Island on Fire Read online

  His theory described an ocean bottom in which the youngest ocean crust is closest to the mid-ocean ridges, and the oldest crust is that smashing into the continents. Conveniently, this idea could readily be tested by oceanographers, and several 1960s expeditions did just that, towing magnetic detection instruments behind ships to read the magnetic orientation of rocks on the seafloor.

  Magnetic studies can reveal the ages of rocks thanks to a peculiar habit of Earth’s magnetic field: it flips direction every few hundred thousand years, or at even longer intervals. When this happens, the north magnetic pole essentially turns into the south magnetic pole, and vice versa. If you were around during one of these flips and holding a compass, you would see its needle turn from north to south. It might, however, take you 1,000 or 10,000 years to watch the entire flip.

  The seafloor rocks hold a record of this magnetic switch. When lava cools, its iron-rich crystals become frozen in a particular orientation, pointing toward magnetic north like a forest of tiny compasses. The last magnetic field reversal took place 780,000 years ago, so any rocks that cooled in the last 780,000 years would have compasses pointing toward what we know as north today. The period before that, when rocks would cool with their compasses pointing south, lasted between about 950,000 and 780,000 years ago.

  As seafloor rocks form and move away from the mid-ocean ridge, then, they should preserve a record of this alternating magnetic polarity through time. And that’s exactly what the oceanographers found when they drilled and retrieved crust from the seafloor: stripe after stripe of normal magnetism, then reverse magnetism, then normal magnetism. It all stretched away from the seafloor spreading centre, symmetrically on each side of the mid-ocean ridge, like a huge tape-recording machine capturing more than 100 million years of seafloor history.

  The Earth’s crust is divided into about a dozen major tectonic plates, plus a clutch of smaller ones.

  With this confirmation of seafloor spreading, geologists had the full picture of plate tectonics. Volcanic activity from below created the mid-ocean ridges. Fresh crust moved away on each side of the ridge, slowly and steadily, until it smashed into a continent. The oceanic crust, being denser than the continent, plunged beneath it, in a process that geologists call subduction. Finally, scientists had both the evidence that continents moved, and – the biggest piece that Wegener never got – the reason why they did.

  Today, researchers know that Earth’s crust is divided into about a dozen large tectonic plates and many smaller ones, which jostle against one another like schoolkids elbowing for a place at the lunch table. Over hundreds of millions of years the physical pressure of plates slamming into one another, fuelled by heat from below, have rearranged the oceans and continents. The supercontinent Pangaea ruled the planet around 250 million years ago. It later fragmented into two smaller landmasses and then into the seven continents we know today. Scientists have even calculated how plate tectonics might shift continents in the future: in the next 200 million years, because the Pacific seafloor is being subducted, North America and Asia will merge to form a supercontinent, which has been dubbed Amasia.

  Plate tectonics dictate most of the planet’s geological activity. Where plates meet, huge geologic disasters can happen. Zones of plate subduction, such as where Pacific oceanic crust dives beneath South America or Japan, are often the sites of Earth’s greatest earthquakes. The part of the plate diving down usually sticks, building up stress and then releasing it in periodic spasms – like the magnitude 9.0 earthquake (and resulting tsunami) that devastated Japan in March 2011.

  At the same time, the subducting ocean plate also leads to volcanoes. The plunging plate carries with it sediments from the ocean floor that contain trapped water, which causes the rock to melt at a lower temperature than it otherwise would, so that the ocean slab and the sediments on top begin to melt fairly soon after diving beneath the continent. This melting feeds new magma chambers which, in turn, feed volcanoes above them. This is how the volcanoes of the Pacific Northwest, like Mount St. Helens and the rest of the Cascades, are made: part of the old Pacific ocean plate is plunging beneath North America, and molten material is rising to fuel the Cascades. On a grander scale this is also why the entire Ring of Fire exists, encircling the Pacific with a chain of active volcanoes. Scientists nicknamed this chain long before they understood the plate tectonics that explained its existence.

  Subducting ocean plates: a downward-plunging tectonic plate can generate volcanoes in the overlying crust.

