Department of Cryology and Polar Research,
Institute of Geography,
Nicolas Copernicus University,
Fredry 6/8, 97-100 Toruń, POLAND,
Irek Sobota, Marek Grześ
Winter balance of Waldemar Glacier in 1996 - 1998
The investigations of snow cover lasted for three spring seasons. The measurements were taken in the first half of May of each season. It was assumed that snow photographs from that period of time correspond roughly with the maximum values. The main aim of the investigations was to determine water resources in snow and estimate the input part of the mass balance equation for the Waldemar Glacier. The measurements included the whole catchment basin of the glacier (4.03 km2) and referred to the following elements: thickness, density, water equivalent, structure, vertical temperature distribution and electrical conductivity. As the outflow from the glacier is also active in winter season, an attempt of assessing its value was undertaken. It was based on the observations of water migration in the snow cover at the glacier's marginal and extra-marginal part.
An aluminium hand sonde was used for measuring depths of snow cover. The measurements were taken three times at every point. If the snow layer was difficult to get through, snow pits were dug. In order to localise the measurement points a 1:1000 map published in 1995 as well as GSP was used. The basic measurement points were the so-called ablation poles installed the previous summer season. The samples of snow for determining the density were collected with a steel cylinder of 100 cm2 of the cross-sectional area. The sample weights were assessed with a professional dynamo-metric balance exact to 5 grams. Temperature and electrical conductivity were measured the equipment of "Elmetron" company. A principle of an even distribution as well as their representativity dictated the choice of the measurement points. The basis for calculations and graphic presentation of spatial variation of snow cover thickness were the results of 125 to 155 soundings, which means about 40 measurements per a square kilometre.
The so-called snow photograph is the basis for estimating the size of snowfall on the areas excluded from systematic observations. The western shores of Spitsbergen receive about 400 mm of precipitation annually. According to J.O. Hagen and others (1993) the central parts of the island does not get even that much. Precipitation values on the glaciers in the western part of Spitsbergen often exceed the equivalent of 2-4-m layer of snow. Snow lingers here for 250-270 days a year and, as K. Pereyma and others (1988) stresses, it is a dominating surface element determining all the climatic and hydromorphological consequences. In the case of such a small glacier, the occurrence of snow blowing as well as its accumulating at the leeward side of any elevations and at the foot of front part is significant. Catabatic winds and local orographical conditions are the main factors responsible for snow cover thickness variation (0-6 m) within the catchment basin of the Waldemar Glacier.
From the point of view of the glacier mass balance assessment, the knowledge of the snow share in the value of annual precipitation is extremely important. The closest meteorological station is in Ny Alesund. In 1995 the snow share there was about 80%. In 1991-1997 the average snow share was about 69%. It may be assumed that those values are representative for the Kaffioyra area as well. Not only the size of snowfall and winter retention belongs to the factors determining mass balance; anemometric conditions are also of great importance. The thickness variation of the snow cover within the Waldemar Glacier's catchment basin exceeded 6 m. The ridges of the ice-morainal ramparts and the steepest parts of front part have no snow cover. The factors, which do not allow for snow redeposition, are winter warmings as well as the occurrence of wind-resistant ice layers. It must be stressed that ice layers worsen the conditions for later redeposition of snow. The size of snow redeposition starts playing a significant role at the wind speed over 4 m/s. In May 1997 and 1998 an attempt to determine the value of snow redeposition during low snowstorms was undertaken. To achieve that a simple snow deflation gauge was used. It was discovered that at the wind speed of 4.8 - 5.0 m/s the deflation index was about 1000 kg/running metre. At the speeds lower than 5 m/s (3.8 - 4.2 m/s) a considerable decrease of the deflation index was noted. Its values reached up to 300 - 350 kg/running metre daily. The measurements were taken on the surfaces of medium hardness values (R2 according to the classification of International Commission of Snow and Ice - ICSI).
In conclusion, all the factors presented above convince that the description of snows conditions on the basis of one snow photograph must be treated only as great approximation of real situation on the glacier.
SEASONAL AND SPATIAL VARIATION OF SNOW ACCUMULATION
Meteorological conditions play a significant role in ice cover forming on the glacier. The snow cover's thickness is tightly related to the value of the snowfall during a given season. The figure 1 shows the course of the temperature line graph on the Kaffioyra area in April and May 1998. The temperature values were taken every half an hour with an automatic meteorological gauge station "Davis". As it is clearly visible, sudden temperature rises above 0°C occurred rather often. Such a phenomenon, especially in winter, leads to ice covers' appearing. Ice covers are an important factor influencing snow redeposition in the glacier's surroundings.
