Island on Fire Read online

  Katla’s 1918 eruption carried massive icebergs (note people for scale) along on its glacial flood, all the way to the south coast and the sea.

  Folklore holds that Katla is named after a cook at a local monastery, who was lucky enough to own a pair of magic trousers in which a person could run forever. When a shepherd used these without permission one day to help bring in his sheep, Katla drowned him in a barrel full of whey. Eventually, realizing she would be caught for the murder, Katla put on the trousers, ran up the mountain, and threw herself into an icy crevasse. Soon afterward an eruption sent a glacial flood coursing downhill toward the monastery: Katla’s revenge.

  Katla’s last eruption, in 1918, was the most powerful of any in twentieth-century Iceland. It sent jökulhlaups racing across the plains at speeds up to 20 kilometres an hour: witnesses reported that it looked as if the snow-covered hills themselves were moving, as house-sized chunks washed down from the top of the ice cap. When the waters subsided, icebergs as tall as eighty metres were beached on the coastal plain. The rushing waters left behind enough new land to temporarily claim the status of Iceland’s southernmost point, until coastal erosion took much of it away.

  Since then Katla has been quiet, other than possible small eruptions in 1955 and 1999. The gap – one of the longest in the mountain’s recorded history – troubles many volcanologists. Especially because Katla has often erupted in tandem with another volcano 25 kilometres to the west, a once-obscure mountain that lurched to international fame in 2010.

  The story of Eyjafjallajökull began uneventfully with what Icelanders call a ‘tourist’ eruption, one that’s scenic but not very dangerous. In March 2010, lava began spewing from a fissure on the mountain’s side, along a barren ridge that serves as a popular day hike. Photographers flocked to capture the fire fountains against the northern lights, and by volcanic standards it looked fairly unthreatening. It seemed as if the most problematic aspect of the eruption – for non-Icelanders, anyway – would be how to pronounce the name of the mountain. (‘Eyjafjallajökull’ means ‘the glacier [jökull] atop the mountain [fjall] overlooking the islands [eyja],’ and a YouTube search will turn up an Icelandic woman singing a ukulele ditty to teach people the word.)

  But in early April, lava stopped coming out of the barren ridge. Something shifted in the plumbing system beneath the volcano and the eruption moved about a few kilometres to the west, directly beneath the glacier that caps Eyjafjallajökull. Suddenly, the magma got much stickier as it began to mix with other, older rocks in the magma chamber. It was also running into ice instead of air. The heat melted the ice from below, and then reacted explosively with the newly formed water. Now, instead of burbling out peacefully in scenic fire fountains, the magma shattered into ash fragments carried sky-high. Eyjafjallajökull was no longer a tourist eruption, but had awoken for real.

  Winds happened to be drifting in just the right direction to ferry the ash toward the British Isles, and so the London centre in charge of volcanic-ash alerts told authorities to start shutting down airspace. That’s because planes and volcanic ash do not play well together. When ash fragments get sucked into the extreme heat of jet engines, they can melt, forming a glassy coating that clogs up the turbines. In 1982, a British Airways flight in Indonesia passed through an ash cloud from Mount Galunggung and lost power in all four of its engines. So too did a KLM flight over Alaska in 1989. In both cases pilots eventually restarted the engines and landed safely, but not before dropping more than 3,000 metres. In the wake of these incidents, aviation authorities drew up new rules that forbid planes from flying in any airspace that could potentially have any amount of volcanic ash in it.

  When Eyjafjallajökull erupted, officials had to abide by these rules. Every day, the London-based volcanic ash advisory centre issued maps of where the eruptive plume had drifted, and where it might go next. Planes could not enter any of that airspace. For nearly a week flights were grounded across Europe, stranding travellers and disrupting the flow of global commerce. The shutdown may have cost businesses as much as five billion euros, and carriers were told they must shell out for hotel expenses for their flightless passengers. Eventually, in reaction to the inevitable complaints, aviation authorities raised the acceptable limit of volcanic ash that planes can fly through.

