Weathering and Erosion

Weathering attacks rock in two different ways. Physical weathering breaks rock into smaller pieces without changing what it's made of: frost wedging is the classic case, where water seeps into a crack, freezes, and expands by roughly 9 percent. That expansion pushes outward with enough force to split rock that a hammer blow would barely dent, because the ice is pushing from inside every crack at once, not striking one spot. Chemical weathering instead changes the rock's composition. Rainwater picks up dissolved carbon dioxide and turns slightly acidic, and that acid dissolves certain minerals outright. Limestone is the textbook example: it reacts with acidic water and slowly dissolves, so a limestone statue in a humid climate erodes much faster than one in a desert, where there's little water to react with and chemical attack stalls.

Weathering and erosion get confused constantly, but they're separate steps. Weathering breaks rock down in place. Erosion is the transport that follows: wind, flowing water, ice, or gravity picking up those broken fragments and carrying them somewhere else. A boulder can weather for centuries without eroding an inch if nothing moves the debris away.

Surface area controls how fast weathering works, because both frost wedging and chemical attack only happen where rock is exposed. Slice a block into smaller cubes and the total surface area climbs even though the total volume stays the same, giving water and acid far more contact area to work on. That's why heavily fractured or jointed rock weathers much faster than a single massive boulder, and it links weathering directly to soil formation and sediment supply, the next stage in the rock cycle.