scree

Scree is a slope of loose, broken rock fragments that has accumulated at the base of cliffs or steep rock faces. The debris—often angular and coarse—forms a scree slope, also called talus, though some authors distinguish the terms by context.

Formation is dominated by physical weathering and gravity. Freeze-thaw cycles, thermal stress, and salt weathering break rock from cliff faces, while gravity causes the fractured material to topple and slide downslope. Continuous rockfall maintains the slope's supply of material, so scree slopes can appear constantly active at some sites.

Composition and structure: fragments range from gravel to blocks, and the surface may be dusted or bare rock. The surface angle of repose depends on particle size and moisture but is typically around 30 to 40 degrees. The slope may be sparsely vegetated by mosses or lichens in favorable climates but is usually barren where temperatures are extreme or precipitation is light.

Distribution and environment: scree occurs worldwide on mountain sides, cirques, and escarpments, particularly in alpine and periglacial zones, but also on desert cliffs where infrequent rainfall allows little vegetation. In some settings, scree shelters wildlife and provides microhabitats.

Hazards and significance: scree slopes are inherently unstable; slipping hazards for hikers and climbers are common. For geologists, they record rates of weathering and rock strength and can obscure underlying bedrock. In archaeology and paleontology, scree can preserve or conceal artifacts and remains beneath the surface deposits.