Mechanical weathering is the breaking apart of rock, cement and other material. Mechanical weathering occurs in several ways. Extreme temperature changes expand and compress rock or rock-like material. This can crack the stone and allow water to get into the crack. Water expands as it becomes ice and wedges the stone apart. Over time, pieces of the stone break apart and eventually render the rock into dust. Windblown sand is abrasive and wears material away. Areas such as Monument Valley in Utah are examples of wind and sand wearing away rock.
Chemical weathering breaks down stone, cement and other materials by chemical changes. Three common ways are dissolution, hydrolysis and oxidation. Dissolution happens when water dissolves minerals. In a dissolved state, the minerals flow away with the water. This process forms limestone caves. Hydrolysis occurs when other chemicals form when water combines with a mineral. If the pH of the water changes to acid it eats away the material. Oxidation occurs when water changes a metal and weakens it by oxidation. When iron or steel gets wet, it eventually rusts. Rust takes away the mass of the metal, causing it to eventually decompose.
Manmade objects such as buildings, tombstones, statues and other materials made from cement, metal, brick and stone are subject to mechanical weathering. Windblown sand wears down sharp edges, causing statues and other objects to lose features and detail. Heat and cold cause expansion cracks that allow water to enter, freeze and expand, causing more damage. Iron or steel exposed to moisture also rust. This causes bridges, buildings and other manmade objects to deteriorate and become hazardous over time.
Erosion occurs when wind and water carry away topsoil. Plants put their roots into soil and hold it in place. This helps prevent dirt erosion. If a hillside doesn't have plants with root systems to hold the dirt in place, it is in danger of having its soil washed away. This can cause buildings to collapse as dirt washes away from the foundation. Drought contributes to erosion because dry soil is easier to blow away than moist soil. A prolonged drought was one of the causes of the Dust Bowl of the 1930s. Wind blew dust from Oklahoma to as far away as New York.