Slope Deposits and Forms

Abstract

On steep bedrock slopes, ground freezing and thawing leads to weathering and the release of rock falls, and where gradients are less, such frost action helps generate a weathering mantle. Debris-mantled slopes are susceptible to solifluction, the combined effect of frost creep and gelifluction. Frost creep results from frost heaving of the near-surface soil by segregation or needle ice and subsequent near-vertical settlement during thaw. Gelifluction occurs during thawing of ice-rich soils when high moisture contents result in a very soft, easily deformed soil mass. When the rate of thaw is rapid, pore pressures may be high enough to release shallow landslides. In mountain regions, rapid saturation of the active layer by intense rainfall can lead to debris flows. Thus, many periglacial slopes become mantled with deposits dominated by solifluction sediments but containing evidence of more rapid mass movement events. In areas with clay bedrocks, shallow translational landslides were often the dominant mechanism of periglacial mass movement, as evidenced by extensive shallow shear surfaces underlying partially remolded clay-rich slope deposits.