The Land Surface

Even the land surface differs as well. And the shaping of the land is largely done by running water that carries away materials loosened and broken up by weathering. This is called erosion. Erosion cuts down the softer rocks and land while the harder ridges of tougher resistant rocks remain uneroded and form rocky structures. This is why land surface is so different.   

Some parts of land are plains. For example, the vast Gangetic plains in India, that is also world's one of the most populated places. Some are mountains, like the Alps, the Himalayas or the Rockies in North America. Some parts are deserts, like the African Sahara, the Australian desert and the icy cold Gobi desert in Mongolia.

Some places are crowded with trees and are called forests. Like, the tropical forest in Africa or the Amazonian Rain forest in South America.

Apart from these, there are some large islands. Some of the world's largest islands are Greenland, New Guinea and Borneo and Great Britain.

This varied contour of the Earth's surface is called its topography. And in rhyme with the varied topography, the soil structure also differs. In some parts it is pure soil, wherein grows a wide variety of trees and greeneries. In some, there are more rocks and dust than the soiled earth. Some soil contains more of sand. The color of some soil is black, some red, and, brown. It is due to the difference in the nature of soil, the type of crops and the fruits grown, differ. 

Deserts are areas where rainfall is very scarce. And plants are scarce as well. Say, hardly 10 inches downpour takes place in a year. They encircle the Earth in two bands. One is above, the other below, the Equator. Though heat and sand are commonest features of deserts, but not for all. Only 28 per cent of the Sahara is covered with sand. There is soil over the remaining stretches where plants can hardly grow. The edges of the ice caps at the two poles and some permanent snow fields are cold deserts. 

Mountains are land masses that stand above the surrounding landscape. They often have steep sides and small summit. Mountains are of four types based on the way they were born. Volcanic, Block, Fold and Residual. Can you tell us what type the Alps Mountain is?

The commonest form of volcanoes is built of alternate layers of lava and fragmental materials. For instance, Vesuvius, Italy; Fujiyama, Japan; Mt. Shasta, California, among many.

Fault block mountains are formed by an uplift of layers of rocky segments along the cracks of faults. Examples include the Vosges, France; and Sierra Nevada, USA, among the others.

The fold mountains are formed when the rock layers fold, buckle and lift above the surrounding land, all due to pressures in the Earth's crust. Examples include the Alps, Europe; Andes, South America; and the Himalayas, South of Asia; among others. 

Some mountains are so deeply worn off and reduced by weathering and river action that they stand out as skeletons. For instance, the Catskill, New York.

In line with these variations in the surface, climate also differs, as we move from one region to another. In some parts it is mostly cold throughout the year. In some it is hot. Some places see both the heat and cold at their extremes. There are some places where it is neither too hot, nor too cold. Somewhere it pours mostly throughout the year. Again there are some regions where dry spell dominates throughout. 
Broadly, it's extreme cold near the two polar caps. As we move away, the ferocity of the cold gets reduced gradually. As we approach the Equator, the climate gets hotter and humid as well. Obviously it is hottest along the two sides of the Equator. Regions lying in between are usually a strict follower to the four main seasonal guidelines. That is, the summer, autumn, winter and  the spring. 

Polar climates have temperatures no warmer than 10 degrees centigrade even in the warmest month of the year. These occur beyond the tree limits of Arctic and Antarctic and at high altitudes in major mountain ranges.

Wet tropical rainy climates are those in which the temperature of the coolest month is above 17 degrees centigrade. This include tropical rain forests where the rainfall is heavy throughout the year. These are located near the Equator near the Amazon Valley, the Congo basin, along the Guinea Coast of Africa, and in large parts of the East Indies. Savannas, which have less rainfall, also belong to this group. More open than tropical rain forests, they have a wet season and a dry season. Usually adjacent to tropical rain forests, grassy savannas occur in the Llanos of the Orinoco Valley of Colombia and Venezuela, the Guinea Highlands in northern and southern America, the Campos of Brazil, the Sudan and the grasslands of northern and southern Africa, and the low grasslands of northern Australia.

Moderate humid climates are those where the coldest month is between 18 and minus 2 degrees. These are located along the western and eastern sides of continents. But they also extend inland about 2000 miles in the Mediterranean region of the southern Europe.

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