Holocene Rockwall Retreat in Svalbard: A Triple-Rate Evolution

Abstract

Volumetric calculations of slope deposits, direct measurements of rockwall retreat and chronological control based on lichenometry provide a wide range of rockwall retreat rates in Svalbard (0-1580 mm ka −1 ) that appears consistent with previous evaluations from other Arctic areas. In northwest and central Spitsbergen (79°N), a triple-rate rockwall retreat is suggested for the last two millennia: very slow biogenic flaking (2 mm ka −1 ), moderate retreat due to frost shattering (100 ka −1 ) and rapid retreat associated with post-glacial stress relaxation (c. 1000 mm ka −1 ). Examination of the distribution of various processes indicates that the Holocene retreat of most rockwalls has not exceeded one or two metres. Bedrock conditions appear to be the main control on retreat rates. The massiveness of igneous and metamorphic outcrops, widespread in Arctic shield areas, largely accounts for the slowness of rockwall retreat, which on these lithologies is primarily due to chemical and biological processes. More rapid rates are usually associated with stress relaxation following glacial surges or with local frost susceptibility of bedrock, often where faulting has induced high joint density. At such sites, rockwall retreat rates are of the same order of magnitude as those reported from Alpine areas (1000-3000 mm ka −1 ) where both bedrock weakening due to tectonic stresses and the greater height of steep rockwalls account for the more rapid rockwall retreat rate.

A nonlinear model coupling rockfall and rainfall intensity based on a four year measurement in a high Alpine rock wall (Reintal, German Alps)

“…A number of direct rockfall measurements have been conducted in the past (Rapp, 1960;Caine, 1976;Sommerhoff, 1977;Luckman, 1978;Douglas, 1980;Fahey and Lefebure, 1988;Matsuoka, 1990;Nyberg, 1991;Becht, 1995;André, 1997;Sass, 1998). Whereas these studies provided qualitative evidence for a general rainfall -rockfall relation, no quantitative models were developed, which are crucial for the prediction of the specific hazard.…”

Controls on Rockfall-Talus Process-Response Systems, Kananaskis, Canadian Rockies

“…Similar to the rock slopes in our study area, talus deposits of the Norman Range area are dominated by limestone. Andre (1997) where the adjacent cliff is formed of calcareous and dolomitic siltstones, sandstones and shales, interbedded with limestones. The erosion rate of 2.9 mm yr -1 found in the present study is much greater than modern values of rockfall activity (e.g.…”

Geometry and dynamics of two lobe-shaped rock glaciers in the permafrost of Svalbard

“…For a reasonable 0.3 mm a ¡1 cliff retreat rate, for instance (cf. André 1997, Berthling 2001, the corresponding age estimate totals 20 ka. The difference between our estimate and the one obtained from lichenometry by André (1994;3-4 ka) can be reduced signi cantly by correcting the latter value for the conveyer-belt effect which makes the oldest, i.e.…”

“…For a retreat rate of 0.3 mm a ¡1 , for instance (cf. André 1997, Berthling 2001) and an ice content of 40% (cf. Vonder Mühll 1996, Berthling 2001 gives an age estimate of approximately 50 ka.…”