Category Geography

How do mountains form?

Mountains are an outcome of the movements of the Earth’s crust, which is the Earth’s outer layer. The Earth’s crust consists of six massive slabs referred to as tectonic plates, which are always moving a few centimeters annually. Two tectonic plates moving against each other cause the thickening and deformation of the crust and land mass is forced upwards to form mountains. Over time, mountains are subjected to erosion from elements such as the wind, ice, and rain, causing their surfaces to be younger than the rocks which initially formed them. Depending on the tectonic forces at work, different types of mountains are formed.

Mountains take millions of years to form. Huge movements deep in the centre of the Earth slowly push rocks into mountain shapes. Some mountains, like the Urals in Russia, started to form about 250 million years ago.      

The Earth’s surface is like a rocky jigsaw.

The outer layer of the Earth is made from giant pieces of rock called plates which lie on top of boiling hot, runny rock called ‘magma’. The plates move about a thumb’s length each year, but we can’t feel them moving. When the plates push into or pull away from each other, rock is forced upwards forming a mountain. This aerial view shows a fault in Tibet in Asia. The Kunlun fault is 1,500 km long. It can be seen running from left to right. Lines of vegetation are shown in red.

Some mountains are still growing!

Some plates that collided millions of years ago are still pushing together, and causing the land to rise upwards. The Himalayas in Asia grow about six centimetres each year. Soft soil above the Asian plate is rising because it is being pushed by the stronger Indian plate.

Geologists study mountain rocks.

Geologists are scientists. They study rock layers and the ways that rocks form. Bu examining rocks, they are able to work out how a mountain formed and even how old it is! Geologists use a range of tools, from hammers and chisels to drills, satellites and computer technology.

Picture Credit : Google

 

What is a mountain?

A mountain is a large landform that rises above the surrounding land in a limited area, usually in the form of a peak. A mountain is generally steeper than a hill. Mountains are formed through tectonic forces or volcanism. These forces can locally raise the surface of the earth. Mountains erode slowly through the action of rivers, weather conditions, and glaciers. A few mountains are isolated summits, but most occur in huge mountain ranges.

High elevations on mountains produce colder climate than at sea level. These colder climates strongly affect the ecosystem of mountains: different elevations have different plants and animals. Because of the less hospitable terrain and climate, mountains tend to be used less for agriculture and more for resource extraction and recreation, such as mountain climbing.

The surface of the Earth is full of bumps, hills and valleys. We call the tallest places on Earth ‘mountains’.  Life in the mountains is cold and harsh but many people, plants and animals are able to live there.

Mountains come in all shapes and sizes.

No two mountains look the same! Some are pointed and jagged. Others are rounder and smoother. There is no agreed definition about when a hill becomes a mountain, but generally mountains are more than 700 metres tall. Mount Everest is the tallest mountain on land and is 8,850 metres tall.

The four principal shapes of mountain ranges include: diamond, pyramid, inverted pyramid and hourglass. For all the range shapes except pyramid, land availability can be greater at higher elevations than it is farther down the mountainside. Yet, people’s idea that land area steadily shrinks as a mountain rises is so entrenched that it has come to guide conservation plans and research.

Mountains are made from rock.

There are three main types of mountain rock, depending on where the mountain is found and how it formed. Granite is very hard and looks grainy, like a mixture of salt and pepper. Sandstone is made of squashed up grains of sand. Limestone is mostly made from the remains of dead plants and animals.

Groups of mountains are called ranges.

Most mountains are grouped together in ranges, such as the Alps in Europe and the Atlas mountains in Africa. The highest range of mountains in the world is the Himalayas range in Asia.

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Why was the Great Wall of China built?

    The Great Wall of China was built in the Third Century B.C. to keep out the raiding Tartars of Mongolia. It is 20 to 30 feet high and 15 to 25 feet wide at the top, with towers 60 feet high every few hundred yards.

   The wall stretches from Shamhaikwan on the yellow Sea to the borders of Kansu and Sinkiang in the west, crossing high mountains and deep valleys. Probably over 500,000 workers were employed to build it. Even today, the wall is in a wonderful state of preservation.

    This marvelous structure is constructed of brick and stones. The sides have battlements-parapets with openings or embrasures through which weapons could be discharged.

   All large cities of China were provided with similar walls, and the gates were closed at night to give the citizens protection against surprise attack. For China has been envied by her neighbors throughout history. Many times these neighbors have invaded the country, seized the capital and begun a new dynasty.

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When was the Colosseum built?

          The great Flavian Amphitheatre, or Colosseum, was built between A.D. 69 and 81 by the Emperors Vespasian and Titus on the site of an artificial lake in the grounds of Nero’s palace, the Golden House. The name Colosseum was bestowed on it, because of its colossal size, sometime after the 8th century.

         In its full magnificence the Colosseum must have been one of the most imposing buildings in the Roman Empire, a gigantic oval measuring 620 feet by 513 feet with a height of 160 feet. Round the actual arena-287 feet by 180 feet-tiers of marble seats provided accommodation for 50,000 spectators.

          The building was constructed to the house gigantic spectacles organized by the authorities for the entertainment-and distraction-of the public. It became a scene of much bloodshed. Here were staged gladiatorial combats (fights to the death between men) and contests between wild beasts or between men and animals. And here, too, many of the early Christians met martyrdom with a courage that helped greatly to spread their faith.

        The highest tiers of seats and the fourth storey were rebuilt in the 3rd century, and the building was seriously damaged by lightning and earthquakes during Roman times and the middle ages. For hundreds of years this symbol of Roman power was used as a quarry. But even today its ruins form one of the most famous buildings in the world.

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Why do clouds have different shapes?

               Clouds vary in shape according to their height and temperature, and they contain minute drops of water or ice particles or a combination of both. And, of course, their forma­tion is greatly affected by wind changes.

               There are basically three groups of clouds: high clouds between 17,000 and, 45,000 feet (cirrus, cirro-cumulus’ and cirro-stratus); middle clouds between 7,000 and 23,000 feet (alto-cumulus, alto­stratus and nimbo-stratus); and low clouds up to 7,000 feet (strato­cumulus, stratus, cumulus and cumulo-nimbus. Their height and temperature decide how much pressure is exerted on them by the atmosphere.

               Finally, the shapes of clouds differ according to the time of day. Towards evening Clouds tend to thin out, rise a little and flatten out.

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What is the date line?

        The Date Line (usually called the International Date Line), is a north-south line through the Paci­fic Ocean where, according to international agreement, the date changes. East of  the Line it is one day earlier than it is to the west.

        The line is necessary because the earth is divided, longitudinally, into 24 one-hour time zones (15° longitude each) which make one full day on the earth. Since the earth rotates eastwards, the time on the clock progresses westward, round the world. Thus, 12 o’clock noon arrives in London (0° longitude) five hours before it does in Washington, D.C. (75° west of London) and eight hours before it does at San Francisco (120° west of London). When it is noon in London it is midnight 180° to the west.

           On either side of the 180th meridian the time is the same. But you would lose a day if you crossed it from the east and gain one if you travelled across it from the west.

           The Date Line has some varia­tions from the 180th meridian to allow for land areas or islands. The line bulges eastwards through Bering Strait to Take in eastern Siberia and then westward to include the Aleutian Islands with Alaska. South of the equator bulges east again to allow various island groups to have the same day as New Zealand.

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