Volcanic island Krakatau explodes

The eruption of the volcano Krakatau completely destroyed the volcanic island of the same name between Sumatra and Java. 36,000 people lost their lives in this natural disaster. Most of the victims drowned in the destructive tidal waves triggered by the exploding volcano. Thousands of kilometres away, the monster flood still wreaked havoc.

Krakatau volcano, located in the busy Sunda Strait, had been relatively quiet for the past 200 years. On 22 August 1883, it began a series of violent eruptions, the last of which completely destroyed the island. The explosion of 27 August was so powerful that it blew up almost the entire volcanic island. Several cubic kilometres of rock shot up more than 30 kilometres into the sky. The thunderclap of the explosion could be heard as far away as the Australian city of Perth, a good 3,000 kilometres away.

But the greatest damage was caused by the tidal waves generated by the volcanic eruption. Several tidal waves up to 30 metres high raced towards the coasts of Java and Sumatra. There they swept thousands of people to their deaths and completely devastated the islands.

Immediately after the explosion, darkness fell and ash rained down. The dust spread high in the atmosphere and went all around the earth. The sky darkened, temperatures dropped by an average of 0.5 – 0.8 degrees Celsius. The disaster was followed by a cool, rainy summer and poor harvests.

Child of Krakatoa

The explosion of 1883 almost completely tore apart the volcanic island of Krakatau. Nevertheless, it lives on: in the middle of the former crater, its child is growing up, the “Anak Krakatau”.

Anak Krakatau was born in 1927, when a violent eruption caused Krakatau’s daughter volcano to rise to the surface of the sea. Since then, it has continued to grow, by several metres every year. Its eruptions are becoming increasingly violent. Now 450 metres above sea level, the volcano is already about half the size of Krakatau before its explosion. Will Anak now be as dangerous as its predecessor?

To prevent a disaster like the one in 1883, the Indonesian authorities are constantly monitoring Anak Krakatau. They measure the temperature on the volcano’s surface and the viscosity of the magma. This is because the more viscous the magma, the more likely it is that the volcano’s vent will become blocked. That, in turn, would increase the danger of an explosion like the one that shook the whole world in 1883.

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 underneath them

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.

Tsunami – devastating harbour wave

A wall of water as high as a house races towards the coast. Near the shore, the gigantic wave breaks and sweeps away everything in its path. Such giant waves, called tsunamis, can destroy entire coastal regions. Many people have already fallen victim to them. The tsunami disaster that devastated the coasts of Indonesia and Thailand in December 2004 is still a terrible memory for many. The same goes for the tsunami that hit the east coast of Japan in March 2011 and triggered the nuclear disaster at Fukushima. Because Japan has a particularly large number of such giant waves, the word “tsunami” also comes from Japanese. It means “harbour wave” – which sounds quite harmless compared to its destructive power.

A tsunami is usually caused by earthquakes or landslides under water. The movement of the sea floor pushes the surrounding water, as it were. A huge wave is created. Far out at sea, this wave is not particularly high at first, but it can reach speeds of several hundred kilometres per hour. It becomes dangerous when such a wave rushes towards the coast. Because the sea becomes shallower and shallower near the shore, there is no room for the wave to swerve. Although the wave is slowed down somewhat in the direction of the land, it piles up many metres high.

Besides earthquakes and landslides, volcanic eruptions can also trigger a tsunami. The eruption of Krakatau in 1883, for example, caused a tidal wave almost 40 metres high.

However, a tsunami does not hit the coast without warning: First, the water runs up further than usual onto the beach and stays there for a few minutes. Then the draining water recedes extremely far, the seabed becomes visible. Finally, the white foam of the tsunami appears on the horizon, approaching the coast at breakneck speed. Anyone who notices such signs should seek higher ground without hesitation in order to escape the giant wave.

Tsunamis are particularly frequent at the northwestern edge of the Pacific Plate. There, observation stations also warn the inhabitants of the coast. To predict a tsunami, they measure the seaquakes in the ocean. Since the earthquake waves are faster than the water waves, they always have a head start on the tsunami. That is why the further away the seaquake is from the coast, the more timely a warning is possible.

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.

What do volcanoes look like?

A steep mountain, flames shooting into the sky, a dark cloud of ash above: this is what a volcano looks like in a picture book. But there are also very different volcanoes. The shape they have depends mainly on the lava that seeps out of the earth’s interior.

