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14.2.1. Weathering

Weathering

The rocks were formed inside the Earth, under conditions different from those on the surface. The environmental conditions of the surface cause physical and chemical transformations in the rocks.

The weathering is the breakdown rocks of the earth 's surface being in contact with the atmospherehydrosphere and biosphere. The transport of these materials does not take place, because if there were, we would speak of erosion.

As a result of weathering, fragments of rocks of different sizes called clasts are obtained. These materials are deposited at the foot of the rocks from which they come, forming a debris.

There are three types of weathering:

Physical or mechanical weathering

The physical weathering  causes disintegration or breaking rock, without changing their chemical or mineralogical composition. The rock is fracturing and the small fragments that are generated can be eroded and transported later .

Some types of physical weathering are:

  • Decompression. Rocks expand and crack because they have been formed with great pressure at great depth, and if they reach the surface, as there is less pressure, they expand, forming cracks or joints that form horizontal slabs.
  • Thermoclasty. If the temperature differences between day and night are very great, the rock continuously expands and contracts. As not all the minerals that form them expand in the same way, the rock ends up disintegrating. For example, in the desert.
  • Gelifraction. The water in the small crevices of the rock freezes, increases in size and, after repeating it many times, ends up fracturing the rock. For example, the fields.

Río de Piedra en Orihuela del Tremedal (Teruel)

Stone River in Orihuela del Tremedal (Teruel)

  • Haloclastism. In marine and arid environments, the water that occupies the pores and fissures of the rocks evaporates leaving the salt. When crystallizing, as its volume is greater, it exerts pressures that can break the rock.
  • Biological. Some living things, such as trees with their roots, can physically fragment rocks. Or burrowing animals, which also make their burrows by breaking up rocks.

Chemical weathering

The chemical weathering produces a chemical transformation, transforming minerals other substances, causing them to lose cohesion and rock is altered.

Some types of chemical weathering are oxidation, dissolution, carbonation, hydration, hydrolysis.

There is also a type of biochemical weathering, produced by the action of organic acids from the decomposition of remains of living beings or by the physical-chemical action of living plants.

Answer in your notebook

14.3.- Explain what weathering consists of. Point out an example of physical weathering and another of chemical weathering.

Answer in your notebook

14.4.- The roots also secrete substances with which they alter the rocks. Would you say that biological weathering could be included within physical weathering, within chemistry, or within both types?