The physical landscape on which human societies develop is not permanent. Mountains rise and erode, coastlines advance or retreat, rivers change their courses, and valleys, slopes, wetlands, and plains evolve through geological and climatic processes. Some transformations occur over millions of years, while others can alter the conditions of human settlement within decades or even within a single event. Earthquakes can elevate or lower sections of land, landslides can reshape entire hillsides, volcanic activity can create new terrain, and changing rainfall patterns can accelerate erosion and alter river systems. Rising sea levels, coastal erosion, drought, and extreme precipitation can further transform the environments in which people live and work.