Snowmelt and slush torrents - Preliminary report from a field campaign in Karkevagge, Swedish Lappland

In May and June 1995, the snowmelt period in general and the release conditions of slush torrents in particular were studied within a joint Swiss-German project during a field campaign in Karkevagge, Swedish Lappland. Measurements and observations comprised all energy balance components and meteorological conditions in the course of the snowmelt period, as well as intra- and subnival meltwater flows and the formation of a saturation zone within the snow cover during the initial period of snowmelt-runoff. In addition, release and movement of a high magnitude-low frequency slush torrent was documented on video and photographs, The results verify that the initiation of slush streams is confined to meltwater accumulation areas in drainage basins. Moreover, it can be demonstrated that both variants of slush streams are released by a hydraulic pressure gradient that is evolving from an inclined water table within the saturated snow cover. This release mechanism allows the initiation of major events without any external triggering. Neither permafrost nor extreme meteorological conditions are prerequisite to slush torrents.