Dune dynamics and cryoturbation features controlled by Holocene water level change, Hietatievat, Finnish Lapland

Abstract

The inland dune field at Hietatievat (Finnish Lapland) is derived from an esker and accumulated during the early Holocene. A spodosol developed in a humid climate at least until the end of the Atlantic. A generalized phase of cryoturbation occurred at that time, in the absence of permafrost and in response to a higher standing water level in autumn. As a consequence of forest fires and a lowering of the water level during the Subboreal, dunes were reactivated during the Subatlantic and are still active today. The frost susceptibility of the clean sand is related to amorphous clays and organic matter accumulated by podsolisation. Cryoturbations resulting from a negative gradient of frost susceptibility (the surface horizon is less susceptible to frost heave than the subsurface) and a high standing water table evolve into hummocks during periods with a low-standing autumn water table. These hummocks develop into pseudo-convective forms (mounds with a central injection). Features observed at Hietatievat are similar to those observed in aeolian sands at the Gåsebu site (Svalbard, continuous permafrost) and are governed by the same laws of mechanical deformation. Permafrost is not a prerequisite for the development of cryoturbation. These deformations can be used as analogs for the understanding of the Late Glacial phenomena of western Europe. Holocene changes in the hydraulic regime observed through the cryopedological approach seem consistent with the results obtained by other methods.