Crevasse

A crevasse is a slit-like opening in the glacier surface, which could pose a risk for high alpine touring skiers, especially when covered with snow, if it is not visible. Visible columns, however, are usually only on aperen glaciers seasonally, have no more snow edition.

Formation of crevasses

Crevasses occur when the steady flow of ice is disturbed. Reasons for this may include:

• Rock outcrops under the ice
• Different gradient of the subsurface
• Confluence of several glaciers
• Different flow rates within the glacier.

Types of crevasses

Cross columns ( perpendicular to flow ) occur there, where the bedrock is a gradient bend and the glacier at the steeper slope is suddenly faster. The brittle top layer can not compensate for the voltage and rips open.

Longitudinal columns - also called radial columns - corresponding to the extension of the glacier space available. Marginal gaps (not to be confused with Randkluft and bergschrund ) usually run obliquely upwards towards the center of the glacier and form preferentially in the zones where occur transversely to the ice movement speed differences - for instance at the glacier margins, the slower advance as the centerpiece. So sometimes, a proper grating of columns arise if the fractures extend not only across the glacier but also parallel to its direction of flow. Most pronounced, this phenomenon is in the so-called seracs. These come about by the intersection of various crevasses that arise and the ice in huge blocks, called seracs divide, due to steep terrain Knicks.

Crevasses as alpine danger

If the glacier aper, ie free of snow and glacier ice visible, there is generally no risk because the columns are exposed and visible columns edges are usually resilient. One can therefore attempt such columns readily to skip or bypass. Dangerous are the columns that are superficially covered with snow. This is true both for old and for new snow. If crud on the column, the risk is mainly due to the daily temperature and thus the strength of the snow together. In the afternoon the risk of falling columns is therefore significantly greater than in the morning in most cases. Snow, however, is independent of its temperature unstable and therefore dangerous. If the snow had fallen in the wind, even small amounts of snow may have already blown over smaller columns. The completely snow -covered column is rarely seen from the fact that the glacier is easily absorbed here. Only after fresh snow fall cases heavy snowfalls across columns occasionally a dell shaped. Altschneedecken deep over columns often for weeks only imperceptibly, as mostly only their top 10 - 20 cm in the midday sun soften while the old snow beneath usually remains stable. Risk passes but not only by invisible columns. It is also where, although the column is recognizable as such, but not their full extent. If the column edge snowy, it is often not clear whether the snow cover with the column terminates in the ice, or if it hangs over the edge columns and the column in truth is much broader than the narrow slot can be seen in the snow. The same risk is also with respect to the length of the column. Pulls out of the visible crack in the snow about 50 m, the crack can be as long in the ice beneath the snow easily double. Here the climbers can break so even if he thinks to bypass the column. The best protection against falls columns provide general precautions, especially a plant of the track by the lowering of the glacier instead of his bulges, since there most likely columns tear, also a return to the snow-free area before noon. Must be a crevasse zone be crossed at noon or after fresh snow often remains only probing by screwing piercing the Eispickelsschafts in the snow. However, the length of the pickle is not sufficient in general to be the stability of the snow cover securely. With snowshoes and even with ski the risk of Einbrechens is because of towards the simple shoe increased load distribution significantly lower - but of course, especially in fresh snow, not eliminated it.

Commission of glaciers and crevasses

The fall in a column can be fatal under certain circumstances depending on the shape and depth of the column. Almost as unfortunate it is when the column down V- shape and has the anamorphosis clamps down due to its case energy. In this case, there is a danger of freezing due to lack of movement and possibility of direct contact with the ice. Often, however, the fall ends up in the column drooping snow accumulations or structures made of icicles on which the Toppled endure unharmed, at best, or even try getting out climbing out of the column. It is illusory to want to call the other hand, because of the almost always at low signal strength with a mobile phone help.

The correct behavior on glaciers:

• The fall into a crevasse can pose a deadly threat, so glacier may only be committed with appropriate Alpine tour equipment and roped. Rope teams should consist of at least three persons who consistently comply with the commission of a 10- meter distance, the rope must always be performed taut.
• Exceptions are usually made ​​in practice when ski mountaineering, when the glacier flat and mainly has a sound blanket of snow - especially in the morning when the snow is frozen hard. In rift zones without ski and in the summer season, however, should be necessarily always roped.
• Every climber should carry a complete Alpine tour equipment, consisting among other things of climbing rope, harness, crampons and ice axes and master the technique of crevasse rescue.
• The crevasse rescue is usually done either by self-rescue using ascenders or Prusik (terminal ) node or by foreign rescue with a simple block and tackle by the fallen man a free sling is let down for latching. If the group is not able to pull the fallen one, this can possibly save the so-called Munchausen technology itself.
• In two and three rope teams is recommended that development braking knot in the rope. If the rope cuts into the column border, is the fall - depending on snow conditions - slowed or stopped eventually.
• On uneven glaciers, the track should never lead you over the hump, but always possible to follow the hollows, as the column formation is lower here.
• Extend the columns parallel to each other, the rope team should at a right angle to move to exclude the overthrow another climbing partner in the column.
• A timely return of the snow region before lunch is advisable because are no longer viable due to the high sun snow bridges by melting, the same danger exists after balmy nights, which generally have an overcast sky.

• Crevasses in the Pitztal