Cornice dynamics and meteorological control at Gruvefjellet, Central Svalbard

Abstract

Abstract. Cornice fall avalanches endanger life and infrastructure in Nybyen, a part of Svalbard's main settlement Longyearbyen, located at 78 • N in the High Arctic. Thus, cornice dynamics -accretion, cracking and eventual failure -and their controlling meteorological factors were studied along the ridgeline of the Gruvefjellet plateau mountain above Nybyen in the period 2008-2010. Using two automatic time-lapse cameras and hourly meteorological data in combination with intensive field observations on the Gruvefjellet plateau, cornice process dynamics were investigated in larger detail than previously possible. Cornice accretion starts directly following the first snowfall in late September and October, and proceeds throughout the entire snow season under a wide range of air temperature conditions that the maritime winter climate of Svalbard provides. Cornice accretion is particularly controlled by distinct storm events, with a prevailing wind direction perpendicular to the ridge line and average wind speeds from 12 m s −1 . Particularly high wind speeds in excess of 30 m s −1 towards the plateau ridgeline lead to cornice scouring and reduce the cornice mass both vertically and horizontally. Induced by pronounced air temperature fluctuations which might reach above freezing and lead to midwinter rainfall events, tension cracks develop between the cornice mass and the plateau. Our measurements indicate a linear crack opening due to snow creep and tilt of the cornice around a pivot point. Four to five weeks elapsed between the first observations of a cornice crack until cornice failure. Throughout the two snow seasons studied, 180 cornice failures were recorded, of which 70 failures were categorized as distinctive cornice fall avalanches. A clear temporal pattern with the majority of cornice failures in June was found. Thus only daily air temperature could determine avalanche from nonavalanche days. Seven large cornice fall avalanches reached the avalanche fans on which the Nybyen settlement is located. The size of the avalanches was primarily determined by the size of the cornice that detached. The improved process understanding of the cornice dynamics provides a first step towards a better predictability of this natural hazard, but also highlights that any type of warning based on meteorological factors is not an adequate measure to ensure safety of the housing at risk.

Snow cornice dynamics as a control on plateau edge erosion in central Svalbard

“…Autumn cornice accretion, winter deformation and opening of tension cracks, and summer melting were investigated in an observation period from September 14, 2010 to July 1, 2011. This improves the basic understanding of the seasonal cornice dynamics adding to the previous description of Vogel et al (2012) from the same site. We qualitatively studied the geomorphological importance of cornices as sediment erosional agents, by their ability to directly entrain rock sediment.…”

“…Consequently, studies emphasized cornice control by blasting or cutting (McCarty et al, 1986) or avalanche defense measures (Margreth, 2008). Studies from the Alps (Paulcke and Welzenbach, 1928;Welzenbach, 1930), Rocky Mountains (Montagne et al, 1968;McCarty et al, 1986) and more recently Svalbard (Vogel et al, 2012), however, have placed special emphasis on the seasonal deformation processes of cornices, driven by meteorological conditions. Montagne et al (1968) found that immediately after accretion, the cornice mass starts to deform due to sintering and creep.…”

“…This process is active and widespread in mountainous arctic barren landscapes, due to large snow source areas and wind redistribution (Eckerstorfer and Christiansen, 2011b) (Figure 1c). Cornices undergo a distinct seasonal cycle (Vogel et al, 2012) and either meltdown or collapse. Latter results in cornice fall avalanches being the most dominant type of avalanche in central Svalbard (Eckerstorfer and Christiansen, 2011b).…”

Arctic rockwall retreat rates estimated using laboratory‐calibrated ERT measurements of talus cones in Longyeardalen, Svalbard

“…Due to the prevailing wind direction west-facing slopes, like the NWfacing slope of Gruvefjellet, are most concerned. The active erosion by snow cornices at the top of the headwall and the sediment transport by dirty sediment-rich avalanches on the specific talus cones, has been monitored and described in detail by Vogel et al (2012) and Eckerstorfer et al (submitted) and may be the explanation for the higher retreat rate on the NW-facing slope compared with the SE-facing slope. This deserves further investigation including more process measurements in different aspects, quantitative studies and work on theoretical and modelling approaches of rockwall retreat and slope evolution (Fisher, 1866;Lehmann, 1933;Statham, 1976;Francou and Manté, 1990;Obanawa and Matsukura, 2008;Utili and Crosta, 2011a, 2011b, Krautblatter et al, 2012.…”

“…The winter snow cover lasts 8-10 months per year (Eckerstorfer and Christiansen, 2011). The prevailing winter wind direction is SE, leading to extensive snow redistribution and the accretion of cornices especially along the NW-facing plateau ridge ( Figure 1) of the Gruvefjellet mountain (Vogel et al, 2012). These eventually deform and can break off resulting in the release of cornice fall avalanches, which often occur on the NW-facing talus slope but only rarely on the SE-facing slope (Eckerstorfer and Christiansen, 2011;Vogel et al, 2012;Eckerstorfer et al submitted).…”