screes

Scree, also called screes in plural, refers to slopes covered with loose angular rock fragments that have fallen from higher cliffs or steep rock faces. The debris ranges from gravel-sized particles to boulders and typically forms a sloping apron at the base of a cliff or along a mountain side, valley wall, or glacier margin. The material is usually poorly sorted and experiences little soil development.

Scree forms through rockfall and weathering processes. Freeze–thaw cycles propagate cracks, leading to breakup of rock; thermal expansion, joint widening, exfoliation, and moisture contribute to fragmentation. Gravity then moves the loosened blocks downslope, accumulating as talus or scree. In places where glaciers once stood, scree can be inherited from deglaciation, or formed by rockfall after glacier retreat.

Scree slopes are often cone- or ramp-shaped, with a steeper proximal zone near the source and a gentler distal slope. Movement on scree is typically slow (soil creep) with occasional sudden rockfalls that reactivate the deposit. Drainage is often stepped and unstable, and vegetation is sparse, though mosses and lichens may colonize larger fragments.

In field work, scree is used to describe both the material at the base of cliffs and the slope made of loose debris on exposed hillsides. Note that some geologists distinguish talus (the mound at the cliff base) from scree (more general hillside debris), though usage overlaps.