What Are the Two Types of Weathering?

Physical Weathering

• Physical weathering is also known as mechanical weathering. It occurs when rocks are broken down as a result of direct contact with atmospheric factors, such as water, heat, ice and pressure. It results in rocks that are smaller than the original but have the same general composition. Eventually the particles of rock are so small they combine with organic material and create soil.

Types of Physical Weathering

• Water can cause physical weathering when it enters fissures in rocks and goes through cycles of freezing and thawing that can fracture the rock. Heat can weather rocks in the form of fire or expansion and contraction from the sun's heat. The release of pressure and abrasion also cause weathering that does not affect the rock's chemistry. At a large scale level, the uplifting of landmasses can lead to weathering. At a micro level, plant root growth can also push cracks in rocks wider apart.

Chemical Weathering

• Chemical weathering occurs when the rock is broken into smaller pieces, but the chemical composition changes. The minerals in the rock are broken down by chemical reactions rather than fragmentation. Chemical processes tend to depend on the availability of water and occur more in warm, tropical climates than in dry and cold areas. Clay is a common product of chemical weathering.

Types of Chemical Weathering

• The three main types of chemical weathering are oxidation, hydrolysis and carbonation. Oxidation occurs when metallic ores combine with oxygen and water to form oxides, such as the rusting of iron. Hydrolysis allows minerals to dissolve. Carbonation is when atmospheric carbon dioxide, or acid rain, leads to solution weathering. So they can attach more easily to the surface, mosses and lichens growing on rocks can also produce acids that chemically weather the rocks.