Spatial distribution of glacier snow thickness is implied by local conditions, no matter what the weather conditions are. A characteristic feature of most glaciers is that snow accumulation grows with the increase of the height above sea level. This phenomenon is a result of different weather conditions at the individual parts of the glacier. It is especially visible in the case of the glaciers of big difference between firn part and front part. In spite of its small area, the Waldemar Glacier shows great spatial variation of snow accumulation. This glacier also follows the above rule. Snow accumulation was different during the individual seasons. The highest increase of the snow accumulation with the change of the altitude was observed in 1996 (Figure 2); the gradient of accumulation 30 cm of w.e. per every 100 m of height. The discussed season snow accumulation was highest, mainly in the firn part. The increased snow accumulation there, if compared to the two next seasons, at the same accumulation at front part of the glacier resulted in accumulation gradients being much lower in 1997 and 1998. Their values were 20 cm of w.e. and 16 cm of w.e. respectively every 100 m of height. The predominant direction of wind during accumulation is also important (J. Jania 1993). The size of the snow cover at front part of the glacier plays a significant role in the value of gradient. That is the zone where the processes of snow redeposition take place due to wind influence. At front part of the Waldemar Glacier there are the places which lack the snow cover. Big amounts of blown snow accumulate at the Waldemar River gap area. Snow redeposition, beneath the breaking of the long profile is a factor determining accumulation increase as well. Such an occurrence was noted at the glaciers of the south Sitsbergen by K. Migała and J. Pereyma (1988) among others. Interrelations between the size of snow accumulation and the height above sea level confirm the values of the correlation coefficient: 0.95; 0.95 and 0.85.
Fig. 2 Snow accumulation changes of Waldemar Glacier in the vertical profile in 1996, 1997 & 1998.
A great spatial variation of snow accumulation is noted on the Waldemar Glacier (Figures 3 - 5). During the winter season of 1995/96 the thickest layers of snow were noted in the northern part of the glacier, on its firn part as well as at the foot of the Grafjelet range surrounding the glacier from the south (Figure 3). The highest values of the water equivalent amounted to 120 cm. The lowest values of snow cover thickness were observed in the front part of the glacier and at the foot of the medial moraine (up to 30 cm of w.e.). In 1997 the spatial distribution of snow was similar (Figure 4). The accumulation values, however, reached only a half of the previous values, mainly in the firn part (60 cm of w.e.). A patter of winter snow accumulation recorded in 1998 was very much alike (Figure 5). The thickest layer of snow, 60-80 cm of w.e., was characteristic for the glacier areas located at the foot of the mountain ranges surrounding the glacier. A bit lower amounts of snow were noted in the centre of the firn part, which was the result of intense snow blowing out there. The size of snow accumulation at the front of the glacier and at the foot of the medial moraine was, as during the previous seasons, lowest (10-20 cm of w.e.).
The size of winter snow accumulation was highest in 1995/95 season (75 cm of w.e.). In 1996/97 and 1997/98 in was similar and amounted to 48 cm of w.e. and 42 cm of w.e. respectively. V. I. Mikhaliov and E.M. Singer (1975) as well as J. Jania and J.O. Hagen (1996) recorded similar values for other Svlabard glaciers. Average snow accumulation estimated for the years 1967-93 for the Midre Loven Glacier, which has similar morphometry that the Waldemar Glacier and is located about 35 kilometres to the north from it, is 75 cm of w.e. (J. Jania i J.O. Hagen 1996). That value does is not much different from the average snow accumulation for the years 1995-98 for the Waldemar Glacier, which reached about 60 cm of w.e.
Some kind of pattern in the spatial distribution of winter snow accumulation on the Waldemar Glacier is observed every winter season. The biggest accumulation is noted in its firn part and at the foot of mountain ranges. Most glaciers follow that rule. The distribution of the lowest values of snow accumulation, however, is more complicated. The Waldemar Glacier's zones of the thinnest snow covers exist at the front part up to the height of 220 m above sea level and at the foot of the medial moraine. That is the result of the wind conditions as well as the highest value of glacier's slope in that part of it. The slope of the front part of the glacier up to the height of 200 m above sea level is 10 - 11° (K.R. Lankauf 1997). The spatial variation of winter snow accumulation determines summer ablation to a great extent. Asymmetry of snow cover thickness is observed in nearly all the height zones. A similar pattern of snow distribution was described on the Hans Glacier (J. Jania 1993). The lowest snow cover thickness is noted at the places were the surface ablation values are the biggest. In the years 1995-98 snow accumulation on the Waldemar Glacier was 160 cm of w.e. It is 100-130 cm on average at the altitude of the year balance line (ELA). That value is similar for other glaciers of this part of Svalbard (V.S. Koryakin and others 1985).
