Diapirism in soils due to thaw of ice-rich material near the permafrost table

The unstable bulk density profiles and viscous nature of wet soils with per mafrost facilitate flow of soil by diapirism. Soil material with low bulk d ensity due to very high ice content is commonly present near the permafrost table. Horizons with gravimetric water contents of 1 to 2 kg water per kg dry soil were found within 1 m of the surface in soils on the North Slope o f Alaska. This material has bulk density that is up to 0.8 Mg m(-3) less th an the overlying drier mineral soil material. As a result of this unstable bulk density profile, diapiric upward movement of the low-density soil mate rial is likely when it thaws. Quantitative comparisons of diapir scale mode ls and theory from the literature with measured soil bulk densities and vis cosities from arctic Alaska indicate that several decimetres of diapir move ment could easily occur during a single thaw season. Movement of diapirs is probably an important mechanism in the formation of involutions and mudboi ls. Copyright (C) 1999 John Wiley & Sons, Ltd.