Mountain rescue refers to search and rescue activities that occur in a mountainous environment, although the term is sometimes also used to apply to search and rescue in other wilderness environments. This tends to include mountains with technical rope access issues, snow, avalanches, ice, crevasses, glaciers, alpine environments and high altitudes. The difficult and remote nature of the terrain in which mountain rescue often occurs has resulted in the development of a number of specific pieces of equipment and techniques. Helicopters are often used to quickly extract casualties, and search dogs may be used to locate them.