Irek Sobota
Department of Cryology and Polar Research,
Institute of Geography,
Nicolas Copernicus University,
Fredry 6/8, 97-100 ToruŮ, POLAND, irso@geo.uni.torun.pl

Irek Sobota


Ablation and outflow from Waldemar Glacier during summer season 1997

The studies of the ablation and the outflow from the Waldemar Glacier conducted in 1997 were a part the programme encompassing the glacierís mass balance that began in 1995. An attempt was made to connect the degree of ablation with the outflow from the basin and also with the outflow from the characteristic parts of the glacier.
The Waldemar Glacier possesses an area of 2.66 m2 and occupies 61 % of the basin closed by the ice-moraine ridges at the varine of the river. The ice cirque lies at 380-490 m a.s.l. and the front of the glacier at 130 m a.s.l.. The ablation measurements were taken every 5 days in 30 cities. Aluminium ablation poles were installed 1.1 m below ground level. To assess ablation, the figures from the measure sites installed on Waldemar Glacier in April and May 1997 were used as well.
The observed winter (1996/1997) accumulation amounted to 44 cm w.e.. It was 32 cm w.e. lower than the previous yearís (1995/1996) winter accumulation. Despite the small area and a relatively minor difference in height between the front and firn (365 m), a considerable spatial and temporal differentiation of ablation was observed. Besides the height gradient, this was caused by local conditions (exposure, ice melting, gradient, density and configuration of supraglacial stream beds). The highest figures of ablation for the period in question were observed at 250 m a.s.l. (Fig. 1). It amounted to 119 cm w.e. at 150 m a.s.l.. The gradient of ablation in particular periods circulated between 0.3 - 3.6 cm w.e. for 100 meters.
The term-surface ablation is not entirely precise. In the measurements of a melted ice layer, the so-called "ablation layer" was taken into consicleration. It is commonly known that ice melting takes also place on the border of crystal, which finally gives way to the white colour of the glacierís surface. The thickness of this layer was assessed each time. In the summer 1997 it amounted to 20 cm and disappeared entirely after heavy rains. The only case when one can talk about true surface ablation is when there is no "ablation layer". The development and the decline of the ablation layer will be a key issue of detailed studies in the upcoming summer.


The changes in the position of glacial zones on the summer were observed. The local conditions of ice melting are a key factor here (the kind of ice, moraine material, gradient) but the spatial differentiation of winter accumulation plays an important role as well. In the middle point of July the ablation zone encompassed 28 % of the glacierís surface. The surface included in the ablation zone was growing in time: 47 % (21.07.), 69 % (03.08.), 93 % (19.08.). At the end of the ablation season the zone embraced nearly the whole surface (98 %). During the ablation season in the upper parts of the glacier, at the foot of the mountains, there was a zone of dry snow. In the places of low gradient there was slush. Within the time of ablation a big area of slush was observed in the middle part of the glacier, between 240-300 m a.s.l. where the accumulation of snow was at its peak. What is more, a similar zone in the second half of the season was to some extent observed in firn. There was also another phenomenon noticed, namely slush avalanches.

Fig. 2 Characteristic balance areas on the Waldemarbreen - division (summer 1997) Outflows measurements points: number - stream bed -the dehydrated area of the glacier 1 - the Waldemar river - A+B+C 2 - the stream bed dehydrating the northern part of the glacier - A 3 - the stream bed dehydrating the southern part of the glacier - B+C 4 - the outflow from the dammed lake - C+BA 5 - the stream bed going parallel with the central moraine - BB 6 - the inflow to the dammed lake - CA+BA 7 - the stream bed flowing from firn - BA B = BA+BB+BC; C = CA+CB


Taking into account the whole period of the studies (last measurement 01.09.), the ablation of the Waldemar Glacier amounted to 66.9 cm w.e.. Converting to into the potential outflow, it made 1.739 mln m3 of water. The assessment of ablation made by means of the hydrogram of the outflow was based on the analysis of single runoffs from particular basins. It was only this analysis that gave satisfactory results. In the light of the aforementioned analysis it was observed that the contribution of the surface ablation in the total outflow (2.893 mln m3) amounted to 60 % and was 19 % lower than the one in 1996 (I. Sobota 1996, 1997). The reasons for this must be sought in high rainfalls. Between July 27th and September 31th 1997 the rainfall in upper part and at the glacierís front amounted respectively to 196 and 121 mm. The lower (59 %) winter accumulation of snow had also an impact on this. The glacier was divided into characteristic balance surfaces (Fig. 2). The borders roughly agreed with the partial watershed on the glacier. The analysis of the relation between the outflow and the ablation in this area did not produce any straight-forward interdependence. In some cases outflow exceeded ablation, in others the relation was reverse (Tab. 1, Fig. 2). This testifies to a very complicated system of the glacierís drainage and outflow. The Waldemar Glacier is very passive. In fact, it is deprived of cracks and glacial wells.

Table 1 Ablation and outflow from the characteristic areas of the Waldemar Glacier in the summer 1997.

The number of the stream bed
/the glacierís being dehydrated
Area [km2]Ablation [cm e.w.]IIIIIIIVV
1/A+B+C2,666,9100,01739400289267260,11,7
2/A0,7793,3139,5718410603158119,10,8
3/B+C1,8368,1101,81246230162578976,71,3
4/C+BA1,2458,587,472540082762587,61,1
5/BB0,5 42,964,121450042595250,42,0
6/CA+BA1,1357,585,9649750467078139,10,7
7/BA0,8483124,1697200---
I - The relation between the ablation of a given area and the total ablation of the glacier cm w.e. (%) II - The outflow from the glacierís surface (according to ablation), (m3) III - The total outflow of stream beds dehydrating particular areas of the glacier (m2) IV- The participation of the surface outflow (according to ablation) in the total outflow (%) V- The relation between the total outflow of stream beds and the ablation outflow from characteristic areas of the glacier

An important role in the outflow from the Waldemar Glacier is played by a dammed lake that appeared on the glacier. The lake collects considerable amounts of ablation water from about 1/3 of the glacierís area. About 29 % of the total outflow is being transformed in the lake. The drain lake is an inglacial tunnel in the central moraine ridge.
Together with the measurement of the outflow the marks of electric conductivity and suspension loads were mapped. The decrease in conductivity is proportional to the increase in the intensity of the main flow. It was also noted that the load of suspension goes up markedly when the intensity of flow increases. However, this relation applies only to proglacial stream beds and is connected with sunder plains and ice-moraine ridges being washed away.
It is impossible for now to depict the relation between ablation and outflow in move precise terms. The barriers are not only pure methodological difficulties. It is also a matter of relatively superficial knowledge of the Waldemar Glacier as regards its drainage system and outflow.


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