Why is the sea racing ashore

Waves and monster waves

Wind and waves - these two forces of nature are inseparable. Because, unlike the ebb and flow of the tides, waves are generated by the wind. The wind slides over the surface of the water and pushes the water in the process. How high the waves get depends on the strength of the wind and the distance over which the wind whistles across the water.

When the waves hit land on the coasts, they get higher. This is due to the fact that with decreasing water depth there is less and less space for the water, it moves upwards. In shallow water, the wave is braked on the bottom. The corrugated crown, on the other hand, tilts forward without braking and "breaks". The whirling up of the water in the air creates white foam crowns, the spray.

If an extremely strong wind blows across the sea, a storm surge occurs. Storm surges are particularly common in spring and autumn. With their power, they can cause severe flooding and completely change the shape of the coast. The North Sea coast with the German Bight is particularly at risk from storm surges. Because the North Sea is very shallow, the water here can build up very high in a storm.

In addition, there are some particularly steep waves that are much higher than the waves in their vicinity. For a long time, such monster waves or "cavalry men" were considered to be "seaman's yarn", that is to say, extremely exaggerated adventure stories by seafarers. However, satellite images and precise measurements can now prove that such monster waves really do exist. They can reach heights of up to 40 meters and are therefore also a serious danger for large ships. How they arise has not yet been clarified exactly. Presumably they are formed by the meeting of slow and fast waves, combined with ocean currents.

Unlike waves and monster waves, tsunami waves develop after earthquakes or volcanic eruptions. Tsunami waves can be devastating: In Japan, after a violent earthquake in March 2011, a ten meter high tsunami rolled over the north coast of the country. Thousands of people fell victim to the disaster.

11.9.1995

On the night of September 11th, a huge wall of water rushes towards the "Queen Elizabeth 2". The monster wave that approaches the cruise ship over the Newfoundland Bank and finally rolls over it is over thirty meters high. As if by a miracle, passengers and crew survived the natural event almost unharmed. However, the ship is badly damaged.

The "Queen Elizabeth 2" was en route from Southampton to New York. There had been a warning the previous evening. "Today it will be a little stormier," said Captain Ronald Warwick to his passengers. A little later at dinner, dishes flew from the table, the musicians interrupted their playing, and all guests had to go to their cubicles. Nobody suspected that the foothills of Hurricane Luis were piling up a gigantic wave over the Newfoundland Bank. The shallow water off the coast is already known for its high swell.

In the early hours of the morning, the 33 meter high wave hit the ship. "As if we were steering straight into the white cliffs of Dover," Warwick later described the approaching wall of water. According to the crew, the monster wave was a three-sister phenomenon: three huge waves followed each other at an interval of 13 seconds. None of the people on board were harmed. The luxury ship was still fit to drive after the accident, but it was badly damaged.

For scientists, this has proven that monster waves really do exist. For a long time, similar adventure stories were not taken very seriously by seafarers, but now a measuring buoy near the ship provided evidence: The wave that rolled over "Queen Elizabeth 2" was 33 meters high.

Monsters of the sea

It seems to be the year of the monster waves. Only nine months before the collision with the "Queen Elizabeth 2" a single gigantic wave hit a Norwegian oil platform. The 26-meter-high Kaventsmann hit the oil rig on New Year's Eve during a storm on the North Sea. This is proven by the measurements of the automatic shaft measuring system. Up until that point, it was believed that waves couldn't get higher than 15 meters. Descriptions of much higher waves were considered a sailor's thread, all ships and drilling rigs were constructed according to a maximum wave height of 15 meters. That should now finally be over. Ships and drilling platforms will have to arm themselves against possible monster waves in the future.

16.1.1362

Friesland. On the night of January 16, the waves hit the top of the dike more than two meters high. 21 dikes broke on the coast of North Frisia. The devastating storm surge is believed to have cost thousands of lives. Whole stretches of land and several localities in North and East Frisia were sunk in the sea.

The "grote Mandränke", as the storm surge is called, wreaked havoc on the North Sea coast. The low summer dikes could not withstand the destructive masses of water. The floods tore terps (populated hills) along with houses and people and left a landscape in chaos.

Nothing on the North Sea coast is like it was before. Large parts of the islands and Halligen between Sylt in the north and Eiderstedt in the south, the so-called "Utlande", sank in the North Sea. The thriving settlement of Rungholt, a major trading post on the island of Strand, was simply washed away, along with seven other communities on the island. The land is lost forever.

