass wasting events.

            One of our other lurking entities has greater knowledge about what sort of system the Swiss have in place, but I haven’t seen him post lately.

          • Switzerland is on the northern boundary of the Adriatic Plate, where the latter meets the Eurasian Plate. So tectonically interesting.

  11. For any of you Navy guys or anyone interested in ships, the Nautilus is diving on the USS Independence off the coast of San Francisco. It was scuttled in 1952. It was involved in the atomic testing at Bikini Atoll.

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