SNOW COVER CHARACTERISTICS
Snow cover shows specific physico-chemical features. In its vertical profile many kinds of snow can be distinguished. They differ in the level of metamorphism metamorphosis, hardness and moistening. Very distinct snow layers can often be found with clear upper and lower limits. Snow structure reflects weather conditions existing at the time of snow cover forming. The snow surface changes thanks to snow deposition, melting, evaporation, erosion and sublimation. Detailed measurements of physico-chemical features, including temperature, electrical conductivity and hardness) as well as structure of the snow cover were taken at a few points of the Waldemar Glacier. The individual parameters were analysed according to the snow features and symbols used by International Commission of Snow and Ice (S.C. Colbeck 1990).
One of the most important features of snow cover is its density. To determine the snow density on the Waldemar Glacier, snow samples were collected with the use of a steel cylinder 100 cm2 of the cross-sectional area. The sample weights were assessed with a professional dynamo-metric balance exact to 5 grams. Snow density on the Waldemar Glacier ranged from 0.31 g/cm3 to 0.52 g/cm3 maximum. The lowest density values were noted in the surface layer of snow (Figure 6). It is mainly made of fresh snow of low level of compaction. A considerable density increase with the depth is observed in most profiles. It is the result of compaction of upper snow layers. A layer of strongly blown, coarse-grained snow of lower density can often be found at the bottom part of a snow cover.
Fig. 6 Snow density, temperature and conductivity on Waldemar Glacier (May 1998).
The average snow density of the Waldemar Glacier amounted to 0.42 g/cm3 in 1997 and 0.41 g/cm3 in 1998. As far as the glaciers of south Spitsbergen are concerned, these values amounted to 0.40 - 0.50 g/cm3 (K. Migala and J. Pereyma 1988).
High interrelation between snow depth and its temperature was observed at the most measurement points. The values of the coefficient were -0.87, -0.90, -0.92. The temperature on the surface is the highest and lowers distinctly when going deeper. The highest temperature value on the surface was -2.4°C at the height of 260 m above sea level (1998). In 1997 the lowest snow temperature -10.1°C, was measured at the depth of 100 cm, while in 1998 the lowest value, which amounted to -9.7°C, was found at the depth of 60 cm and altitude of 440 m above sea level. The average snow temperature on the Waldemar Glacier is -7.4°C.
The analysis of snow pits showed big differentiation of the character and features of snow cover in 1988. In 1997,on the other hand, snow cover was not differentiated (Figure 7). Fine- and medium-grained snow, which had vertical homogenous distribution with no interbeddings and ice layers, prevailed. Snow hardness analysis, according to International Commission of Snow and Ice symbols, informed about big snow homogeneity as well as hardness increase with depth. Snow of low (R2) and medium (R3) hardness degree predominated. Only one place of ice layer occurrence was found at the altitude of 380 m above sea level. Lack of ice layers indicates that the winter of 1996/97 was smooth.
The snow cover of 1998 had much more complicated character (Figure 8). All the analysed snow profiles layers of different graining and hardness were found. Fresh and fine-grained snow was discovered on the surface in most snow pits, whereas frozen and coarse-grained snow was found in the layer located directly on ice. The hardness values ranged from low (R2) to very high (R6). The fact that numerous ice layers existed should be stressed. The biggest amount of them was in the profiles of 410 and 440 m above sea level. Ice layers could be the result of catabatic winds, blowing during snow accumulation, which bring short periods of warmings and thus snow melting. The discussed profiles had highly diversified snow size composition and hardness. In the profile at the height of 440 m above sea level the following types of snow were found: fresh, fine-, medium- and coarse-grained as well as solid frozen snow. At the altitude of 410m the distinguished snow kinds included: fresh, fine-, medium- and coarse-grained as well as frozen with numerous ice layers. A great number of ice layers was also observed in the snow cover at the glacier's front (160 and 220 m above sea level). Ice layers of all the profiles were situated in their lower parts, thus they came into being at the beginning of winter. That conclusion finds its confirmation in the warmings easily observed in the course of temperature registered at the meteorological station in Ny Alesund. Ice layers compose an important indicator of seasons' beginnings at different parts of the glacier. In 1998, in spite of a big number of ice layers observed there, the winter snow accumulation began in the firn part of the Waldemar Glacier. A bigger number of ice layers at the front part of the glacier indicates that summer season was longer there.
Ice layers play a significant role in snow deposition. Moreover, their existence proves that snow short-term melting is possible despite fresh snow accumulation.
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