The disaster hits mainly the march farmers in the area. Thousands of people drowned in the floods, and most of their fertile fields and pastures were swallowed up by the masses of water. In the meantime, the devastating flood is already being interpreted as a sign of God. He is said to have punished the people for their easy-going lifestyle and wastefulness with a storm surge.

Eyewitness account of a monk:

A Dominican priest witnessed the events of the storm night and reports of the terrible devastation: “On the night of Marcellus Day, at midnight, a terrible storm arose that the strongest buildings, churches and towers collapsed and the thickest trees were blown over. It caused a flood that inundated the Westermarsch and parts of East Frisia. The dikes are breaking everywhere, the cattle are drowning in the stables. The people fight against the floods, but their fight is completely hopeless. The immense masses of water carry everything with them that gets in their way. "

18.2.1962

A heavy storm surge devastated Hamburg and large parts of the North Sea coast on the night of February 16-17. Hurricane gusts of 130 kilometers per hour and meter-high waves caused the dikes on the North Sea coast and on the Elbe and Weser to break. Entire parts of the city were flooded, and over 300 people lost their lives in Hamburg's worst flood disaster.

The hurricane "Vincinette" swept over northern Germany overnight. The storm pushed the water of the North Sea into the German Bight and up the Elbe as if through a funnel. By morning the dykes broke in 60 places. The water level reached a height of 5.70 meters above sea level. The entire port area was flooded, and many parts of the city were cut off from the outside world. The power supply and the telephone network collapsed.

The Elbe island Wilhelmsburg and its 80,000 residents were particularly badly hit. In this part of the city, many bombed-out victims of the war are housed in makeshift homes. Completely surprised by the masses of water, they fled to roofs and trees and hoped for quick help.

Around 20,000 helpers fought against the floods and against time. The rescue operations continued throughout the night and the following day: the helpers were able to rescue thousands of people using helicopters and boats. For some, however, any help came too late. 317 people lost their lives in the storm surge, 207 of them from Wilhelmsburg. An estimated 20,000 people are in emergency shelters because their homes have been destroyed or badly damaged. The calls for better flood protection and a suitable early warning system are getting louder after this disaster.

The flying angels

The situation on the morning after the storm is completely chaotic: reports of dike breaches, the homeless and drowned people are rolling over the air. Police Senator Helmut Schmidt acted quickly and also involved the Bundeswehr in the rescue operation. Civilian military operations are actually against the law, but now rapid aid is a matter of life and death. Schmidt calls on engineer troops, assault boats and helicopters from the Bundeswehr. With their help, 400 people could be rescued from roofs on the day after the storm surge. The rescuers risk their own lives: With their bare hands they pull completely hypothermic people from the roofs into the helicopters. Those who are locked in by the water in the house are provided with blankets and food from the air. Soon the helpers in the helicopter have lost their nicknames. The people of Hamburg only call them: "Flying Angels".

How is wind created?

A fresh wind often blows on the coast. If it blows particularly hard, there is also talk of a stiff breeze. But not only by the sea - air is in motion all over the world. Only in a few places on earth does not the slightest breeze blow, as in the Kalmenzone at the equator - named after the French word for calm: "calme". This windless area was previously feared by seafarers, because the sailing ships stayed there for weeks. But why is it that sometimes there is calm and sometimes a violent storm sweeps across the country?

Wind is mainly created by the power of the sun. When the sun's rays heat up the ground, the air also warms up. The warm air expands and thus becomes thinner and lighter: the air mass rises upwards. This creates low pressure near the ground. In contrast, where it is cold, the air sinks and high pressure builds up on the ground. In order to equalize the pressure difference between neighboring air masses, colder air flows where warm air rises. This happens all the faster, the greater the temperature difference between the air layers. This is how the air gets into action - a more or less strong wind is blowing.

The formation of wind at the sea can be observed particularly well. During the day, the air warms up faster over land than over water. The warm air masses rise and suck in the cool and heavy air over the sea: The wind blows from the sea to the land. At night the wind changes direction. Because the water stores the heat longer than the land, the air above it is even warmer and rises. Then the wind blows from the land to the sea.

Where the wind blows from is always indicated with the direction of the compass. In our latitudes this is often from the west, we live in the so-called west wind zone. The hot trade winds, on the other hand, reliably blow from the east towards the equator. And the polar easterly winds transport icy air masses from the pole to the arctic circle.

