Feature NURUL HIDAYAT/ANTARA FOTO/BISNIS INDONESIA VIA REUTERS FOTO/BISNIS HIDAYAT/ANTARA NURUL When Anak Krakatau in Indonesia erupted on 22 December 2018, part of the island collapsed into the ocean, causing a deadly tsunami. THE VOLCANOLOGY REVOLUTION Forty years after the Mount St Helens eruption galvanized volcano science, researchers are harnessing powerful new tools to forecast and understand eruptions. By Jane Palmer arly in 2018, the volcano Anak Krakatau the mountain began showing obvious signs of killed at least 430 people along the nearby in Indonesia started falling apart. It was unrest. It spewed fiery ash and rocks into the sky coasts of Java and Sumatra. Although nobody a subtle transformation — one that in a series of small eruptions. And it was heating foresaw that disaster, a 2019 study found that nobody noticed at the time. The south- up. Another satellite instrument recorded ther- satellite and ground-based instruments had ern and southwestern flanks of the vol- mal emissions from Anak Krakatau that reached picked up a suite of precursory signals that cano were slipping towards the ocean 146 megawatts — more than 100 times the could help forecast similar events in the future at a rate of about 4 millimetres per normal value. With the increased activity, the at Anak Krakatau and other peaks. month, a shift so small that research- slippage jumped to 10 millimetres per month. The unexpected collapse at Anak Krakatau Eers only saw it after the fact as they combed Then, on 22 December, the southern flank shows some of the challenges facing research- through satellite radar data. By June, though, crashed into the sea, triggering a tsunami that ers as they try to monitor thousands of 256 | Nature | Vol 581 | 21 May 2020 ©2020 Spri nger Nature Li mited. All rights reserved. ©2020 Spri nger Nature Li mited. All rights reserved. potentially dangerous volcanoes around the time frame, much as meteorologists dole out hummocks — large hills and mounds that had world — each one unique. But it also highlights the chances of rain or snow on any specific day. been transported downslope in intact blocks. several advances in the field that promise to “I think that when people look back on this These features matched those found near give scientists a much better chance of fore- period, they will imagine this is the golden era many volcanoes around the world. And from casting disasters. of physical volcanology,” says volcanologist the historical record, volcanologists recog- Volcanologists are making substantial Christopher Kilburn at University College nized that around 1,000 similar landslides had headway, thanks to a torrent of data from sat- London. taken place on more than 550 volcanoes. “Tall ellites that can detect subtle movements of volcanoes collapse, they’re not just growing, mountains, ground-based sensors that track Historic blast they’re collapsing,” says volcanologist Thomas molten rock moving deep underground, and The first hints of trouble at Mount St Helens Walter at the German Research Centre for gas-sniffing devices that drones can carry over came on 16 March 1980, with a series of small Geosciences in Potsdam. seething mountains. And the theoretical under- earthquakes. Then, a week later, steam explo- The eruption of Mount St Helens taught other standing of volcanoes has grown markedly as sions burst through the ice on top of the volcano, lessons, such as the deadly impact of super- researchers have learnt to combine all these carving out a crater that grew to 400 metres heated volcanic ash and gas racing down the data into models of what is happening within across within days. Teams of researchers mountain at hurricane speeds, and the power volcanic systems. Researchers are now exper- arrived from the USGS and other institutions of mudslides that destroyed everything in their imenting with machine learning to sift through to keep vigil over the mountain. Planes flew path. The eruption also spurred a huge growth the flood of data to identify subtle patterns, in volcanology. In the decade after the blast, the such as the early movement of Anak Krakatau “Tall volcanoes collapse. USGS established volcano observatories in the months before it showed signs of waking. Pacific Northwest, Hawaii and Alaska. The field has made huge strides since the They are not just growing, Funding for the USGS’s volcanic hazards greatest volcanic crisis in US history exactly they’re collapsing.” programme today is nearly ten times what 40 years ago — the eruption of Mount St Helens it was before the Mount St Helens blast. And on 18 May 1980 in Washington state. That after a volcanic mudslide in Colombia killed event — which started with the largest land- over the smoking crater to measure the gases 23,000 people in 1985, the USGS established slide in recorded history — killed 57 people and escaping from the volcano, and seismometers the Volcano Disaster Assistance Program