Thin lava flows quietly and evenly out of the crater. It cools only slowly and flows far apart. This creates extensive surfaces or flat mountains that look like large shields. This is how these volcanoes got their name: Shield volcanoes. Typical examples are the Hawaii volcanoes with their glowing lava lakes and diameters of up to 400 kilometres.

Viscous lava, on the other hand, does not get far – it sometimes gets stuck in the volcano’s interior and clogs it. Underneath, magma continues to push upwards. The pressure increases until the lava plug is blown out of the volcano like a cork out of a champagne bottle in a huge explosion. Scraps of lava and rock fly into the air and crash down on the volcano. A layer of ash descends on the surrounding area. In the course of time, a pointed mountain of ash and rock debris piles up, growing higher layer by layer with each eruption. Well-known examples of these stratovolcanoes are Mount Etna in Sicily or Mount St. Helens in the USA. Because of their explosive eruptions, stratovolcanoes are particularly dangerous.

In addition, there are also volcanic explosions that take place underground. When hot magma meets groundwater at depth, the water vaporises abruptly. The resulting pressure is so high that the soil above is blown up. What remains is a hole in the earth’s surface shaped like a bowl or funnel, a maar. Water often collects in this crater, then a maar lake is formed, such as Lake Laach in the Eifel.

When the magma chamber is empty after a volcanic eruption, the volcano above can collapse. This creates a depression in the landscape, a caldera. The size of the caldera gives an idea of the dimensions of the collapsed magma chamber. Some are huge, like the caldera of the Ngorongoro in Tanzania with a diameter of about 20 kilometres. When magma rises again from the depths and emerges as lava, a new volcano is formed in the caldera; this is called a daughter volcano. Mount Vesuvius, for example, is such a daughter volcano: it was formed in the caldera of Mount Somma.

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.

Buried alive!

At midday on 24 August 79 AD, the summit of the volcano Vesuvius explodes. The terrible volcanic eruption claims thousands of lives. Hail of rock, lava flows and ash rain bury the inhabitants of Pompeii beneath them. The two cities on the Gulf of Naples are completely destroyed.

Until 24 August, Pompeii is a flourishing trading city. The day begins sunny, crowds and noise reign in the alleys, merchant ships dock at the harbour. The inhabitants have no idea of the approaching disaster. They know nothing of the lava plug that has been blocking the exit of Vesuvius for centuries like a cork in a champagne bottle. A violent earthquake 17 years earlier had loosened this plug dangerously. When it loosened around noon on 24 August, it shot up into the air along with the top of the volcano with a tremendous bang – the beginning of Pompeii’s downfall.

Soon there is a hail of stones, a layer several centimetres thick forms on the roofs of the city. The boulders grow larger and with them the horror of the inhabitants. Fist-sized and red-hot pumice stones fall from the sky, smashing windows and roofs. The first fatalities occur. Violent earth tremors shake houses and streets. Many of the 20,000 Pompeians try to flee, others take refuge in the cellars. But their houses become a trap: the following night, Vesuvius spews out deadly gases that descend on the city. Anyone who inhales them suffocates in agony. In the course of the following day, three lava flows burn and bury everything that is left of the city. Finally, Vesuvius spreads a thick layer of ash over the already completely devastated city.

The neighbouring town of Herculaneum with 4000 inhabitants is also razed to the ground by the eruption.

Witness to the downfall

From Misenum, a harbour town 30 kilometres from Pompeii, the 17-year-old Pliny followed the volcanic eruption and the sinking of Pompeii. In a letter, he describes the course of the catastrophe and the death of his uncle. He was a Roman fleet commander and set off by ship to rescue people from Pompeii.

He hurried to where others were fleeing from and headed straight for danger. Ash was already falling on the ships, hotter and denser the closer they came, and soon pumice and black, half-charred stones cracked by the fire. The sea suddenly receded and the shore became impassable due to a landslide. For a moment he was undecided whether to turn back, then he called out to the helmsman who had advised him to do so: “Fortune favours the brave, go to Pomponianus!”

Pomponianus is a friend of the uncle who lives in Stabiae. There too there is panic and people want to flee. Pliny’s uncle tries to calm them down.

In the meantime, from Vesuvius, in several places, wide hearths of flame and high columns of fire were shining, their radiant brightness intensified by the dark night.Together they discussed whether they should stay indoors or go outdoors, for as a result of frequent, strong earth tremors, the buildings swayed and seemed to sway back and forth as if they had been loosened from their foundations. In the open air, the raining down of glowing, but only light, pieces of pumice was a cause for concern. They put pillows over their heads and tied them with cloths; this offered protection against the falling rocks.

