Prediction of Downslope Flows

What can be done to reduce the damage and human suffering inflicted by mass movements? Greater understanding of the dangers and specific triggers of mass movements can help reduce casualties from individual catastrophes, but long-term planning is needed to reduce the costs from damage to structures and infrastructure inflicted by downslope movements of all types. one approach to reducing the hazards is to produce maps that show areas that have suffered or are likely to suffer from mass movements. These maps should clearly show hazard zones and areas of greatest risk from mass movements, and what types of events may be expected in any given area. These maps should be made publicly available and used for planning communities, roads, pipelines, and other constructions. It is the responsibility of community planners and engineers to determine and account for these risks when building homes, roads, communities and other parts of the nation's infrastructure.

several factors need to be considered when making risk maps for areas prone to mass movements. First, slopes play a large role in mass movements, so anywhere there is a slope there is a potential for mass movement. In general, the steeper the slope, the greater the potential for mass movements. In addition, any undercutting or oversteepening of slopes (from coastal erosion or construction) increases the chances of downslope movements, and anything that loads the top of a slope (like a heavy building) also increases the chance of initiating a down slope flow. slopes that are in areas prone to seismic shaking are particularly susceptible to mass flows, and the hazards are increased along these slopes. slopes that are wet and have a buildup of water in the slope materials are well lubricated and exert extra pressure on the slope material, and are thus more susceptible to failure.

The underlying geology is also a strong factor that influences whether or not a slope may fail. The presence of joints, bedding planes, or other weak

Slump of former State Highway 287 into Hebgen Lake, Montana, following an earthquake, August 1959 (USGS)

nesses increases the chance of slope failure. Additionally, rocks that are soluble in water may have large open spaces and are more susceptible to slope failure.

These features need to be considered when preparing landslide-potential maps, and once a significant landslide potential is determined for an area, it should be avoided for building. If this is not possible, several engineering projects can be undertaken to reduce the risk. The slope could be engineered to remove excess water, decreasing the potential for failure. This can be accomplished through the installation of drains at the top of the slope, and/or the installation of perforated pipes into the slope that help drain the excess water from the slope material, decreasing the chance of slope failure.

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