Birth of an island

30 kilometres south of Iceland, an island has been born from the sea. Since 14 November, a young volcano has been spewing fire and ash here. Its lava masses have already grown an island 40 metres high and a good 500 metres long.

White-grey ash clouds hang in the sky and darken it. Fine volcanic rock pelts the surroundings, each lava eruption is accompanied by thunder. The column of smoke caused by the volcanic eruption rises 10 kilometres into the air. And an island off Iceland’s south coast continues to grow in the process.

The eruption of the underwater volcano came unexpectedly, but not without precursors. Seismologists had already measured smaller earthquakes in the capital Reykjavik a week earlier – signs that something was happening at the plate boundary of the Mid-Atlantic Ridge. In addition, a research vessel had noticed that the sea was warmer than usual. And residents of the nearby coastal region thought they smelled hydrogen sulphide. When the volcano erupted on the seabed at a depth of 130 metres, it initially went unnoticed. Its explosions were attenuated by the water pressure. But as it grew, it approached the sea level and finally broke through it, spewing wildly. That was the birth of an island in Iceland.

The new island off the south coast already has a name: “Surtsey” after Surt, the fire giant. According to a Nordic legend, Surt hurls fire and destroys all life with his glowing sword.

How Iceland came into being

Iceland is actually nothing more than the culmination of a huge mountain range in the Atlantic: almost 20,000 kilometres long is the Mid-Atlantic Ridge, which stretches from north to south across the entire Atlantic. At the height of Iceland, the North American and Eurasian plates drift apart, by about two centimetres every year. Where they straddle, hot magma from the Earth’s interior rises to the surface. These volcanic eruptions have been piling up mountains under water for millions of years and caused Iceland to rise above sea level 17 to 20 million years ago. These volcanoes are still active today. And now they have once again given birth to an island: Surtsey.

Volcanic Mountains

The snow-covered Kilimanjaro can still be marvelled at from afar. As a single mountain massif, it towers far above the African steppe – quite different from the typical fold mountains like the Alps or the Himalayas. This is because Kilimanjaro was not formed when the earth’s plates collided. About one and a half million years ago, several volcanoes erupted in the region in close proximity. The mighty Kilimanjaro massif grew out of the lava masses. Today, its highest peak is Kibo at 5895 metres above sea level.

There are also volcanic mountains in Germany, for example the Siebengebirge near Bonn. 25 million years ago, several volcanoes became active here and hurled their hot rock masses to the earth’s surface. Today they are long extinct, but they are still clearly recognisable as mountains and hills of the low mountain range.

Incidentally, the longest mountain range on earth is also of volcanic origin – it lies submerged in the sea: the Mid-Atlantic Ridge stretches a full 20,000 kilometres through the middle of the Atlantic Ocean. The Mid-Atlantic Ridge is one of the mid-ocean ridges. These lie where two oceanic plates move away from each other. A fissure forms between the two plates at the bottom of the ocean, from which hot magma gushes. At such plate boundaries, long and high mountain ranges form under water. In some places, their peaks rise above sea level. This is where Iceland, the Galapagos Islands or the Azores see the light of day.

What happens during a volcanic eruption?

It steams and bubbles, it smokes and hisses. Scalding hot rock shoots up from the earth’s interior. A cloud of ash rises, lava pours out of the volcano and flows over the earth’s surface. During a volcanic eruption, enormous forces are at work. But how does a volcano actually erupt?

In the earth’s mantle, the layer of rock beneath the earth’s crust, temperatures of over a thousand degrees Celsius and very high pressure prevail. If the heat and pressure are high enough, the rock melts and becomes a viscous mass called magma. This magma expands and rises to the top. There it first collects in cavities, the magma chambers. However, all this does not happen overnight, but takes tens of thousands or hundreds of thousands of years.

