The Höfðahólar rock avalanche (sturzström): Chronological constraint of paraglacial landsliding on an Icelandic hillslope

Abstract

The Höfðahólar rock avalanche, in the Skagafjörður area of northern Iceland, was investigated on the basis of a geomorphological analysis of its landforms and close surrounding environment. Thanks to sound chronological constraints (14C dating from birch remnants in peat areas that developed within depressions over the chaotic rock-avalanche deposit, tephrochronological sequences resulting from subsequent ash fallouts over the deposit, calibration of an age–depth model of peats and previously dated raised beaches), we define the rock-avalanche implementation with a wider timeframe between 10,200 and 7975 cal. yr BP and with a narrower frame between 9000 and 8195 ± 45 cal. yr BP. Such a well constrained timing proposes one of the most precise datings of an early-Holocene major slope failure in Iceland. This result fits well in the known chronology of the deglaciation in this area and in the prevailing Icelandic theory of a generalized phase of landsliding that occurred shortly after the deglaciation of the area. The main driver for the rock-avalanche occurrence is associated to a paraglacial origin; glacio-isostatic rebound, associated to rockwall debuttressing, is thought to be the main factor in the genesis of this Boreal major disequilibrium.

Gravitational spreading of mountain ridges coeval with Late Weichselian deglaciation: impact on glacial landscapes in Tröllaskagi, northern Iceland

“…His theory of a post-Weichselian origin of Icelandic landslides has been corroborated by recent investigations (Decaulne et al, 2010;Cossart et al, 2014;Mercier et al, 2013), suggesting that the main landslide activity probably occurred during Preboreal/early Holocene transition times, in good correlation with the timing of the maximal rate of post-glacial rebound (between 10,000 year ± 300 year BP and 8150 ± 350 year; Rundgren et al, 1997;Biessy et al, 2008;Le Breton et al, 2010). These time constraints are consistent with significant paraglacial controls on landslide triggering.…”

“…North of the town of Hofs os, beach deposits standing at similar elevations (60 m a.s.l.) suggest that the northern coast of the Tr€ ollaskagi peninsula was deglaciated at a similar time (Mercier et al, 2013). This minimal age for the Late Weichselian deglaciation in Skagafj€ orður indicates that the IIS receded more than 100 km from its LGM maximal extent, in only a few thousands of years.…”

“…In many ways, the mountains of the Tr€ ollaskagi peninsula represent an ideal location to investigate large-scale paraglacial ridge readjustments to post-LGM deglaciation. Indeed, post-glacial rock slope failures and other paraglacial readjustment processes have been extensively described throughout the area (J onsson, 1957, 1976P etursson and Saemundsson, 2008;Mercier et al, 2013;Cossart et al, 2014;Feuillet et al, 2014). Moreover, the uniform lithology and relatively simple tectonic structure of the region provides an opportunity to isolate the paraglacial controls on gravitational readjustments.…”

The origin of glacial alpine landscape in Tröllaskagi Peninsula (North Iceland)

“…These macro-mass movements developed as a result of deglaciation during the early Holocene (Mercier et al, 2013;Cossart et al, 2014;Coquin et al, 2015), although in fact some are still active (Wangensteen et al, 2006). In addition, highly active solifluction processes were widespread on the slopes of the Tröllaskagi, especially during the coldest periods at the end of the Pleistocene and the Holocene, as occurred during the Younger Dryas and the LIA (Veit et al, 2011).…”

“…The temperature increased definitively from 10 ka onwards. Many of the large-scale landslides which have been dated in Skagafjödur coincide with this date, indicating that the valleys were recently deglaciated (Mercier et al, 2013;Cossart et al, 2014;Coquin et al, 2015).…”