valleys

Valleys are elongated low-lying areas that lie between hills, ridges, or mountains. They often host rivers or streams and serve as corridors for ecosystems, human settlement, and transportation. Valleys vary in size, shape, and formation, and can be dry for parts of the year or seasonal wetlands.

Valleys form through several geomorphic processes. River valleys develop as running water downcuts and erodes laterally, creating V-shaped cross sections and yielding floodplains and terraces. Glacial valleys are sculpted by moving ice, typically producing broad floors and steep, straight sides with a U-shaped profile. When glaciers retreat, rivers or streams may occupy the valley floor. Tectonic activity can create fault-block or rift valleys that drop between blocks of crust, often long and steep-sided. In arid regions, wind-driven erosion can also deepen and sculpt valleys and canyons.

Valleys have characteristic features such as a valley floor, banks or valley walls, tributary streams, and sometimes terraces or deltas on alluvial fans. The valley climate and soils influence vegetation and agriculture, making valleys among the most favorable areas for human settlement. They also commonly serve as routes for roads, railways, and cities.

Notable examples include the Yosemite Valley in California, a classic glacial valley; the Nile Valley and other river valleys in arid regions; and the East African Rift Valley, a major tectonic structure. The study of valleys is a central topic in geomorphology and physical geography.