Age and development of active cryoplanation terraces in the alpine permafrost zone at Svartkampen, Joutunheimen, southern Norway.

Schmidt-hammer exposure-age dating (SHD) of boulders on cryoplanation terrace
treads and associated bedrock cliff faces revealed Holocene ages ranging from 0 ±
825 to 8890 ± 1185 yr. The cliffs were significantly younger than the inner treads,
which tended to be younger than the outer treads. Radiocarbon dates from the regolith
of 3854 to 4821 cal yr BP (2σ range) indicated maximum rates of cliff recession of ~0.1
mm/year, which suggests the onset of terrace formation prior to the last glacial
maximum. Age, angularity and size of clasts, together with planation across bedrock
structures and the seepage of groundwater from the cliff foot, all support a processbased
conceptual model of cryoplanation terrace development in which frost
weathering leads to parallel cliff recession and hence terrace extension. The
availability of groundwater during autumn freeze-back is viewed as critical for frost
wedging and/or the growth of segregation ice during prolonged winter frost penetration.
Permafrost promotes cryoplanation by providing an impermeable frost table beneath
the active layer, focusing groundwater flow, and supplying water for sediment transport
by solifluction across the tread. Snowbeds are considered an effect rather than a
cause of cryoplanation terraces and cryoplanation is seen as distinct from nivation.