Showing papers on "Accumulation zone published in 1989"

Calculation of Glacier Ablation from Air Temperature, West Greenland

Abstract: Recent measurements by the Geological Survey of Greenland (GGU) confirm a relation between glacier ablation and air temperature expressed in the form of positive temperature sums. The relation has already been used for the simulation of runoff from glacier-covered basins but might also be suitable for calculating ablation under alternative climates.

Hydrological Investigations at Biafo Glacier, Karakoram Range, Himalaya; an Important Source of Water for the Indus River

Abstract: Over 80% of the flow of the Upper Indus River is derived from less than 20% of its area: essentially from zones of heavy snowfall and glacierized basins above 3500 m elevation. The trans-Himalayan contribution comes largely from an area of some 20 000 km2 of glacierized basins, mostly along the axis of the Greater Karakoram range and especially from 20-30 of the largest glacier basins. Very few glaciological investigations have so far been undertaken in this the major glacierized region of Central Asia. Biafo Glacier, one of the largest of the Karakoram glaciers, drains south-eastwards from the central Karakoram crest. Its basin covers a total area of 853 km2, 628 km2 of which are permanent snow and ice, with 68% of the glacier area forming the accumulation zone. This paper describes investigations of snow accumulation, ablation, glacier movement, and glacier depth undertaken in the period 1985–87, set against a background of investigations carried out over the last 130 years. Biafo Glacier differs from most of the other Karakoram glaciers in being nourished mainly by direct snowfall rather than by avalanching; this has the advantage of allowing extensive investigation of accumulation over a broad range of altitude. Snow-accumulation studies in the Biafo Glacier basin have indicated that annual accumulation varies from 0.9 to 1.9 m of water equivalent between 4650 and 5450 m a.s.l. This suggests an annual moisture input above the equilibrium line of approximately 0.6 km3. Monopulse radar measurements indicate the presence of ice thickness as great as 1400 m at the equilibrium line, although these results may not be completely reliable. Mean surface velocity during the summer of 0.8 m d−1 has been measured near to the equilibrium line. Calculations of annual ice flux through the vertical cross-profile at the equilibrium line indicate a throughput of 0.7 km3 a−1. Estimates from stake ablation measurements also suggest that ice loss on Biafo Glacier is about 0.7 km3 a−1. The close agreement between these three sets of measurements is reassuring, indicating that the ablation zone of Biafo Glacier, whose area covers 0.09% of the whole Upper Indus basin, produces approximately 0.9% of the total run-off. However, it should be mentioned that this estimate does not include water originating from seasonal snow melt, either above or below the equilibrium line, or from rainfall. Net annual ice losses due to wastage of the glacier since 1910 are probably of the order of 0.4-0.5 m a−1; this would represent between 12 and 15% of annual water yield from melting ice.

The storage of water in, and hydraulic characteristics of, the firn of South Cascade Glacier, Washington State, U.S.A.

Abstract: The porosity and water saturation of the firn of South Cascade Glacier were measured in order to determine both the volume of water stored in it and the significance of this water content for the water volume stored in the glacier. The distance to water below the firn surface was found never to be greater than 4 m, and the average thickness of the water-saturated layer was estimated to be 1.25 m. The average firn porosity was 0.15, the water saturation was 0.61, and the total volume of water stored in the firn was approximately 1.78 × 105 m3 representing about 12% of the total spring storage. The water table was found to exhibit a pattern of diurnal fluctuation which starts in late June or early July, indicating that melt water from the accumulation zone may pressurize the bed at diurnal frequencies. The depth-averaged permeability was found to be 1.5 × 10−5 m/s, a value which compares favorably with those from other studies.

Mass Balance and Volume of South Cascade Glacier, Washington 1958–1985

Abstract: The mass balance of South Cascade Glacier has been calculated by means of snow accumulation and ice ablation measurements since 1958. The summation of the net balance values for the 1958–85 period is −10.0 meters water equivalent. Topographic maps of the glacier were made from late summer vertical aerial photography in 1958, 1961, 1964, 1977, 1980 and 1985. In addition, the topography in the late summer of 1970 is well known from the theodolite survey of about 10 points on the glacier surface. The mass balance and photogrammetry are independent measurements of the cumulative volume change. The volume change between 1958 and 1985, measured from maps and adjusted for the density of ice, is −12.7 m, multiplied by the area of the glacier. This discrepancy can be reconciled by using the density of firn in the accumulation zone, rather than ice, to convert the volume change to water equivalent. Differences between the methods within the 27 year period are probably due to map errors, and indicate the need for caution in this type of comparison.

Mass balance history of blue glacier, washington, usa

Abstract: Mass balance and weather data have been collected for Blue Glacier since 1957. Annual net balance has been determined by combining the total mass loss from ice and firn melt with the residual snow remaining at the end of the summer season. In order to define confidence limits for the historical mass balance data set, it is necessary to quantify several sources of potential error. Preliminary analysis of the spatial variance of ice melt within the ablation zone and the variance of snow density within the residual snow of the accumulation zone indicate that neither of these parameters are likely to be a source of significant error. The largest potential source of error in computing the mass balance of the glacier as a whole is the migration of an ice divide.

SOME DYNAMICS STUDIES ON URUMQI GLACIER No. 1, TIANSHAN GLACIOlOGICAl STATION, CHINA

Abstract: The zero isopleth of surface areal strain-rate is roughly parallel to, but below, the equilibrium line of the glacier. In the middle and lower parts of the ablation area, the basal temperature is either close to or at the melting point, whereas above and around the equilibrium line the glacier is frozen to its bed. The basal bulk ice is deforming continuously and inhomogeneously but, in the inner parts of the glacier, where the strain- rate is smaller, homogeneous deformation can only be assumed conditionally. In the ablation area, pure shear is predominant near the base of the glacier and simple shear becomes progressively more important from the inner parts of the glacier towards its margins.