Which river contributed to the creation of the Grand Canyon?
How are valleys formed?
River and valley are inseparable. But why? How do these elongated hollows, called valleys, come about at all? A valley forms wherever water runs off in small streams or large rivers. 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 gradually deposit the cargo it has carried along with it on the ground again. Erosion takes place here 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, with 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.
A special form of valleys are 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.
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 forms 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 meadows. 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 planes out notch-shaped river valleys to form 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.
Glaciers shape the landscape
Wherever glaciers move, they shape the landscape. Stones enclosed in the ice act like coarse sandpaper: They grind rock from the subsurface at the edges of the glacier. The ice masses carry away the rubbed off rubble. The glacier scrapes out the rock. This creates valleys that look round like a U in cross-section and are therefore called U valleys.
Sand and boulders that are dragged along by the glacier ice remain at the edges and at the bottom of the glacier on the way down and form small and large hills. Such boulders on the edge of the glacier are called moraines.
When it is very cold for a long time, the glaciers grow and advance further and further into the landscape. If, on the other hand, it becomes warmer, the ice masses melt and the glaciers retreat. The moraines of rubble remain, however. Centuries later you can still tell from them how far the glacier had penetrated. The place that the glacier once excavated and covered with its ice is shaped like a tongue. One therefore speaks of a tongue pelvis.
What causes erosion?
When rock weathers, it seldom remains in its original location. Rock debris often rolls down the slope, is washed away by the water or pushed away by masses of ice. The wind can also carry fine rock dust or sand with it. Regardless of whether the rock is removed by water, ice, wind or gravity, all of these processes are called "erosion".
The erosion by running waters is particularly drastic. Streams and rivers dig a bed in the ground, rock slides down, a valley forms. If a glacier rolls down the valley, it planes this valley wider through the scree it has carried along with it. Long after the ice has melted, you can tell from such trough valleys that there was a glacier here. The surf of the sea, however, attacks the coast. Steep cliffs are hollowed out and collapse, sandy beaches are washed away by the waves. In deserts, the wind sweeps away large areas of sand. The harder it blows, the more sand it can take with it. A sandstorm gradually removes obstacles made of solid rock like a sandblasting fan.
When rain and wind wash or blow away the soil cover over large areas, we speak of soil erosion. Soil erosion is also used in the case of landslides on slopes. The problem: The fertile upper layer of the soil disappears. In the worst case, it can no longer be used for agriculture.
If the soil is overgrown with plants, this slows down erosion. The roots of the plants hold the soil in place and prevent the wind and water from carrying it away. If the plant cover is destroyed, for example by deforestation, the soil lacks this support and it is eroded.
Carved in stone - landscapes made of sedimentary rock
Like the layers of a cake, different sedimentary rocks can be stacked on top of each other. If the subsoil beneath the layers rises, they are tilted. If tectonic plates collide, they are compressed and unfolded like in the Alps. Weathering and erosion have gnawed these sediment layers over millions of years. Depending on the hardness of the sediment, the forces of water, cold and wind leave their traces and carve impressive landscapes into the rock.
A famous example of this is the Grand Canyon in Arizona: Here the Colorado River has dug a channel through various layers of rock. It is easy to see how soft and harder rock alternate: The soft rock gives way quickly, creating sloping slopes, the harder rock remains standing and forms steep, almost vertically sloping walls. These sediment steps lead down like a staircase to the current course of the river and offer the visitor a spectacular sight.
A well-known large landscape in Germany also formed from sediment layers: the south-west German layer level country, which extends from Baden-Württemberg via Hesse and Bavaria to Thuringia. After the Upper Rhine Graben collapsed, the sediment layers stood here at an angle. Depending on the hardness of the rock, the individual layers were eroded to different degrees. Hard limestone formed steep steps, while soft, clayey layers were washed out more and now make up the landscape as gentle slopes and wide stepped areas. On the left side of the Rhine this landscape is - almost mirror-inverted - facing the northern French plains.
Shaped by the ice, flooded by the sea
It is a breathtaking sight: the rock walls on Norway's fjord coast rise up to a thousand meters. Even large cruise ships can easily enter this fantastic mountain backdrop. Not only was the surf of the sea at work here, but one thing above all: ice!
During the Ice Ages, Northern Europe was under a huge ice sheet. Huge glaciers flowed towards the Atlantic and scraped deep valleys with steep walls into the subsoil. After the end of the ice ages, the sea level rose and the water flooded the trough valleys of the glaciers. The result is the famous fjords. In Greenland, Alaska and on the west coast of Canada, fjords were also formed which, because of their depth and their protected location, are well suited as locations for harbors.
The glaciers of the Ice Age did not only create fjord coasts. The small islands in the Baltic Sea between Sweden and Finland also bear witness to the Ice Age. As the huge glaciers rolled over the land, they grinded angular rocks and mountains into smooth, round cusps. After the ice masses melted, the rounded hump landscape was washed over by the sea. The humps that did not sink into the water now jut out of the sea as small islands: the skerries. The many small islands form their very own coast, called the archipelago.
Gullies and basins that were excavated by meltwater during the Ice Ages flooded the sea after the climate warmed up. Today they have become valley-shaped bays that extend far into the country. The result is a fjord coast, as we know it from the Kiel fjord, for example. The gently undulating landscape of ground and terminal moraines also partially sank into the water on the coasts. The hills of the terminal moraines formed the coast with its typical flat and wide bays, inland there are often flat lakes. Such a coast is called the Bodden coast, as it can be found, for example, in Western Pomerania between the Lübeck and Oder bays.
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