Physical Weathering
Physical Weathering Processes Rocks that are broken and degrade by processes other than chemical alteration are physically or mechanically weathered. A rock broken in to smaller pieces exposes more surface area of the original rock. Increasing the exposed surface area of a rock will increase its weathering potential. Animals and Plants: Animals burrow into Earth's substrate and move rock fragments and sediment on Earth's surface, thereby aiding in the disintegration of rocks and rock fragments. Fungi and Lichens are acid-producing microorganisms that live on rocks and dissolve nutrients (phosphorus, calcium) within rocks. These microorganisms assist in the breakdown and weathering of rocks. Temperature Variation: minerals in rocks expand and contract in climates where temperature ranges are extreme, like in glacial regions of the world, or when exposed to extreme heat, like during a forest fire. Crystal structures of minerals become stressed during contraction and expansion and the mineral crystals separate. For instance, repeated cycles of freezing and thawing (known as Freeze-Thaw) of water in rock cracks further widens cracks and splits rocks apart. Frost-wedging forces portions of rock to split apart. Although one weathering process can dominate in a given area, physical and chemical weathering processes occur simultaneously to break down rock parent material. Rocks that are formed under intense temperature and pressure and cool rapidly forms crystalline structures in minerals that are less stable when exposed to low temperatures and pressures at Earth's surface, so they will weather more rapidly. Rocks that are formed under intense temperature and pressure, but cool more slowly and later in the volcanic magma cooling process, are more stable when exposed to the low temperatures and pressures at Earth's surface. Bonds holding atoms together determine mineral hardness. Rocks that have cooled more slowly have time to build stronger bonds, so they are more resistant to the forces of weathering. Since some minerals weather more rapidly than others and weathering processes vary in intensity and combination, weathering products contain different mineral combinations. Pedologists, or soil scientists, classify these weathered mineral products as soil separates. Soil separates range in size and are known as sand, silt, and clay
