protalus rampart

Talus, or scree, is the broken rock lying at an angle of repose at the foot of a cliff or fracturing wall. This angular debris dislodges from rimrock or the face of a headwall through frost-weathering, exfoliation, or chip-spalling under impact. When this broken rock slides across the surface of a glacier or perennial snow patch at the base of the wall before coming to rest, it is known more specifically as pro-talus. Protalus ramparts are prominent mounds and ridges formed where these stones collect on or beyond the ice or snow. Accumulating in a line parallel to the headwall, they resemble moraines. Cirque walls on many a mountain in the West, having been scooped out by alpine glaciers, generate protalus ramparts, especially in winter when their basal tarns are frozen. Though forbidding, these ramparts and the rockslides that spawn them support a specialized fauna, including pikas, marmots, and arctic alpine butterflies perfectly cryptic against rock and lichen.

Robert Michael Pyle