Supervolcanoes: The NZ-based scientist who can tell us when to worryby Veronika Meduna
Colin Wilson, this year’s recipient of the country’s highest science honour, says he’s been fascinated by volcanoes since his teens.
Wilson, 61, has dedicated his career to deciphering the geological remains of these monster events, from the large-scale deposits they leave behind to the microscopic analysis of crystals in the rocks they create. His fieldwork at Taupo, and at the Long Valley and Yellowstone volcanic areas, in California and Wyoming respectively, has unearthed detailed evidence of how supervolcanoes go from a rumbling slumber to an explosive eruption. It has also shown that the North Island’s volcanoes are all linked in one complicated supervolcano system.
English-born Wilson now leads a five-year, multi-institution project to model supervolcanoes to allow scientists to forecast the risk of future eruptions. This month, his work earned him New Zealand’s highest science honour, the Rutherford Medal.
Your PhD research almost four decades ago into the Taupo eruption in 232AD – the largest and most violent of the past 5000 years – asked whether this eruption enhanced European sunsets. Did it?
Alas, the paper I wrote with colleagues in 1980 linking the eruption to atmospheric phenomena in Europe and China is incorrect, and the story has now become an urban myth with a life of its own. Nonetheless, the eruption was powerful enough that the explosions would have been heard in Australia by Aborigines and in Indonesia, and I infer that there would have been extensive global atmospheric effects, which may have been recorded.
Large explosive eruptions affect the climate by carrying fine ash and acidic gases (aerosols) high into the atmosphere, where they can persist for years. These aerosols reduce the energy from the sun, leading to lower surface temperatures. In 1816, the ”year without a summer” followed the large 1815 eruption of Tambora in Indonesia; the consequences of a super eruption have been proposed to generate a volcanic winter that might last for several years, with worldwide effects.
The Taupo eruption is notable for its volume – in all, probably about 100cu km of pumice and ash, including that now concealed beneath the lake – and its extreme vigour and violence. At one point, the plume probably reached 45-50km in height and laid down pumice deposits over an area about 160km wide that stretched over to the east coast and out into the Pacific Ocean. During the final stage, something happened, and the vent area was ripped open in an enormously powerful blast-like event, the deposits from which form the Taupo ignimbrite. My work suggested that the material was erupted in only about 400 seconds, so it travelled at speeds exceeding 200m a second or 700km/h and travelled about 80km in all directions across all obstacles – except, possibly, the top of Ruapehu – in about 10 minutes.
The flow travelled so fast that it flattened the forests, and these have been investigated by botanists as examples of pre-human flora.
Taupo is one of the world’s five young supervolcanoes. Its earlier super explosion 25,500 years ago reshaped the North Island and changed the course of the Waikato River. How and why do such supervolcanoes form? Where are the others?
A supervolcano is simply one that has experienced a super eruption. If we take the past 2.6 million years of Earth’s history, then there have been 10 super eruptions recorded from five volcanoes or volcanic areas: one in Argentina (Cerro Galán, 2.08 million years ago), one in eastern California (Long Valley, 765,000 years ago), Yellowstone with two super eruptions (2.08 million and 631,000 years ago, respectively), Toba in Sumatra, Indonesia, with two events (840,000 and 74,000 years ago) and four eruptions in New Zealand. These are the Ongatiti eruption (1.27 million years ago) from a centre now buried in the area near Mangakino; the Kidnappers eruption (1 million years ago), also from the Mangakino area; the Whakamaru eruption (350,000 years ago) from an area north of Lake Taupo; and the Oruanui eruption (25,500 years ago) from where Lake Taupo is now.
A super eruption seems to be the product of the normal processes that occur at the many volcanoes worldwide that erupt the silica-rich magmas known as dacite or rhyolite, but magnified to great size. For reasons that are still under investigation, it looks as if the amounts of magma being fed from deep in the Earth [the mantle] into these areas increases, and creates a huge volume of material that is partially molten, known as mush, in the Earth’s crust. This material is too stiff [viscous] to erupt under most normal circumstances. Something disturbs this mush and the melt [plus lesser amounts of crystals] pools and collects, and this body is what is erupted.
To get a super eruption, you have to have a large volume of mush – about 10 times more than the volume that is actually erupted – extract the melt and hold it in a body that doesn’t burst prematurely and give you a smaller eruption. As you can imagine, there is still a lot of debate over how this happens. This debate is made more important because supervolcanoes don’t just have super eruptions, they also have small eruptions. If we could understand why, we’d move a long way towards understanding how these sorts of volcanoes operate.
The Yellowstone supervolcano is experiencing a swarm of earthquakes – 2500 quakes since June. Is that a prelude to volcanic activity?
Almost certainly not. These big volcanoes are like people asleep – when you are asleep, you snore, roll over, toss and turn, all without waking up. Volcanoes do the same. It’s one of the big challenges that we face – that of deciding when the volcano is actually going to wake up and how fast.
What do you make of Nasa’s plans to drill into the Yellowstone volcano’s magma chamber to cool it down, as a way of preventing a super explosion?
