A recurrent theme throughout this series has been the unknown and understudied which with our current understanding of geology and volcanology could pose a danger to millions of people. From the water-enriched and thus highly explosive magmas of Kelut to Aso, the problems of a giant edifice such as Mayon, the understudied Taal and Bali volcanoes, the inexplicable volcanism of the Cameroon Volcanic Belt (Mt Fako/Mt Cameroon), the unusual geological setting and complexity of the Trans-Mexico Volcanic Belt and the threat posed by even moderately large eruptions such as at Campi Flegrei and Apoyeque, there is one major threat that we have not yet looked into: the one posed by a submarine “supervolcano”.

Some of the most destructive and disruptive eruptions in human history have been from volcanic islands where the collapse of the edifice has allowed water to come into contact with the upper magma chamber, something that has compounded the magnitude of the eruptions manifold. The 1883 eruption of Krakatoa is something of a household name even amongst people not interested in volcanology, films have been made about it. The ~1650 BCE eruption of Thera is an even better example. Not only did it all but wipe out the Minoan civilization and not only has it been linked to Biblical events in Exodus. It has left indelible imprints in almost all of our European languages such as the adjectives “terrible” and “terrific”, not to mention the prefix “tera” as in terawatts, teraton etc. Yet neither Thera nor Krakatoa are representatives of the very worst possible scenario, one where barely subaerial or wholly submarine volcanic eruptions are concerned. There actually are very large submarine volcanoes in many places around the world, submarine volcanoes capable of a VEI 7 “supereruption” and our choice for #1 in this series is such a volcano. This volcano has shown an enormous amount of inflation over the past 1,000 years and is the strongest candidate that we are aware of for a future VEI 7 eruption. It threatens several of the most densely populated as well as some of the most developed areas of the World. Its name is Ioto, Sulphur Island, formerly known as Iwo-Jima.

The main problem of submarine volcanoes are that they for obvious reasons are neither well-studied nor easily monitored. Thus our knowledge of them as compared with volcanoes such as Etna, Vesuvius or Mt Fuji is rudimentary. Hence, there is little or no information available. Consequently, any article on such a volcano will have to be highly conjectural. This is one of the reasons why we have chosen to present this article in the form of a work of fiction. The other is that if our conjectures should be correct, or even in the adjacent ballpark, the potential death count is staggering and the consequences for civilization as we know it dire. The threat from Ioto however is real and this story is based on published literature.

Just a few facts before we go into the story. Uplift at Ioto is the greatest known as far as we are aware of with an annual average uplift quoted as 0.25 m per year over the past 500 years. The beach where the surveyors of Captain James Cook landed in 1776 now lies more than 40 metres above sea level. The WW II landing beaches are 17 m above present sea level. As with all volcanic uplift, the actual volume intruded is twice the surface expression which gives minimum figures of 250 m over the past 500 years, >80 m over the last 239 years and 40 m in the past 71 years alone. The actual size of the magmatic intrusion depends on the horizontal extent of the body into which it intrudes. Even if we accept not two but just the one of the proposed sill structures with a side (=diameter?) of 5 km directly below Ioto, we arrive at a figure of at least 5 km3 over the last 500 years and no less than 0.7 km3 since 1944 alone – and these are very much minimum figures. With such a copious inflow of fresh magma, the question is not if Ioto will have a major eruption but when.

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As you read, please remember that this is a work of fiction and that many of the interpretations of the scientific data presented are dramatised for effect and not necessarily accurate.

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The knocking on the door would not go away. In his dream, Chris Schofield had just taken his seat on the KLM/Air France flight from Fukuoka to Amsterdam he was scheduled to board tomorrow morning at 11:05, Japan time. The flight would take just over twelve hours and after touching down at 15:25 CET, he had to take a connecting flight on to Manchester. All in all, it would take him more than eighteen hours and by the time he got home, he would be jet-lagged dog tired. He managed to open his eyes to cast a glance at the red LED display. 03:41 A.M. “Ohhgod, nooo! Go away!” He really did need his sleep this morning.

“Dr Schofield? Chris! Please wake up! It’s me, Toru. Toru Hiryoki.” The insistent knocking would not stop.

