Small rock-slope failures conditioned by Holocene permafrost degradation: a new approach and conceptual model based on Schmidt-hammer exposure-age dating, Jotunheimen, southern Norway.

John Matthews, Stefan Winkler, Peter Wilson, Matt Tomkins, Jason Dortch, Richard Mourne, Jenny Hill, Geraint Owen, Amber Vater

    Research output: Contribution to journalArticle

    4 Citations (Scopus)

    Abstract

    Rock‐slope failures (RSFs) constitute significant natural hazards, but the geophysical processes that control their timing are poorly understood. However, robust chronologies can provide valuable information on the environmental controls on RSF occurrence: information that can inform models of RSF activity in response to climatic forcing. This study uses Schmidt‐hammer exposure‐age dating (SHD) of boulder deposits to construct a detailed regional Holocene chronology of the frequency and magnitude of small rock‐slope failures (SRSFs) in Jotunheimen, Norway. By focusing on the depositional fans of SRSFs (≤103 m3), rather than on the corresponding features of massive RSFs (~108 m3), 92 single‐event RSFs are targeted for chronology building. A weighted SHD age–frequency distribution and probability density function analysis indicated four centennial‐ to millennial‐scale periods of enhanced SRSF frequency, with a dominant mode at ~4.5 ka. Using change detection and discreet Meyer wavelet analysis, in combination with existing permafrost depth models, we propose that enhanced SRSF activity was primarily controlled by permafrost degradation. Long‐term relative change in permafrost depth provides a compelling explanation for the high‐magnitude departures from the SRSF background rate and accounts for: (i) the timing of peak SRSF frequency; (ii) the significant lag (~2.2 ka) between the Holocene Thermal Maximum and the SRSF frequency peak; and (iii) the marked decline in frequency in the late‐Holocene. This interpretation is supported by geomorphological evidence, as the spatial distribution of SRSFs is strongly correlated with the aspect‐dependent lower altitudinal limit of mountain permafrost in cliff faces. Results are indicative of a causal relationship between episodes of relatively warm climate, permafrost degradation and the transition to a seasonal‐freezing climatic regime. This study highlights permafrost degradation as a conditioning factor for cliff collapse, and hence the importance of paraperiglacial processes; a result with implications for slope instability in glacial and periglacial environments under global warming scenarios.
    LanguageEnglish
    Pages1144-1169
    Number of pages26
    JournalBoreas
    Volume47
    Issue number4
    Early online date23 Jul 2018
    DOIs
    Publication statusPublished - 1 Oct 2018

    Fingerprint

    slope failure
    permafrost
    Holocene
    rock
    chronology
    cliff
    dating
    exposure
    glacial environment
    periglacial environment
    Hypsithermal
    wavelet analysis
    natural hazard
    boulder
    probability density function
    conditioning
    freezing
    global warming

    Keywords

    • Small rock-slope failures
    • Permafrost degradation
    • Holocene
    • Norway

