Are Icelandic rock-slope failures paraglacial? Age evaluation of seventeen rock-slope failures in the Skagafjörður area, based on geomorphological stacking, radiocarbon dating and tephrochronology

Mercier, Denis; Coquin, Julien; Feuillet, Thierry; Decaulne, Armelle; Cossart, Eitienne; Jónsson, Helgi Páll; Sæmundsson, Þorsteinn

doi:10.1016/j.geomorph.2017.08.011

Cited by 31 publications

(23 citation statements)

References 79 publications

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“…The temporal pattern of activity is therefore a typical paraglacial response (Ballantyne 2002). Causal factors that may account for such a pattern include glacial unloading, glacial debuttressing, stress-release fracturing, enhanced groundwater pressure in rock joints and permafrost degradation, all closely associated in time with deglaciation (Fischer et al 2006;Cossart et al 2008;McColl 2012;McColl & Davies 2012;Ballantyne et al 2014a, b;B€ ohme et al 2015;Deline et al 2015;Mercier et al 2017). Hermanns et al (2017) found nearly half of 22 dated rock avalanches in southwest Norway occurred within the first millennium following local deglaciation.…”

Section: Previous Models Of the Timing Of Rsfsmentioning

confidence: 99%

“…However, previous research has primarily focused on modern examples, spectacular cases or small numbers of massive rock-slope failures (MRSFs;~10 8 m 3 ), which, in combination with uncertainty associated with current geochronological approaches, limits our understanding of the fundamental geophysical processes and environmental controls that determine RSF occurrence. Particular studies of RSFs have used avarietyof techniques and, on some occasions, a combination of geochronological methods (Lang et al 1999;Hermanns et al 2000;Crosta & Clague 2009;Deline & Kirkbride 2009;Prager et al 2009;P anek 2014;B€ ohme et al 2015;Moreiras et al 2015;Mercier et al 2017), but the opportunities for accurate dating are relatively rare.…”

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confidence: 99%

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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

Winkler

Wilson

et al. 2018

Boreas

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October): 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.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 RSFoccurrence: 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 (≤10 3 m 3 ), rather than on the corresponding features of massive RSFs (~10 8 m 3 ), 92 singleevent 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 SRSFactivity 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 interpretationis supported bygeomorphological evidence, as the spatialdistributionofSRSFs isstrongly correlatedwith the aspect-dependent lower altitudinal limit ofmountain permafrost in clifffaces. Resultsare 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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Section: Previous Models Of the Timing Of Rsfsmentioning

confidence: 99%

mentioning

confidence: 99%

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

Winkler

Wilson

et al. 2018

Boreas

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“…These macro‐mass movements have been described as the paraglacial response of the deglaciation during the Early Holocene (Mercier et al . , ; Cossart et al . ; Coquin et al .…”

Section: Study Areamentioning

confidence: 99%

The rapid deglaciation of the Skagafjörður fjord, northern Iceland

Andrés

Palacios

Sæmundsson

et al. 2018

Boreas

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The Skagafjörður fjord in northern Iceland is located between the Tröllaskagi Peninsula in the east and the Skagi Peninsula in the west. The tributary valleys of the fjord originate in the highland area about 15 km north of the Hofsjökull icecap. The results of this work improve the knowledge of the deglaciation pattern in Skagafjörður and explore the adequacy of the 36Cl cosmic ray exposure dating method in an Icelandic environment, where this method has rarely been applied to deglaciated surfaces. The 36Cl dating method was applied to 13 rock samples taken on a transect from the coastal areas towards the highlands. All samples were obtained from rock outcrops with glacier‐polished surfaces from the Last Glaciation and from one of the few well‐preserved erratic boulders. The cosmogenic results, combined with previous radiocarbon results, indicate that the ice margin was situated in the outermost sector of Skagafjörður at approximately 17–15 ka BP. Subsequently, it retreated and occupied the central part of the fjord between 15 and 12 ka BP and then the innermost sector of the fjord about 11 ka BP. The samples collected between this position and the highlands show an average age of approximately 11 ka, indicating rapid deglaciation after the early Preboreal. These results agree with earlier studies of the deglaciation history of northern Iceland, reinforce previous deglaciation models in the area and enable a better understanding of glacial evolution in the North Atlantic from the Late Pleistocene to Holocene transition.

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“…Another study in Northern Ireland relying on 36 Cl cosmogenic isotope and radiocarbon dating indicates that most RSFs occurred during or immediately following deglaciation (18–17 ka), whereas some ages suggest some smaller scale events during the Lateglacial and/or early Holocene (14 to 9 ka; Southall et al, ). Similarly, a recent study in Iceland suggests that 94% of RSFs investigated occurred prior to 10 ka, whereas later events occurred before 8 ka, being difficult to identify the final trigger for each individual event (Mercier et al, ).…”

Section: Introductionmentioning

confidence: 99%

Timing of paraglacial rock‐slope failures and denudation signatures in the Cantabrian Mountains (North Iberian Peninsula)

et al. 2018

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Glacial erosion of hillslopes and stress changes induced by the transition from glacial to nonglacial conditions exert a strong influence on slope instability and are considered among the scope of paraglacial geomorphology. Failure mechanisms and coupling between paraglacial rock-slope failures (RSFs) and fluvial erosion are difficult to define. Here we show a preliminary spatio-temporal framework of paraglacial RSFs in a small catchment of the central Cantabrian Mountains, the San Isidro valley, with a dense concentration of RSFs. Preliminary radiocarbon dates obtained from two floodplain sequences deposited upstream from RSFs indicate that their sedimentation started as consequence of valley impoundment by RSFs after glacier retreat (after approximately 16.1 ka), consistent with the deglaciation pattern of nearby valleys. RSFs continued during the Holocene. Glacier erosion, debuttressing, and stressrelease conditions played an important role in slope destabilization as preparatory factors in all cases and probably triggered the oldest events. However, the long prefailure endurance (approximately 12 ka) between RSFs points to other factors such as rainfall and fluvial down-cutting of hillslopes as triggers for Holocene events.Postglacial fluvial incision rates of 2.2-2.5 mm a −1 were estimated along gullies carved into bedrock areas nonaffected by RSFs. These values are one order of magnitude higher than previous rates based on other geomorphological proxies (~0.2 mm a −1 ), suggesting accelerated fluvial incision following the last deglaciation. Local RSFs contributed to increase in fluvial incision rates by a factor of three. This study provides a quantitative perspective of postglacial land degradation relevant for understanding postorogenic landscape evolution.

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Are Icelandic rock-slope failures paraglacial? Age evaluation of seventeen rock-slope failures in the Skagafjörður area, based on geomorphological stacking, radiocarbon dating and tephrochronology

Cited by 31 publications

References 79 publications

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

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

The rapid deglaciation of the Skagafjörður fjord, northern Iceland

Timing of paraglacial rock‐slope failures and denudation signatures in the Cantabrian Mountains (North Iberian Peninsula)

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