When a rock is exposed at the surface of the Earth chemical and mechanical weath

Question

When a rock is exposed at the surface of the Earth chemical and mechanical weathering processes may act upon it. a) Explain why the rates of the chemical weathering processes that may act upon the rock may be enhanced in warmer, wetter environments, compared to cooler, drier climates? In contrast, explain why some mechanical weathering processes may actually be enhanced in colder environments, particularly those where temperatures may regularly drop below 0 degree C? Explain why both chemical and mechanical weathering rates are increased when acting upon a rock that is heavily jointed and fractures compared to a rock that is massive in texture?

Explanation / Answer

a.The rate of chemical weathering increases in the moist and warmer climate. Since the rainfall combines with carbob dioxide present in the atmosphere to form carbonic acid. This acidic rainfall then chemically corrodes the rock and dissolves it. Whereas in cooler and colder climate there is little rainfall to weather the rock chemically. Therefore rate of chemical weathering increases in warmer and wetter climates as compared to the cooler and drier climate.

b. the main agent of weathering is water in the colder climates and the active catalyst is the fluctuations in the temperature. The temperature which fluctuates near 0 degree celsius, water freezes into ice and melts into water in a repeatable manner. When the water freezes about 9-10% of the volume increases so the water freezes into cracks and fissures developed into the solid rock mass expand. These water in the cracks wedge apart the masses of rock. Thus mechanical weathering is increased in the colder climates where temperature drop between below the 0 degree mark.

c. The chemical and weathering are both increased when the rock is heavily jointed and fracture. Since these joints and fractures are the preexisting planes of weakness in the rock. It is easier to break a rock with preexisting weakness planes like joints and fractures than to break a massive rock with no such weakness planes.

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