When the magma chamber is full and cannot hold any more material, the hot magma makes its way out. It penetrates through channels and fissures to the surface and emerges there as glowing hot lava – the volcano erupts. The channel through which the magma flows upwards is called a vent, its exit a crater.

Some volcanoes regularly spew lava, for example Stromboli in southern Italy. Its eruptions can be observed daily. Other volcanoes remain quiet for centuries, but are not really extinct. Often their craters are clogged with lava and debris. This makes them very dangerous, because when they erupt, there can be huge explosions; well-known examples are Vesuvius near Naples or Krakatoa in Indonesia. Such explosive eruptions blow millions of tonnes of rock into the air. The ash cloud that rises from the eruption can remain in the air for a long time and be widely dispersed by the wind. Only slowly does this cloud then settle on the earth as a fine layer of ash.

Lava that is not ejected into the air flows down from the crater rim as a glowing hot stream of molten rock. When this lava flow cools, it solidifies into lava rock. Gradually, lava flows, ash and rock debris build up a mountain around the crater – the volcanic cone

Consequences of volcanic eruptions

Volcanic eruptions can have terrible consequences. Hail of rocks, ashfall, poisonous gases and glowing lava flows have already cost hundreds of thousands of people their lives. The eruption of Mount Vesuvius in 79 AD alone, which buried the cities of Pompeii and Herculaneum, killed about 5,000 people. In Colombia, too, an entire city was wiped out: the eruption of the icy volcano Nevado del Ruiz triggered several mudslides in 1985. The avalanches buried the town of Armero, 47 kilometres away, and 25,000 inhabitants.

Tsunamis can also be caused by volcanic eruptions: The explosion of the volcanic island of Krakatau in 1883 caused a tidal wave that flooded regions thousands of kilometres away. Even earthquakes sometimes follow such explosive volcanic eruptions. During these quakes, built-up tensions in the earth are discharged.

In Iceland, the eruption of over a hundred volcanoes in the Laki Fissure in 1783 triggered a famine. The eruption released toxic gases into the air. The poison settled and contaminated the sheep pastures. The animals died from the poisoned feed, and an estimated ten thousand people died because of the famine that followed.

The “Laki fires” on Iceland were followed by a cooling that could still be felt far away. The rising ash cloud darkened the sky, strong winds arose and the temperature dropped. All of northern Europe then experienced an unusually cold winter. Volcanic eruptions do indeed change the climate. The main culprits are the emitted sulphur gases, which form fine sulphuric acid droplets in the air that remain suspended in the atmosphere for a long time. Sunlight is scattered by the droplets and partly reflected back. This can cause the average temperature to drop all over the Earth.

Where on earth are there volcanoes?

There are not volcanoes everywhere on Earth; they are distributed quite unevenly. The vast majority of them are located along the plate boundaries – where the Earth’s plates rub against each other, where one plate dips below the other or where they drift apart. At these fractures, hot magma from the Earth’s interior can rise to the surface.

A particularly large number of active volcanoes can be found around the Pacific Ocean, for example Mount St. Helens in the USA, Popocatepetl in Mexico and Bezymianny in Russia. They are all part of a chain of volcanoes about 40,000 kilometres long, the Pacific Ring of Fire. This is because all around the Pacific Ocean, the Pacific plate is sliding under other plates. As the Pacific plate descends, the earth’s crust is melted. Magma collects in these places and volcanoes form above it.

Volcanoes exist not only above but also below sea level – and most of them are still completely unknown to us. These underwater volcanoes are called “seamounts”. They include the volcanoes of the Mid-Atlantic Ridge, a huge underwater mountain range in the Atlantic. There, plates are drifting apart and therefore magma is constantly rising up there. Sometimes the volcanoes also reach the surface of the sea: in 1963, south of Iceland, a new volcanic island – Surtsey – grew out of the sea within a few months. Iceland itself was also formed by volcanism on the Mid-Atlantic Ridge.

