Iwo Jima has long been of particular interest to VC. It is an enigmatic volcano with a very human history. One of the pivotal battles of the second world war took place here, at immense human cost which arguably changed the way the war ended. The island remains home to the Japanese navy, and visits are restricted to those coming for memorials – of both sides. The people who visit find many reminders of the past. But in spite of the memories, the island has changed. The beach where the US marines first landed is now more than 10 meters above sea level. The island is also larger than it used to be. The volcano below is stirring.
Early September there was a report of increasing earthquake activity, which was followed by a minor eruption on September 12. It happened just off the south coast, and witnesses reported seeing water fountaining 10 meters high. But no pictures have emerged of the eruption, and after the event things quickly calmed down again. In itself, this was a normal event. Iwo Jima has such minor explosions every few years, sometimes on land, sometimes off the coast, although they have become much more frequent over the last decade.
We have found one (and only one) image which caught the effect of the eruption. A SkySat satellite photographed half the island on Sept 13. It uncovered strong discolouration in the water, on the south side of the island, in the general region where the fountaining was said to have occurred. Older images show nothing similar in this location, and it is likely volcanic ejecta. But the exact location of the outburst is not clear from the image: it will be either inside the coloured patch or just to the right in the region that was missed.
This post aims to bring together what is known about Iwo Jima, which perhaps is less than we should know. It is an extraordinary place, where the long-term inflation is among the largest seen anywhere in the world. The inflation is clearly volcanic: since 1889, 45 separate eruptions have been recorded. It deserves a closer look.
But first some background. The Volcano Islands (Kazan-rettō in Japanese) are a group of three small volcanic islands,of which Iwo Jima is the middle one. North of it is Kita-Iō (San Alexander Island), and south of it Minami-Iō (San Augustino Island).
Iwo Jima was (probably) discovered by the Spanish sailor Bernardo de la Torre, in 1543. On September 25, ‘they had sight of certain islands which they named Mal abrigos [‘bad anchorage’]. Beyond them they discovered Las Dos Hermanos (Two Sisters). And beyond them they also saw four [or three] islands more which they called Los Volcanes’. (Edited from Thomas Suarez, early mapping of the Pacific, 2013. For a more detailed report of the expedition, see the bottom of this post.) The first two islands are believed to be the Daito islands, and the last four or three islands are assumed to include Iwo Jima. Various sources state that he landed on Iwo Jima and named it Sufre (or sulfur) Island, but this appears not to be true: no landing is mentioned and the name was given by Cook’s expedition, two centuries later. In either case, the name has stuck: ‘iwo’ is sulfur, and ‘jima’ is island. (There are a number of ‘sulfur islands’ with a similar name, and it is not uncommon that an image of the wrong island accompanies a report on Iwo Jima. Anything showing a smoking volcano should immediately be discarded.) The official name was changed in 2007 to Ioto, and this should reduce the confusion. The new name has the same Japanese characters and meaning, but a different pronunciation and it is argued to be more historically correct. It will be hard though to remove the name Iwo Jima from memory. Too much has happened here under that label.
Kirk Cook is reported to have investigated the island in 1779. His journal contains a rather discouraging description of the (re-)discovery of the island:
‘Between 9 & 10 o’clock we passed by the island within a mile from the shore, and as it appeared to be barren and uninhabited we kept on our course without making any stay on it. At the southwest point of it stands a round hummock which appeared to be a volcano as we saw some brimstone on it; at the north east point stood a number of remarkable rocks close to the beach not unlike in their appearance to Stonehenge; the island is about 6 or 7 leagues in circumference & the land low & much of it covered with low shrubbery but no trees of any kind. ‘
A remarkable detail is that this was on 15 November 1779, which is 9 months after Cook had died; there must be some doubt about his involvement! This discovery from beyond the grave was in fact done by James King and John Gore, who had taken joint charge of the expedition. The discoverers were sailing north to south, so the fact that they picked out the southwestern point as the notable feature means it really stood out. The expedition did not land on the island, in contrast to what is claimed on wikipedia. The journal states that Iwo Jima is one of three islands they saw. De La Torre may have seen four.