It was already daytime elsewhere, but there it was night, blacker and denser than any other night. They decided to go to the beach and see for themselves from close up whether the sea was already permitting them to go out. But it still remained rough and hostile. There my uncle lay down on a spread blanket, asked for a sip of cold water now and then and took it. Then flames and, as their harbinger, the smell of sulphur chased the others into flight and startled him. Leaning on two slaves, he rose and immediately collapsed dead, presumably because the dense smoke took his breath away and closed his gullet .

Birth of 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 through 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

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.

Tsunami disaster in Japan

The seaquake that shook the seabed off the coast of Japan on Friday, 11 March 2011, has had devastating consequences. The quake triggered a tsunami more than 10 metres high, which rushed towards the coast at several 100 kilometres per hour. The water flooded a 1000-kilometre-long coastal strip and left a picture of devastation. It is not yet known how many people died in the disaster. The monster waves also hit the Fukushima nuclear power plant and destroyed its cooling system. Explosions at the reactor blocks raise fears of a core meltdown.

With a magnitude of 8.9, it was the worst earthquake in Japan’s history. It began at 2.45 p.m. local time, its epicentre was 130 kilometres east of the city of Sendai in the north-east of the country. A tsunami more than ten metres high swept over the coast of the Japanese main island of Honshu a few minutes later. The powerful tidal wave hurled ships inland, swept buildings away and buried the coastal strip under a layer of mud. Tens of thousands of people were victims of the floods, countless are missing. Emergency shelters are completely overcrowded. 100,000 soldiers are now helping with the clean-up.

At the same time, fear of a super-GAU is growing in Japan. At the Fukushima nuclear power plant, the cooling system for the fuel rods has failed. It is possible that the meltdown has already begun. The government has declared a nuclear state of emergency. Thousands of residents have been evacuated in the meantime.

Tsunami warning for Europe?

Even Europe is not safe from a tsunami. The Mediterranean region is tectonically active and earthquakes are the result. After particularly strong seaquakes, the feared giant waves could therefore pile up in the Mediterranean and even in the Atlantic. This already happened about 2000 years ago, when a quake off Crete was followed by a tsunami that devastated the coasts of the eastern Mediterranean. In 1755, a quake off Portugal and the subsequent tsunami destroyed the city of Lisbon. And a quake off Sicily also caused a giant wave in 1908. Because people are now more aware of these dangers again, experts are now working on a tsunami early warning system for Europe.

Explosion in the Eifel

Lake Laach glistens quietly in the sunlight. But the idyllic tranquillity is deceptive: 13,000 years ago, hell raged here on earth – this landscape is the result of a volcanic eruption. And scientists expect the Eifel volcanoes to erupt again. The only thing that is unclear is when …

The first volcanic eruptions occurred in the Eifel 600,000 years ago. The series began with the volcanoes in the Western Eifel: ash volcanoes, craters and maars formed here. Later, the volcanic area of the Eifel expanded to the southeast. After that, the volcanoes came to rest.

This calm ended, however, almost 13,000 years ago, with a bang: a huge explosion inside the earth tore a large hole in the landscape. Metre-high streams of mud rolled down into the valley. The Rhinelanders were taken completely by surprise by this catastrophe – this is shown by skeletons found in the layers of earth. Lake Laach was formed at the site of the volcanic explosion. The last volcanic eruption in the Eifel took place 11,000 years ago, when the Ulmener Maar was formed.

Smaller earthquakes between Lake Laach and Koblenz today indicate that the earth has not yet finally come to rest. The quiet bubbling in Lake Laach is also evidence of volcanic activity. The carbon dioxide bubbles that rise from the water here come from the hot volcanic underground. The Eifel is on the move – so will it soon surprise us with a new volcanic eruption? A question that even science cannot answer.

Ant alarm

Volcano researchers have observed the behaviour of ants and want to use it to develop an alarm system for volcanic eruptions. They believe that ants would notice an impending volcanic eruption at an early stage and leave their nests. They assume that the reason is that ants flee from the poisonous gases that escape during volcanic activity. Biologists, however, do not really believe in this idea: they have found that ants also move several times a year.

But the volcano experts continue their research and observe more than 2000 anthills in the Eifel. For although the Eifel is volcanic, there are only a few fixed measuring stations here that could warn of a volcanic eruption. And the volcanoes in the Eifel, the researchers suspect, will not sleep forever!