Hallgeir Elvehøy

Glacier mass-balance and length variation in Norway

Abstract The importance of glaciers in mainland Norway for runoff is reflected in the extensive glacier measurement record. Mass balance has been measured for 42 glaciers. Length (or front-position) records exist for about 60 glaciers, and nearly half of these are presently measured. The mass-balance and front-position data have been analyzed with respect to spatial and temporal variations. The maritime glaciers with a large annual mass turnover have had a mass surplus between 1962 and 2000. In contrast, the continental glaciers with smaller summer and winter balances had a mass deficit over the same period. Since 2001 all monitored glaciers have had a marked mass deficit. The Norwegian glaciers have all retreated during the 20th century. However, both local and regional variations have been observed. Advances were recorded around 1910, around 1930, in the second half of the 1970s and around 1990. This last advance stopped in most glaciers at the turn of the century.

Distributed mass-balance and climate sensitivity modelling of Engabreen, Norway

Abstract Assessing the impact of possible climate change on the water resources of glacierized areas requires a reliable model of the climate–glacier-mass-balance relationship. In this study, we simulate the mass-balance evolution of Engabreen, Norway, using a simple mass-balance model based on daily temperature and precipitation data from a nearby climate station. Ablation is calculated using a distributed temperature-index method including potential direct solar radiation, while accumulation is distributed linearly with elevation. The model was run for the period 1974/75–2001/02, for which annual mass-balance measurements and meteorological data are available. Parameter values were determined by a multi-criteria validation including point measurements of mass balance, mass-balance gradients and specific mass balance. The modelled results fit the observed mass balance well. Simple sensitivity experiments indicate a high sensitivity of the mass balance to temperature changes, as expected for maritime glaciers. The results suggest, further, that the mass balance of Engabreen is more sensitive to warming during summer than during winter, while precipitation changes affect almost exclusively the winter balance.

Using aerial photography to study glacier changes in Norway

Abstract The Norwegian Water Resources and Energy Administration has photographed glacial areas in Norway for several decades. Detailed maps or digital terrain models have been made for selected glaciers from vertical aerial photographs. Multiple models of seven glaciers have been used here to calculate glacier volume change during the time between mappings using the geodetic method. Analyses and results are presented and compared with traditional mass-balance measurements. We estimated uncertainties of ±1.3–2.7mw.e. for the geodetic method, and ±1.3 –3.5mw.e. for the traditional method. The discrepancies between the methods varied between 0.4 and 4.7 mw.e. All glaciers decreased in volume from the 1960s/70s to the 1990s, except Hardangerjøkulen. This glacier experienced a significant increase in volume: the geodetic and traditional methods showed net balance values of +6.8m and +9.4mw.e., respectively. Trollbergdalsbreen had the largest total volume loss: the geodetic and traditional methods showed net balance values of –12.3 and –16.8mw.e.

Investigations on intra-annual elevation changes using multi-temporal airborne laser scanning data: case study Engabreen, Norway

Abstract Key issues of glacier monitoring are changes in glacier geometry and glacier mass. As accurate direct measurements are costly and time-consuming, the use of various remote-sensing data for glacier monitoring is explored. One technology used and described here is airborne laser scanning. The method enables the derivation of high-quality digital elevation models (DEMs) with a vertical and horizontal accuracy in the sub-metre range. Between September 2001 and August 2002, three laser scanner data acquisition flights were carried out, covering the whole area of Engabreen, Norway, and corresponding well to the measurement dates for the mass-balance year 2001/02. The data quality of the DEMs is assessed (e.g. by comparing the values with a control area which has been surveyed independently or GPS ground profiles measured during the flights). For the whole glacier, surface elevation change and consequently volume change is calculated, quantified and compared with traditional mass-balance data for the same time interval. For the winter term, emergence/submergence velocity is determined from laser scanner data and snow-depth data and is compared with velocity measurements at stakes. The investigations reveal the high potential of airborne laser scanning for measuring the extent and the topography of glaciers as well as changes in geometry (Δarea, Δvolume).

Geodetic mass balance of the western Svartisen ice cap, Norway, in the periods 1968-1985 and 1985-2002

Abstract The geodetic mass balance of the western Svartisen ice cap in northern Norway is determined, in this work, from photogrammetry on vertical aerial photographs taken in 1968, 1985 and 2002. The existing 1968 digital terrain model (DTM) was generated using analogue photogrammetry, and the 1985 and 2002 DTMs are newly generated using digital photogrammetry. The geodetic mass balance for 1968–85 is –2.6±0.8mw.e., and for 1985–2002 it is –2.0±1.6mw.e. The area of western Svartisen decreased from 190 km2 in 1968, to 187 km2 in 1985 and to 184 km2 in 2002. The outlet glacier Flatisen in the southeast retreated 1700 m over the two periods. The geodetic mass balance is also determined for Engabreen drainage basin, as –2.1±0.9mw.e. for the first period, and –0.3±2.4mw.e. for the second. The results for Engabreen are compared to traditional mass balances, and the large deviations cannot be explained from uncertainties determined for the geodetic method. The assessed errors contributing to the uncertainty in the geodetic mass balance are elevation errors, uncertainties from the applied melt correction, and the use of Sorge’s law, assuming constant snow thickness and density.

Velocity measurements on Engabreen, Norway

Abstract Horizontal velocity measurements on the lower part of Engabreen, Norway, were made from repeat aerial photography. IMCORR software, which has been widely used to measure velocities from satellite images, was used to make the measurements. This is the first known successful use of IMCORR on aerial photographs. Supplementary horizontal velocity measurements were made from repeat measurements of stakes, giving velocities over different periods and also in areas that are too slow-moving to register a measurable velocity after only a few days.

Calculation of drainage divides beneath the Svartisen ice-cap using GIS hydrologic tools

The Svartisen Hydropower Scheme is Norways most recent hydropower development. Most of the runoff from West Svartisen (221 km2, Fig. 1) is delivered to the power station via 60 intakes around the western and eastern ice-caps, including one subglacial intake located beneath the Engabreen outlet glacier. Estimates of water input to each intake are important for management of the power station. Average water inputs are obtained by integrating area-specific runoff over the intake catchment area. Previous calculations of the positions of catchment divides on Svartisen have been based upon ice surface topography alone and are thus a mapping of ice divides. However, meltwater flow along the glacier bed is driven by a gradient in hydraulic head, which is dependent on bed topography as well as ice surface topography. Calculations on other glaciers (Bjornsson 1988, Kennett 1990) show that the positions of water divides can differ significantly from ice divides.

Modelling of historic variations and future scenarios of the mass balance of Svartisen ice cap, northern Norway

Abstract In glacier-dominated catchments, glaciers have an important effect on the water balance. It is important to understand the glacier control on inflow in order to assess historic trends and future scenarios. The mass balance of a 100 km2 glacier sub-basin of Svartisen ice cap, northern Norway, was reconstructed for 1917 to 1995. The reconstruction was carried out using three different methods, the hydrological method, the correlation between mass balance and meteorological observations and a precipitation-degree-day model. Calibration data were derived from field observations, map comparisons and correlation of observations at different glaciers. The reconstructed series showed a total loss of ∼3 × 109 m3 of water, most of which occurred between 1920 and 1950. After 1950, the net balance increased gradually and is currently near equilibrium with the present climate. Suggested climate scenarios for this region gave a loss between zero and 5 ×109 m3 of water until the year 2050.