My Science School

          During winter mornings, sometimes we see a smoky cover on the Earth’s surface. This is called fog. When becomes very dense, the visibility is poor, and it becomes difficult to see anything.

          Fog is a kind of cloud, which comes in contact with the ground. It is formed by the condensation of water vapour present in the air near the ground. We know that water vapours are always present in air. Air cannot hold more than a certain amount of water vapour at a given temperature. The water vapours in excess of that limit are converted into small particles of water or ice. When such condensation takes place near the Earth’s surface, a cloud of fog is formed. The minute particles of water present in the fog reduce visibility to a great extent. During winter, the Earth’s surface is cool in the mornings, as such, water vapour present in the air condense into fog.

          The layers of fog are thicker in big cities than in villages and smaller towns. This is so because there is a greater degree of dust particles and smoke in big cities. Dust particles and smoke get mixed with water particles present in the fog and make it denser. This type of fog is also called smog. You must have noticed that fogs are denser in those cities where there is more of smoke due to the large number of factories. In big industrial cities like Bombay, Calcutta and Delhi, this type of dense fog is a common feature.

          The presence of fog causes a great inconvenience to the transport system. Sometimes, planes and motor cars meet with accidents because of the poor visibility due to fog. In 1955, a chemical method was developed to clear the fog. In this method, silver iodide or calcium chloride is sprayed in foggy areas which enable water particles present in the fog to fall down on the Earth in the form of raindrops. However, no system has succeeded fully in clean ring fog so far. 

          Rain is often accompanied with thunder and lightning. Even though lightning and thunder are simultaneously produced in the clouds, the flash of lightning reaches us much before the sound. This is because light travels much faster than sound.

          Although lighting seldom reaches the Earth, there have been instances of death by lightning. When it flashes, a bright streak is drawn in the clouds. In reality, this streak is there either between two clouds or between the clouds and the Earth. Whenever a charged cloud approaches the Earth’s surface, opposite charge is produced in it. When the potential difference between the two is much higher than the resistance of the air, electricity flows through the air towards the Earth. As a result, lightning flashes. Similarly, when two charged clouds approach each other, there is a flash of lightning. This flash can be as long as 50 km.

           The lightning produced between the Earth and the clouds, is dangerous for high buildings. In order to protect these buildings from lightning, pointed metallic rods are fixed at the roof-tops of these buildings and these rods are taken through the walls down to the Earth and buried in it. They are called lightning conductors. Buildings fitted with these conductors cannot be damaged by lightning.

          Scientists are of the view that once you have seen the flash, you are completely safe from the ill-effects of the lightning. Thus, when lightning flashes, one should not get frightened and rush indoors, but come out in the open.

 

           A mountain is a tract of land rising considerably above the surrounding surface. Mountains are usually found connected in chains or ranges.

           Geologists have made extensive study of mountain formations. It has been revealed by these studies that they are formed as ranges. The ranges of mountains along with many small and big hills extend over long distances. To study their formation in a systematic way, geologists have divided them into four categories. Different types of mountains are formed in different ways. But all the mountains have been formed due to the violent changes on the Earth’s surface, millions of years ago. The formation of four types of mountains can be understood in the following way.

           The first type of mountains is the volcanic mountains. These mountains are made of lava and ash. Due to the agitations in the Earth’s interior, the Earth’s surface breaks at places from where the internal matter of the Earth comes out as lava. The volcanic mountains are cone-shaped with a large hole or crater at the top. The Vesuvius of Italy, the Fujiyama of Japan, the Hood and the Ranier of the United States of America are the famous volcanic mountains of the world.

                                                                                                                                                                                     The second type of mountains is the folded mountains. These are made of many layers of rocks. These layers are formed because of extreme contractions and pressures inside the Earth. The Alps mountain ranges have been formed in this way.

 

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The word river is derived from the Latin word ‘ripa’ meaning river bank. In the ancient times, a stream of water with definite banks was called a river. According to contemporary definitions, giant streams of water without any definite banks are called rivers. Smaller streams of water are known as brooks.

