Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 1994
Publication Date: N/A
Interpretive Summary: When soil freezes the ice that is formed fills the pores that usually conduct water, which greatly reduces its permeability. This can lead to flooding and accelerated erosion. The processes involved are different from unfrozen soil erosion, which is much better understood. For example, runoff and erosion can occur without any rainfall (just snowmelt). The additional soils information needed to simulate frozen soil processes are: when the soil is frozen, how deep the soil is frozen, the effect of freezing on permeability and the effect of freezing on how erodible the soil is. Current computer simulation models can calculate when and how deep the soil freezes with reasonable accuracy. However, those models are much less accurate in estimating the effect of freezing on permeability and erosion. This is largely due to the fact some water in the soil remains in liquid state even when the soil freezes. This is difficult to measure, but affects both the permeability and erodibility. Another problem is that field conditions can be extremely variable so that it is hard to determine which input values to apply to the models. In order to accurately estimate runoff and erosion from frozen soils, we need to be able to integrate those variable values into effective values that apply to larger areas.
Technical Abstract: Surface runoff and erosion from frozen soils are widespread phenomena that have been reported in most regions of the world that have significant soil freezing. In the interior Pacific Northwest, frozen soil is associated with the majority of flooding and erosion events. The processes involved in frozen soil erosion are different from those in unfrozen soil erosion, which is more commonly studied. When the soil solution freezes, a portion of the total water content remains as liquid water. This is critical because the amount of ice formed largely determines the impact of soil freezing on the soil properties that affect erosion. Soil with high ice content may be essentially impermeable so that when the soil surface thaws it becomes highly erodible. These conditions can generate runoff and erosion with little or no rainfall (e.g., during snowmelt). Accurate estimation of runoff and erosion from frozen soils requires knowledge of soil freezing occurrence and depth, the effect of freezing on infiltrability and surface runoff, and the effect of freezing on soil erodibility. Current models can accurately predict frost occurrence and depth but not infiltrability or erodibility. Field observations of frozen soil runoff have shown extreme spatial and temporal variability over a range of scales. Accurate description of the effects of soil freezing on surface runoff and erosion on rangelands will ultimately require that models incorporate landscape-scale processes.