  Most of the world’s volcanoes, then, can trace their origin either to new ocean crust being created at mid-ocean ridges, or to subduction zones. But some iconic volcanoes sit far from these violent collisions of tectonic plates. Consider the Hawaiian islands, for instance. They sit in the middle of the Pacific, but far from any mid-ocean ridge, and experience essentially no earthquakes other than the small ones caused by the Hawaiian volcanoes themselves. Part of the explanation for Hawaii’s existence lies with another geological wonder: plumes of hot rock that rise all the way from the mantle, like a welder’s torch switched permanently to ‘blast’. In a mantle plume, a jet of volcanic heat fuels a constant, massive outpouring of lava on the seafloor. Scientists think that a few dozen mantle plumes dot the planet, of which the Hawaiian islands are the most famous example.

  The Hawaiian islands get progressively older the further northwest you go. Kilauea, the currently erupting volcano, is on the active Big Island in the southeast. The scenery here is an eerie moonscape of black-as-night lava flows. Go northwest, through Oahu and Maui, and the travellers’ paradise gets progressively lusher. By the time you get to Kauai in the far northwest the volcanoes haven’t been active for six million years. That’s why Kauai’s landscape is so verdant and full of coffee and fruit plantations: it has had plenty of time for its lava to erode into a soil that can nurture plant life.

  Hawaii can be explained by a combination of plate tectonics and mantle plumes. Over time, as the Pacific crustal plate drifted over the stationary mantle plume beneath, the blowtorch heat created one island after another, embossed like Braille dots on a moving sheet of paper. Follow the chain even further to the north and west, and you’ll encounter Midway Island at 28 million years old, and then a sharp kink, with volcanoes around 43 million years old, where the underwater Emperor seamounts take over, at ages regularly stair-stepping up to 65 million years. This bend marks a time when the Pacific plate must have taken a sharp turn and moved in a different direction over the mantle plume. It is geological history written as islands.

  In Iceland, though, mantle plumes and mid-ocean ridges come together. Beneath the island lies a plume that has been active for the past 65 million years. It has poured out some 10 million cubic kilometres of magma – 50 times the volume of Iceland itself – across the North Atlantic. Traces of its activity range from Scotland to Greenland.

  This prodigious plume helped the Atlantic to split where it did. As the Eurasian and North American tectonic plates pulled apart, about 25 million years ago, the mid-Atlantic ridge locked onto the mantle plume rising from below. Plume and ridge have been delivering a double dose of magma to Iceland ever since. Geologically speaking, the island is but a babe. If Earth’s history were compressed into a year, with the planet being born in the first second of 1 January, then Iceland wouldn’t have shown up until the afternoon of 30 December. It is still growing, as eruptions add more fresh land to the island than is lost to the sea. Today the centre of the mantle plume lies beneath the northwestern part of the Vatnajökull icecap, to the north and east of Laki. The plume continues to build the island and fuel its volcanoes.

  It also dictates how Iceland pulls itself apart. As the mantle plume remains fixed in place, the mid-ocean spreading centre keeps moving to the northwest, by fractions of a centimetre per year. The plume works to adjust the crustal stresses by creating new rifts. A map of Iceland reveals these geologic forces battling one another: the mid-Atlantic rift runs up from the southwest of th
e island, bends toward the east along its centre, and finally turns northward again and exits the island. Each of these rift segments has its own collection of volcanoes and earthquakes.

  In Iceland, volcanism is exposed in all its raw glory. You can observe the island’s geological turmoil at Thingvellir National Park, about an hour’s drive east of Reykjavík. Just past the parking area for tour buses on the popular ‘Golden Circle’ day trip, the mid-Atlantic rift appears as giant ridges of fresh lava. You can walk along the rift here; a paved pathway takes you along the base of a huge lava cliff, which was raised as the land split apart. To your east, the Eurasian tectonic plate is moving away from you; to your west, the North American plate is doing the same thing. From time to time, the tourist pathway gets destroyed by the ongoing rifting, which happens at about the rate that fingernails grow.

  The Mid-Atlantic Ridge splits Iceland in half, with North America on the west and Eurasia on the east.

