Runoff and soil erosion on frozen soils in northeastern Oregon

ABSTRACT: Frozen soils, snowmelt, and rain on snow all were key factors in major soil loss events during the 1979–1980 winter at four erosion monitoring sites in north central Oregon. Snowmelt and/or frozen soils were responsible for 86 percent of the observed soil loss events. While soils were frozen at all four sites, high dewpoint temperatures, associated with the intrusion of warm, moist Pacific air masses, liberated large quantities of heat (of vaporization)at the snow-air interface. This heat accelerated snowmelt beyond that expected from sensible heat, radiation, and the heat content of rain. Heat balance calculations for a typical rain-on-snow event showed that condensation melt accounted for as much as 38 percent of total hourly melt and averaged 21 percent for the entire event. The accelerated runoff from partially thawed soil thus produced severe soil movement. Rainfall energy could not have contributed significantly to soil erosion because the raindrops fell on the snow surface throughout most events.