The journal of Cook’s voyages (authored by William Bligh & James Cook) contains drawings of the island. They show the view towards the east-northeast. The ‘hummock’ dominates, with a low neck and a rocky dome. At the far end there are some rock plugs on a small dome, only just above sea level, with presumably formed the ‘Stonehenge’ feature he refers to.
The map of the island shows the thin neck, the two high areas, and the surrounding shallows. It also indicates three areas further from the coast which presumably are rock reefs.
The basic features that Cook found still exist. They have acquired names since. The southwest ‘hummock’ is called Suribachiyama (or Mount Suribachi). The round dome is Motoyama, and the sandy neck in between is called Chidorigahara.
The risen land
But even though those features are still there, much has changed. On Cook’s profile of the island, Suribachiyama stands around 2.5 times higher than the highest point of Motoyama, and Chidorigahara is only just above the water line.
The recent situation is shown below, using profiles re-published by Kenneth LaJoie, in 1986. They show Motoyama almost as high as Suribachi, and Chidorigahara 40 meters above sea. Surabachi is currently about 160 meters tall. If it was this high also in Cook’s days, the old map suggests that at that time Motoyama was 60-70 meters tall. Nowadays it rises to 120 meters. Chidorigahara has gone from near-zero to 40 meters above sea. The conclusion is that much of the island has risen by 40-60 meters since 1779, where Motoyama has probably risen a bit more than Chidorigahara.
The recent data shows the beach lines of the past. The one labeled ‘1779’ is suggested to be the beach seen by Cook, assuming that Motoyama and Chidorigahara have risen by the same amount (in reality, Motoyama is likely to have risen more). The line labeled ‘0.5-0.7 ka’ is for a layer which contains carbon-dated coral. Clearly, this layer was below water when the coral formed, somewhere around 1450+-100 AD. Nowadays, it is 100 meters above water. But the entire top of Motoyama shows coral fragments and rounded pebbles, showing it was entirely under water until quite recently.
So Motoyama has been coming up at an average rate of 20 cm per year, over at least 500 years! If Bernardo de la Torre did indeed see the same island, it must have looked a very different place, with Suribachi and Motoyama forming two separate islands. Perhaps this is why he may have reported four islands where later explorers found three (but see the bottom of the post).
The island has not only grown up. It has also grown out. The most current image comes from a satellite view obtained in August 2018. I have attempted to put the old map of Cook on top of the current view. This was done by assuming that Suribachi and Motoyama haven’t moved, and using these to align the two images. The overlay may not be perfect!
The comparison shows how much Chidorigahara has widened. Much of the dotted parts of the old map, indicating shallows, are now land. The east and west side of Motoyama have especially grown. The northeast coast, where the old ‘Stonehenge’ must have been located, has not moved as much. The coast here is quite steep.
The rock reefs are an interesting problem. One of the reefs on Cook’s maps, Kamaiwa, has become incorporated in the beach (this happened around 1968). His two other reefs have disappeared. Two new features have taken their place. On the west, there is a new island (called Kangoki-iwa) which is close to merging with the main island, and on the east side there is a new reef (Higashi-iwa) where the rocks come up to just above the water line. It is a little suspicious that two reefs have gone missing while two new ones have come up. It is possible that both were misplaced on the map.
The growth of the island has been followed now for over a century. Below are a series of maps compiled by Norio Oyagi and Takashi Inokuchi, and published in Geology of Iwo Jima. The maps depict the changes between 1911 and 1983. Until 1952, the coast line was fairly stable, apart from a slight extension on the west side. After 1952, growth took off. The changes on the west became spectacular. Cook’s old reef which since had acquired the name of Kamaiwa used to be 1 kilometer off the coast. The channel between it and the coast was 36meter deep and navigable. After 1952, the beach extended into the channel by as much as 50 meters per year, and in 1968, Kamaiwa became connected to the coast. Beyond it lies the island of Kangoki-iwa. It used to be more than 1.5 kilometers from the coast, far enough that it was used to house prisoners. The shark infested waters provided an escape proof barrier. By 1983 Kamaiwa formed the closest part of the coast. The beach has continued to grow since, and in the 2018 image above, is only a few hundred meters from Kangoki-iwa. Escape finally beckons for the prisoners, albeit too late to be of any use.
