Types of Weathering of Rocks

Mechanical Weathering

• Physical strain exerted from the environment or living things is a constant contributor to the mechanical weathering of rocks. Plants or animals using rocks for habitat adds weight and spatial stress. This stress causes fractures and cracks called joints to occur in rock forms. Natural disasters such as volcanoes or earthquakes are dramatic but less frequent weathering sources. When rocks are mechanically altered they retain their original mineral composition. Even in the case of molten rock, or lava, the rocks have only undergone a physical phase change due to heat stress. Frost wedging is when rainwater can freeze inside the cracks of rocks expanding and straining what is referred to as the crystalline structure of rock molecules.

Chemical Weathering

• Down in the soil where rocks and the environment are in constant communication is the site of most chemical weathering sources. Water is a key player in this process, contributing to three separate sources of weathering. Water readily breaks up the mineral composition of rocks through a process called hydrolysis. This process involves the exchange of hydrogen ions from water to rocks that compromise the structural lattice of rock molecular composition. Carbonic acid is another source of weathering caused by water. Carbon dioxide produced naturally in the soil readily reacts with water to produce this acid, which oxidizes the rock material forming new compounds and degrading the rock composition. In addition, water can be absorbed into the rock lattice and create a completely different material and mineral structure. When chemically degraded rock material is washed or blown away, the whole process is called erosion. Leaching occurs when mineral ions react with agents and the rock is degraded. Oxidation and dehydration are also examples of chemical weathering.

Results and Impact

• Results of chemical weathering generally produce salts, clay, sand or silica, canyons and gorges. Mechanical weathering produces mountains, cliffs and plateaus, gravel, and islands. The origin of our salt-based marine environment can be traced to the salt by-product from chemically weathering rocks on land being moved and sequestered in the oceans for billions of years. Mountains and islands are the result of massive physical weathering caused by huge shifts in continental plates that smash together to make mountains or break off and create islands.