Bernd Etzelmüller

Glacier-permafrost interaction in Arctic and alpine mountain environments with examples from southern Norway and Svalbard

Abstract The interaction between glaciers and permafrost was long ago addressed for glaciers in Arctic regions. Analogies from modern environments have been used to understand landform development at the margins of Pleistocene ice sheets. During more recent decades many systematic measurements of permafrost in boreholes, geophysical soundings and temperature monitoring have revealed permafrost to be more abundant in many more high-mountain areas than previously thought. This suggests that permafrost may be a governing factor not only for periglacial landform evolution in these areas, but also, given the potential for glacier-permafrost interaction, for glacial landform generation. This paper presents and discusses observation and study results on the geomorphological significance of the interrelationship between glaciers and permafrost, in relation to geomorphological processes, landform generation and response of the system to climate fluctuations.

Aspects and concepts on the geomorphological significance of Holocene permafrost in southern Norway

This review paper aims at discussing aspects and concepts of the significance of the spatial and temporal distribution of permafrost on glacial and gravitational processes in southern Norway. The study first reviews the distribution of mountain permafrost in southern Norway in comparison with high-relief alpine areas like the Alps, and then discusses the influence of permafrost on gravitational and glacial–geomorphological processes. The basis for the paper is a regional-scale distribution model of mountain permafrost in southern Norway, which is analysed in relation to topographic variations within the same area. The model allows a crude extrapolation to past and future permafrost distribution, which is discussed in relation to geomorphic processes.

Mapping and modelling the occurrence and distribution of mountain permafrost

This paper reviews the principles related to the mapping and modelling of the occurrence and distribution of mountain permafrost. It gives a state-of-the art report about this topic and defines future research needs.

Glacier characteristics and sediment transfer system of Longyearbreen and Larsbreen, western Spitsbergen

Two small high-Arctic glaciers (Longyearbreen and Larsbreen) on Svalbard (78°N 15°E) were studied with respect to glaciological and hydrological characteristics. Fieldwork during the melting season of 1993 and 1994 was coupled with digital map analysis based on high-resolution digital elevation models (DEM) to reveal the dynamics and temperature regime of small glaciers in a high-Arctic environment, and its relationship to the material transport and sedimentation of these glaciers. The study showed Longyearbreen and Larsbreen to be low activity glaciers, cold-based with temperate patches, and thus having a low potential of basal erosion. The transport of ions and suspended solids in the glacial meltwater implies storage of material in and around the glacier which comes into contact with the meltwater. The study suggests that small Arctic glaciers couple the slope system with the fluvial system and therefore build a highly effective denudation system. Small polythermal glaciers are therefore important in understanding Pleistocene and Holocene landform development in cold regions.

On the Quantification of Surface Changes using Grid‐based Digital Elevation Models (DEMs)

This paper discusses the quantification of vertical surface displacements by means of grid-based digital elevation models (DEMs). The surface changes are quantified by comparing altitude and different topographic parameters, which have a geomorphic significance with respect to surface changes. This paper describes the choice of different spatial calculation techniques, considering DEM accuracy and the propagation of error for the different topographic parameters involved. The techniques are illustrated on two grid-based DEMs from Finsterwalderbreen, a 35 km2 sized valley glacier on south-western Spitzbergen, Norwegian High Arctic.

Modeling the impact of wintertime rain events on the thermal regime of permafrost

In this study, we present field measurements and numerical process modeling from western Svalbard showing that the ground surface temperature below the snow is impacted by strong wintertime rain events. During such events, rain water percolates to the bottom of the snow pack, where it freezes and releases latent heat. In the winter season 2005/2006, on the order of 20 to 50 % of the wintertime precipitation fell as rain, thus confining the surface temperature to close to 0 C for several weeks. The measured average ground surface temperature during the snow-covered period is−0.6C, despite of a snow surface temperature of on average−8.5C. For the considered period, the temperature threshold below which permafrost is sustainable on long timescales is exceeded. We present a simplified model of rain water infiltration in the snow coupled to a transient permafrost model. While small amounts of rain have only minor impact on the ground surface temperature, strong rain events have a long-lasting impact. We show that consecutively applying the conditions encountered in the winter season 2005/2006 results in the formation of an unfrozen zone in the soil after three to five years, depending on the prescribed soil properties. If water infiltration in the snow is disabled in the model, more time is required for the permafrost to reach a similar state of degradation.

