# Why are the tides higher at night

### 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 get 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 attraction of the moon, because this 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.

1.9.2004

A six-meter-long humpback whale got lost in the reservoir of the Annapolis tidal power station in Canada's Bay of Fundy. Since one does not want to hurt the whale, the turbines of the power plant were switched off. It remains to be seen how long the operators can be economically responsible for a failure.

The Annapolis tidal power station has stood there since 1984, where the world's largest tidal range is. At high tide, billions of tons of ocean water are artificially dammed there. At low tide, the water shoots back through the turbines into the ocean and generates around 20 megawatts of electricity. Animal rights activists have long been against the operation of the power plant. Whales have often swam into the reservoir and cannot find their way back through the locks. A life-threatening situation for an endangered animal.

### The voice of the moon

"The voice of the moon" is what the Canadians at the Bay of Fundy call the deafening din of trillion liters of ocean water that shoots into the bay at high tide. In just six hours, the 60 kilometer narrow and 220 kilometer long bay on the east coast of Canada is full like a bathtub. Every day the residents and tourists experience the impressive natural spectacle: the change between ebb and flow, like no other. Because the Bay of Fundy has the largest tidal range in the world. The ebb and flow of the tides are between 15 and 21 meters in altitude. You could sink a four-story house into it.

### The world of the oceans

To this day, many secrets lie dormant in the depths of the oceans. Large parts of the world's oceans are still completely unexplored. We even know the moon better than the deep sea. But what we do know: Almost all of the water on earth - 97.5 percent to be precise - ripples in the five oceans.

The largest of all oceans is that Pacific. Its water surface measures a total of 180 million square kilometers! It makes up about half of all ocean areas. At the same time, the deepest point on earth is located in this ocean: it descends up to 11,034 meters into the Vitja Depth in the Mariana Trench, a deep-sea trench in the western Pacific.

The Atlantic is the second largest ocean. It was formed about 150 million years ago when the supercontinent Pangea broke up. With its 106 million square kilometers, it covers a fifth of the earth's surface.

The Indian ocean is mostly in the southern hemisphere. With an area of ​​almost 75 million square kilometers, it is a good deal smaller than the Atlantic and Pacific. Its deepest point is called Diamantina Depth, which is 8,047 below sea level.

The Southern Ocean is also called the Southern or Antarctic Ocean. It includes all marine areas south of the 60th parallel in the southern hemisphere. It is considered by seafarers to be the stormiest of all seas. The large tabular icebergs floating in its water are also typical of the Southern Ocean. They broke off the ice shelf that formed around the Antarctic continent.

That's all around the North Pole Arctic Oceanalso known as the Arctic Ocean. It is the smallest of the five oceans. About two thirds of the Arctic Ocean is covered with ice in winter. However, like the ice in the Southern Ocean, its ice cover continues to melt as a result of global warming.

Even if we live a few hundred kilometers away from them, oceans are very important to us. Their currents and the evaporation of sea water have an enormous influence on our weather. A large part of the air we breathe is also created in the world's oceans: algae that live here convert carbon dioxide into oxygen when exposed to sunlight.

### The blue planet

Seen from space, the globe appears in a strong blue. This is because almost three quarters of the earth is covered with water. Small amounts of water are transparent, but from a certain depth onwards it becomes more and more blue. Because we see the mighty oceans blue, the earth is also called "the blue planet". The term south of the equator is particularly applicable. Because the southern hemisphere is almost completely covered by the sea, because a large part of the continents have migrated to the north due to plate movement.

The vast oceans contain almost all of the water on earth. There is a lot of salt dissolved in sea water, which is why it is not suitable as drinking water. The little fresh water on earth is frozen mainly in glaciers and ice caps. Only a tiny fraction of freshwater is found in groundwater, in lakes and rivers, or in the air.

But the view from the outside is deceptive: the earth's surface is largely covered by water, but measured by the diameter of the earth, the oceans are only a very thin layer. Therefore, the water makes up only a fraction of the earth's mass. For comparison: if the earth were the size of a basketball, all the water on earth would fit into a table tennis ball. And the drinking water would be proportionally even smaller than a single popcorn.

### What is the moon

It is the brightest celestial body in the night sky: the moon. It shines so brightly on full moon nights that some people find it difficult to sleep. It appears as big as the sun and the stars look like tiny points of light next to it.

But the impression is deceptive: In reality, the moon (diameter: 3474 km) is only about a quarter the size of the earth (12742 km) - and the sun (1.39 million km) is even four hundred times larger. The moon only seems the same size to us because it is so close to us - the sun (distance to the earth about 150 million km) is also about four hundred times further away than the moon. (384,400 km, an airplane needs 18 days for this distance!)

The bright light is also deceptive: unlike the sun, the moon does not shine by itself, but is illuminated by the sun. Some of this light is then reflected back from the surface of the moon and hits the earth. Just because the moon is so close to us, enough light arrives on earth to light up the night - at least if the moon doesn't just seem to have disappeared without a trace ...

### 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 distances 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 crest of the wave, 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 “sailor's yarn”, that is, 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.