to blanketed much of Washington and nearby registered the tremors from magma — molten help other countries prepare for volcanic states with ash, shutting down the region for rock — moving beneath the surface. Volcanolo- crises — a project that soon proved its worth days. But it was also a turning point for vol- gists climbed the mountain’s slopes to measure when USGS researchers worked with scientists canic science, sparking a huge influx of money the bulging northern flank using tape measures in the Philippines in 1991 to assess the risk from and people into the field and setting the stage and laser-surveying equipment. Mount Pinatubo. Tens of thousands of people for rapid improvements in understanding. Magma was clearly rising high in the volcano were evacuated from the region before the Scientists had flocked to the mountain in and pushing against the slope, and research- volcano’s cataclysmic eruption. the months before the blast and had carefully ers warned that a major eruption could hap- Researchers today rely on many of the tracked its behaviour, including frequent pen soon. But what happened next caught lessons learnt at St Helens, Pinatubo and dozens earthquakes, gases fuming from its crater and scientists by surprise. of other volcanoes. Typically, seismic shaking an ominous bulge that swelled from its north- At 8:32 a.m. on 18 May, a massive landslide is the first sign that a volcano is stirring. Erup- ern flank. “It was the first really significant crashed down the mountainside, taking the tions occur when magma pushes to the surface, eruption that was captured by modern-day summit and snow and ice with it. The release but even as magma begins to rise from Earth’s scientific instrumentation,” says Seth Moran, in pressure uncorked the volcano, triggering mantle, it can trigger quakes. Today, seismic scientist-in-charge at the US Geological Sur- a powerful explosion. A blast of rocks, ash, gas networks are monitoring dozens of some of the vey (USGS) Cascades Volcano Observatory and steam was propelled upwards and out- most dangerous volcanoes around the world. in Vancouver, Washington. “And so, in a lot of wards at supersonic speeds, and travelled as That same magma movement can cause ways, it’s become a benchmark for the ways far as 25 kilometres northwards. volcanoes to inflate, as Mount St Helens did that people go about looking at volcanoes “We learnt from the May 18th eruption how before its blast. Researchers can now record around the world.” unstable steep-sided volcanoes are, and how movements safely and continuously, using The proliferation of ground- and space- they can fail and generate a big surge or lateral GPS receivers and, more recently, satel- based monitoring data since then, coupled blast,” says Don Swanson, a research geologist lite-borne radar — which detected the move- with increases in computing power, has revolu- at the USGS Hawaiian Volcano Observatory, ment at Anak Krakatau. tionized scientists’ understanding of volcanic who was involved in monitoring the 1980 Even before warning signs can be seen or systems. Ultimately, researchers are hoping eruption. “What seems so obvious now, wasn’t felt, rising levels of carbon dioxide from a that new tools and techniques will nudge them obvious before that time.” volcano’s crater or vents can hint at trouble closer to being able to assign probabilities to After the eruption, scientists analysed ahead. Magma contains dissolved gases and the chances of a volcano erupting in a given the landscape and found it littered with as this molten material rises and the pressure 10 s 42 s 52 s 60 s USGS On 18 May 1980, a giant landslide — the largest in recorded history — carried away the north flank of Mount St Helens, triggering an eruption. Nature | Vol 581 | 21 May 2020 | 257 ©2020 Spri nger Nature Li mited. All rights reserved. ©2020 Spri nger Nature Li mited. All rights reserved. Feature decreases, gases separate off and travel programmed the system to send automatic activity ever recorded,” says Walter. “So, this upwards. Carbon dioxide, one of the least e-mail and text-message alerts to the civil-pro- was clearly anomalous behaviour.” soluble of the volcanic gases, escapes first, tection department in Rome and to the city of The researchers also used satellite radar while the magma is still deep in the volcano. Catania close to the volcano. observations, which can detect small changes “In principle, you should get a gas signal The researchers’ original motivation for in vertical and horizontal motion, to find that long before the magma reaches the surface developing the system was to find a way to the volcano’s flank was already slipping at a rate in an eruption,” says volcanic-gas geochem- detect eruptions at unmonitored volcanoes, of 10 millimetres per month before it collapsed ist Alessandro Aiuppa at the University of because even remote blasts can have far-reach- (see ‘Island on the move’).