Rocks: Breaking Down Or Chemically Modified By Climatic Or Biological Elements

Weathering- is a process where rocks are physically broken down or chemically modified by climatic or biological elements. Works through 3 processes: physical weathering, chemical weathering and biological weathering.
Physical weathering- is the breaking down of rocks into smaller fragments brought about by physical (mechanical) forces. Works through 4 processes: alternate expansion and contraction, frost action, pressure release and salt crystal growth.
Alternate expansion and contraction- this process occurs in areas such as desserts. The rock expands during the day because of the heat and contracts at night when temperatures drop below freezing point (0 degrees). Constant expansion and contraction of the rock causes cracks within the rock.
Water containing dissolved mineral salts seeps into the cracks of a rock and the water evaporates the salt remains and it crystallises within the pores. As the mineral salt grows into larger salt crystals which exerts pressure on the sides of the crack causing it to break down over time.
Frost action- occurs in mountainous areas where there is large amounts moisture and temperatures fluctuate below freezing point. When water enters the crack of a rock and temperatures drop below freezing point at night the water freezes and its volume increases by 9% which exerts pressure on the cracks causing it to deepen. In the day temperatures rises above freezing point and melts then more water enters the crack and freezes causing the crack to deepen further. When this process is constantly repeated the rock eventually splits apart into angular fragments.
Pressure release- occurs when igneous rocks are exposed at the surface after erosion. After overlying material is removed the rock expands due to heat. Cracks are formed parallel to the surface. Over time rock fragments peel off due to further weathering and becomes domed shaped (exfoliation