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.

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.

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.

Not every time is the movement of the plates “to blame” for an earthquake. Collapses can also shake the environment. This happens when natural or man-made cavities collapse. However, such quakes do not reach as far and are not as strong as quakes triggered by the movement of the earth’s plates.

The exact point from which an earthquake originates is the earthquake focus, also called the hypocentre. From here, the earthquake waves spread out in all directions – comparable to the waves after a stone has plunged into the water. The greater the distance from the earthquake focus, the weaker the earthquake waves that cause the earth to sway.

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 plates collide

When two vehicles collide, their sheet metal is crumpled together. Something similar happens when two plates of the earth’s crust collide. Then their rock is pushed together and very slowly folded into enormous creases – this is how fold mountains are formed. What the crumple zone is in a car accident, the mountain range is in a plate collision – except that a car accident takes place in a fraction of a second, whereas a plate collision takes many millions of years.

The Alps were formed in exactly the same way: Africa pressed against the Eurasian continent and folded up the mountains. The Himalayas in Asia and the Andes in South America also owe their origin to the collision of moving crustal plates.

In such a crash, the rock of the lighter plate pushes upwards, the heavier one sinks into the depths. This process is called subduction, and the area where the plate dives is called a subduction zone. Along these zones there are often deep gullies, which is why they are easy to recognise. The deepest of these is the Mariana Trench in the Pacific Ocean. This deep ocean channel is located where the Pacific Plate dips below the Philippine Plate.

The further the earth’s crustal plate disappears into the earth’s interior, the hotter it gets. The rock melts and magma forms in the depths. The growing pressure can force it upwards again. Where it reaches the earth’s surface, volcanoes spew lava and ash. There are whole chains of such volcanoes around the Pacific Plate, for example in Indonesia. Because one volcano follows another here, this plate boundary is also called the “Pacific Ring of Fire”.

Not only do volcanoes erupt at such plate edges. Often, the earth also shakes because the plate movement causes enormous pressure and growing tensions. As soon as these are discharged, quakes shake the earth’s surface. In Japan, for example, three plates meet at once: the Pacific, the Philippine and the Eurasian. This is why Japan is so often hit by violent earthquakes.

Continents on the move

For a long time, it was thought that the earth’s land masses stood rigidly in place. Later it turned out: the opposite is the case. The continents of our planet are moving! Like huge ice floes, they drift in different directions, albeit not very fast. Their speed is about the same as the growth of a fingernail. But why are the continents constantly on the move?

The earth’s crust that envelops our planet is brittle and cracked. It resembles a cracked eggshell and is composed of seven large plates and many smaller ones. Some of them form the continents, others the ocean floor. These plates of the earth’s crust drift around on a hot, viscous rock mush and are driven by movements in the earth’s interior, or more precisely: by currents in the earth’s mantle. Experts also say: they drift. All these processes surrounding the movement of the Earth’s plates are called plate tectonics, and the movement itself is also called plate drift.

Where the individual plates border on each other, the Earth is particularly active. At some of these plate boundaries, hot rock from the Earth’s mantle penetrates upwards and cools down. New crust forms here: the two plates grow and are pushed apart as a result. In contrast, where two plates collide, the lighter of the two – the continental crust – is crumpled and folded into mountains. The heavier of the two – the oceanic crust – slowly disappears into the depths. The heat in the Earth’s interior melts its rock again. While the edge of the plate sinks into the depths, it pulls the rest of the plate behind it and thus additionally drives the plate movement.

Volcanic eruptions, earthquakes, long mountain ranges and deep ocean trenches accumulate along such plate margins. Most of the turmoil on the Earth’s surface is caused by the largest of its plates: it is the Pacific Plate, which is moving northwest at a rate of about 10 centimetres per year. Most of the earth’s active volcanoes are found at its edges, and violent earthquakes shake the region. Because of the frequent volcanic eruptions and quakes, this plate boundary is also called the “Pacific Ring of Fire”.

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.

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.

Earthquake in Switzerland

A series of violent earth tremors reduced the city of Basel to rubble on 18 October 1356. From the afternoon until midnight, the earth trembled again and again. Many houses and part of Basel Cathedral collapsed. The quake and the subsequent fire razed the city to the ground. It is not yet known exactly how many victims there were.

It is the worst natural disaster in the history of Switzerland. At around four o’clock in the afternoon, the first earth tremor caused numerous houses and the choir of Basel Cathedral to collapse. Many of the inhabitants of Basel were seized by panic and fled to the fields outside the city gates. The flight was their salvation. For in the late evening, strong tremors followed again, which could still be felt at a distance of 50 kilometres. Even the strongest walls collapsed.