Dr Torunasuke Hiryoki was his JMA host, Japan Meteorological Agency, the authority responsible for amongst other things volcanic monitoring and hazard mitigation. At one point, there had been concern that Aso was about to have a major eruption and Chris had been detached from his post at Manchester University in order to follow events on location. In the end, Aso hadn’t done anything too spectacular, unless one counts a seven-weeks long outburst of mainly Strombolian to Vulcanian explosions, totalling not much more than a VEI 2, as such. It was just another deep intrusion of fresh magma, substantially larger than preceding ones, true, but nowhere near large enough to cause a major eruption.

Soon after his arrival in Japan a couple of months ago, before the eruptions had begun, Chris had proposed a model based on then current data that in the end had turned out to be pretty close to what had actually transpired. The models used by his JMA hosts had predicted a much larger event, possibly even including the collapse of the central portion of the caldera.

As a scientist, Chris was somewhat controversial because where others interpreted available data very much within the generally accepted model or models, he was not afraid to go out on a limb. Where others saw business as usual, he was inclined to point out and emphasise the danger signs. Where others were alarmed at the potential for disaster, he would calmly point out the reasons why disaster was unlikely. When the crisis at Aso was in its early stages, he had told Toru Hiryoki that long-term, he was more concerned by Aira Caldera because uplift continued in spite of the safety valve that Sakurajima volcano constituted being fully open since the early 1950s.

He swung his legs over the edge of the bed and stumbled over to the door. As he opened it, he was greeted by the smell of coffee that reminded him of the link between intelligence and early morning activities.

“Come in Toru, excuse me for a moment.” He motioned his friend inside and made a grab for the proffered cup before disappearing into the bathroom.

When he returned, cup gratefully held in hand and by now half-empty, Dr Hiryoki had seated himself and taken out a small stack of papers from a portfolio.

“Chris, I doubt you will have seen these before but will you please read them and give me your impressions? They are somewhat on a need-to-know basis and it has been decided that you have that need.” As he handed the papers over, Chris saw that they were scientific papers on Ioto, Sulphur Island, better known as Iwo Jima. He took a quick look at Hiryoki whose face held that inscrutable look cultivated by the Japanese not to give away any information at all. If he had still been in the least groggy from being woken in the middle of the night, not even the strongest Kopi Luwak could have been more effective. Adopting the same attitude, Chris was now fully awake. He grabbed the stack and began to read:

Iwo-jima is a small volcanic island belonging to the Izu–Ogasawara island arc located 1250 km south of Tokyo, related to the subduction of the Pacific plate underneath the Philippine Sea plate (Fig. 1). The bulk of the island is located within a mostly submarine caldera… …An extremely high uplift rate (averaging 0.25 m/a over several hundred years) characterizes the volcanic activity of Iwo-jima. This deformation is believed to be due to post caldera uplift… … leveling and trilateration surveys from 1976 to 1995, and GPS surveys from 1996 to 2002. These observations have detected two patterns of continuous crustal deformation: concentric subsidence around Motoyama at the center of the Iwo-jima caldera and uplift surrounding the subsiding area… …The best-fitting subsidence source geometries for 1998–2000 and 2000–2002 are horizontal, squared-shaped sills with side lengths of 4 and 5 km, respectively……the continuous subsidence and uplift may be explained by movement of volcanic fluids (probably geothermal) to balance the vertical load of the volcano, while the episodic uplift appears to be related to magmatic unrest.

At this point, there was the sound of several cars driving up outside the hotel, stopping to disgorge their occupants. There was what sounded like orders given and a stamp of feet. Chris looked up from his reading and raised an eyebrow inquiringly.

“The police. A helicopter has been dispatched to take us to Tokyo. Please Chris, there is not much time.” The implications hit Chris like sledgehammer blows. There was a volcanic crisis at Ioto. For some weird reason, his opinion was sought. For a brief moment, the child’s impatience to know struggled with the scientist within. Then he returned to his reading:

The Iwo-jima volcano is a large stratovolcano The bathymetric topography indicates that the volcanic edifice is 40 km in diameter at the sea bottom with a caldera rim of about 10 km at the top. Iwo-jima island is small, 8 km long and 4 km across, and the main part of the island is located within the submarine caldera. The island is divided into three topographical areas: Motoyama, Suribachiyama, and Chidorigahara. Motoyama is a post caldera, shield-shaped, central cone, with its highest terrace 100 to 120 m above sea level. Suribachiyama, the island’s highest peak (167 m), is a scoria cone with lava flows located on the caldera rim. (Kamaiwa is also close to or on the caldera rim.) Chidorigahara is a sandy isthmus located between Motoyama and Suribachiyama.

