Ninth International Conference on Permafrost ... - IARC Research

The Omnsbreen Glacier:Possible Aggrading Permafrost, Southern Central NorwayIntroductionKarianne Staalesen LilleørenDepartment of Geosciences, University of Oslo, NorwayOle HumlumDepartment of Geosciences, University of Oslo, NorwayThe Omnsbreen Glacier is a small (< 0.5 km 2 ) mountainglacier situated in southern central Norway about 1500m a.s.l. Presently, the glacier exists approximately 100 mbelow the regional equilibrium line altitude (ELA), due tolocal accumulation of wind-redistributed snow.During the “Little Ice Age” (LIA), the glacier was of aconsiderable size and extent (approximately 6 km 2 ) andoccupied the whole valley, where today it occupies onlyparts of the western slope. The maximum size was reachedaround 1750, as for most of the glaciers in southern Norway(Andreassen et al. 2005). At that time, the effect of snowaccumulating by wind on the glacier was significantlyreduced because of the glacier’s different geometry, fillingup the valley.From the LIA maximum and until around 1930, the glacierremained relatively stable in shape and size. Between 1930and 1985, however, the bulk of the glacier disappeared.Since then, the glacier has lost mass at a much lower ratecompared to the years before, until recent years when theglacier apparently has stagnated with a fairly constant size.An ongoing study aims at explaining the rapiddisappearance of Omnsbreen since 1930 by using local andregional climate data (temperature, precipitation, and wind)and also tries to explain the apparent recent stagnation ofthe glacier. Couplings between the glacier, the climate, andmountain permafrost is investigated (Lilleøren 2007).Climatology and Area DescriptionLocationThe Omnsbreen Glacier is located close to Finse (1220 ma.s.l.) at the northwestern margin of the flat Hardangerviddaarea (Fig. 1). Finse is situated in a transition zone betweenthe marine western coast and the more continental easternparts of Norway, and has a high mountain climate. The meanannual air temperature (MAAT) was -2.1°C (1970–2000),and the mean annual precipitation in the same period was1030 mm, according to measurements by the NorwegianInstitute of Meteorology at Finse (DNMI 2007).TemperatureIn the before-mentioned ongoing study of the Omnsbreenarea, Tinytag-Loggers measuring air temperature, bottomtemperature of winter snow cover (BTS), and groundtemperature were placed in the area close to the glacier, andthe mean difference in air temperature measured betweenFinse and Omnsbreen was found to be 2.1°C, with the lowestNOmnsbreenFinseFigure 1. Location of Finse and Omnsbreen, southern centralNorway.temperatures at Omnsbreen for the period 06/08/22 through07/08/19. The picture is complicated by large temperatureinversions in the area, especially during the winter. Finse issituated in a valley bottom that efficiently traps heavy coldair cooled in higher elevations.WindMapping of snow cover surface forms demonstrated thatthe mean winter wind direction is from the west or slightlysouthwest. Omnsbreen’s valley has a north –south extension,and snow transported by westerly winds can efficientlyaccumulate in the valley’s east-facing slopes. When studyingthe wind directions measured by the meteorological stationat Finse, it seems like there has been a shift in the winddirections since the 1970s, from a wide directional spreadduring the winter to a more consistent wind direction fromwest in the 1980s. This shift also coincides with the reductionin the mass loss from the Omnsbreen glacier.Permafrost?Of the loggers measuring the BTS today (four places) inthe area earlier covered by ice, one had a stable temperatureclose to -4°C, which can be interpreted as an indicationof permafrost in the area (Fig. 2). The MAAT in the areapresumably is too high to allow widespread permafrost,but some sporadic permafrost may exist at this altitude atwind-exposed sites. Situated in a transition area betweenmaritime and continental climate types, the area experienceslarge differences in snow cover from one year to the next,185