Unit 7 weathering of rocks
Words to be remembered:
weathering – выветривание; эрозия
to expose – подвергать
to decompose – разлагать, разрушать
decomposition = disintegration – разложение, распад, разрушение
influence – влияние
phenomenon (pl. phenomena) – явление
be referred to – упоминаться, называться
cause – причина
to take place – происходить, случаться, иметь место
with the succession – (зд.) при смене
to expand – расширяться, увеличиваться в объеме
expansion – расширение
to contract – сжиматься, сокращаться
contraction – сжатие
to occur – происходить, случаться
to crack – трескаться, растрескиваться
crack = fissure = fracture – трещина, излом
hardly noticeable – едва заметный
to facilitate – облегчать, ускорять
to freeze (froze, frozen) – замерзать
lateral pressure – боковое давление
i.e. = id est – т.е. = то есть
abundant – широко распространенный
to resist – сопротивляться, противостоять
resistant – стойкий, сопротивляющийся
to solve – растворять
solvent action – растворяющее действие
soluble – растворимый
carbon dioxide – CO2, углекислый газ
to destroy – разрушать
All rocks which are exposed on the Earth's surface (high mountain peaks, deserts) are decomposed to a certain degree. The process of rock disintegration by the direct influence of local atmospheric conditions on the Earth's surface is called weathering. This phenomenon is often referred to in geology because weathering is an active process. It takes place in the upper layers of the Earth's crust.
The decomposition of rocks under the direct influence of heat and cold is called physical weathering. The main cause of physical weathering is the change in temperature that takes place with the succession of day and night. This phenomenon can best be observed in the deserts and high mountains where the changes in temperature are common. During the day under the influence of heat, rocks expand whereas at night they begin to contract. As rocks are generally composed of different minerals, their expansion and contraction do not occur uniformly. As a result of this rocks crack. At the beginning these cracks or fissures are hardly noticeable but gradually they become wider and deeper until the whole surface of rock is finally transformed into gravel, sand or dust.
In the regions of a moderate or cold climate, where the temperature in winter goes down to below 0 (zero) the decomposition of rocks is greatly facilitated by the action of water. When water freezes it increases in volume and develops enormous lateral pressure. Under the action of water, rocks decompose to pieces of varied forms and sizes.
Rocks are subjected not only to physical decomposition but also to chemical weathering, i.e. to the action of chemical agents, such as water, carbon dioxide and oxygen. In a general way, chemical weathering is an acid attack on the rocks of the Earth's crust, in particular an attack on the most abundant minerals — quartz (sand) and aluminosilicates (clays). Only few minerals and rocks are resistant to the action of natural waters. The solvent action of water is stronger when it contains carbon dioxide. Water causes more complex and varied changes. With the participation of oxygen and carbon dioxide up to 90 per cent of rocks is transformed into soluble minerals, which are carried away by the waters.
Organisms and plants also take part in the disintegration of rocks. Certain marine organisms accelerate the destruction of rocks by making holes in them to live in. The action of plants can often be even more destructive. Their roots penetrate into the fissures of rocks and develop the lateral pressure which fractures and destroys rocks.
Questions on the text:
1) What process is called weathering? 2) What process is called physical weathering? 3) Where can the phenomenon of physical weathering be observed? 4) What facilitates the decomposition of rocks in the regions of a moderate or cold climate? Describe this process. 5) What process is called chemical weathering? 6) What substances can act as solvents? 7) What are the most abundant minerals? 8) Are all minerals and rocks resistant to the action of natural waters or only few minerals and rocks can resist the action of it? 9) How do organisms act on the destruction of rocks?