What Are the Four Causes of Mechanical Weathering? By Wayne Shirey; Updated April 24, 2017 The process of weathering breaks down rocks exposed to the elements into smaller particles that can be carried away by wind and water erosion. Weathering is divided into three broad categories: mechanical or physical weathering, chemical weathering, and biological weathering. Mechanical or physical weathering is further divided by its causes into four different categories; the causes are mechanical exfoliation or unloading, thermal expansion, frost wedging, and abrasion.