Category Geology

            Earthquakes are common occurrences. We often read about them in newspapers or listen over the radio. Do you know how they are caused?

            When an earthquake occurs, that particular part of the Earth experiences tremors. Sometimes it is so mild that it passes unnoticed. But, often, it is quite strong and creates vast openings in the Earth’s surface – buildings fall down and many lives are lost.

            We know that the Earth’s surface is composed of various kinds of high and low rocks. Due to the internal upheavals of the Earth or the uneven pressure, malformation sets in the rocks. Due to the excessive pressure, the layers of rocks crack suddenly. After breaking, they either go up or down inside the Earth. At the places where such changes take place in the rocks, the Earth’s crust experiences big shocks. These shocks cause vibrations which spread through the Earth’s surface. All those areas through which these vibrations travel are said to be affected by an earthquake and, as a result of these vibrations, buildings fall down and lives are lost. The point of origin of an earthquake is called the epicentre of the earthquake. 

            Some places on the Earth are prone to earthquakes. Japan has the highest incidence of earthquakes. The Earth surface in Japan is uneven throughout and so the occurrence of earthquakes is very common there.

             San Francisco, Lisbon, China, India and Japan have all suffered great loss of lives and property from the occurrence of earthquakes.

            Scientists have developed an instrument called the seismograph to study earthquakes. This instrument has arrangements to study the seismic waves caused by the earthquakes. Seismographs have been installed at various places in the world to record the seismic vibrations with a view to help mankind from the dangers of earthquakes. But it is impossible to forecast an earthquake or prevent it from happening.

           Lakes are large masses of water formed mainly in low-lying areas of the Earth. Their main sources are rain-water or molten snow or, at times, a small river or a stream. Do you know how these lakes are formed? 

                                                                                                 Lakes are formed in many ways. Some lakes lie in the natural hollow of an old volcano. For example, the crater lake of Oregon in South America. Due to some upheavals, like falling of a meteor large ditches were formed on the surface of the earth, which later got filled with rain water – for example, Lake Bosuntui in Ashanti crater in Ghana.

                                                                                                                                                                                       The Glacial lakes are formed because the sliding glaciers cause big ditches on the Earth’s surface which become lakes after rain-water and molten snow accumulates there. The Winnipeg Lake of Canada was formed by glaciers.

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            Sometimes a stream of water suddenly bursts out from an opening in the Earth in the form of a fountain. This is called a spring. Springs generally erupt out of rocks. Springs are of cold water usually but some are hot springs or sulphur springs.

            When it rains, the Earth absorbs a part of the rain-water while the remaining water gets evaporated. Due to the Earth’s gravitational force, the water so absorbed keeps on going down through the holes and cracks in the Earth. And, when this water encounters some rocks on the way, it accumulates there. When this accumulated water finds an opening to come out, it bursts out as a spring. They are often found where permeable rocks lie above impermeable one, particularly in low lying areas. 

            Sometimes the water accumulated inside the Earth has to pass through sections containing sulphur and lime. The sulphur and lime dissolve in water and when this water comes out in the form of a spring, it contains sulphur. Hence, water of such springs has the smell of sulphur and they are called sulphur springs. In India, there are many such springs in Kashmir, Haryana and Uttar Pradesh.

                                                                                                Sometimes water from the Earth’s surface reaches deep down in the Earth’s interior. It then starts boiling due to the Earth’s heat. When it comes out through such opening in the Earth in the form of a spring, its water is hot. Such springs are called hot springs. There are many such springs in the United States of America and New Zealand.

          A body of water falling down from a mountain rock is known as a waterfall. If water falls from a great height in the form of a large stream, it is called a cataract. But if the falling stream is narrow, it is called a cascade.

          It is essential for the formation of a waterfall that water flows through certain hard rocky areas. Hard rocks should be followed by soft soil which water can easily cut through. At some places, due to natural changes, the river flows through areas which are higher than the sea level and thus water falls from a height. Sometimes flow of the river is obstructed by landslides. Water accumulates there and later falls down in the form of a waterfall. There are many kinds of waterfalls at many hilly places.

             The Angel waterfall of Venezuela in South America is the highest waterfall of the world. Here water falls from a height of 1000 metres. This was discovered in 1835 by Jimmy Angel, pilot of the US.

            The highest waterfall of Asia is the Gersoppa waterfall in India. The Niagara waterfall is also world-famous for many reasons. Situated 25 km Northwest of New York in the U.S.A., this waterfall of Niagara River is divided into two parts. One part is in the possession of the U.S.A., while the other is in possession of Canada. This waterfall actually acts as the international boundary between these two countries.

            The Ribbon waterfall of California in America is the highest narrow-stream waterfall of the world. A narrow stream falls into the Merced River from a height of 490 metres. The widest waterfall of the world is the Khoni waterfall having a width of 11 km.

            Some waterfalls have proved very useful to man. Hydro-electricity produced from waterfalls is used for innumerable purposes. 

            Glacier is a large mass of moving ice. We see glaciers in various mountain ranges and vallies of the world. In the Alps alone there are as many as 1,200 glaciers. In the high mountains of the Alaska, there are around thousands of glaciers with length, ranging from 30 to 60 kilometres.

            The process for the formation of glaciers is described below. During snowfall snow slides down on the slopes of mountains. After a considerable time it accumulates in big quantities. As this accumulated snow does not melt even in summers, its quantity keeps on increasing. As the quantity of snow increases, the pressure on the lowest layer of the snow also increases. Due to the increased pressure and other atmospheric effects, air leaks out from the lowest layer of snow and consequently, it becomes hardened. This process goes on till a time comes when glaciers become heavy enough to flow downhill under their own weight.

            Glaciers are mainly of two kinds. The first type is the valley glaciers. When there is snowfall on the mountains, the snow slides down on the slopes. This gets deposited in the spaces between the mountains. When snow accumulates in big quantities, it often starts sliding down. The slow moving river of ice is called the valley glacier. Large chunks of stones coming in the way of this river move forward with this river and break into pieces due to friction and collisions with other stones. They spread uniformly in all directions. The motion of the glacier thus forms valleys.

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       Everybody knows that sea water is salty. This means that some salt in the dissolved form is present in sea water. One gallon of sea water contains about one hundred grams of salt. In general sea water has 4% to 6% salt in it. In comparison to open seas, the quantity of salt in closed seas like the Mediterranean and the Red Sea is more. If salt of all the oceans is collected and dried, one can make a 288 km high and 1.6 km thick wall with this salt, which will be long enough to encircle the entire perimeter of the Earth along the equator.

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