moräne

Moräne, or moraine, is an accumulation of unconsolidated glacial debris, or till, transported and deposited by a glacier or ice sheet. Moräne form at the margins or under the surface of a glacier and record its former extent and dynamics. The debris consists of clay to boulder-sized rocks, largely unsorted, and is typically derived from bedrock and surface material scraped by the ice.

Types of moräne include terminal moraines, which mark the furthest advance of a glacier and form a ridge at its snout; recessional moraines, a series of ridges indicating pauses in retreat; lateral moräne, which run along the sides of a glacier from debris falling from valley walls; ground moräne, consisting of till deposited beneath the glacier; and medial moräne, forming when two glaciers merge and a central debris ridge remains along the combined ice.

Formation and deposition occur as glaciers advance and accumulate material at their terminus and sides; during retreat, meltwater streams can rework and re-deposit some material, but much of the debris remains as ridges or sheets when the ice withdraws. The texture is typically unsorted, with a mix of clay, silt, sand, gravel, and boulders.

Moraine landscapes are common in formerly glaciated regions and provide clues to past glacier size and behavior, aiding paleoclimatic reconstructions. Dating methods include stratigraphy, radiocarbon dating of organic layers, luminescence dating of sediments, and relative dating through soil development and surrounding features.