Translations of Encyclopedia about Geology

Rocks, Mountains, and Valleys

The earth's surface is the result of a combination of many different changes. Forces causing these changes on the earth's surface are at work both on the exterior as well as the interior of the earth.

Convective flow, movement of the plates, volcanoes, earthquakes are some of the interior forces. Water in the lakes, rivers, and oceans, wind, and moving ice are the exterior forces.

All these forces leave visible marks all over the surface of the earth and are the cause of important changes. Mountain ranges form when layers of rock fold as a consequence of a tectonic plates collision.

Mountain ranges quite clearly differ from their lower-situated surroundings by their foothills. In accordance with the height and shape, we distinguish between highlands, where the difference between the summit and the foot is between 500 and 1000 metres and their shape is generally rounded, and high mountain ranges, where the difference of altitude is over 1000 metres. High mountains are often steep and jagged, and in many cases they reflect the changes wrought by glaciers.

From the geological point of view, we classify mountain ranges into volcanic, and in accordance with the type of formation, into fault-block fold, and fault-fold mountains. Residual mountains remain while minerals in the surrounding rocks are being eroded, and then they are carried away by wind or water.

Similar formations are the rocks in the shape of a mushroom, occurring in the desert. Winds close to the surface blow sharp particles of sand against its lower part, leaving it in the end standing on a sort of thin stem. The sand may be deposited in the form of dunes. Dunes are subjected to constant changes as well, because the landscape lacks protective vegetation and the impact of the wind is especially intense.

Caves form when water containing acids flows through limestone and dissolves it. When such a cave collapses, it may create large ravines. We often find on the earth's surface long cavities between jutting rocks. They were formed by flowing water or moving glacier.

However, all forms of the earth's surface are subjected in particular to weathering and erosion. How much these forces will affect everything depends on the climate, type of rock, and the degree of chemical decomposition.

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