Chapter 3 Effects Of Freeze-Thaw Cycling On Soil Erosion Lawrence W. Gatto, Jonathan J. Halvorson', Donald K. McCo01 3 , and Antonio J. Palazzo' 'US Army Engineer Research and Development center; 2 USDA-ARS Appalachian Farming Systems Research Center; 3 USDA-ARS Land Management and Water Conservation center 1. INTRODUCTION 1.1. Landscape Evolution and Soil Erosion Landscapes evolve as a result of the interactions of topography, climate, hydrology, vegetation conditions, rock-weathering processes, soil conditions, sediment transport and deposition processes, and land use. An integral part of understanding and modeling that evolution must be a knowledge of the spatial and temporal dynamics in soil erodibility and runoff erosivity and how these dynamics affect the mechanics of soil erosion. Soil is naturally eroded by water flowing down the surface of bare or partially vegetated hill slopes, and erosion is a function of soil-particle detachment and transport capacity of this runoff. The capacity of runoff to transport soil particles (i.e., erosivity) is a function of velocity and turbulence; the detachability of soil particles (i.e., erodibility) is a function of interparticle friction, bonding, and interlocking. The strength of soil-particle interactions 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). Compaction and crusting of the soil surface also increase the resistance of soil particles and aggregates to erosion. Thus, many factors affect soil erodibility and Landscape Erosion and Evolution Modeling, edited by Harmon & and Doe III, Kluwer Academic/Plenum Publishers, New York, 2001. 29 r