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

John Matthews, Peter Wilson, Stefan Winkler, Richard Mourne, Jennifer Hill, Geraint Owen, John Hiemstra, Helen Hallang, Andrew Geary

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    Abstract

    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.
    Original languageEnglish
    Pages (from-to)641-664
    JournalQuaternary Research
    Volume92
    Early online date9 Sep 2019
    DOIs
    Publication statusPublished - 1 Nov 2019

    Keywords

    • cryoplanation terraces
    • Schmidt-hammer exposure-age dating
    • mountain permafrost
    • periglacial processes
    • alpine landform development
    • frost weathering
    • nivation

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