Category Physics

Gorges, also called ‘ravines’, ‘flumes’ or ‘canyons’, are deep, narrow valleys with sharply steep cliffs. They are formed mostly due to the action of flowing water when a stream or a river digs into the surrounding rock. The most famous gorge is the Grand Canyon in the USA, Arizona; it is almost 1800 m deep in places. Over a period of 600 million years, the Colorado River carved the Grand Canyon by eroding the surface of the Colorado Plateaus, which are to a large extent made up of sandstone and argillite. 

Different types of landscapes such as plains, wide valleys, gorges, dunes, rounded hills, and rugged ridges are formed largely by the forces of water, wind, and moving ice, which nibble, sharpen, and polish the surface of the Earth. Experts call this process ‘erosion’. These forces are much stronger than they appear. For instance, flowing water can move whole blocks of rock. The largest bits of rock thus eroded later become sand, which may be fine or coarse in texture and red, white, or grey in colour. Human beings also contribute to the constant changes taking place on the face of landscapes. 

Waves are formed as a result of the constant friction between water and wind. If a wind is blowing over the water surface, it carries away particles of water with it. The water starts moving in this way. Therefore, the distance between the ‘waves crest’ is determined by the wind. A constant wind gives rise to long, soft waves, which are also known as ‘groundswell’; a high wind, on the other hand, causes small and strong waves, the typical ‘motion of the sea’. Unlike the tsunamis, these waves occur only at the surface of the water. At a depth of a few metres, the waves do not create any disturbance. 

The icebergs in the North Atlantic are large pieces of ice that have broken off from the glaciers of Greenland. Since frozen water is lighter than liquid water, the broken pieces float as icebergs on the sea. They are pointy and often interspersed with debris. In contrast, the icebergs in the South Atlantic are mostly flat. They are broken pieces of the flat sea ice, which surrounds the Antarctic. Icebergs can float for thousands of kilometres before they melt. Only one-ninth of an iceberg stays above the water. If the part above the water is 100 m high, then the part below is 800 m deep. 

A storm tide is a natural phenomenon, and hence cannot be prevented. It happens when the normal water level raises high along the shore due to strong onshore winds and/or reduced atmospheric pressure as in the North Sea. It is not an open ocean, being blocked from the ocean by the British Isles. As a result, the water dams up very quickly. The waves whipped up by the wind destroy or flood the dikes and beach dunes. Parts of the coast are also washed away. The Halligen Islands in Germany, for instance, have emerged as a result of storm tide action. These are small islands on the coast of Schleswig-Holstein, which were earlier connected with the mainland. They are regularly inundated by flood waters. 

When rain falls on the ground and seeps below it, it washes away substances from the soil and rocks. It carries these substances into the river and the sea. You can read the names of these substances on the label of a bottle of mineral water. River water contains only a little salt – about 1 g/I, whereas the salt content of the sea is much higher – about 35 g/I, on an average. The reason is that the salt remains in the sea. Although the rivers continue to deposit new salts, the seas do not become ‘over salty’ because animals and plants in the sea absorb the salts in their bodies. When they die, they sink to the seabed and decompose into sediments.