The weathering process produces chemical or physical decay of exposed rocks on the earth's surface. The quantity of rain, degree of temperature change and length of exposure to the elements determine the rate of weathering and decay.
According to Eastern Illinois University, mechanical weathering that causes rocks to crumble includes freezing and thawing processes --- frost wedging (frozen water expands) and exfoliation (sheets of exposed rockfall away) --- and the sandblasting effects of abrasion by wind.
Chemical weathering occurs as a result of a rock's mineral's reacting with outdoor triggers such as water and air. Air oxidises the rock's minerals, and water turns them to a clay consistency or dissolves them altogether.
Water (Frozen and Flowing)
Water reacts with minerals in the rocks by hydrating them and causing the rock integrity to break down. The expansion of water in cold weather (ice expands in cracks and weakened areas of the rock) and contracting in hot weather further breaks down the rock's integrity.
In regions with wide daily temperature ranges (e.g., deserts), with cold or freezing temperatures contracting rock at night and high temps causing thermal expansion during the day, the weathering process proves quite powerful. Rocks in hotter regions (deserts, equator, temperate regions) weather more quickly than those in colder regions.