Rock glacier

Rock glaciers are debris Eisgemenge that move slowly tal- or downslope in the active state.

They consist of frozen unconsolidated material, such as scree or moraine. As the rock - ice mixture is hidden under the superficial debris of the thaw, rock glaciers are often difficult to recognize for laymen. They are considered as a typical element of the landscape of alpine permafrost ( permafrost ) and occur in many high mountain regions of the world. Optimal formation conditions for rock glaciers prevail in mountainous and mountainous areas under wintry climates a more continental climate. A lack or little snow cover thickness and long lasting strong negative temperatures lead too intense deep -reaching cooling and freezing of the substrate. Has a sufficiently thick snow cover > 80 cm formed only at the beginning of the Ablationsphase in spring, this acts as a preservative to the Bodengefrornis. Rock glaciers are therefore found in the Alps, especially in the inner-Alpine dry valleys of Engardin (eg rock glaciers MURTEL ) and the Eastern Alps (eg rock glaciers oil pit in the Kaunertal; Schober group). Far greater rock glaciers can be found in more continental climate Tien Shan mountains (Kazakhstan / Kyrgyzstan ). The geomorphological lower limit of the rock glacier is generally regarded as the lower limit of the zone of discontinuous permafrost. An exception are very fast flowing rock glaciers that can penetrate to the montane altitudinal zone.

Rock glacier types

In contrast to glaciers in the true sense rock glaciers are not superficial ice body. After the formation there are two types:

• Rock glaciers are considered typical symptoms of alpine and high mountain permafrost, is glued in the erosion debris with frozen ground water, ie a form of ground ice
• You can also arise from back -melting, debris-covered cirque glaciers, where the stone content is rampant

Depending on the degree of activity differentiates three types of rock glaciers:

• Active rock glaciers are mass movements, such as pure ice glaciers lava flow or creep up murartig flow. They typically move at 0.10 to 1 m / year.
• Inactive rock glaciers do not move, but still contain frozen material. One speaks of climatic inactivation when the rock glacier has moved in non- permafrost areas or when the ice has melted out, for example by a climate warming. Dynamic inactivity occurs when the rock glacier has moved too far away from its rubble slope, so that it is cut off from its rubble and ice dispenser.
• Fossil rock glaciers are ice-free debris deposits, because the ice has melted out by an extended stay in non- permafrost areas. With the melting water the fine-grained silt and clay fractions were flushed - that together formed with the ice the Eiszement who is responsible for the flow with / sliding of the rock glacier. A fossil rock glacier may thus also in reduction of the permafrost, the permafrost depression ( PFD), are no longer active.

Recently, two types are distinguished in the literature on the basis of the geological properties of the material of a rock glacier:

• Siliceous rock glaciers ( Pebbly rock Glacier ): They consist of typically 15-20 cm wide scree material ( pebble, gravel ') and are less than 200 meters in length, usually shorter than rocky rock glaciers. These are nourished by a mostly less than 50 meters high cliff of less resistant rock.
• Rocky rock glaciers ( bouldery rock Glacier ): They consist of larger debris material ( boulder, boulder '), which they receive from a higher, usually over 100 meters high cliff of resistenterem rock. They are regularly over 200 m long and form a steeper frontal forehead and a beaded surface in contrast to the pebbly rock glaciers from.

Structure and flow of rock glaciers

Show rock glaciers - regardless of the level of activity - similar geomorphology as other glaciers, they can make as Bodeneiskörper various size large plateau, the terrain embedded ice lenses to overlap - up tongue-shaped ice bodies on slopes and in valleys that clearly stand out from their surroundings ( tongue shape: length> width, praise shape: length < width), as well as complex shapes. The latter are at the confluence of several rock glaciers into a single tongue, when splitting a rock glacier in several tongues at rock material from different times and in different rock sources. They are typically several hundred meters long and 100-200 meters wide, but also reach lengths of several kilometers. Their thickness is usually in the range of 30-50 meters.

Usually it is a mixture of debris and ice with a volumetric ice content of an average of 40-70 %, which flows down the valley slope or - but slower than a glacier in the proper sense. Here, the characteristic of active rock glaciers frontal forehead and superficial ridges form. The forehead is a typical steep embankment from unfrozen debris layer, with a slope angle of about 40 °.

Inactive rock glaciers have a generally flatter front end and a smoother transition between front and top. The lack of movement, vegetation can up to the size of shrubs and even small trees to settle on them. Relict forms are influenced because of this status fully melted ice by irregular structures and through a collapsed top.

Many rock glaciers have a considerable age. The rocks of the near-surface layers act as insulation and protect the ice from melting off.

History of research and investigation

The exact dynamics of alpine rock glaciers has been explored for the first time in more detail in the 1970s. The corresponding investigations initiated Professor Adrian Scheidegger, who was professor of geophysics at the University of Vienna until about 1995. The German geomorphologist Professor Dietrich perch and the Swiss Professor Wilfried Haeberli Kryosphärenforscher decisively contributed to scientific knowledge about rock glaciers.

Actually, they are not the subject of Glaciology or hydrology, but the geomorphology and hydrogeology. Unlike glaciers as such they are formed in the substrate, while the latter are produced on the surface caused by the accumulation of snow.

The rock glaciers have the interest of science excites relatively late, mainly for four reasons:

• Their importance as water resources - especially in dry ( semi-arid ) regions such as the Chilean Andes, where mountain lakes and glaciers store barely larger amounts of water. At the same time they are there ( because of the climate and the specific rock erosion) very frequently and will according to the (ice) glaciers represents the second most important water resources

• Conversely, they also make a previously consider contributing to snowmelt water yield in mountain regions, and are therefore to be considered as a hydrological factor in flood modeling.

• You are climate indicators. The lowest occurrence of active rock glaciers correspond to the lower limit of permafrost in high mountains, the example in the -1 - ° C isotherm lies. Therefore, they are indicators of the present temperature conditions. Fossil rock glaciers that are (almost ) no longer contain ice, are indicator for deeper layers of permafrost and therefore colder climatic phases (see the Little Ice Age in Europe in 1850 ).

• You can download the high alpine soils to stabilize. As manifestations of permafrost replace in arid areas, the effect of vegetation - which exist, for example, in Santiago de Chile only to 3000 meters. In the Andes, the rock glaciers are often the only factors which will help the scree slopes to a certain strength. Without permafrost soils would slide faster, and it could devastating processes such as debris flows and large landslides occur and numerous high-altitude settlements threaten.

The dynamics of the movement is an interesting challenge for several geoscientific disciplines such as soil mechanics, or pedology, geodesy, geology, geophysics, hydrology and geotechnical engineering, and their modeling for geoscience computer science. You can de facto be successful only in interdisciplinary collaboration.