Fluvioglacial sediment

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Internal structure of an Os ( Badelundaåsen ) near the Swedish Anundshög (Badelunda)

Fluvioglacial sediments or glacifluvial sediments are a subgroup of fluvial sediments that owe their formation to the interaction of glaciers and their meltwater .

On its way to the glacier front, the ice scrapes or tears larger and smaller rock particles out of the subsoil (“plucking erosion”) and carries them with it. From the glacier front, the meltwater transports the fine and finest-grained material ( glacier milk ) down the slope and deposits it in the foreland in the form of extensive sand areas . Sometimes the sand blocks separate dead ice blocks from the rest of the glacier, which after melting turn into typical hollows or mountain lakes.

Within the fluvioglacial sediments dominate those parts that formed during the cold ages (glacials) of the Quaternary Ice Age in the Pleistocene . The material from their sand was later transported to the main valleys, where today it can form hundreds of meters thick valley fillings (in the Eastern Alps e.g. Inn or Drautal) and occasionally it was also eroded into river terraces . The material of the alluvial cones , which were pushed into the valleys by water-rich streams, is also largely of glacifluvial origin . The climatic and development phases can be reconstructed from the grain sizes of the bed load and sand.

Fine-grained components of the fluvio-glacial sediments can later have been transported again by wind , which resulted in thick layers of fly loess in the periglacial area during the “Ice Age” .

The actual glacial sediments are to be distinguished from the fluvio- glacial sediments , which mainly appear in the form of moraines (lateral, central and terminal moraines ) and consist largely of marl boulder ; the occasional boulders that remain are called boulders .

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