Why did the beach extend so quickly and by so much? This was more than just uplift. It turns out that it was related to the uplift of the coast to the north. The steep coast line here eroded while it was uplifted, perhaps hastened by the regular typhoons (several pass though here each year). The eroded sand was moved by the current and waves, and deposited on the west side. Sometimes the sea just can’t win. But it does try.
This image (from iwojima.com) shows the typical lineation of raised beaches. Look above the cliff, and the lineation continues in the rocks, suggestive of earlier periods of wave erosion.
Iwo Jima is doing more than just grow up and grow out. It is also frequently volcanically active. The eruptions are small, short-lived explosions, and come from a number of different locations. The same location can erupt again, even after decades. Interestingly, although the activity is centered on Motoyama, the outbursts are rarely there. They seem to follow the edge of the dome. But some eruptions have happened on Motoyama itself, in particular in December 2016 and in late 1969. The larger explosions can leave holes tens of meters deep and wide.
Fumarole activity is widespread, mainly from the crater on Suribachiyama and its steep western slope, and from the northern part of the island. The fumaroles deposit sulphur which was commercially mined until the war. At the top of Motoyama there are even some boiling mud pits. The vents move around, old ones go extinct and new ones appear.
On the map above, from Ueda et al., 2018, the numbered circles indicate the known locations of eruptions since 1890. The most frequently erupting location is ‘1’, with 13 outbursts, and ‘7’ with 10. These two locations are next to each other.
The 12 September 2018 eruption is close to location ‘10’ which previously erupted in 2001. It is a repeat offender.
The map also indicates four seismic stations. One, 0605, is located at Suribachi; the others are at and around Motoyami. They have provided continuous GPS measurements since the late 1990’s. Before that, measurements were taken every two years. Between 1980 and 2000, the GPS data showed relative little change: the rapid changes in the 1950’s and 60’s had given way to a quiet few decades. But after 2000, renewed uplift began to show, and since 2010 it has accelerated further. This was accompanied by increasing earthquake activity. Suribachi remained relatively unaffected, with minor uplift beginning to show only in the last few years. But the movement near Motoyami has been extreme.
Station 0604 has risen by 5.5 meters since 2000, most of which happened after 2011. Not many volcanoes in the world have shown such large movements! This continued from the pre-1980 events: between 1920 and 1980, the maximum uplift on the island was 11 meters. The peak at that time was north and west of Motoyama, while Motoyami itself rose by 6 meters. This time, the uplift seems centred on the south side.
Volcanic activity also accelerated. Over the past 7 years, there have been 20 separate volcanic explosions. During the 7 years before that, there was only a single event, in December 2007. There is more here than meets the eye: there are developments below ground.
Below the water
Iwo Jima forms the top of a strato-volcano. Remove the sea, and a large mountain appears, 2 km tall and 40 km across.
The plots below (from Sohei Kaizuka, 1992, Quaternary International, Vol. 15/16, pp. 7-16, 1992) show the detailed bathymetry, Iwo Jima is surrounded by a smooth under-water plateau at a depth of some 15 meters. At the outer edge of the plateau, there is a drop to a depth of about 100 meters, followed by a patchy rise which in a few places sticks out above the water. Outside of this rim, the mountain steeply falls to the sea floor, 1500-2000 meters below. It is a sizable volcano!
The patchy rim runs roughly from Kaimawa and the island of Kangoku-iwa, around the north side, to Higashi-iwa, 2 kilometers off the east coast. The rim is about 1 km wide. This is wider than Kangoku-iwa: there are four rocks which just break sea level a few hundred meters on the seaward side of the small island, which also are located on this rim. Two of these are visible as white spots on the August 2018 image above, west and northwest of Kangoku-iwa. On the north side, the raised rim is located some 100 meter below sea level. But to the south, the plateau ends with a sharp fall, without a clear raised rim. The profiles shown above have rims at positions A, B, D and F, but there is no indication at positions C and E.
The rim is argued to form a 10-km wide caldera. Iwo Jima and its plateau covers much of the caldera; Motoyama is near the centre. But the classification as a caldera may not be fully certain. The raised rim only extends halfway around the island, with Suribachi placed outside it.
The inner part is unusually shallow for a caldera. But this flat top, 10-km wide, on a mountain 40-km wide, unusual for a volcano, makes sense from the point of view of wave erosion. This has kept removing the top, down to the depth where waves can reach, some 15-20 meters. A caldera would imply a massive explosion removing the entire top of the stratovolcano down to exactly sea level. Erosion can do the same thing, but takes longer.
The rim has had volcanic activity. Kongaku-iwa consists of lava. Higashi-iwa looks like a volcanic cone, similar to Suribachi. Suribachi itself is just outside the rim. But the volcanic outbursts over the past century have been minor crater-forming explosions, rather than cone building, and have taken place on the plateau and the island, and not on the rim. Clearly Iwo Jima can do much more than what we have seen in recent years.
In fact, the island has in the past blown its top, and it has done so more than once. The evidence is everywhere. Motoyama is covered by pyroclastic deposits. Suribachi has its own pyroclastic layer, with some lava. Kangoku-iwa consists of lava. Bore holes at Motoyama going 150 meters have found alternating layers of lava and pyroclastic deposits. This adds a warning from history to the on-going inflation. It would be useful to know the full volcanic history of Iwo Jima.
Pyroclastic deposits surround both Motoyama and Suribachi, but they form separate layers and do not come from the same eruption. It appears that Motoyama erupted first. Carbon dating has been done on the lowest layer of ignimbrite and on the rocks of Kaiwama beach. Lava is itself of course not date-able: the carbon is obtained from whatever organism was buried by it. At Kaiwama these were shells, which were dated to 131+-20BC and 31+-20 BC. At Motoyama, interestingly, it was carbonized wood and twigs, dated to 761+-20BC and 762+-20BC. This means that Motoyama, at the time of the major explosion, was partly above water and was forested.
Around 2700 BP, this forested island was destroyed by an explosion. The island disappeared below water, were the ignimbrite rained down. Next, lava came and build up a new dome, but it remained submerged. The lava had an unusual composition called trachyandesitic. More eruptions followed, with layers of pyroclastics. How long this lasted is not known. Based on the carbon dates of the shells, it may have continued for over 500 years. It left a yellow, soft tuff, used in the war to dig shelters.
Suribachi formed afterwards, but how much later is not really known. It existed in the time of Cook, and probably also in 1543, and must therefore have formed earlier. That still leaves us a 2000 year window. Trachytic magma was erupted at Suribachi three times, first as marine pyroclastic eruption, second effusive in shallow water, and finally form a pyroclastic cone on land.
Now the third phase started, where Motoyama calmed down but inflated, at an average rate of 20 centimeter per year. Precisely when the inflation started is not known. At has lasted at least 1000 years, but may also have begun shortly after the Motoyama eruption. And it is still continuing, with frequent volcanic activity. The fact that the top of Motoyama is littered with old coral shows that there was no lava associated with the rise. It was pushed up from below, not build up from above.
In this history, Motoyama is the sum of the 2700-2100 BP eruptions pushed up by the subsequent inflation. The under-water plateau surrounding the island may be the result of the volcanic ejecta, less affected by inflation and continuously decapitated by the waves. Suribachi is a separate eruption, perhaps 1000 years ago, perhaps older.
What about the caldera rim? If this is a caldera, it existed already before the eruption at 2700 BC. There must have been a massive eruption, but all we can say is that it was earlier than 2700 BC. There is no evidence for this other than the partial ring. However, there is another layer of lava underneath the Motoyama lava, called the Hanareiwa lava, and this shows that there were earlier eruptions. The age is unknown.
Seismology indicates that below the Hanareiwa lava is another lava layer. Together, the three layers are 200 meters thick. Between 200 and 500 meter deep is a high velocity layer, presumed to be tuff. This must be from an even older eruption and perhaps this was the caldera forming eruption. Below this is even more lava.
