Management of mass movements : Managing landslide hazards
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Management of mass movements Managing landslide hazards 1. Modifying the event Slope stability can be increased by a variety of engineering techniques, which although expensive, enable control of land sliding to be largely successful. There are 2 key issues with this approach to landslide hazard management: cost and responsibility. Government funding may be available for emergency stabilization. However, building codes can enforce some user if these techniques by private developers. 2. Modify vulnerability Most mass movements are not very rapid and thus forecasting, warning and evacuation are possible techniques. Community preparedness can be used if people are aware of the early signs of mass movement such as bulging walls, tension cracks, tilted poles and fences and new areas of waterlogged ground. Hazard mapping is increasingly being used especially in MEDC's, as the factors that favour land sliding can be assessed to produce a hazard map.
There are 3 main forms of snow avalanche with different characteristics of slope failure, flow and occurrence - loose snow, slab and slush. Slab avalanches are the most dangerous since large masses of snow are involved. Snow builds up in layers following each snowfall event. Initially the density is low, but as snow continues to be added the density in the lower layers increases as air is squeezed out to form firn. However, in some snow packs the snow becomes less dense in places as ice and snow crystal grow and the voids between them are enlarged. This forms a weak layer in the snow called a depth hoar. Thawing and freezing between different snowfalls produces boundaries which act as weaknesses within the snow pack.
What techniques are used for modifying the hazard event? Avalanches can be managed through artificial avalanche creation. By creating a series of smaller avalanches at safe times, the hazard can be controlled as the snow pack is removed. This approach is expensive and uses explosives and military weapons. Modifying the vulnerability Warning systems are common for avalanche hazards and nearly 30 countries have systems in operation, which use both forecasts and prediction. Forecasts are used for day-to-day management of winter sports area, whereas predictions are used for hazard land zoning. Forecasting is not precise but involves regular snow stability tests and meteorological data. Avalanches triggers by storms are the easiest to forecast but snow pack changes are more difficult. In Switzerland avalanche hazard maps have existed since 1878. Three zones are used: high potential hazard, moderate, and no hazard. These are based on topographic maps, field observation, long term records, and run out distance. This approach needs much financial and time investment.
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