Fluvioglaziale Sedimente EarthCache

Fluvioglacial (or glaciofluvial) sediments

Fluvioglacial sediments or glacifluvial sediments are a subgroup of fluvial sediments (deposited by rivers) that owe their formation to the interaction of glaciers and their meltwater. In general, sediments (moraines) deposited by glaciers are characterized (and distinguished from fluvial sediments) by the fact that the grain size of the deposited gravel and sand varies and does not reveal any uniformity. In addition, glacial deposits, i.e. deposits caused by a glacier, are far less rounded than fluvial sediments (deposited by streams or rivers) and, due to the shorter transport distance, are somewhat rounded, but far more angular than fluvial sediments.

Fluvioglacial sediments (deposits) are created by the abrasion of glaciers and the further transport of sediments (sand, rubble...) by meltwater rivers leaving the glacier. On its way to the glacier front, the ice scrapes or tears larger and smaller rock particles from the subsoil and carries them with it. From the glacier front (the end of the glacier), the meltwaer transports the eroded material downslope and deposits it in the glacier foreland.

Fluvioglacial landforms of the glacial series

Sanders

Sanders are alluvial fan-like, wide, gently sloping embarkments that were formed in front of the ice edge of an ice sheet or glacier. Sanders usually consist of sand and gravel. A typical part of the glacial series, they arise when glacial melt streams cut through the terminal moraine and widen as a river in the plain behind. As a result, the melt stream loses speed and the material it carries is deposited as fluvioglacial sediment. Basically, material is sorted in which the coarser parts are deposited near the edge of the ice and the smaller grain sizes are deposited up to the edge of the alluvial fan. Sanders usually consist of sand and gravel and form infertile soils that are colonized by pioneer plants such as pine trees.

Oser

Oser are wall-like, often curved fluvioglacial meltwater deposits that were sedimented in deep ice crevices in or under the ice. Oser usually consist of layered gravel and sand, which rises like a railway embarkment over the relief of the flat ground moraine landscape after the ice has melted. With a maximum height of 30 meters, they can range from a few to several hundred kilometers long. Oser differ from terminal moraines in their composition: terminal moraines, which were transported by glacial ice, show unsorted sediments of various grain sizes. In flowing water, where sediments of what size settle depends on the flow speed - in Osers, as fluvioglacial deposits, there is therefore a clear sorting and layering of the sediments.

Kames

Kames are elevations within glacial embankment landscapes that were created by the deposition of ice and its meltwater on the edge of the ice against an abutment, such as a dead ice block, boulder or slope. The meltwater rivers piled up sand and gravel, but also very fine-grained sand and silt from ice reservoirs, against the abutment. Typical for Kames are layers or lenses of fine sandy and silty material embedded in the gravel deposits, which can show a completely different resistance to erosion compared to the gravel layers, making the stratification even more noticeable. Kames are small forms of the glacial series and are typical part of the ground moraine landscape. In contrast to Osers, Kames do not have a wall-like shape, but rather an irregular or rounded back or crest shape. Their height ranges from a few to a few dozen meters. In fluvioglacial sediments (such as Kames), faults also occur again and again, these are shifts of individual sediment packages due to landslides, where the interruption or displacement of the layers can be clearly seen.

The situation on site

At the coordinates of the Earthcache you can find a rock outcrop that was apparently exposed during the construction of a forest road a long time ago, so the outcrop has been exposed to the effects of wind and weather for a long time. For this reason, the composition of the deposits can be viewed here, but the influence of weathering on the different layers of the outcrop can also be compared very well.

Your tasks to log the Earthcache:

Answer the following questions via my account via message:

1.) Describe in your own words what you can see on site! How can you tell that this outcrop is fluvioglacial sediment?
2.) Take a closer look at the layers and describe the differences (grain size, storage horizon, resistance to erosion...)!
3.) Which fluvioglacial landform do you think is most likely to be the case locally?
4.) What special situation can you observe at stage 2?
5.) Optional: Add a photo of yourself/your GPS on site to your log!


After you have sent me the answers via message, you can log, you do not need to wait for log permission. If something is wrong, I will contact you via message.

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