Magma on the move
But what is causing this extreme, long lasting inflation? Intermittent inflation and deflation in large calderas is common, and normally caused by moving hydrothermal water. But the inflation at Iwo Jima is far too large for that. It is caused by accumulating magma. The geodesic measurements show that there are shallow sills underneath Motoyama. They grow, erupt and deflate, pushing the summit of Motoyama up and let it come down again. But at the same time a much larger area is continuing to inflate. That indicates a deeper, and growing, magma reservoir.
And what is causing the eruptions? They are phreatic, meaning caused by water. It appears that there is water inside the deep tuff layer, 200-500 meter under ground. Rising heat brings pockets of this water to the boil, but it can’t get out because of the seal of solid lava above. The lava is pushed up but the agitated water, causing rapid inflation and earthquakes at ground level. After a few days a crack develops in the lava seal. Now we get a sudden explosion, as happened on 12 September this year. The eruptions are primarily in the region where the rise of the central region has caused faults, around Motoyama but within the caldera rim. Two such faults became active shortly after the war.
So where is the magma? The shallow sills are thought to be 800 meter to 1 kilometer deep. It is fed from a deeper magma chamber, where the main inflation occurs. A pulse of magma into the deep chambers brings with it heat, which percolates up into the tuff water. Phreatic eruptions follow. Iwo Jima is currently in such a phase.
In the long term, Iwo Jima seems to repeat itself. The inflation will continue, but eventually a major eruption will break through and destroy the island. Pyroclastics and lava will build a new dome. After a few hundred years, the eruptions cease. Inflation resumes and over time the island reforms. Until the next eruption.
Where are we in the cycle of Iwo Jima? That is not easy to know. However, it is unlikely that the island was much larger than it is now, at the time of the 2700 BC eruption. The build up to the next one is well under way. But when exactly is impossible to say. How large would the eruption be? We can make a maximum guess by assuming that a 100 meter high island, 23 km2 in size, is replaced by a 200-meter deep hole. That suggest something in the range 5-10 km3. This the DRE value: the tephra will be several times larger. At the top end, a Krakatoa-size eruption might be possible.
But volcanoes do not like being predictable. Sometime before 2700 BP, perhaps long before, it may have done a significantly larger eruption. Just to keep us on our toes.
Iwo Jima has played a part in shaping the post war world. The memories of that event run deep and have left scars, but scars are also signs of healing. We should not forget what happened here, but it belongs in the past. While Iwo Jima keeps rising, the volcanic heritage will become more and more important. One day, it will happen again.
Albert, October 2018
Recent papers on Iwo Jima, extensively used for this post:
Volcanic History of Ogasawara Ioto(Iwo-jima), Izu-Bonin Arc, Japan Masashi Nagai* and Tetsuo Kobayashi, 2015, Journal of Geography(Chigaku Zasshi), 124, 65–99 (with many images of rocks formations on the island)
Phreatic eruptions and deformationof Ioto Island (Iwo-jima), Japan, triggered by deep magma injection, Hideki Ueda*, Masashi Nagai and Toshikazu Tanada, 2018, Earth, Planets and Space, 70, 38
Appendix: The discovery of Iwo Jima
In 1542, Ruy Lo´pez de Villalobos sailed a Spanish expedition from Mexico to the Philippines. After arrival, and meeting a mixed reception from the locals, Bernardo De La Torre was tasked to find a route back, taking one ship from the six of the expedition: San Juan de Letra´n, in order to ask for reinforcements. This task failed: the first successful eastward crossing of the Pacific happened only in 1565. De La Torre sailed a route roughly north/northeast, reaching 30 degree north and finding a number of new islands, but eventually was forced back by storm and lack of water. The chronicles of his journey appear to be lost, but the trip is mentioned in several documents from the 1540’s and 1550’s. These reports are second-hand and in some places are contradictory. The most likely actual journey was pieced together by Bernhard Welsch, in 2004, and I am following his arguments here.
De La Torre departed from the central Philippines on 26 August 1543 (the dates in use at that time were the Julian calendar. The Gregorian calendar was not adopted until 1582). He sailed east for a few days before turning north, eventually crossing the tropic of cancer. (Typically, reported latitudes are reliable, but longitude could not yet be measured.) Several islands and groups of islands were discovered on this leg, before he was forced to turn back.
On 25 September 1543 they sighted a small island at 26°N which they called Mal abrigo (bad anchorage) because the sea was breaking against it. They sighted two more islands 26 leagues further which they called Duas yrmaas (Las dos hermanas, meaning The two sisters), but didn’t land there. (A spanish nautical league at this time was not perfectly defined, but in practice there were about 15 leagues to a degree, so 26 leagues was a bit less than 2 degrees.) Later they saw three (one of the reports says four) more islands, at 24 and 25°N. One of these was volcanic with fire in three places. These islands were called Balcones (Volcanoes).
On 2 October 1543, they sighted an island they called Forfana (the orphan), beyond which there was a high mountain or rock, with fire at five places. But the story here appears confused, because the description ‘fire at five places’ sound very similar to the previous ‘fire at three places’. The first is reported in one of the second-hand sources, and the second in another. It seems likely the two sources were reporting the same observation, but attributed this to different islands. In reality, only one active volcano was seen.
On 18 October 1543, between 29° and 30°N, after hitting a northerly storm, they became worried about their supply of drinking water. They turned around and after 13 days arrived back at the departure point. On the way back, they came across some smaller islands ranging in a north–south direction from the 15th to the 16th degree N latitude, which were the Ladrones (the Marianas), but they did not anchor there.
So which islands did they find? The first ones, Mal abrigo and Los Dos Hermanos, are accepted to be the Daito islands. Mal abrigo appears to be Oki Daito, 24.5°N and surrounded by coral reefs, and the two sisters are Minami-Daito and Kita Daito, about 1.5 degree due north of Oki Daito and less than 10 km apart. One of the old but second-hand reports places the first island at 16°N, and this is therefore often identified with Farallon, but this appears unlikely: the Daito islands, 10 degrees further north, fit much better with the descriptions.
The three ‘Volcano’ islands are identified with the Kazan Retto group, 10 degrees due east of the Daito islands; Iwo Jima is the middle one of the three islands of this group, and it is located at 24.8°N. That identification was first suggested in 1803 by Burney, a member of the Cook expedition. Burney wrote :
‘it will appear very probable, that the Sulphur Island, with the North and South Islands, seen by the Resolution in her return from the last voyage of Captain Cook, are the islands which were called the Volcanes, discovered by the San Juan. Their agreement in number, their spreading nearly a degree in latitude, and in the same parallels, and their appearance so well corresponding to the name, form a combination of circumstances that amount to very little short of conviction.’
The next island that was discovered was called ‘Forfana’, and is said to be an uninhabited island 30 leagues (150-200 km) from ‘Volcanes’. It was sighted on 2 October 1543. The direction is somewhat problematic. One source says it was east to northeast from the Volcanes, where only empty ocean exists. But this source also states that the second Daito island discovered is northeast of the first, while in reality it lies due north. If the same mistake was made here, the final island really lies in a north-northeasterly direction. And there are islands there: the southernmost part of the Osagawara archipelago, where the nearest island is 150 km from the Volcano Islands. This makes ‘Forfana’ to be Hahajima, the southernmost of the major islands, or one of the small islands which surround it at 2-3 km away. This fits well with the description of an ‘orphan’ (Forfana) beyond which was a high mountain. The highest mountain on Hahajima is over 400 meters.
The route from the Daito islands to Iwo Jima and on to Hahjima is not straight. It runs a bit south, and turns northward. If De la Torre passed through the Iwo Jima groups east-west, he could well have missed either the southern or northern island of the group. If Iwo Jima consisted of two separate islands at the time, as seems likely, it is perhaps possible that of the three Volcano islands he saw, Iwo Jima accounted for two. But this is speculative and mainly illustrates the uncertainties around the story.
After Hahajima, De La Torre sailed on for two more weeks into the open ocean, but eventually was forced to turn around, found Vila Lobos gone, and finally met up with the expedition around the Moluccas (not far from Sulawesi) in early 1544.
