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Terrestrial sedimentary environments V - Glacial

Glacial environments

Fundamentally, glacial ice differs from water in being much more viscous, such that it carries clasts of all sizes in laminar flow. Don't forget, any given parcel of glacial ice always flows downhill, conveyoring its sediment load to its toe. The exact location of this toe varies over time as the glacier advances and retreats. The key is that any place that has been occupied by the toe of a glacier will contain glacial sediment unless some subsequent process (stream erosion, a new glacial advance, etc.) has removed it. This is true even in regions where aggradation is not widespread.

Processes of Glacial erosion:

Erosional features:

Erosional land forms that form from valley glaciers: These are what we think of as the typical features of regions like the Alps and high mountains of western North America. They may be occupied by active glaciers or may be left over when the glacier melts.

Glacial sedimentation:

Q: Do glaciers deposit sediment while they are advancing?

Such moraines remain prominent features of the landscape long after the glacier is gone but note: They only preserve the most recent glacier at a given spot. Earier remains would have been bulldozed away by newer glaciers.

Associated fresh water environments

Outwash streams reworking till into stratified drift. E.G. the source of the Matanuska river at the Matanuska glacier, AK, right)

Proglacial lakes: Lakes of meltwater impounded by moraine or glacial ice. These result in the deposition of pockets of lacustrine and associated sediments, including small deltas, laminated lake deposits and dropstones. E.G. Jöküllsárlón, Iceland, right)

Glacial deposits in the rock record:

Land forms resulting from continental glaciers: Continental scale glaciation creates interesting opportunities for ice to interact with large volumes of sediment. Results include: