Volcanic Fallout . Soil failure . Violence and Terrorism . Vector-Borne Diseases . Nuclear Attack .
Floods constitute one of the most destructive natural hazards facing Montana.
Flooding occurs when abnormally high streamflow overtops the natural or artificial banks of a water course. This type of flood occurs in river systems whose tributaries may drain large geographic areas and include many independent river basins. The duration of riverine floods may vary from a few hours to many days. Factors which directly affect the amount of flood runoff include precipitation amount, intensity and distribution, the amount of soil moisture, seasonal variation in vegetation, snow depth and water-resistance of the surface due to urbanization. In contrast to riverine flooding, this type of flood usually results from a torrential rain on a relatively small drainage area.