Weathering is the physical disintegration and chemical decomposition of rock at or near Earth's surface. Different types of weathering are:
Physical weathering which is the physical disintegration or fracture of rock, mainly due to pressure, for example frost wedging. Water enters cracks in the rock. When it freezes, it expands, and pressure breaks the rock apart. Underground water can also freeze resulting in frost heaving which causes fractures and bulges in pavements. Building foundations should be laid below the frost line to prevent frost heaving. Permafrost occurs in cold latitudes when subsurface soil is frozen all winter. Spring and summer thaw makes the ground wet and spongy.
In warm climates, ground water with high salt concentrations seeps into porous rock. Evaporation of water results in salt crystals. Their pressure on the surrounding rock, salt wedging can loosen and fracture the cementing material holding the sand grains.
Roots of plants and burrowing animals loosen and bring soil to the surface. Human activity also causes changes in the Earth's surface.
Chemical weathering involves a chemical change in the rock's composition. Rain water absorbs and combines with carbon dioxide (CO2) in the atmosphere to form carbonic acid (H2CO3). As this water moves through limestone, it produces calcium bicarbonate Ca(HCO3)2 which dissolves in water and is carried away.. Caverns are carved out over long periods. Occasionally, the cavern ceiling collapse causing sinkholes.
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Erosion is the downslope movement of surface and near-surface materials due to gravity. The agents that cause such movements are water, ice (glaciers), wind, and waves.
Running water are streams and rivers that erode the land surface and transport the eroded materials. The erosion caused by overland flow is known as sheet erosion. Stream load is the eroded material in a stream.
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