Glacial morphology

The Glazialmorphologie describes and explains the structure and the formation of surface shapes by glacial arise and the melting water.

etymology

Glacial morphology is a word hybrid, it is a combination of words of both Greek and Latin origin. "Glacial" is derived from the Latin word "glacies" and means ice, metonymically often brittleness or hardness. “-Morphology” is again of Greek origin: “-morph-” comes from the Greek μορφή, morphé = shape or form, “-logos” from λόγος, lógos = word, doctrine, reason.

The word as a whole thus means the "doctrine of the ice forms", which means the glaciers and other ice deposits and their geophysical traces.

Construction of glaciers

Glaciers basically consist of a nutrient area (= accumulation area ) and a depletion area (= ablation area ), the former being at altitudes where more snow falls than thaws or sublimates . The glacier merges below the snow or firn line into the Zehrgebiet, where more ice melts than is created (= ablation).

Glacier surfaces are usually torn apart by numerous crevices that are created by the movement of the glacier, which in turn is made possible by regulation . Cross crevices are found where the glacier flows over obstacles such as boulders that are buried under the ice or when the subsurface becomes steeper, the glacier ice then flows faster on the surface and tears up. Edge crevices are found where the glacier flows faster in the center than at the edge and so the ice tears open there, similar to the water turbulence that occurs in rivers at the edge. Edge fissures, on the other hand, arise when the glacier ice melts more intensely due to the heating of the surrounding rock on the edge of the glacier. Longitudinal crevices are usually located on the face of the glacier, in the area of the glacier tongue, where it becomes wider and the ice has more space to spread to the left and right and thus fan out.

Moraines

Glacier tracks

The entirety of the material transported by a glacier is called a moraine . As a solid body, glaciers can transport all grain sizes , from clay to sand to large blocks ( boulders ). Furthermore, glacier ice can absorb a lot of material, so that the transport capacity is also very high. In contrast to the deposits of the water, the rock materials in moraines are unsorted and mostly not stratified.

The term moraine is used today in various contexts.

On the one hand, this describes the material that an active glacier is currently transporting. Depending on the location in or on the glacier, a distinction is made between upper, inner, lateral, central, lower or frontal moraines. This material is still in motion. While all types of moraines can occur in valley glaciers and related glacier types, glaciers related to the ice sheet usually only have sub-moraines. The other types of moraines are mostly formed by falling rocks from towering valley flanks. The material then remains on the glacier or can be worked into the glacier by the flow of ice.
On the other hand, sediments and forms that are deposited by the glacier and therefore no longer move are called moraine. If you can still see where they were transported compared to the glacier, the same terms are used for valley glaciers as for active moraines.
The terms ground moraine and terminal moraine are mostly only applied to the corresponding forms today. The sediment of the ground moraine, however, is as glacial till or & Till.

Moraine species

Lateral moraines already accompany the glacier in the upper part of a trough valley . He deposits the rock falling on him to the side and pushes it down into the valley. The rubble is arranged in waves that flank the flowing ice. At the confluence of glacier tongues ( confluence ), the lateral moraines on the inner edge are united to form the central moraine . It separates the ice flows from the different areas of origin and remains as a rubble wall in the glacier. While the flowing waters mix very quickly in a river, the glacier ice flows side by side in the so-called composite glaciers.

The terminal moraine (= frontal moraine) is a rubble wall at the end of the glacier, semicircular surrounding the glacier tongue. However, the prerequisite for the formation of such a moraine is that the glacier must stay in the same place for a long time, that it be stationary. If the glacier pushes forward again and again, the terminal moraine is compressed and pushed together (compression moraine). The slope facing the glacier is steeper here than the outside of the moraine wall.

If a glacier melts, several moraine walls can arise if longer holding phases are activated. Terminal moraines act like dams (they are often up to 200 m high), many lakes in the foothills of the Alps and the Alps were created together with the erosive force of the glaciers because the basins were filled with water.

The sub moraine ( ground moraine ) is found on the underside of a glacier stream, where a lot of rock material is transported. The debris comes from the surface of the glacier, where it gradually sinks to the bottom of the ice flow or directly from the material that the glacier carved out of the underground. The rock pieces of the ground moraine are more intensely rounded than those from other moraine, the proportion of fine grain sizes is also higher, but there are also large boulders ( boulders ).

Deposits and forms of meltwater

The shapes and deposits of meltwater (technical term: glazifluvial) are not referred to as moraines.

Melt water forms systems of channels, gullies and shafts under the ice in the glacier, it combines at the bottom of the glacier and then reappears at the glacier gate. It is usually mixed with rock flour so that it has a white to gray color, which is why it is called glacier milk. Apart from melting, the glacier can also lose substance by breaking off chunks of ice; this happens when the glacier empties into a lake or the sea. This process is called “calving” .

See also: Glacial Series , Firn , Os , Kame , Drumlin