The Elbrus (Fig. 2) is a stratovolcano with a double peak (west peak 5642 m and east peak 5621 m), which has not been active since the Ice Age and has been heavily glaciated since then. The main ridge of the Caucasus reaches a height of approx. 3700 m and is characterized by the characteristic features of the high alpine mountains. The highest point of the main ridge is the summit of Dongusorun (4454 m). He wears a cap of firn about 120 m thick (Fig. 3).
About 10 km in front of the main ridge, the Elbrus sits on a side ridge. The Elbrus volcanic massif forms an isolated glaciation center, which emanates from the glacier domes of the double summit and towers over its surroundings up to 2000 m like a compact highland. The Elbrus also differs from the main ridge in the composition of the rocks. On a crystalline base are u. a. in addition to basalt rocks, andesites, liparites and tuffs (Fig. 4).
In the Pleistocene (2.5 million years to 10,000 years BC) the tip of the volcanic cone was blown away during a volcanic eruption, leaving a crater. Two new volcanoes emerged on its edge, which formed today’s double peak. However, the magma had previously looked for new ways of exiting the slopes. This created side craters in the east and west. The Kjukjurtlu in the west has a wall of 480 m. More recent eruptions of the side craters occurred 25,000 to 1,500 years ago (Fig. 5). Since then the Elbrus has been “sleeping”.
The Elbrus and its glaciers
The fiery lava was only one phenomenon on Elbrus, the second phenomenon is snow and glaciers. The glaciers have been working on the Elbrus for thousands of years and up to the present day. Their activity was only partially and temporarily influenced or stopped by lava flows. The glaciated area in the Elbrus area (166 glaciers) covers 190 km².
Of this, 53 km² are covered by 7 Elbrus glaciers. These include the Großer Asau (20 km²), Irik (11 km²), Kleiner Asau (10 km²) and Terskol (8 km²) glaciers. The largest Elbrus glacier is the Dshikaugenkes (28 km²). Together with 9 other Elbrus glaciers, it drains into the Malka Valley to the west. There are a total of 29 glaciers on the Elbrus within the Elbrus area.
Among the glacier types, the Kar glaciers and the wall glaciers are the most common. But they have only a small area (up to 0.5 km²). The largest glaciated area on Elbrus is made up of the Kegelberg glaciers, which start directly at the double summit, e.g. B. the Dshikaugenkes. You will be followed by the valley glaciers. When Kegelberg glaciers merge into valley glaciers, great glacier lengths are created. The Great Asau Glacier thus reaches a length of 10.2 km. The largest pure valley glacier in the Elbrus area is the Schchelda glacier (5.6 km², 9.7 km long), which attaches to the main ridge (Figs. 7 and 8).
The surface of the glaciers in the Elbrus region is severely fissured due to deep longitudinal and transverse crevasses, glacier breaks and ice pillars (Fig. 9).
The annual precipitation of approx. 1100 mm on the Elbrus increases the snow cover by approx. 3 m. However, up to 50% of the amount of snow that has fallen is lost due to wind shifting. In other places, snow depths of up to 17 m can be piled up. The mean thickness of the snowpack varies considerably on the slopes. B. at the double summit approx. 60 cm, at 3800 meters (firn line) approx. 3 m, below that there is only a seasonal snow cover. Also the annual meltdown(Ablation) of the snowpack is differentiated. The thawing processes begin at an altitude of 4000 m and increase continuously depending on the slope position, solar radiation, slope inclination, degree of pollution of the snow and its reflectivity (albedo) until they reach approx. 2 m annually at the glacier tongue of the deepest glaciers. This happens, for example, on the Great Asau Glacier, which ends at an altitude of 2080 m.
The glaciers move only at low speed. It depends on the size of the glacier, its altitude, the location of its parts (edges, tongue) and its nature (glacier breaks). On the Elbrus, glacier movements between a few millimeters and 140 cm were measured daily. H. from a few meters to 5 km per year.
The thickness of the glaciers in the saddle of the double summit is approx. 25 m, at 5000 m at the west summit approx. 90 m, at the east summit approx. 30 m and at the firn line approx. 80 m. These are usually retained until the end of the tongue.
In the middle of the 19th century the continuing retreat of the glaciers began, which was only interrupted by brief stops and advances. Since 1889 the glaciated area of the Elbrus massif (including the side ridge) has decreased by 20% and that of the main ridge by 15% in the Elbrus area. The glaciers have receded by an average of 800 to 900 m, and a maximum of 2700 m. The decline at the Great Azau Glacier was 2450 m.