Following the first recorded activity in 1889, a total of 20 phreatic eruptions, mostly small steam explosions, have been reported… …Geothermal activity in Iwo-jima is very high and the rate of total heat discharge was estimated to be an order of 108 cal/s . On the island many active fumaroles occur, and the temperature of the fumarolic gas ranges from 100 to 128 C… …Volcanic rocks from Iwo-jima are trachyandesite with a SiO2 content of 54% to 58%. Although the topographical structure of Iwo-jima suggests a large caldera-forming eruption (similar to Crater Lake, in Oregon), no clear evidence of a large eruption has been found mainly because of the island’s remote location. Thick pumiceous tuffs overlying glassy lava cover the Motoyama area. 14C ages from charcoal associated with the tuffs give ages of 2700–2800 BP, suggesting that the caldera-forming eruption occurred no earlier than that time, and that the uplift represents post caldera deformation… … A comparison between survey measurements and aerial photographs taken in 1952 and 1968 demonstrates that the coastline on the north to northeast part of the island was uplifted about 9 m during this interval, an uplift rate of more than 0.5 m/a. Overall the uplift was highest along the coasts and lowest at the center of the island with maximum uplift (9 m) around the northern coast and minimum uplift (5 m) near Motoyama. During this same period, Suribachiyama was deforming at a slower rate (1 to 3 m of uplift).

“They construe an uplift of 1 – 3 metres as evidence of subsidence? Because it is less than the 9 metres observed elsewhere? But…?” He leafed through to the several pages of maps showing uplift and lateral movements. “This does not fit! With one or two exceptions these maps clearly show that the centre of uplift lies to the NW of Ioto. Look!” He pointed to the maps. “Uplift is almost always highest in the NW, substantially greater than in the SE. And this is accompanied by a lateral motion towards the SE!”

Hiryoki remained as inscrutable as ever and made no reply. As Chris bent back to his reading, he got up and walked to the door in response to footsteps heard approaching from the corridor. He opened it to let in the JDF MP detail. Out of respect for Chris, their conversation was in English.

“Sergeant, please see to it that Dr Schofield’s luggage is taken care of.” A short command in Japanese and the two MPs accompanying the sergeant immediately complied. Chris was mostly packed as was his habit to do the evening before travelling. After quickly adding the few items not packed, the detail went on its way, bearing Chris’ suitcases leaving his cabin luggage and jacket behind.

In the meantime, Chris had moved on to the second and third papers. They mainly repeated and bulked out the conclusions of the first; that the caldera was the result of ‘a large caldera-forming eruption similar to Crater Lake in Oregon’, but that ‘no clear evidence of a large eruption has been found mainly because of the island’s remote location.’ Chris snorted derisively. Had the Ioto caldera truly been the result of such an eruption the resulting caldera would have been far deeper and Ioto island would still most likely have been many hundreds of metres below the surface. Then a couple of microphotographs caught his attention:

Representative microphotographs showing sizes of ash particles from pyroclastic deposit. a: Motoyama pyroclastic deposit. b: Stratified tuffaceous deposit of Suribachiyama upper pyroclastic deposit. Samples were passed through a sieve with 125 um holes. (Nagai & Kobayashi, 2014)

“Proof! Look, Toru!” He pointed to the photographs. “If there really had been a caldera-forming eruption such as Crater Lake, there would not have remained a magma chamber capable of holding such large, well formed crystals that these are fragments of. Let alone erupting them so peacefully centuries later. It is still there, that eruption could still happen”. Chris was referring to the “similar to Crater Lake” eruption invoked by the first paper. In the background, they could hear a helicopter approaching, the sound growing to a thunder as the pilot skilfully set it down at the edge of the hotel parking lot. The MPs were back to escort them. Hiryoki took possession of the papers while Chris hastily grabbed his jacket and shoulder bag.

