4. Debris-Covered Glaciers

Debris-covered glaciers are characterised by a mantle of rock material, the supraglacial debris, spread over part of the ablation zone. The debris material origins from the catchment above and the bedrock below the glacier and appears at the glacier surface in the ablation zone. It often forms medial moraines in the upper areas which increase down glacier until the glacier is covered across its full width. Debris-covered glaciers are located in all high relief areas around the world, but quantitative information on global scale does not exist. A debris cover affects the ablation of the subjacent glacier ice by increasing it below thin covers and protecting the ice below thicker ones. The critical debris thickness is usually a few centimetres. The surface morphology of debris-covered glaciers can be hilly and ruptured by supraglacial lakes and ice cliffs, which play an important role in glacier mass balance as they are regions of significantly enhanced ice melt. The glacier snouts of debris-covered glaciers are often very slow or stagnant, and the terminus positions are stable over long periods. In this case, only small amounts of debris are transported from the glacial into the proglacial system. It is still a matter of discussion, if debris covers protect glaciers from mass loss due to climate change. They are important sediment sources and are deposited as very large lateral moraines, as lateral–frontal moraines or, after glacier wastage, as supraglacial melt-out. Additionally, a thick debris cover can serve as habitat for animate beings.