Maps of Geomorphology and Natural Hazards of Grindelwald, Switzerland: Scale 1:10,000^∗, ^†

Abstract

This paper discusses the problems of natural hazard mapping in mountainous regions through the example of actual production of two types of map: a basic geomorphological map, and a map of combined natural hazards derived from the former. The hazards considered are those associated with mass movements on or below the surface and include snow- and ice-avalanches, landslides, rockfalls, icefalls, torrents, and floods. The mapping scale is 1:10,000 and the area chosen for study was the environs of Grindelwald, 60 km southeast of Bern, Switzerland.

The mapping was based upon extensive fieldwork combined with airphotograph interpretation. To emphasize the practical concerns of the land-use planner, the traditional approach to geomorphological mapping was substantially modified. Thus, special attention was given to those processes and associated forms of surface instability that constitute a danger or obstacle to man and his effects. Prominent amongst these in the Grindelwald vicinity are landslides, torrents and avalanches.

Since the aim of the mapping was to provide a practical basis for land-use decision-making, only strictly objective scientific criteria have been employed. More than 4000 unit areas with estimated hazard ratings were demarcated, using the geomorphological map, topographic and geologic maps, and stereoscopic air photography. These demarcations' were then further checked by additional fieldwork. Field indications of former and actual movements provided the principal means of assessing the degree of current danger, using the stumme Zeugen of Aulitzky (1973). In some instances simple calculations have been used; for the avalanche hazards, however, technical calculations were made by the Avalanche Service of the Forestry Office. To ensure a high degree of objectivity, check lists and test systems have been developed. Degrees of hazard are represented by different colors ranging from red (maximum danger) to white (no danger). Letters identifying the specific hazard involved are superimposed on the color. On the 1:10,000 mapping scale many practical problems arose and these are discussed at length in the text.

The final hazard map shows that the upper slopes of the Grindelwald basin are most prone to avalanche, icefall, and rockfall activity; the area between the eastern part of the village and Grosse Scheidegg and the area south of Wärgistalbach (torrent under the Eiger north wall) experience serious problems from landsliding; the lower sections of the basin are threatened by floods from glacial lakes, while part of this area is also endangered by torrent activity. The work demonstrates that applied geomorphological mapping can produce an effective basis for rational land-use planning.