The ocean floor

The surface of the ocean glistens in a dark blue. It is hard to believe that the sea floor is sometimes many kilometers deeper and that a spectacular underwater landscape is hidden there below. Because the sea floor is not as smooth as the bottom of a swimming pool: On the sea floor there are high mountains, deep trenches and lava-spewing volcanoes as well as extensive plains.

The water in the oceans is not the same depth everywhere. The shallow shelf seas lie around the continents. Here the seabed slopes gently down from the coastline until it reaches a depth of around 200 meters below sea level. The bottom of the shelf seas consists of continental crust. Therefore it actually belongs to the mainland, even if it is washed over by sea water.

Only many kilometers away from the coast, on average after 74 kilometers, does the flat shelf area end with the shelf edge. From this edge it goes down steeply like a slide to a depth of about four kilometers. This steep slope forms the transition to the deep sea, into which no light can penetrate. That's why no plants grow down there. Only a few animal species were able to adapt to this habitat, despite the hostile conditions.

In the midst of the oceans rise mountains, the mid-ocean ridges. These underwater mountains stretch across the world's oceans for long stretches. In some places they protrude as islands above sea level. Iceland, for example, lies directly on the mid-Atlantic ridge, the longest mountain range in the world.

Deep trenches also crisscross the oceans. Most of them are in the Pacific. One of them is the Mariana Trench, the deepest trench in the world. It reaches down to 11,034 meters below sea level. Only two people have ever been down there: the oceanographer Jacques Piccard and his companion Don Walsh on their record dive in 1960.

Tsunami - devastating harbor wave

A wall of water as high as a house rushes towards the coast. The gigantic wave breaks near the shore and carries with it everything that gets in its way. Such giant waves, called tsunamis, can destroy entire coastal regions. Many people have already fallen victim to them. The tsunami catastrophe that devastated the coasts of Indonesia and Thailand in December 2004 is still a terrible memory for many. Likewise the tsunami that hit the east coast of Japan in March 2011 and triggered the nuclear disaster in Fukushima. Because there are so many such giant waves in Japan, the word “tsunami” comes from Japanese. It means "harbor 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 arises. Far out in the sea, this wave is initially not particularly high, but it can be several hundred km / h fast. It becomes dangerous when such a wave rushes towards the coast. Because the sea is getting shallower and shallower, it lacks the space to evade. The wave is slowed down a bit in the direction of the land, but it piles up many meters high.

In addition to earthquakes and landslides, volcanic eruptions can also trigger a tsunami. For example, the Krakatau eruption in 1883 caused a tidal wave nearly 40 meters high.

A tsunami does not hit the coast without warning: First of all, the water runs wider than usual onto the beach and remains there for a few minutes. After that, the running water retreats extremely far, the sea floor becomes visible. Finally the white head of the tsunami appears on the horizon, which is approaching the coast at breakneck speed. Anyone who notices such signs should go to higher places without hesitation in order to escape the giant wave.

Tsunamis are particularly common on 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 waves of the water, they always have a head start on the tsunami. That is why a warning is possible the earlier the further the seaquake is from the coast.

ebb and flow

Anyone who has already vacationed at the North Sea or the Atlantic knows the problem: You go to the beach to swim and the water is much further away than when you last bathed. The water level has sunk: it is ebb tide. If you want to go into the water now, you either have to walk a bit over damp sand and silt or wait a few hours until the tide comes in and the water rises again.

Ebb and flow alternate in a regular rhythm. This change is called the tide. The time interval between ebb and flow is a little more than six hours. There are twelve hours and 25 minutes between one flood and the next. How much the water rises and falls depends on the coast. At the North Sea, the difference between high and low water is about two to three meters. Elsewhere, however, it is much larger: In the Bay of Fundy in Canada, the water level fluctuates by 15 to 21 meters - this is the highest tidal range in the world!

But why is it that the water sloshes back and forth in the oceans? The solution lies in the gravitational pull of the moon. This force causes two huge flood mountains under which the earth rotates. One of the two comes about directly through the gravitational pull of the moon, because it pulls the water towards itself. The second flood mountain is exactly on the opposite side of the earth. This arises because the earth does not rotate perfectly evenly due to the gravitational pull of the moon, but rather "rocks" a bit. As a result, there is a centrifugal force that pulls the water away from the moon. Both flood mountains are about half a meter high.

Not only the moon, but also the gravitational pull of the sun has an effect on the water. If the sun and moon are on the same line, the tide rises higher than normal due to the mutual attraction: there is a "spring tide". If, on the other hand, the sun and moon are at a 90 degree angle to the earth, then their forces partially cancel each other out. The result is a less high tide, the nipp tide.