  The larger question is whether the annoying Eyjafjallajökull might set off the far more deadly Katla. Although seemingly separate on the surface, the two volcanoes may be linked by stress changes deep in the earth. Katla has regularly erupted on its own, but the last three times when Eyjafjallajökull erupted prior to 2010 – in 1821, 1612 and possibly the year 920 – Katla went off soon after. The connections between the two volcanoes aren’t clear, and it’s entirely possible that there is no real link between them, but volcanologists do think Katla could erupt at any time, and scientists and emergency planners are maintaining a very close eye on it. As if to keep everyone on their toes, in the summer of 2011 seismic activity within Katla’s caldera shifted slightly toward the east, and a glacial flood washed out a nearby bridge.

  A May 2010 satellite image of Eyjafjallajökull shows its ash plume heading south and east toward Europe.

  Heat from the buried Grímsvötn volcano causes lakes to pond atop the Vatnajökull ice cap (seen here in August 2011, a few months after an eruption).

  Hekla may be the queen of Iceland’s volcanoes, and Katla may be the most feared for its flood potential, but the title of most active volcano goes to Grímsvötn. Look at a satellite picture of Iceland and your eye will be immediately drawn to the big blob of white in the country’s southeast. That’s mighty Vatnajökull, the largest ice cap in Europe. Beneath it lies the subglacial lake known as Grímsvötn, created by a volcano with the same name that has erupted more than any other in Icelandic history. Chronicles from the sixteenth and seventeenth centuries talk about the eldar, or ‘fires’, that regularly come from this region.

  Grímsvötn is a sort of natural geothermal plant. The equivalent of several thousand megawatts of continuous power create a meltwater lake atop the volcano, beneath the overlying ice. When enough water accumulates in the lake, the pressure forces an opening in the ice cap and the water pours out, draining most of the lake in a matter of days. This happens about once every five to ten years, although Grímsvötn’s most recent eruption, in 2011, didn’t cause any great flooding (perhaps because it had been drained relatively recently by another jökulhlaup). But the floods can be immensely powerful, leaving behind ‘sand plains’ that stretch for kilometre after kilometre all the way to the coast. The floods also knock out the sturdiest of Icelandic bridges: on the sand plains east of the town of Kirkjubæjarklaustur, you can stop to marvel at the twisted steel wreck of a bridge, tossed aside like a child’s toy during a 1996 eruption.

  Grímsvötn is but a single volcano, but it’s the hub of a so-called fissure system, a network of long narrow cracks along which magma can rise to the surface. From the southwest corner of the Vatnajökull ice cap a couple of long linear features stretch out across the barren ground, as if a giant had reached down and scraped his fingernails across the landscape. These are the marks of some of the most powerful eruptions from the past millennium. Here, twice, lava has poured out in quantities greater than anywhere else in recent times. No wonder Icelanders call this area the Fire Districts.

  The northernmost of these two great scrapes arrived in the year 934, in an event that takes its name from the mighty canyon known as Eldgjá, or ‘fire fissure’. For six years it vomited more lava onto the landscape than any other eruption in the last millennium. Spread all the Eldgjá lava into a strip as wide as the Champs Elyseés, and it would run from Paris to Berlin as a wall 500 metres high. Mere decades after Iceland’s first settlers had begun tilling the rich land, this pile-up of lava forced the Skaftá River to change its course. Many farmers fled, while others tried to clear their land as the deluge of ash fell onto it. They must have been choking on the eruption’s fumes as they worked – Eldgjá
also takes the title of the most polluting volcano of the past millennium. It pumped some 220 million tonnes of sulphur dioxide into the atmosphere, more than twenty times the amount released by Mount Pinatubo in the Philippines in 1991.

  Almost no records of the terrible Eldgjá eruption survive, and local memories may have faded over time. But more than eight centuries after its lava cooled to vast featureless plains, Icelanders were to see a second set of violent eruptions in the Fire Districts. These were to come along a second set of giant fissures located just a few kilometres further south – on each side of a small mountain called Laki.