Er, excuse me … we’ve been doing this in New Zealand for nearly 60 years. It’s called utilisation of geothermal energy. The damned Yankees are always pretending to come up with something new that someone else has been doing for years. And there’s almost no way that the environmental rules would be bent to allow drilling in the national park – “almost” because there’s almost nothing the US President wouldn’t permit if he thought industry would benefit and it cut across the environmental efforts of the Obama administration. Nature is cooling these magma chambers all the time, and in the long run they are doomed to fall back into slumber; it’s just that sometimes the magma system seems to get its act into gear and generate an eruption. The chambers that failed to erupt and the dregs left behind by successful eruptions stay behind to form granites, like the ones at the northern tip of the Coromandel, or in the north-western part of the South Island.
Does the analysis of past explosions help to predict future activity?
It is very important in establishing the style and personality of a volcano as a guide to future activity, just as studying the past behaviour of a person is a guide (not necessarily infallible) to future behaviour. Some volcanoes, such as Mt Ngauruhoe before 1975, behave very regularly: their activity is confined within reasonable limits of eruption size, style and violence, and it occurs frequently enough that any indications of a resumption of activity can be fitted within that framework.
If a volcano has not erupted for a long time, or shows a wide range in its eruption style, the past is still a guide for future activity, but then the challenge is in deciding, if the volcano shows signs of unrest, whether an eruption is going to happen, and if so, how big it is going to be. So the past is the key to the future, but quite often (for example, at Taupo) the record of the past is so greatly variable that it is hard to be specific about when the next eruption will occur, or how big it will be.
You’ve recently begun work on a national volcanic hazard model, with colleagues at GNS Science and elsewhere. Do we know what to expect and are we well prepared?
The paper that was submitted was only the beginning of the work, setting out as a starter the kinds of things that will need to be done. There’s a lot more work needed before the model is completed. We know within reasonable bounds what to expect when any one of New Zealand’s volcanoes erupts again. What we don’t know is, (a) how many episodes of unrest we will see before the volcano actually decides to get its act into gear; (b) how we can tell unrest from eruption before the magma hits the surface; (c) exactly how big an eruption we are in for (which will determine the levels of hazard); and (d) how long we will have in reality to get the answers to points (a), (b) and (c) before the eruption provides those answers.
New Zealand is reasonably well prepared, but we can and are trying to do more to reduce the uncertainties around eruptions (especially at the big supervolcano system in the heart of the North Island), to educate and inform. One bonus of this kind of work is that the methods we will be trying to develop have applicability at other large or supervolcanoes worldwide.
Are you keeping an eye on Bali’s Mt Agung?
Oh, yes. When it last erupted in 1963, it affected the climate over much of the globe. Although not huge in the amount of material erupted, it was an important eruption in terms of alerting the scientific community to the potential effects of eruptions on the climate.
What made you decide to make New Zealand home in 2009?
I first came here in 1978 as a PhD student, following my supervisor, then after shifting between here and the UK, I settled here in early 1993. I came back because I liked the place and I was offered a job. My work has always been internationally focused, so where I’m based is not always very important, although I have done most of my work on New Zealand volcanoes.
Are there any early moments that made you decide to study geology and focus on volcanoes?
I’d always enjoyed geology. As a teenager, I used to travel up to London on the train and visit the Natural History Museum and the Geological Museum in South Kensington. I found stuffed animals boring and dinosaurs vaguely interesting, but the rock and mineral collections fascinating. When the time came to apply to go to university, my first choice was Imperial College, which happened by strange coincidence to be in the same block of real estate as those museums. Just before I went up for an interview in 1973, Eldfell volcano on the Icelandic island of Heimaey erupted on the outskirts of the only town. The pictures and descriptions enthralled me, so when asked about what interested me in geology, I waxed lyrical about volcanoes. I scraped into a place there, then as a new undergraduate was allocated to a most remarkable individual, George Walker, who was the father of modern quantitative volcanology. We hit it off and my course of study was set. I’d like to think he would have been pleased with my progress. I cannot imagine doing anything else.
How important is fieldwork for you and where’s your next field site? How do you manage to be in the field without a mobile phone?
The next field trip will be to Taupo, then Waitomo. Fieldwork is vital. The more people tell me about their theories and computer models, the more I remain certain that nature is far more interesting and strange than any models can yet cope with. Models are built out of what we know. I’m interested in what we don’t know, and even what we don’t know that we don’t know – echoing Donald Rumsfeld, for whom I otherwise have little regard. Models would not have predicted the Taupo ignimbrite, yet it happened.
Working on an active or potentially active volcano can be a bit exciting, and several volcanologists have been killed in the course of duty by volcanic eruptions. In the work I have done, I have always accepted the risks involved and avoided situations where the gaining of knowledge was outweighed by the hazards.
My lack of a mobile phone has been deliberate, and with due consideration for health and safety. Fieldwork requires concentration and should be enjoyable. To be at the mercy of others is not freedom. My job nowadays does not permit as much time for fieldwork as I’d like, and the ageing carcass gets more reluctant to be hauled up mountains than it did. That’s why having keen younger students is important.
This article was first published in the October 28, 2017 issue of the New Zealand Listener.
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