Ministry of Environment Terrain

Assessment of Geomorphological Hazards

Geomorphological hazards are naturally occurring processes and conditions that present a risk to life and property. Hazards portrayed on terrain maps result from gravity-induced downslope movement of materials, and processes involving water and wind. They range from catastrophic and dramatic effects, such as avalanches and rockslides, to barely perceptible but persistent processes such as slow earthflows. Geomorphological hazards resulting from earthquake and volcanic activity are not identified.

A Geomorphological hazards map can be derived from a terrain map by identifying and coding, usually by colour, areas that may be vulnerable to the various types of hazardous processes. The following table provides a key for the identification of hazard-prone terrain units.

Terrain Units That May be Affected by Geomorphological Hazards

* * any texture may be shown; any surface expression may be shown

* commas are used to separate alternative symbols. e.g. a,r means that either 'a' or 'r' or both may appear in the terrain unit symbol.

Geomorphological process symbols that indicate geomorphological hazards

Note: These symbols may appear in any terrain unit symbol.

Potential users should be aware that a geomorphological hazards map produced by this process has certain limitations. It indicates only those types of geomorphological processes that may be active under present-day conditions. It provides no information about the intensity, frequency, or time of occurrence of any process, nor does it permit areas to be rated with regard to high-medium-low hazard potential. The identification of two or more processes within a unit does not indicate that the area is potentially more hazardous than a unit modified by only one process. The potential hazards implied on the map may not affect the whole unit; the map merely indicates that a certain geomorphological hazard may exist within a designated area.

The hazards map is a derivative map and is no more accurate than the original terrain map. Since most terrain maps are prepared from air photo interpretation supplemented by limited ground checking, both terrain and hazards maps should be used only to indicate the general condition of the land surface over large areas. Detailed ground investigations will be necessary for assessment of small areas and specific sites.

Geomorphological hazards maps should be used for regional planning purposes. They can be applied to the delimitation of potential development areas, selection of corridors for roads, and preliminary identification of town or industrial sites. An example of a colour- coded geomorphological hazards map is shown below. The table on page 14 is the map legend. Areas undergoing modification by two or more processes are identified by a different colour hatching.