Mechanical weathering may occur due to thermal fractioning, frost wedging, hydration shattering, exfoliation and abrasion. During mechanical weathering, external forces cause solid rock material to break into smaller sediments.
Mechanical weathering is similar to chemical weathering, and their effects sometimes overlap. Abrasion is the process in which an external force such as water movement or gravity causes rock material to grind together, which may break apart the outer layers of the affected rock. Mechanical exfoliation, or pressure release jointing, occurs when layers of rock parallel to surface ground are exposed, causing them to expand and break apart in rows.
Thermal fractioning occurs when extreme temperature changes cause the rock to expand or alter its chemical structure, which weakens the rock and breaks it apart over time. Frost wedging, also known as frost shattering, occurs when water seeps into open spaces of rock material and freezes, causing the water to expand and possibly break apart the rock's layers. Hydration shattering is similar to frost wedging and occurs when water causes certain materials in a rock such as clay to expand and break down the rock material.