  CHAPTER THREE

  Supervolcanoes

  The world’s hotspots

  NOWHERE IS THE VIOLENCE AND BEAUTY of our planet so apparent as in Yellowstone, America’s first national park and home to what could be called the world’s most dangerous volcano. Tourists flock to Yellowstone for the views: snowcapped peaks, lushly forested valleys, and teeming herds of bison and elk. Equally astounding is the park’s vast array of geothermal features. ‘Paint pots’ of burbling mud spray red, white and other vibrant tints across a geological artist’s palette. Bacterial mats the colour of autumn leaves stain the banks of the Yellowstone River. Steaming water percolates out of the ground and runs downhill, fashioning giant terraced and pillared structures out of minerals. And, of course, geysers like Old Faithful gush boiling water across the landscape. Yellowstone is home to a greater concentration of geysers than anywhere else in the world.

  All this action arises from a hotspot of molten rock much like the mantle plume that lies beneath Iceland, though probably not as deep. The Yellowstone hotspot taps into heat about 200 kilometres below the surface, where rock melts and rises into a magma chamber just a few kilometres beneath the Wyoming countryside. This giant reservoir is what heats groundwater above to create the many geysers, mud pots and hot springs.

  Geysers are plumes of water superheated by volcanic activity. A slumbering supervolcano beneath Yellowstone National Park, in the western United States, fuels an intense concentration of geysers there.

  Sixteen million years ago, the Yellowstone hotspot spewed out lava in what is today southeastern Oregon. Over time, as the crustal plate drifted westward above the hotspot, the plume punched out progressively younger tracks across the Snake River plain of southern Idaho. (The interstate highway that runs through Boise traverses these featureless plains of black lava. Idahoans have famously made the best of it by tilling the soil to grow potatoes.)

  By the time the hotspot reached what is now Yellowstone, it let loose its wrath in three colossal eruptions. All three spread ash and debris – enough material to fill the Grand Canyon – over nearly the entire western half of the United States, and left behind colossal craters known as calderas, formed as magma beneath the ground drained out. The most recent eruption happened around 640,000 years ago and was about 2,500 times the size of the 1980 eruption of Mount St. Helens. The oldest of the three Yellowstone blowouts happened 2.1 million years ago and was 6,000 times bigger than Mount St. Helens.

  That makes Yellowstone the quintessential example of a ‘supervolcano’, a word that has little technical merit but that is helpful for thinking about the relative scale of eruptions. BBC producers coined the term in 2000, to describe planet-altering eruptions that disgorge an immense volume of ash and other rock fragments – as a general rule, the volume of material that settles onto the ground is about two to three times the volume of the magma that fuelled the eruption.

  In order to rank eruptions, volcanologists have developed the Volcanic Explosivity Index, or VEI, a scale that runs from 0 to 8. A VEI rating takes into account not only how much stuff a volcano blows out but also how high its eruptive plume rises. Each notch on the scale represents roughly a tenfold increase. An eruption with a VEI of 1, for instance, spits out more than 10,000 cubic metres of material and has a plume between 100 and 1,000 metres high. (Italy’s Stromboli does this almost constantly.) A VEI 2 eruption will blow out more than 1 million cubic metres of stuff, with a plume between 1 and 5 kilometres high. This kind of eruption might go off once a week somewhere around the globe. Going on up the scale, a VEI 3 eruption happens perhaps annually.

  After that, things get really interesting. ‘Cataclysmic’ eruptions with a VEI of 4, such as the 2010 eruption of Eyjafjallajökull or the 1783–84 eruption of Laki, send a plume between 10 and 25 kilometres high. The archetypal VEI 5 eruption (aka ‘paroxysmal’) is the May 1980 eruption of Mount St. Helens, which ripped the top off the mountain and sent the largest recorded landslide roaring down the valley below. A VEI of 6 (‘colossal’) is something that happens only once every century – like Mount Pinatubo, which blew up in the Philippines in 1991, sending ash more than 30 kilometres high to encircle and cool the globe for several years. As if that weren’t enough, a VEI 7 eruption gets dubbed ‘super-colossal’ for spewing more than 100 cubic kilometres of material. The last time this happened was in Tambora, Indonesia, in 1815.

