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Show Nature Monument protected by the state On February 15, 1928, this rock boulder, weighing approximately 200t, was lifted from the stream bed by the pressure force of the descending " Wanglaui" and thrown to its present location. The boulder was carried over a distance of 46m at an altitude difference up-slope of about 5m. Such avalanche relics are preserved indefinitely and bear witness to the large forces associated with avalanches. Ground avalanches generally carry with them a lot of dirt, stones and vegetation which is preserved long after the snow has melted. A classic example from Engelberger Valley shows how the air blast and parts of large powder snow avalanches have an effect over long distances. From the area of the Wendenjoch and the Firnalpli glacier, the Firnalpli avalanche plunges down into the valley of the Engelbergeraa. The starting zone of this avalanche is large and measures about 150 hectares. The track is 2500m long, but slopes only 47% in the middle. The mountain pasture, Herrenruti, is located opposite the avalanche slope on the other side of the valley. Above, it is bordered by the forested area of the Spicherrain at the foot of the Furrenhohfluh. Within the last few years, the dust avalanche has repeatedly crossed the 560m wide valley and uprooted entire patches of forest on the opposite slopes. It even crossed the trench of the Aawasser, which is located in between the valley slopes and is 50m deeper than the destroyed forest areas. Strangely enough, buildings that were also situated in between escaped damage, but the avalanche coated the walls facing it with a hard layer of compacted snowdust. Through the years, avalanches have selectively uprooted mostly stands of spruce, but left standing deciduous trees, such as maple, ash, and beech which, defoliated, offer less exposed surface area. It was mentioned in Chapter I that since 1955 a renewed effort has been made to compile a Swiss avalanche cadaster. All observations made dealing with avalanches should be recorded in this register. Avalanche slopes and avalanche areas in general should be marked on zoning maps that are drawn to scales of 1: 50' 000 to 1: 10* 000. A thorough description of every important avalanche should be attached. Such descriptions can be supplemented by sketches and photos. The quality of the register is dependent on the availability of topographic plans, and on the ability of researchers and local observers. Its usefulness for avalanche zone planning will therefore vary. One must be aware that in many cases, the register does not include 13 |