Mountain permafrost in Central-Eastern Norway

Earlier studies suggest that the altitudinal permafrost limit decreases from the west to the east in Southern Norway and that the lowermost altitudinal permafrost limit in Southern Scandinavia occurs in the eastern part of Southern Norway. Most investigations on mountain permafrost have been undertaken in Jotunheimen and Dovrefjell further west, and in order to validate this regional pattern, the distribution of permafrost has been mapped on the mountains Sølen and Elgåhogna in the Femunden region, Central-Eastern Norway. Empirical-statistical models based on BTS and logistic regression were developed for each mountain, and validated with DC resistivity measurements. Permafrost was found to be probable down to 1100–1300 m a.s.l., which validates the regional west–east gradient in the altitudinal permafrost limit. Elevation is the main controlling factor for permafrost distribution on both Sølen and Elgåhogna. In addition, potential solar radiation and the surface wetness pattern were significant in the Sølen and Elgåhogna models, respectively. Mean annual ground surface temperatures are high and generally above zero, which contradicts the results from the BTS and DC resistivity. This together with observed air ventilation funnels through the snow cover suggest thermal advection and strong thermal offsets in the openwork blockfields.

A REGIONAL INVENTORY OF ROCK GLACIERS AND ICE-CORED MORAINES IN NORWAY

Lilleøren, K.S. and Etzelmüller, B., 2011.Aregional inventory of rock glaciers and ice‐cored moraines in Norway. Geografiska Annaler: Series A, Physical Geography, 93, 175–191. DOI: 10.1111/j.1468‐0459.2011.00430.x Abstract Landforms in Norway indicating present and former permafrost have been compiled in order to discuss Holocene landform development patterns. In total 307 permafrost landforms have been mapped, consisting of rock glaciers and ice‐cored moraines. The landforms were classified as active/inactive (intact) or relict landforms, and by origin. In northern Norway, permafrost landforms exist down to sea level and the majority of the landforms are relict talus‐derived rock glaciers. In southern Norway, permafrost landforms are restricted to high elevations and the majority of the landforms are connected to glacial activity and classified as active. In the present paper, this contrasting pattern is interpreted to reflect that different processes leading to a permafrost landform also represent different ages and climatic regimes during their formation. The inventoried landforms reproduce the modelled permafrost distribution for Norway satisfactorily.

Factors Controlling the Distribution of Mountain Permafrost in the Northern Hemisphere and Their Influence on Sediment Transfer

Abstract The distribution of mountain permafrost in the northern hemisphere depends on topographic and climatic factors, ranging from the maritime conditions of Iceland over transitional conditions in southern Norway to continental conditions in Mongolia, and from alpine mountains to paleic mountains. This study discusses the different environmental factors that govern permafrost distribution based on personal studies and a literature review. It is hypothesized that the thermal state of the ground is an important parameter to understand the time and spatial scale of sediment transfer and landscape development in cold mountainous regions. This is exemplified for the cases of rock walls, glacier forefields, rock glaciers, and the case of sediment remobilization due to glacier advance. The authors propose that thorough knowledge of the ground thermal regime is an important basis for addressing sediment budgets in space and time.

Small-scale variation of snow in a regional permafrost model

The strong winds prevalent in high altitude and arctic environments heavily redistribute the snow cover, causing a small-scale pattern of highly variable snow depths. This has profound implications for the ground thermal regime, resulting in highly variable near-surface ground temperatures on the metre scale. Due to asymmetric snow distributions combined with the nonlinear insulating effect of snow, the spatial average ground temperature in a 1 km2 area cannot be determined based on the average snow cover for that area. Land surface or permafrost models employing a coarsely classified average snow depth will therefore not yield a realistic representation of ground temperatures. In this study we employ statistically derived snow distributions within 1 km2 grid cells as input to a regional permafrost model in order to represent sub-grid variability of ground temperatures. This improves the representation of both the average and the total range of ground temperatures. The model reproduces observed sub-grid ground temperature variations of up to 6 C, and 98 % of borehole observations match the modelled temperature range. The mean modelled temperature of the grid cell reproduces the observations with an accuracy of 1.5 C or better. The observed sub-grid variations in ground surface temperatures from two field sites are very well reproduced, with estimated fractions of sub-zero mean annual ground surface temperatures within±10 %. We also find that snow distributions within areas of 1 km2 in Norwegian mountain environments are closer to a gamma than to a lognormal theoretical distribution. The modelled permafrost distribution seems to be more sensitive to the choice of distribution function than to the fine-tuning of the coefficient of variation. When incorporating the small-scale variation of snow, the modelled total permafrost area of mainland Norway is nearly twice as large compared to the area obtained with grid-cell average snow depths without a sub-grid approach.