  And then there are the VEI 8 eruptions, which start to edge off the scale of possible description. ‘Mega-colossal’ the ranking scale calls them. These furious explosions send out more than 1,000 cubic kilometres of debris, with plumes reaching more than 50 kilometres high. That’s almost to the edge of space.

  Yellowstone’s eruption 2.1 million years ago ranked a VEI 8. But that’s far beyond the reach of human history. To understand what a VEI 8 eruption can do in more recent times, you have to look to Toba, Indonesia. The most recent VEI 8 blast happened there, 74,000 years ago, and is almost beyond believability.

  Toba was destined to blow from the start. The volcano nestles on the northern part of the island of Sumatra, where the Indo-Australian tectonic plate dives beneath the Sunda plate. The collision fuels the chain of fire mountains that make Indonesia the most volcanically active place in the world.

  In the past million years or so, Toba has erupted four times, culminating in the one 74,000 years ago. Numbers such as ‘VEI 8’ don’t really do justice to this sort of devastation. When volcanologists think about the worst-case eruption, the kind of colossal blast that changes the planet forever, Toba is what they think of.

  The eruption blasted an ash cloud across most of Southeast Asia. Landscapes were buried. Rivers choked and stopped flowing. The first scientists to identify Toba’s ash thought the eruption must have covered some 5 million square kilometres, itself an astounding number. Other geologists later found the Toba signature even further away, in seafloor cores taken from the South China Sea and the Indian Ocean south of the equator. That geographical spread roughly doubles the amount of ash that Toba must have disgorged. In all, the volcano buried 1 per cent of the planet’s surface at least 10 centimetres deep in debris.

  The eruption of Indonesia’s Toba volcano, 74,000 years ago, left behind a 100-kilometre-long lake – clearly visible in this space shot.

  Rocks falling out of the sky would have levelled trees and killed animals on the ground. The skies would have darkened noticeably, to be somewhere between an ordinary overcast day and something almost as dim as a moonlit night. The combination of the lava, the rocks and the gases belching out of Toba would have eradicated all life around the mountain. The neighbouring island of Mentawai, 350 kilometres away, somehow escaped the worst of the damage because it remains home to monkeys and squirrels that would have become extinct had Toba’s debris fallen heavily on the island’s rainforests.

  Further afield, the sulphur from the volcano would have quickly turned into small particles that reflected the sun’s incoming rays back into space, shading and cooling the planet beneath. In fact, Toba has become something of an archetype for scientists who are trying to understand how volcanic eruptions can affect global climate. The first research into its climatic effects took place in the 1970s, around the time researchers were beginning to assess the atmospheric impacts of a possible nuclear war between the United States and the Soviet Union. It turns out that debris from a nuclear bomb would spre
ad around the globe much as an ash cloud does, cooling and triggering a ‘nuclear winter’ that could freeze people and crops worldwide. Similarly, geologists proposed that an eruption such as Toba could set off a ‘volcanic winter’ that would devastate the planet for years.

  To figure out how temperatures changed, some researchers look for environmental records such as fragments of ancient plants, while others use state-of-the-art climate models to simulate how temperatures may have fallen as the volcanic pall spread around the globe. General consensus today holds that Toba caused global temperatures to plummet by as much as 10 degrees Celsius for a year or more. The climate would have stayed dramatically colder for a decade or two, followed by generally cooler temperatures and lower precipitation for several more centuries.

  Most controversially, the eruption may have even affected human evolution. Toba went off at around the time that modern humans, Homo sapiens, were moving out of their evolutionary birthplace of Africa and into Asia. It’s hard not to wonder what those newcomers must have thought when they looked up and saw a towering ash cloud moving toward them. Scientists have long known that early humans went through population ‘bottlenecks’, in which many died out and only a certain number emerged to continue passing their genes from generation to generation. In 1998, Stanley Ambrose of the University of Illinois linked one of these population bottlenecks to the Toba eruption. For early humans desperately looking for things to eat, the big chill would have been just too much to handle, Ambrose proposed. ‘Toba’s volcanic winter could have decimated most modern human populations,’ he wrote in the Journal of Human Evolution.