  This dramatic setting made Thingvellir an appropriate site to hold the world’s first democratic parliament, the Althing, a millennium ago. Chiefs from various parts of Iceland regularly travelled to Thingvellir to discuss topics of common interest and come to general decisions. At any given time the designated speaker stood at the base of the cliff, a spot that amplified his voice and spread it over the gathered crowds. In the year 1000, this natural megaphone came in handy when the Althing began debating whether Iceland should convert to Christianity.

  What happened next is a national legend. As the chieftains argued among themselves, a messenger appeared with the news that a nearby eruption had sent a fresh lava flow coursing toward the farm of one of the attendees. This, surely, was a sign that the old Norse gods were angry at the idea that Icelanders should abandon them in favour of Christianity. But then the Speaker of the gathering, a man named Snorri Godi, spoke up. Gesturing across the plains of the Althing, he asked: ‘What angered the gods when the lava burnt which we are standing on now?’ After a moment for the message to sink in – that eruptions were a natural part of life in Iceland – everyone concurred. The Althing voted to adopt Christianity as the island’s religion.

  With Christian theology came such concepts as Hell. For those looking to instil a fear of an afterlife of subterranean torture, Iceland’s fiery mountains provided a powerful aid: the openings through which lava poured became the gateways to damnation. The main gateway was Hekla, the immense volcano that rises from the lava plains near the great geyser fields east of Reykjavík. Seen from one direction Hekla assumes a classic cone shape, an icon of volcanic majesty; seen from another it stretches like an overturned boat, a snow-capped ridge reaching more than 1,490 metres high. Its name may derive from the Norse word for ‘cloak’, after the mists that often enshroud the mighty mountain.

  Travellers from abroad soon began journeying to Iceland to see this otherworldly portal, through which arose the sounds of souls being tortured. As early as the twelfth century, visitors from continental Europe marvelled at its fury; one French cleric reported that Sicily’s famed Mount Etna was ‘like a small furnace compared to this enormous inferno.’ Lest the main message be lost, the monk added:

  Who now is there so refractory and unbelieving that he will not credit the existence of an eternal fire where souls suffer, when with his own eyes he sees the fire of which I have spoken? … But whosoever will not believe in or hear spoken of the punishments of eternal fire that are prepared for the Devil and his friends, he will later be hurled into that place which he cares not to avoid while he can.

  In the sixteenth century, the German physician and traveller Caspar Peucer continued the theme: ‘Out of the bottomless abyss of Heklafell, or rather out of Hell itself, rise melancholy cries and loud wailings, so that these lamentations may be heard for many miles around… Whenever great battles are fought or there is bloody carnage somewhere on the globe, then there may be heard in the mountain fearful howlings, weeping and gnashing of teeth.’ In the seventeenth century, a travel book described how the devil would pull souls out of Hekla and throw them onto the sea ice, cooling them off temporarily in order to exacerbate their torture when tossed back into the inferno. And when English poet William Blake needed somewhere to banish the spectre of winter, he did so in Iceland: ‘The mariner cries in vain… till heaven smiles, and the monster is driv’n yelling to his caves beneath mount Hecla.’

  Most Icelanders, however, never went in much for the concept of Hekla as Hell’s doorstep – they regarded the mountain’s fire as just another natural phenomenon of their extraordinary island. In 1540, an Icelandic cleric visited the Danish king in Copenhagen and wondered why he was asking so many ‘unneedful’ questions about Hekla. Some Icelanders began a public-relations campaign to fight back against the notion of their island nation as an inferno for the damned. A bishop named Gudbrandur commissioned a scholar to write booklets to be published in Europe, correcting what he saw as misinterpretations of Iceland. It didn’t work: authors kept on associating the country with the flames of perdition. But the scholar who wrote the booklets, Arngrímur Jónsson, was inspired to write an influential history of Iceland, the Crymogaea, which served to alert Europe to the fact that the country had its own cultural heritage and was not just some lava-scorched backwater.

  Still, the combination of volcanic flames and Norse heritage was too powerful not to influence Icelandic mythology. The thirteenth-century Poetic Edda, one of the foundation texts of Scandinavian literature, includes a description of the sky darkening so that the sun and stars disappear, as smoke and flames rise toward heaven. Some scholars have argued that all Scandinavian myths of an apocalyptic conflagration, such as the great battle of the gods at Ragnarök, draw heavily on observations of eruptions in Iceland. Researchers have even linked the very concept of Ragnarök to specific eruptions of the Bardabunga volcano, beneath the Vatnajökull ice cap, or to Katla, below a smaller ice sheet to the west.