There are some lessons from this story. The San Juan was nowhere near where the sailors thought it was. It sailed a complex route, first east, than due north, east-southeast again, and finally north-northeast, putting the ship far to the west of where it though it was going. If you can’t measure longitude, the course can be a bit of a guess. Some of the deviations can be explained by tacking against a predominantly northeasterly wind, and others by the effect of the west-flowing north equatorial current, which becomes the northeast-flowing Kuroshio current in the region of the journey of De La Torre. Some may have been deliberate. He may have been aiming to catch the returning North Pacific current across the Pacific, at 30N, and therefore trying to gain latitude before turning east. Or he may have been deliberately looking for islands, in order to obtain water. We can only guess.
We have further learned that Iwo Jima was discovered after 25 Sept but before 2 Oct 1543 (Julian dates). Often, the first date is given, but that is for the Daito Islands. Looking at the distances involved, the most likely discovery date is 30 September 1543. We have found that the name ‘Sulphur Island’ comes from the Cook expedition: De La Torre’s name for the islands was just ‘Volcanes’. What we do not know is what Iwo Jima looked like, however as it was clearly labeled as ‘volcano’, the peak of Suribachi must have existed, as this is the only obvious volcanic feature seen from a distance.
That fire-belching volcano
There is one final point to solve. What was that erupting volcano that so impressed the sailors that two second-hand accounts tell the story, albeit attributed to different islands? One account places it at the Forfana group, i.e. the eruption was at or near Hahajima. This group of islands is indeed of volcanic origin, but far from recent. The eruptions were several million years ago, the chain has gone quiet and the eruptions are nowadays at a separate chain of islands further west, where for instance Nishinoshima is located. In spite of the statement placing ‘a high mountain or rock, which was belching forth fire at five places‘ at Forfana, this event cannot have been here.
The other account places it at the Volcano islands: ‘‘they sighted three more islands; one being a volcano belching fire at three places’. This narrows it down to one of three possible islands. Assuming both accounts are for the same event, we are looking for a high mountain with multiple eruption sites.
The three Volcano islands are, from north to south, North Iwo Jima (Kita-ioto), Iwo Jima (Ioto), and South Iwo Jima (Minami-ioto): together they make up the Kazan Retto group. The southern island is a single, 900-meter tall cone, about 2-km wide at sea level. There was a marine eruption a few kilometers off the coast in 2005, where lava floated to the surface. The northern island, Kita-ioto is larger but slightly less tall, at 800 meters: it appears more eroded. The summit of Kita-ioto is extinct, but there have been several eruptions off the coast over the past two centuries. Neither island is known to have had historical activity on the main mountain on-land. But the description clearly refers to an eruption on land. Although neither can be excluded, given that Iwo Jima itself is known to erupt on-land, it is a likely candidate for the erupting mountain.
But Iwo Jima also shows little or no evidence for recent lava. The most recent ‘fire’ eruption was probably the one which caused the top pyroclastic layer around Suribachiyama, and this could be as young as 1543. But the description gives no mention of explosive activity, just multiple fires. Phraetomagmatic explosions, similar to the current activity, can also be excluded, because it lacks associated light. Was the entire description made up, or greatly overstated?
There is an alternative. The crater of Suribachiyama, and other places on Iwo Jima, can show heavy fumarole activity. Looking at the dates and distances, De La Torre probably passed here around 30 September. Two days later, Oct 2 1543, was a full moon. Did he perhaps pass at night, and see very active fumaroles reflecting the light of the nearly full moon? That might have looked like fire to people unfamiliar with fumaroles, and it would explain the multiple locations where fire was seen. A night vision could even explain the confused reports about the actual location of the event.
So, event though the circumstances of its discovery are now clarified, the volcanic fire that so impressed the sailors remains a mystery. If only we could recover the lost chronicles of the discovery! Second-hand reports, even from within a few years of the events, leave too much unclear.
Main source: (2004) Was Marcus Island discovered by Bernardo de la Torre in 1543?, The
Journal of Pacific History, 39:1, 109-122, DOI: 10.1080/00223340410001684886