Geologically, the Alps are a relatively “young” mountain range, in that falls and slides (mountainside creep, landslides, debris flow) often occur on their steep mountainsides. Since the end of the last Ice Age 16,000 years ago, the valleys have been decisively shaped by these processes in the mountain range, and have formed the present-day landscape.
Large-scale falls and slides – for example large-scale landslides or mountain rockfall – pose a threat in the Alps which cannot be mastered by technical means. When measured against human lifespans, however, they occur very seldom.
Such mass movements, which are often connected to earthquakes or tectonic processes, have for example occurred in Austria on the Dobratsch near Villach (Carinthia), at Köfels (Tyrol) or in the Gradenbach in the upper Mölltal (Carinthia), as well as in other areas in the Alpine region.
Falls and landslides on a smaller scale, such as falls of stones and rock, landslides or debris flow occur more frequently on steep mountain slopes and often threaten settlements and traffic networks. These natural hazards can especially be found near lines of tectonic disturbance, at the foot of unstable rocky slopes, on slopes rich in springs or on geological subsoil with landslide tendencies.
Falls of stones and rock are characterized by high fall speeds and power. Depending on rock size, they can break through the walls of buildings, roofs or windows and even partly destroy buildings.
Steel nets offer effective protection against rockfall by slowing down the speed of fall before the endangered area and catching the rocks. The falling rocks are deposited at embankments and rockfall control grounds. Anchorage or support structures can prevent falls of loose rock masses.
Slides usually occur in connection with fine-grain loose stones, where the ground is saturated with water or through subterranean sliding horizons (geological layers that tend to slip due to their physical structure).
Buildings standing on sliding subsoil are exposed to powerful traction and pressure forces. The results are cracks or even the collapse of portions of buildings, and usually the occurrence of large-scale deposits of earth and rock masses.
Protection measures against landslides are designed according to type of movement and the depth of the sliding horizon. Technical preventive measures are usually stakes or anchorage constructions, drainage or support structures.
The causes of many landslides, however, lie so deep that they either cannot be stabilized or else stabilize only very slowly after slope drainage. We have at our disposal methods from modern metering technology (e.g. movement sensors) for investigating landslides and keeping movements on mountainside under observation
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