  The undisputed queen of Icelandic volcanoes is still Hekla, which has erupted at least twenty times since the island was settled. As far as Iceland’s new residents were concerned, the mountain first rumbled to life in 1104. This ‘first fire in Hekla’ blasted rock fragments across much of the northern part of the country, making it the second biggest eruption in Iceland’s recorded history. But the volcano has done even worse things in the distant past, such as burying nearly the entire island in ash around 2,900 years ago. By digging trenches to study the build-up from past eruptions, geologists have been able to work out a detailed chronology for how often Hekla has blown, and when. (In Reykjavík shops you can buy a cube of notebook paper with layers in different colours, each representing a different Hekla ash layer from the time of settlement to the modern era.)

  Time and again, Hekla showered nearby farms with ash, rock and other debris. Carbon dioxide from eruptions crept down the sides of the volcano and collected in nearby hollows, smothering livestock until farmers could dig ditches to drain away the deadly gas. Further from the mountain, fluorine-laden ash settled onto fields, where sheep grazed on the poisoned grass and died from the toxins they had ingested. Through it all, Icelanders continued to regard Hekla as a troublesome neighbour, whose occasional outbursts were to be understood and worked around rather than feared.

  Abraham Ortelius’s map of Iceland, seen here in a 1612 engraving, depicts the volcano Hekla in eruption. It was a popular cartographic reference.

  A chronicle of the mountain’s eruption in 1300 C.E. describes people being unable to make their way across the countryside or put to sea in boats because of the ‘sand’ that blackened the skies and covered the ground all around. In 1845, Hekla sent a finger of lava down a gully toward its northwest flank, cutting off the water supply to a farm that had stood closest to the volcano for almost as long as there had been settlers in the island. Rather than panic, the farmers pragmatically tore down their barns and homes and rebuilt them on the other side of the lava flow.

  Then, for the first time in the era of modern volcanology,
Hekla rumbled to life in the early morning of 29 March 1947. Local farmers felt their bedrooms shaking and saw a brown cloud rising from the cloud-covered summit. Within hours, volcanologists packed a plane and left from Reykjavík to scout out the eruption. ‘No words can describe the awful grandeur of the sight which there met our eyes,’ wrote the university’s Sigurdur Thorarinsson in his book Hekla on Fire:

  From the northeastern part of the ridge there rushed forth dark, greyish-brown eruption columns, monstrously big around and so closely set that they formed a solid wall. In swirling puffs resembling gigantic heads of cauliflower these columns rose to a height of 10,000 metres. In the upper reaches their colour turned a lighter grey, and at the top they showed almost white against the blue sky. From time to time the fiery glow of the fissure showed through, and occasionally lightning flashed inside the cloud.

  The 1947 eruption spewed around a cubic kilometre of material across the landscape. Had Hekla erupted at this rate once a century since Iceland was born, it would have built the island six times over by itself.

  Hekla’s most recent eruption, in 2000, lasted only eleven days and did little damage. But Icelanders know their ‘old lady’ will undoubtedly go off again. In the meantime, they watch, wait, and wonder if it will be Hekla that erupts next – or one of the island’s many other volcanoes. One strong contender is Katla, the country’s second most active volcano, which lies about 50 kilometres to the southeast. If Hekla is the gateway to Hell, then Katla is the very devil.

  Unlike Hekla, which is a barren mountain capped with only a little snow, Katla lies buried beneath hundreds of metres of solid ice. Whenever Katla erupts, it melts that ice from below. And that means lots and lots of water. Katla is one of Iceland’s biggest sources of glacial outburst floods, in which water surges down the mountain and washes out any bridges, roads and farms that get in the way. Such sudden floods, called jökulhlaups (‘glacier bursts’), are often the only indication that an ice-buried volcano has erupted. Jökulhlaups are the reason why many people call Katla the country’s most dangerous volcano.