WEATHERING IS THE BREAKING DOWN of rocks on the Earth’s surface. There are two main types: physical (or mechanical) and chemical. Physical weathering may be caused by temperature changes, such as freezing and thawing, or by abrasion from material carried by winds, rivers, or glaciers. Rocks may also be broken down by the actions of animals and plants, such as the burrowing of animals and the growth of roots. Chemical weathering causes rocks to decompose by changing
their chemical composition—for example, rainwater may dissolve certain minerals in a rock. Erosion is the wearing away and removal of land surfaces by water, wind, or ice. It is greatest in areas of little or no surface vegetation, such as deserts, where sand dunes may form.
