Overland Erosion due to FreezeThaw Cycling
LAWRENCE W. GATTO AND MICHAEL G. FERRICK
Soil is naturally eroded by water flowing down the surface of bare or par-
tially vegetated hill slopes. The quantities and rates of erosion depend on the
transport capacity of the runoff and the resistance of soil particles to detachment.
In turn, the capacity of runoff to transport soil particles is a function of velocity
and turbulence, and the detachability of soil particles is a function of inter-
The capability of a soil to resist erosion depends on soil-particle size and
distribution, soil structure and structural stability, soil permeability, water
content, organic matter content, and mineral and chemical constituents (Lal and
Elliot 1994). Also, Pall et al. (1982) proposed soil erodibility as a time varying
rather than static characteristic because of significant seasonal soil density and
soil moisture changes. Many investigators have recognized that FT generally
increases soil erodibility (Bryan 2000) and that this FT effect varies with soil
texture, moisture, and the extent of freezing. Thus, many factors affect runoff
erosivity and soil erodibility and determine the volume of sediment eroded
during a runoff event.
Processes of soil FT cycling
As air temperature drops, heat is lost from the soil surface. When sufficient
heat is lost, the water in the soil begins to freeze. Freezing and thawing of soils
cause movement of soil water and solutes in the soil profile (Radke and Berry
1997, Gatto 2000). Water moves upwards towards the freezing front to fill soil
voids and freeze or to form ice layers or lenses within a soil mass, thus depleting
water from the soil below.