To make matters worse, the city began to burn: Fireplaces and candles in the collapsing buildings caused fires to break out several times. What the earthquake had not destroyed was destroyed by the fire, which raged for a whole eight days after the quake. When the flames finally died down, the cathedral and many churches and monasteries were badly damaged. Not even a hundred houses remained standing; most of the buildings are in ruins. The number of dead is currently estimated at 300. Many survivors no longer have a home. They now live in makeshift tents outside the city gates.

Help from the neighbourhood

Many people in Basel have lost everything due to the earthquake and fire. They lack the most basic necessities, especially food. The rural population in the surrounding area is very helpful, providing food and drink to those affected. Cities further away, such as Strasbourg, Freiburg and Colmar, also offer their support. They are sending helpers with tools and horse-drawn carts to help clear alleys and rebuild houses. Donations have also been pledged. As soon as possible, the long-suffering city of Basel and its cathedral should be back as it was before the great earthquake.

Tension grows in California

No state in the USA is more densely populated than California. Los Angeles alone has almost four million inhabitants. And this despite the fact that the region is on extremely shaky ground: California is an earthquake zone. At some point, the earth will shake violently here again. Experts warn that the time could come soon. Is the big quake – “The Big One” – imminent?

For many years it has been remarkably quiet in California. Too quiet, some fear. True, there are smaller quakes all the time and many of them are so weak that they are not noticeable. But the last big quake happened 100 years ago: In April 1906, it destroyed San Francisco. The reason for the increased earthquake risk is that a large rift runs lengthwise through California: At the San Andreas Fault, two plates of the earth’s crust meet. If their rock masses move jerkily, the earth’s surface cracks violently. And the tension at the edges of the plates grows daily.

Geologists have calculated that a destructive earthquake with a magnitude of more than 6.7 is very likely in the next 20 to 30 years. According to experts, the question is not if the catastrophe will come, but when. Californians seem to be taking the tension in the rock calmly. Although the skyscrapers are earthquake-proof, many older buildings are not. Whether the nuclear power plants are safe enough is uncertain. And every now and then, radio stations and newspapers encourage the population to have the bare essentials in the house for the worst case scenario: food, drink and cash.

The Great San Francisco Quake

It was 100 years ago, but the inhabitants of California still have terrible memories of the day: In the early morning hours of 18 April 1906, the earth began to shake violently in San Francisco and the surrounding area. The main quake lasted only about 40 seconds, but the consequences were fatal. Whole quarters of the burgeoning city collapsed. Fires broke out in many parts of the city, adding to the scale of the disaster. It is not certain how many people died in the earthquake. Officially, the death toll is 3000, and thousands more were left homeless. There were also many victims and destruction in the San Francisco area. Property damage was in the tens of millions of dollars. The quake hit California completely unexpectedly. No one had expected such a catastrophe at the time.

Bold theory: the earth’s parts are moving!

During a conference of the Geological Society in Frankfurt, the meteorologist and polar researcher Alfred Wegener put forward a daring theory: According to him, the continents move around the earth. Colleagues in geology expressed scepticism to the point of rejection.

If Alfred Wegener had claimed that the Earth was a disc, he would hardly have caused any more astonishment among his listeners. According to Wegener, all the continents of our earth were united into a single land mass a long time ago. He calls this supercontinent Pangaea, which moved along the Earth’s mantle and broke into two parts 200 million years ago. These two parts of the earth are said to have continued to divide and shift. There are clear indications of the break-up and movement of the continents: they fit into each other like pieces of a jigsaw puzzle. It is also striking that the same animal species occur on different continents.

So Africa and South America should have been one? For the experts, Wegener’s speech sounds as credible as a fairy tale from the Arabian Nights. After all, to this day we are convinced that the earth’s crust is firmly connected to its subsoil. According to current knowledge, the continents are fixed and were once connected to each other via land bridges. Many geologists still disparagingly refer to Wegener’s continental drift as the “geopoetry of a weatherman”. For what remains unexplained is above all the motor of the movement: What is driving the continents? But research can no longer ignore Alfred Wegener’s theory. Can it be proven?

Alfred Wegener – an airhead?

The meteorologist Alfred Wegener became famous for a record he set in balloon flight: On 5 April 1906, he ascended together with his brother Kurt and stayed in the air for over 52 hours. This beat the previous world record by 17 hours. But the balloon flight was not only for fame, but above all for science: the Wegener brothers wanted to explore the atmosphere and test methods for determining locations. Alfred Wegener’s interest was not only in the weather and aviation, however, but also in the eternal ice. In the very year of his world record, he set off to explore Greenland. He returned from this Greenland expedition in 1908. Since then, the 32-year-old natural scientist has been a lecturer in meteorology, astronomy and physics at the University of Marburg.