    Cite this

    Matthews, John ; Winkler, Stefan ; Wilson, Peter ; Tomkins, Matt ; Dortch, Jason ; Mourne, Richard ; Hill, Jenny ; Owen, Geraint ; Vater, Amber. / Small rock-slope failures conditioned by Holocene permafrost degradation: a new approach and conceptual model based on Schmidt-hammer exposure-age dating, Jotunheimen, southern Norway. In: Boreas. 2018 ; Vol. 47, No. 4. pp. 1144-1169.
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    abstract = "Rock‐slope failures (RSFs) constitute significant natural hazards, but the geophysical processes that control their timing are poorly understood. However, robust chronologies can provide valuable information on the environmental controls on RSF occurrence: information that can inform models of RSF activity in response to climatic forcing. This study uses Schmidt‐hammer exposure‐age dating (SHD) of boulder deposits to construct a detailed regional Holocene chronology of the frequency and magnitude of small rock‐slope failures (SRSFs) in Jotunheimen, Norway. By focusing on the depositional fans of SRSFs (≤103 m3), rather than on the corresponding features of massive RSFs (~108 m3), 92 single‐event RSFs are targeted for chronology building. A weighted SHD age–frequency distribution and probability density function analysis indicated four centennial‐ to millennial‐scale periods of enhanced SRSF frequency, with a dominant mode at ~4.5 ka. Using change detection and discreet Meyer wavelet analysis, in combination with existing permafrost depth models, we propose that enhanced SRSF activity was primarily controlled by permafrost degradation. Long‐term relative change in permafrost depth provides a compelling explanation for the high‐magnitude departures from the SRSF background rate and accounts for: (i) the timing of peak SRSF frequency; (ii) the significant lag (~2.2 ka) between the Holocene Thermal Maximum and the SRSF frequency peak; and (iii) the marked decline in frequency in the late‐Holocene. This interpretation is supported by geomorphological evidence, as the spatial distribution of SRSFs is strongly correlated with the aspect‐dependent lower altitudinal limit of mountain permafrost in cliff faces. Results are indicative of a causal relationship between episodes of relatively warm climate, permafrost degradation and the transition to a seasonal‐freezing climatic regime. This study highlights permafrost degradation as a conditioning factor for cliff collapse, and hence the importance of paraperiglacial processes; a result with implications for slope instability in glacial and periglacial environments under global warming scenarios.",
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    Small rock-slope failures conditioned by Holocene permafrost degradation: a new approach and conceptual model based on Schmidt-hammer exposure-age dating, Jotunheimen, southern Norway. / Matthews, John; Winkler, Stefan; Wilson, Peter; Tomkins, Matt; Dortch, Jason ; Mourne, Richard; Hill, Jenny; Owen, Geraint; Vater, Amber.

    In: Boreas, Vol. 47, No. 4, 01.10.2018, p. 1144-1169.

    Research output: Contribution to journalArticle

    TY - JOUR

    T1 - Small rock-slope failures conditioned by Holocene permafrost degradation: a new approach and conceptual model based on Schmidt-hammer exposure-age dating, Jotunheimen, southern Norway.

    AU - Matthews, John

    AU - Winkler, Stefan

    AU - Wilson, Peter

    AU - Tomkins, Matt

    AU - Dortch, Jason

    AU - Mourne, Richard

    AU - Hill, Jenny

    AU - Owen, Geraint

    AU - Vater, Amber

    PY - 2018/10/1

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    AB - Rock‐slope failures (RSFs) constitute significant natural hazards, but the geophysical processes that control their timing are poorly understood. However, robust chronologies can provide valuable information on the environmental controls on RSF occurrence: information that can inform models of RSF activity in response to climatic forcing. This study uses Schmidt‐hammer exposure‐age dating (SHD) of boulder deposits to construct a detailed regional Holocene chronology of the frequency and magnitude of small rock‐slope failures (SRSFs) in Jotunheimen, Norway. By focusing on the depositional fans of SRSFs (≤103 m3), rather than on the corresponding features of massive RSFs (~108 m3), 92 single‐event RSFs are targeted for chronology building. A weighted SHD age–frequency distribution and probability density function analysis indicated four centennial‐ to millennial‐scale periods of enhanced SRSF frequency, with a dominant mode at ~4.5 ka. Using change detection and discreet Meyer wavelet analysis, in combination with existing permafrost depth models, we propose that enhanced SRSF activity was primarily controlled by permafrost degradation. Long‐term relative change in permafrost depth provides a compelling explanation for the high‐magnitude departures from the SRSF background rate and accounts for: (i) the timing of peak SRSF frequency; (ii) the significant lag (~2.2 ka) between the Holocene Thermal Maximum and the SRSF frequency peak; and (iii) the marked decline in frequency in the late‐Holocene. This interpretation is supported by geomorphological evidence, as the spatial distribution of SRSFs is strongly correlated with the aspect‐dependent lower altitudinal limit of mountain permafrost in cliff faces. Results are indicative of a causal relationship between episodes of relatively warm climate, permafrost degradation and the transition to a seasonal‐freezing climatic regime. This study highlights permafrost degradation as a conditioning factor for cliff collapse, and hence the importance of paraperiglacial processes; a result with implications for slope instability in glacial and periglacial environments under global warming scenarios.

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