New evidence for active talus-foot rock glaciers at Øyberget, southern Norway, and their development during the Holocene

Atle Nesje, John Matthews, Henriette Linge, Marie Bredal, Peter Wilson, Stefan Winkler

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    Abstract

    Synthetic aperture radar interferometry (InSAR) measurements demonstrate that lobate, blocky depositional landforms, located in southern Norway at an altitude of ~530 m above sea level, with an estimated mean annual air temperature of ~1.6°C, currently exhibit deformation attributed to viscous creep. Five years of InSAR measurements for six lobes demonstrate average surface velocities of 1.2–22.0 mm/year with maximum rates of 17.5–55.6 mm/year. New Schmidt-hammer exposure-age dating (SHD) of two proximal lobes reveals mid-Holocene ages (7.6 ± 1.3 ka and 6.0 ± 1.2 ka), which contrast with the early-Holocene SHD and 10Be ages obtained previously from distal lobes, and late-Holocene SHD ages presented here from two adjacent talus slopes (2.3 ± 1.0 ka and 2.4 ± 1.0 ka). Although passive transport of boulders on the surfaces of these small, slow-moving rock glaciers affected by compressive flow means that the exposure ages are close to minimum estimates of the time elapsed since lobe inception, disturbance of boulders on rock glaciers is a source of potentially serious underestimates of rock-glacier age. Rock-glacier development at Øyberget began shortly after local deglaciation around 10 ka before present and continued throughout the Holocene in response to microclimatic undercooling within the coarse blocky surface layer of the talus and rock-glacier lobes. We suggest this enhanced cooling lowers mean annual surface-layer temperature by at least ~3.6°C, which is needed at such a low altitude to sustain sporadic permafrost and avoid fast thawing as atmospheric temperatures rise. Our results point to circumstances where inferences about rock glaciers as indicators of regional climate should be interpreted with caution, and where they may be less useful in palaeoclimatic reconstruction than previously thought.
    Original languageEnglish
    Pages (from-to)1786-1796
    Number of pages11
    JournalThe Holocene
    Volume31
    Issue number11-12
    Early online date15 Aug 2021
    DOIs
    Publication statusPublished - 1 Dec 2021

    Bibliographical note

    Funding Information:
    We thank Wilfried Haeberli, Colin Ballantyne, and others for their informal comments on our previous interpretations of the ?yberget rock glaciers, some of which we have taken the opportunity to correct in this paper. Further thanks are due to Wilfried Haeberli and Richard Shakesby for their reviews and suggestions relating to the present manuscript. Anna Ratcliffe prepared the figures for publication. This paper represents Jotunheimen Research Expeditions Contribution No. 219 (see http://jotunheimenresearch.wixsite.com/home). The author(s) received no financial support for the research, authorship, and/or publication of this article.

    Publisher Copyright:
    © The Author(s) 2021.

    Keywords

    • InSAR
    • Schmidt-hammer exposure-age dating
    • active and relict landforms
    • microclimatic undercooling
    • permafrost
    • rock-slope failure
    • talus-derived rock glacier

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