In the beginning of the creation of the universe, when mountains and seas formed on the Earth, rains still continued. The rain-water used to travel from mountains via zigzag paths and would finally fall into the sea. The continuous flow of water made these tracks deeper and wider. These streams of water underwent many changes and subsequently became rivers.

With the passage of time, the forms of rivers have changed. Now most of the rivers originate from mountains. The water in these rivers is molten snow coming down from heights. Rains also contribute to the water flowing in the rivers.

Some rivers are formed by the movement of glaciers. The uneven areas coming in the way of glaciers become plain and take the shape of a river. Sources of some of the rivers are springs and lakes. A river flows very slowly near its origin, but as it advances, its depth reduces and its banks become wide because of soil erosion. A river becomes very slow at its fag end. There is enough accumulation of soil at the point where a river meets the sea or a lake and the place where they meet is called a delta. Those areas where river deposits silt brought by it become very fertile.

Rivers continue to be an important means of transportation of goods. Steamers and boats are plied in rivers. Dams are constructed in rivers to accumulate water, and by making water fall from a height, electricity is generated. This water is also used for irrigation purposes.

               Caves have for long been linked with the history of civilization in many interesting ways. In the stone age, men used to live in caves to protect themselves from cold and animals. Ancient people had many strange notions about caves. The people of Greece believed that their gods Zeus, Pan, Dionsus and Pluto lived in caves. The Romans believed that caves were the homes of nymphs and sibyls. People of Persia worshipped caves considering them to be the abodes of God. Today, huge and beautiful caves all over the world have become centres of attraction for the tourists. Do you know how these caves were formed?

               A cave is a deep hollow space in a mountain. It is formed in different ways. When water waves coming from the sea, collide with the mountains, they wash away the soft stones present in between the layers of the rocks. This process continued over a period of thousands of years and created large spaces inside the mountains which we call caves.

               Some caves are found below the Earth’s surface also. These have been formed by the water streams flowing below the Earth’s surface. The underground water streams wash away the lime-stone from the rocks and the voids so created are called caves.

               Quite often, waterfalls create hollow spaces within the rocks which ultimately become caves. Such caves have been formed below the Niagara Falls.

               Caves are also formed by the volcanic changes taking place in the earth’s layers. Some caves are very long while some are very deep. The deepest cave is ‘Guffre de la piere st.’ situated on the border of France and Spain. It is 1310 metres (4300 ft) deep. The longest cave, ‘Flit Ridge cave system’ is situated in America and is 116.8 km (73 miles) long.

               The longest single cavern in the world is the Sarawak chamber in Eastern Malaysia. It is 700 metres long and was discovered in 1980. Mammoth Cave National Park in the US State of Kentucky is the largest cave system of the world about 307 km long. In India, caves of Ajanta and Ellora are famous for their beautiful sculptures. 

            A volcano is a mountain having an opening on the surface of the Earth from which fire, smoke and ashes come out continuously. Mountains of this type are created by upheavals inside the Earth.

            The formation of volcanoes can be understood as follows. Temperature inside the Earth goes on increasing as we go into the interior of the Earth. At a depth of approximately 30 km, the temperature is so high that it can melt rocks. When rocks inside the Earth get melted, they start expanding. These molten rocks are known as magma. In some parts of the Earth, this magma starts coming up through openings in the Earth’s crust. When the pressure exerted by this magma is considerably high and the Earth’s crust at some places is weak, the crust breaks at those places and, as a result, hot gases, liquid and solid material of the red molten rocks start coming out. This is called volcanic eruption. The ejected hot smoke, ashes and stone pieces constitute what we call lava. This lava goes on solidifying in the shape of a cone and, on cooling; it takes the form of a mountain on the surface of the Earth.

            Fire and smoke keep on flowing out of the opening of the volcano until the molten material inside the Earth is exhausted. Such volcanoes from which lava stops coming are called dead volcanoes. There are more than 450 volcanoes in the world. The number of volcanoes in Indonesia is quite large. The highest dead volcano of the world is in Argentina; it is 6,960 metres high. One of the most violent volcanic eruptions was on the island of Krakatau, near Sumatra in 1883 which produced tidal waves in the oceans throughout the world.

 

            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.