Natural geographic processes

Processes in nature run under internal (endogenic: volcanism, earthquakes, tectonic movement) and external (exogenic) forces. Exogenic forces are solar heat, gravity, surface and underground water, wind and organisms. They produce weathering (physical, chemical, organic), erosion (washing away by running water; areal and linear), abrasion (wearing by waves), deflation (wind removal and transport), mudflows, landslides, karst and avalanches. A mudflow is a fast stream of stones and mud in mountain valleys after heavy rain. Karst makes cavities in soluble rocks (limestone, gypsum, salt). Anthropogenic factors strengthen these processes: wrong irrigation causes irrigation erosion and salinisation, mining causes landslides and subsidence, and taking too much water, as the Aral Sea shrank, exposes a dry bed from which salt and dust are blown. Special rules and instructions apply to building in places where such processes are common.