The situation is quite different with the volcanoes on Hawaii: these lie far away from plate boundaries, in the middle of the Pacific Plate. But below Hawaii, the Earth’s mantle is particularly hot; this is called a “hotspot”, a hot spot in the Earth’s mantle. Here, hot magma rises upwards and can easily break through the crust – then a volcano is formed. When a plate of the Earth’s crust slides over a solid hotspot, a new volcano always bores through the crust. This is how a whole chain of volcanoes is formed, such as the island chain of Hawaii. There, the Kilauea volcano is active at the moment because it currently lies over the hotspot.

When the earth shakes

The earth trembles, cracks gape in the ground, trees sway and houses collapse – earthquakes are natural forces with destructive power. When the earth shakes, entire city districts can collapse. In certain areas, the earth shakes particularly often, namely where the plates of the earth’s crust adjoin each other. This is the case, for example, in Japan, on the west coast of the USA or in the Mediterranean region.

The cause of earthquakes is the movement of the plates. They float on the viscous material of the earth’s mantle, whose currents drive them like an engine. Where two plates border on each other, their rock masses can get caught and stalled. The problem is: the currents in the Earth’s interior continue to drive them. This creates enormous tensions between the two plates. If the tensions become too great at some point, one of the plates jerks forward. The tension discharges: the earth shakes.

Earthquakes often happen where two plates slide past each other at different speeds, like on the coast of California. Where plates collide, this does not happen smoothly either. For example, the African plate drifts towards the Eurasian plate and dives under it. Because this plate boundary runs through the Mediterranean region, the earth shakes again and again in Italy and Turkey. Earth tremors also occur where the earth’s crust is being torn apart, for example in the Upper Rhine Graben. Although these have been less severe in past centuries, there have also been violent tremors here: In 1356, a strong quake caused great damage in the city of Basel.

Directly above the focus or hypocentre is the epicentre on the earth’s surface. The destruction caused by an earthquake is usually greatest around this epicentre. How strong an earthquake is can be measured with special devices. The strength is usually indicated by values on the open Richter scale. The strongest earthquake measured so far was the one in Valdivia on 22 May 1960, also called the Great Chile Earthquake. It reached a magnitude of 9.5 on the Richter scale.

Where slabs diverge

A long deep crack gapes in the earth and grows wider and wider. Huge forces are tearing the earth’s surface into pieces: The East African Rift runs through the continent along this fracture. Africa began to break apart here 20 million years ago. Hot magma from the earth’s interior pushed upwards and tore the earth’s crust apart. Since then, the pieces of crust have been drifting apart, by about a centimetre every year. The fact that the earth is very active here can also be seen from the many volcanoes that rise along the trench. Should seawater penetrate at some point, the East African Rift will become an ocean. Something similar happened at the Red Sea. There, the African and Asian continental plates have been separating for 25 million years. The resulting rift was flooded by seawater.

Where continental crust breaks apart, a rift valley forms. In contrast, where oceanic crust pieces move away from each other, mountains grow on the sea floor: the mid-ocean ridges. They consist of magma that penetrates upwards from the Earth’s mantle through the oceanic crust. New plate material is formed here. It squeezes between two oceanic plates, so to speak, and solidifies into basalt rock that continues to pile up.

The seabed

The surface of the oceans glistens in dark blue. It is hard to believe that the seabed lies many kilometres deeper in places and that a spectacular underwater landscape is hidden down there. For the seabed is not as smooth as the bottom of a swimming pool: On the seabed there are high mountains, deep trenches and lava-spewing volcanoes as well as vast plains.

The water of the oceans is not equally deep everywhere. Around the continents lie the shallow shelf seas. Here the seabed slopes gently downwards from the coastline until it reaches a depth of about 200 metres below sea level. The bottom of the shelf seas consists of continental crust. Therefore, it actually belongs to the mainland, even though it is covered by seawater.

