Snow avalanches in central Svalbard : a field study of meteorological and topographical triggering factors and geomorphological significance

• Published in: Arctic, Antarctic, and Alpine Research
• Main Author: Eckerstorfer, Markus
• Other Authors: Hanne H. Christiansen, Karel Kriz
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2013
• Subjects: VDP::450; Longyearbyen; Longyeardalen; Midwinter; Plateau Mountain; Svalbard; Antarctic and Alpine Research; Arctic; North Atlantic; Permafrost and Periglacial Processes; The Cryosphere; University Centre in Svalbard
• Online Access: http://hdl.handle.net/10852/34832; http://urn.nb.no/URN:NBN:no-33570

Snow avalanches are a natural phenomenon occurring in snow covered alpine areas all over the world. A complex process combining gravity, topographical conditions, physical and mechanical properties of snow and meteorological conditions control avalanche release. Due to this process complexity, avalanche research has a remarkable interdisciplinary nature, from physical geography, to geomorphology, meteorology, geophysics, engineering and natural hazards. Hazard related avalanche research is of most importance, as an improved process understanding of how, when and where avalanches release is crucial for avalanche warning and forecasting. Besides this natural hazard focus, avalanches are also studied to improve the understanding of their geomorphological role. Their importance as rock sediment erosion, transport and depositional agents in high relief terrain is of main interest. Surveying the scientific literature indicates that until 2009 no basic avalanche research has been published in Svalbard. This is somewhat surprising, as the alpine Svalbard landscape with its snow cover, existing for a maximum of 10 months per year, is prone to avalanching. In addition, with the permanent settlement Longyearbyen, where the University Centre in Svalbard is located, infrastructure certainly exists to conduct year-round slope process studies, with very easy field access to avalanche terrain. Moreover there is an increasing population that is living and working in an active landscape, visited also by an increasing number of tourists. Therefore my PhD thesis is a field based and interdisciplinary study of the meteorological and topographical triggering factors and the geomorphological significance of avalanches in central Svalbard. All data was obtained by direct observations, data recording by instruments and by direct measurements in the field between 2003 – 2012; with my own data gathering beginning in 2008, but primarily during my 4 year PhD study from 2009 to 2012. Thus, it should be kept in mind, that results and conclusions are based on a short but unique dataset. The main characteristic of the snow climate in central Svalbard is a thin, discontinuous snowpack that is highly stratified with several ice layers and meltform layers overlying a persistent depth hoar base. Depth hoar and secondly facets are the most prominent weak layers in the snowpack. The main characteristic of the avalanche regime in central Svalbard is the dominance of cornice fall avalanches, due to the sedimentary plateau mountain topography, the lack of high vegetation and a prevailing winter wind direction. The timing of cornice fall avalanche releases is identified to be within 3-5 weeks after cornices start deforming rapidly enough that tension cracks open between the cornice and the snow of the plateau. Slab avalanches are the second most observed avalanche type. For the release of natural dry slab avalanches the best meteorological predictor variable are sums of precipitation and snowdrift in periods of 24, 48 and 72 hours before an avalanche day. This is in agreement with previous studies from other areas. Wet slab and slush avalanches had the longest runout distances observed. Such were studied during two midwinter wet avalanche extreme events in January 2010 and March 2011. Both these extreme cycles resulted from slowly passing low-pressure systems, with air temperatures several degrees above freezing, and 100-year record monthly rainfalls. Analyzing the occurrence of such extreme meteorological conditions for the last 100 years, no correlation between a warming climate and wet avalanche cycle frequency was found. In conclusion, low-pressure frequency and magnitude largely determine avalanche activity at present in Svalbard. As the low-pressure frequency is modeled to decline in the North Atlantic in a warming climate, avalanche activity will be reduced. However, cornice fall avalanches are mainly controlled by the topography and the prevailing winter wind direction, and will therefore increase in dominance. The geomorphological role of avalanches as sediment transport agents is significant, primarily due to rock erosion, transportation and deposition by the cornices and cornice fall avalanches. Cornices can increase rock weathering and thus erosion by keeping the ground thermal regime underneath them ideal for ice segregation. The weathered rock debris is then eroded from the backwall by plucking as the cornice detaches from the plateau. Cornice fall avalanches, consequently can transport rock debris downslope throughout winter and spring. Therefore, high rockwall retreat rates with associated large avalanche sedimentation on the avalanche fans below have been quantified for leeward facing slopes in Longyeardalen. This identified cornice fall avalanches as the most efficient geomorphological slope process at present and during the Holocene. The conducted research focusing on the natural hazard perspective and on the geomorphological effects of avalanches represents the first basic research on the natural phenomenon snow avalanche in central Svalbard. Hopefully my study will trigger more research on avalanches in Svalbard, but also be a useful basis for a future avalanche forecasting service in Svalbard.