Category Earth Science

            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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         About three-fourth of the Earth’s total surface is covered with water. Only one-fourth of Earth’s surface is land. The total area of the Earth’s surface covered by oceans comes to 361.100 million sq. km. Do you know how and when these oceans were formed?

          It is not yet fully known when oceans were formed. However, at the beginning of the formation of Earth, there were no oceans. The age of oceans has been calculated on the basis of the minerals present inside them. It is estimated that oceans were formed some time between 500 to 1,000 millions years before.

            The story of the origin of oceans is very interesting. The Earth was a giant burning fire ball at the time of its birth. Its surface was formed by molten rocks. When the Earth started cooling slowly, it was enveloped by clouds of gases. These clouds became very heavy after cooling. They started raining heavily, but the Earth’s surface was still so hot that the raindrops falling on it would evaporate and mix with the atmosphere again. This would again come down to the Earth in the form of rains. This cycle continued for millions of years. The Earth’s crust became cold and tough and the rain-water would boil no more, but the heavy down-pour continued for thousands of years. The low-lying areas of the Earth were filled up with the water of these heavy rains. These vast lakes of water on the surface of the Earth are today’s oceans. 

          Dead Sea is the only sea on earth which has no plant or animal life. It is, therefore, appropriately called Dead Sea. In fact, Dead Sea is a saline lake situated between Jordan and Israel. This is 77 km long and its breadth ranges between 5 to 18 kilometres. The water level of Dead Sea is the lowest on the Earth. It is lower than the sea-level by 396 metres. Millions of years ago the level of Dead Sea was, however, higher than the present one by 427 metres. At that time aquatic animals were living in Dead Sea. All of a sudden, there was a draught and the water of this sea evaporated. Gradually this sea acquired the present state.

          No river originates from this sea. The Jordan River and some small canals end up in this sea. Since no river comes out of this, the water of this sea depletes only by evaporation. Consequently, the amount of salt and other soluble minerals brought into the sea by the Jordan River and other smaller canals goes on increasing. You will be surprised to know that the amount of salt present in Dead Sea is the largest in comparison to the other seas. In general, the amount of salt present in any sea is 4% to 6%. But even this make you sick as it contains large quantities of magnesium chloride and other poisonous substances. Due to the presence of large quantities of salt and other poisonous materials no living being can survive in this sea. Hence fish and other acquatic animals of the Jordan River die as soon as they enter the water of this sea.

 

          Generally, Sea Mountains are those mountains which are at least one kilometre above the seabed. A number of such mountains have been discovered.

          Upheavals at the bottom of the sea are responsible for the formation of these mountains. Volcanic eruptions in the seabed also make mountains. Generally, these mountains are one to three kilometres high. Majority of these mountains remain submerged in water, but some of them have surfaced above also. The flat mountains coming above water are called islands. The Hawaii islands were formed in this manner.

          There are many mountains in the midst of oceans. The mid-ocean ridge is continuous and it winds for 60,000 km through all worlds’ oceans. There are many mountains in the north-east part of the Pacific Ocean. Most of these mountains are submerged in water, but some of the mountains of the Hawaiian chain have surfaced above. They are called the Hawaii Islands. The highest mountain of the Hawaiian chain is the Mauna Kea. The height of this mountain is 4,200 metres above sea level, but the total height of this mountain from the bottom of the sea is 9,686 metres. That means the height of this mountain inside the sea is 5,486 metres. If its height is taken in full, this is the highest mountain of the world.