Lahars

The name lahar is Indonesian for volcanic breccia transported by water (van Bemmelen, 1949, p. 191) but has come to be synonymous in geological literature with volcanic debris flow, a mass of flowing volcanic debris intimately mixed with water. The term lahar refers both to the flowing debris-water mixture, and also to the deposit thus formed. A classic review of the various origins of lahars is that of Anderson (1933). A more recent discussion of lahar deposits by Parsons (1969) is included in a review of volcanic breccias. Crandell (1971) gives an account of the origin and characteristics of post-glacial lahars from the slopes of Mount Rainier volcano (Washington), and Neall (1976) has prepared a bibliography of their global occurrences. The recent eruptive phases of Mount St. Helens (Washington) produced lahars in a variety of ways (Christiansen, 1980; Janda et al., 1980; Janda et al., 1981; Harrison and Fritz, 1982) but investigations of these have not been completed to date.