How is a waterfall created
Water in free fall
The water masses of the Salto Ángel in Venezuela fall 978 meters deep. The highest waterfall on earth falls from a table mountain, partially atomizes into water vapor and then collects again to form a river. After a further step, he plunges hundreds of meters into the depth again with a deafening roar. How tremendous the power of water is can be heard, seen and also felt particularly well at a waterfall.
Most waterfalls form in places where hard rock overlies soft rock. If the water flows over these layers, it carries away the underlying soft rock more quickly. This happens mainly through sand and stones that the water carries with it. These sand the soft rock more and more and hollow out the bottom of the river more and more. A whirlpool hole is created between the two rock layers, which becomes larger over time. At this point the water plunges deeper and deeper - one speaks of a waterfall.
Because the soft rock under the hard rock edge is hollowed out more and more, an overhang forms. If the weight of this overhang becomes too heavy, it will break off. Its boulders hollow out the ground again. Again an overhang arises, which finally breaks off under its own weight. So the waterfall wanders back towards the source. This movement upstream is measurable: for example, the Niagara Falls on the border between the United States and Canada recede about 70 centimeters per year.
Niagara Falls. It is an unreal picture: where otherwise around 4 million liters of water per second plunge into the depths, only a bare edge of rock protrudes into the air. Engineers have drained the US portion of Niagara Falls. The water is currently drained via a tributary.
The reason for the diversion of the river is a fear of geologists: Over time, the Niagara Falls could erode the rock so much that the Niagara River would eventually take a different route. Then the world-famous waterfalls would also be a thing of the past. Two rockfalls on the American side of the falls had broken off tons of rock in 1931 and 1954. At the foot of Niagara Falls, the rock debris is already over 30 meters high. So the tourist magnet Niagara Falls is in serious danger. To prevent further rock falls, concrete is now being poured into the cracks in the rock on the American side. The aim is to secure the river bed above the falls and prevent further erosion.
Soon the river will be able to resume its normal course. Hopefully the Niagara Falls will be preserved for posterity for a long time to come.
Through the Niagara Falls in a wooden barrel - teacher survives stunt!
It is on the afternoon of October 24, 1901. The 63-year-old American teacher Annie Taylor climbs an oak barrel about a mile above Niagara Falls. It is padded on the inside for your protection. With this vehicle she wants to plunge down the Niagara Falls - no one has survived it yet! At 4:05 p.m. she starts her daring journey. After just 18 minutes, the barrel falls down on the Canadian side of the falls. Driven off the rapids, it and the teacher can be rescued at 4:40 p.m. Annie Taylor is injured in the back of the head, is in shock and is being rushed to the Niagara Falls hospital. After she has survived the stunt with a lot of luck, she urgently warns those around her not to repeat the breakneck act.
constant dripping wears away the stone
Deep gorges in the mountains, wide sandy beaches by the sea and wide rivers that meander through meadows and fields - all of these are landscapes that we know well. Because they are so varied, we find them impressive and beautiful.
The sculptor of all these landscapes is the water cycle. Sooner or later, water shapes the surface of the earth more strongly than any other force. It washes away soil after a downpour. It digs into the ground and loosens parts of the rock. It carries earth and weathered rock debris with it down into the valley. Where the water drains off more slowly, it lets go of its burden of silt, sand and rubble. When there is high water, it floods the flat areas of a valley, the river floodplains. Here, too, it deposits fine mud. When the water finally flows into the sea, it works the coasts and forms very different landscapes, for example cliffs or long sandy beaches.
Water also shapes the landscape in the form of ice. If water freezes in cracks in the stone, it bursts the stone. As a glacier, it carves out notch-shaped river valleys into round trough valleys. And the moraine landscape in the foothills of the Alps with its boulders and boulders is the result of glaciers that formed the subsoil a long time ago.
How are valleys formed?
River and valley are inseparable. But why? How do these elongated hollows, called valleys, come about at all? Wherever water runs off in small streams or large rivers, a valley forms. This is because flowing water digs deeper and deeper into the subsoil. The soil on the sides slides down towards the river bed. A slope forms to the right and left of the watercourse; this creates a valley along the river.
Valleys can look very different: steep walls or gentle slopes, wide valley floors or just enough space for the river. The shape depends on how strongly the water attacks the bottom and the side walls and how stable the rock is.
It's steep in the mountains, at the headwaters of a river. The water shoots down the mountain with force. Because of its high speed, it transports a lot of sand and debris there. With this rubble, it grinds the ground heavily and can dig itself deep. This creates rather narrow, deep valleys.
Towards the mouth, the river widens and carries more and more water. As the terrain becomes flatter, the water flows more and more slowly. For this reason, the lower reaches of the river are gradually depositing the cargo it has carried along with it on the ground again. Here erosion takes place more on the side walls, so that broad, flat valleys are created.
The rock through which the river flows is also responsible for the different valley shapes: water and rubble dig into solid rock without a lot of rock sliding down the sides. This creates valleys with steep or even almost vertical walls. Soft rock layers, on the other hand, slide quickly and lead to flat slopes.
Valleys are divided into different types based on their shape: Narrow valleys with steep walls are called canyon, in the case of vertical walls one speaks of one Klamm. Narrow valleys with gentler slopes are called Kerbtal or V valley designated. If, on the other hand, the valley floor is significantly wider than the river, it is a Sohlental, or - with steep walls - by one Kastental.
Are a special form of valleys Canyons. Here the water has dug its way through different layers of rock that lie on top of each other like several layers of cake. Some layers were easily removed by the river, they were washed out wide and round, the more resistant layers broke off steeply and angularly. The result is a valley, the side walls of which slope down like steps towards the river. A famous example of such a valley is the Grand Canyon in the US state of Arizona.
From rock to grain of sand - weathering
Today the north of Canada is a gently undulating landscape. However, many million years ago there was a mountain range here. In fact, even high mountains can turn into small hills over a very long time.
The reason for this transformation: The rock on the earth's surface is constantly exposed to wind and weather. For example, if water penetrates into cracks in the stone and freezes, it splits the stone apart. This process is called frost blasting. The rock also becomes brittle through temperature changes between day and night and through the power of water and wind. In other words: it weathers. This process can also be observed in buildings or stone figures. During the weathering, the rock breaks down into smaller and smaller components up to fine grains of sand and dust. Different rocks weather at different rates: Granite, for example, is much more resistant than the comparatively loose sandstone.
Some types of rock even completely dissolve when they come into contact with water, for example rock salt and lime. Rock salt is chemically the same as table salt - and that already dissolves in ordinary water. Lime is somewhat more stable, but limestone also dissolves in acidic water. Acid is formed, for example, when rainwater in the air reacts with the gas carbon dioxide. This “acid rain” attacks the limestone and dissolves it over time. The weathering leaves rugged limestone landscapes on the surface of the earth, and caves are formed below the surface.
But not only solution weathering, heat and pressure also wear down and crumble rock under the earth's surface. Wherever plants grow, roots dig in, break up the rock piece by piece and also ensure that it is removed millimeter by millimeter.
In this way, weathering not only works on individual rocks, it gnaws at entire mountain ranges. It will take a few million years for the Black Forest to be as flat as northern Canada.
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