Only many kilometres from the coast, on average after 74 kilometres, does the shallow shelf area end with the shelf edge. From this edge, it descends steeply, like a slide, to a depth of about four kilometres. This steep slope forms the transition to the deep sea, where no more light penetrates. That is why no plants grow down there. Only some animal species have been able to adapt to this habitat, despite the hostile conditions.

Deep trenches also run through the oceans. Most of them are in the Pacific. Among them is the Mariana Trench, the deepest trench in the world. It reaches down to 11,034 metres below sea level. Only two people have ever been down there: The marine explorer Jacques Piccard and his companion Don Walsh on their record-breaking dive in 1960.

Magmatic rocks

To bite on granite means that something is hopeless. Because of its great hardness, however, granite is not only used as a figure of speech, but also as a paving stone or for building walls. Granite is a rock that lies more than two kilometres below the earth’s surface and occurs frequently in the earth’s crust.

Granite is formed when molten magma solidifies as it cools. The dark mottled gabbro or monzonite also form from slowly cooling magma. When this process takes place deep inside the earth, geologists speak of deep rock, also called plutonite.

If, on the other hand, the hot rock mush penetrates outwards during a volcanic eruption and pours over the earth’s surface, it is called effusive rock or volcanite. Volcanites include light pumice, porous tuff or rhyolite, which was formed from the same material as granite but has a different structure and is less hard because it cools more quickly at the earth’s surface than granite at depth. Basalt is also a volcanic rock. Sometimes it solidifies into hexagonal, closely spaced columns that look as if they have been cast into shape. Basalt forms on the earth’s surface from the same mass as the gabbro in the depths.

Chaos in the airspace over Europe

Following the eruption of Eyjafjallajökull on 20 March 2010, air traffic has been suspended in large parts of Europe. The eruption of the Icelandic glacial volcano had thrown a huge ash cloud kilometres high into the atmosphere. The volcanic eruption led to the longest-ever traffic ban in European airspace from 15 April 2010.

Tens of thousands of flights were cancelled, cargo containers remained on the ground, hundreds of thousands of passengers were stranded. Mattress camps were set up and calm returned to the airports. All of Europe seemed paralysed after the eruption of Eyjafjallajökull. Airlines suffered billions in losses due to the cancellations. Weeks before, slight tremors indicated that the volcano would soon become active. Until then, volcano researchers had classified Eyjafjallajökull as rather harmless. Its eruptions were rare and not particularly violent, but when the thousand-degree magma shot upwards, it hit the 200-metre-thick glacier. The ice evaporated abruptly, the magma from the Earth’s interior was atomised into powder and a cloud of ash was hurled seven kilometres into the air. At this moment, of all times, the wind shifted over Iceland: dust and sharp-edged rock grains contained in the air drifted towards Europe. This made them particularly dangerous for aviation. If an aircraft flies through such a cloud, the dust and grains of rock act like sandpaper. In the worst case, the engines are so badly damaged that they fail and the plane crashes. To avoid such a catastrophe, air traffic in Europe was suspended. After five days, the amount of ash in the air had decreased so much that most planes could take off again.

Sleeping brother

Eyjafjallajökull seems to have calmed down, but nearby its big brother is slumbering. The Katla volcano is only thirty kilometres away and has erupted much more violently than Eyjafjallajökull in the past. Experts warn of an approaching eruption of Katla.

The last one happened in 1918, when the volcano threw ice chunks the size of multi-storey houses into the air, leaving huge holes in the ground on impact. A wave of meltwater flooded an area of 200 square kilometres – the size of a small German town.

In the past, Katla used to spit fire about every 50 years, so it would be long past time for another eruption. Moreover, volcano researchers have found out that both volcanoes are connected: During its last two eruptions, Eyjafjallajökull “fired up” Katla underground, causing it to erupt.

However, there is no need to worry too much. The Katla volcano is more explosive than its little brother. But fortunately no people live in its immediate vicinity.