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The Earth is comprised of concentric layers – the crust, the mantle and the core. Each and every layer has different physical and chemical properties. Their heterogeneity is the source of many natural phenomena, e.g. volcanic eruptions and earthquakes. Rocks are records of our planet’s long history. By examining rocks, we learn where deserts, volcanoes and seas were located in the past. Earth’s surface is constantly transforming. These changes result mainly from natural processes, which had shaped the Earth before mankind and which will continue to mould our planet even after humans cease to exist.

Earth‑forming activity of glaciers and ice sheets

On the Earth, many areas are covered with mountain glaciers and ice sheets, which are formed in appropriate climatic conditions and in places where the shape of the surface is favourable. Ice sheets cover almost the whole of Antarctica and a major part of Greenland. Glaciers form above the perpetual snow line in the mountains of all continents except Australia. As a result of the destructive and building activity of glaciers, many post‑glacial forms are created, e.g. cirque, moraines, sanders or glacial lakes.

Land‑forming activity of rivers and seas

Moving water can mechanically destroy rocks. This phenomenon is called erosion. The upper course of a river is dominated by deep erosion and headward erosion, in the middle course – lateral erosion, and meanders can form there. In the lower course, especially at the mouth of the sea or a lake, the river no longer has its erosive force, it gradually loses its ability to transport material and settles it – this is called accumulation. There are two types of river mouths: estuary and delta.

The sea or the ocean have a strong impact on a narrow strip of land called coast. Waves are constantly moving smaller fragments of rocks on the shore, increasingly crumbling them, creating a beach. This process is called abrasion. As a result of various processes, some coasts grow, others are receding. Depending on the shape of the bottom of the sea and land shores, geological processes, sea currents and some organisms, we distinguish many types of coasts. The most known are: fjord, cliff, Dalmatian, reef, lagoon or skerry.

Land‑forming activity of the wind

The wind can have destructive, transporting and building activities. For these processes to take place, the following conditions must simultaneously occur:

• a strong enough wind must blow;

• rocks in the ground must be finely crumbled;

• the ground must not be wet;

• the ground cannot be covered with abundant vegetation.

These conditions are met in the deserts almost all year round and the land‑forming activity is the strongest there. There are three main types of deserts: erg (sandy desert), serir (gravel desert), hamada (rocky desert). Blowing of fine rock material by the wind is called deflationdeflationdeflation. Blown sand can be moved even over long distances. Mounds made this way are called dunes (e.g. barchan or parabolic dunes). Sand grains carried by the wind can hit rocks, grind, groove, smoothen and scratch them – this is corrasion. Closer to the surface of the Earth, the process of corrasion is the strongest. Various, very fanciful rock forms are created, for example rocky mushrooms, yardangs or ventifacts.

Weathering of rocks

Weathering of rocks is the process of chemical or physical disintegration. Physical (mechanical), chemical (e.g. karst), and biological weathering has been distinguished. Each type of rock weathering occurs under specific climatic conditions. Karst phenomena are all processes and forms, both on the surface and underground, occurring in areas built of soluble rocks (limestones, dolomites, gypsum, chalk, salt).

Mass movements appear on most land areas. Loose rock masses and weathering products (eluvium) can move down the slope under the influence of gravity. Mass movements include: sliding, exfoliating, ripping, creeping.

Volcanism and earthquakes

Volcanism and earthquakes are phenomena that are well known to many inhabitants of our planet. Most of the active volcanoes of the globe are in the Pacific ring of firePacific ring of firePacific ring of fire. Volcanoes are also found in Europe, Africa, Hawaii and the Caucasus mountains.

A place where lavalavalava and other volcanic products escape to the surface of the continents or to the bottom of the sea is called volcano. Magma is hot, molten rocks with an admixture of large amounts of water and gases located under the surface of the ground. Lava is molten rock mass spilling onto the surface. We distinguish conical and shield volcanoes.

The largest and most powerful earthquakes (shakes of the Earth’s crust) are created at the contact zones of the lithosphere plates. The source of the seismic wave propagation has been called the focus of the earthquake. The place located directly above it on the surface of the Earth is the epicentre.

Keywords

earthquake, volcano, weathering rocks

Glossary