As they settled down in the rear compartment, an MP helped Chris and Hiryoki with their helmets. When the MP gave the thumbs-up and closed the door, the civilian who had waited for them spoke up over the intercom.

“Good morning Dr Schofield! My profound and sincere apologies for dragging you away like this but as you may have surmised there is a crisis that requires your particular skills.” He introduced himself as Hiroshoi Yamamoto, secretary to the Minister of Internal Affairs and Communications and yes, he had the honour of being a distant relative of the great Admiral.

“This is a secure line, Dr Schofield. I take it that you have read through the papers given to you by Dr Hiryoki. Please? What are your initial impressions?”

“I’ve only had a quick read-through of the relevant papers and my first impression is that the original researchers may have come to a possibly erroneous conclusion and that subsequent research has committed the error of trying to make the data fit a flawed model”.

“This is part of Japanese culture, I’m afraid. You do not tell a superior that he is wrong. That is for the superior to realise and amend.”

“Not so much a Japanese as a human failing, Mr Yamamoto! It’s ubiquitous. In science, we talk about paradigms and we tend to limit our quest to that for a truth comfortably within the established paradigm. Especially if we are junior researchers.”

“Well Dr Schofield, what then is your outside-paradigm evaluation please? And don’t worry about using technical language. I took a basic course in geology at university and the JMA has, as you may have surmised, kept me filled in with recent developments.”

“That their interpretation of the exceptionally high inflation of Ioto represents the post-caldera movements of a horst or a resurgent dome. Contrary to their interpretation, I find evidence that the main magma chamber of Ioto could not have been destroyed in the 2.7 kA event. At best, it was only partially damaged.”

“And how does that explain the findings of Dr Ume Kiwasawa and her co-workers?”

“They may be partially correct. Do you recall the 2010 eruption of that Icelandic volcano with the unpronounceable name? Well, it began with a flank eruption but then there was a larger quake and the channel was blocked. Two weeks after that the main crater erupted. I believe that something similar can be applied to Ioto.” He then related his interpretation of the GPS data and the proof provided by the microphotographs that the main magma chamber of Ioto was still there and how its presence could explain all the data. Secretary Yamamoto listened, then nodded to Dr Hiryoki who held up a couple of sheets.

“Dr Schofield, two days ago, a major earthquake swarm began below Iwo Jima. Since then the focus has migrated from 27 km depth to about 12 km as of about an hour ago. Gas emissions have increased sharply and there have been reports of minor phreatic explosions. Here is the data for this as well as a printout of the latest data for ground deformation. As you can see inflation over the past 18 hours is 1.3 metres at Kamaiwa in the northwest. And between 0.7 and 0.9 metres in the southern and eastern part of Ioto. But the lateral movement is far greater, slightly more than three metres towards the southeast. I think it’s safe to assume that the model you have just proposed is far more likely to be correct, Dr Schofield.”

Chris leaned forward to accept the print-outs. Then he studied them for a few seconds before he leant back, his eyes focussing on infinity. “Oh my God… It’s Kuwae all over.”

“Please explain Dr Schofield, what is Kuwae.” The voice of Secretary Yamamoto was absolutely calm over the headphones, as if merely shrugging off the minor inconvenience of a delayed dinner.

“Kuwae, Mr Secretary, is a submarine caldera in Vanuatu, about 3,000 km from New Zealand. It is thought to have had a VEI 7 eruption around 1452 CE that caused a tsunami powerful enough to leave palaeotsunami deposits as high as 42 metres in the far north of New Zealand. That’s basically the same as the maximum recorded height of the 2011 Tohoku disaster, at Miyako.”

“So if you are right, what do we do?”

Chris did some rapid calculations on the back of a piece of paper. “What do you do? The question is, what can you do! Look, there’s a great uncertainty with these things; whether or not they are powerful enough to cause mega-tsunamis, let alone ocean-wide ones. Kuwae says they do and if so – God help us all if I am not wrong – if so…” He swallowed hard. “Mr Secretary. Tokyo lies only some 1,250 km from Ioto. The absolute minimum height for such a wave as it reaches land is 25 metres, roughly three times that of the Tohoku tsunami and as that reached as high as 40 metres as it rolled inland…”

He put his hands to his face and tried to rub his temples, a futile gesture as the helmet covered them. Yamamoto and Hiryoki remained silent, each contemplating the implications of what Chris had just told them. Nothing more was said until they had landed on a government helipad on a Tokyo building a few minutes later.

They were immediately escorted into a small conference room and told to wait, but it was not long before a small group of men that included not only the Prime Minister of Japan but also some of the Top Brass entered. The PM had greeted them by saying that regrettably, they did not have time for proper introductions and would Dr Hiryoki please begin his presentation. Only 15 minutes later, Chris had repeated his findings to the PM who had listened attentively without interruption. When he had finished, the PM asked him how certain he was of his projection and what the implications were.

“Look, my off-the-cuff calculation gives a most-likely pre-landfall height of 40 metres, but let’s go with the minimum figure of 25 and pray that I am very, very wrong. At an open-water propagation speed of about 750 km per hour, this wave will strike Tokyo and the East coast of Japan in about an hour and forty minutes after the onset of the major eruption. By the time it hits China and the Philippines about an hour later, the wave will still be in excess of 20 metres. It will follow the Chinese coast and then simply roll up along the Huang-Ho and Yangtsee river valleys, destroying much of China’s agricultural land. Even across the Pacific, the USA and Central America can expect a tsunami wave possibly as high as four or five metres which will have severe consequences. Such a tsunami would kill not hundreds of thousands like the 2004 Indian Ocean one, but rather tens of millions.”

“But the real problem is the aftermath. Displaced survivors numbering in the hundreds of millions without food, potable water, shelter and medical aid. Infra-structure hopelessly blocked or completely destroyed. Even if help could be sent from the rest of the world, how could it get there with harbours and airports inaccessible and the routes leading from then mostly destroyed? Then all the dead bodies, animal as well as human, begin to decompose, poisoning water supplies. Without safe, potable water, how long before dysentery and other epidemics break out, killing the weakened survivors?”

The PM interrupted him by continuing. “And how to maintain law and order amidst such chaos? Will the very fabric of society survive such a disaster or will it unravel and disappear? Dr Hiryoki! As from now the senior representative of the JMA present, what is your recommendation?”

“Prime Minister, this is not a JMA matter as it is not a scientific decision. Do you or do you not inform the public? As a representative of the JMA, it is my duty to advise you of the likely or potential consequences if you do. If and when the public is informed, there will be chaos with everyone desperately trying to save themselves and their possessions. The very resources, human and materiel, needed to sustain and maintain civilised society after such a disaster are very likely to be caught up in this chaos and lost if you do so.”

As he let the implications of his words sink in, Dr Torunasuke Hiryoki glanced out of the windows where dawn had long since won its battle with night. His gaze passed over Tokyo Bay where all the vestiges of night had been banished by the rising sun, to finally rest on the horizon directly due south where they remained as he continued. “Our projections for a mega-disaster indicate that the initial death toll will be similar in both scenarios, but vastly greater afterwards if the public is informed. In the end, Prime Minister, this is a political decision.”

Henrik

(Copyright rests with the author)

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M. Ukawa, E. Fujita, H. Ueda, T. Kumagai, H. Nakajima, H. Morita, ”Long-term geodetic measurements of large scale deformation at Iwo-jima caldera, Japan”, Journal of Volcanology and Geothermal Research 150 (2006) 98– 118

Masashi NAGAI and Tetsuo KOBAYASHI: “Volcanic History of Ogasawara Ioto (Iwo-jima), Izu-Bonin Arc”, Japan, 2014

Taku Ozawa, Hideki Ueda, Motoo Ukawa , Shin-ichi Miyazaki, “Temporal change in crustal deformation related to volcanic activity of Iwo-jima observed by PALSAR/InSAR”, National Research Institute for Earth Science and Disaster Prevention

James Goff, Catherine Chague-Goff and Dale Dominey-Howes “Tracking the extent of the Kuwae tsunami”, Geophysical Research Abstracts Vol. 13, EGU2011-85, 2011

T. Ozawa & H. Ueda, “Research on Monitoring of Volcanic Deformation Using SAR Interferometry”, PI No 357.

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