89 research outputs found
A comparison of glacier melt on debris-covered glaciers in the northern and southern Caucasus
Get PDFThe glacier coverage in the Caucasus Mountains underwent considerable changes during the last decades. In some regions, the observed reduction in glacier area is comparable to those in the European Alps and the extent of supra-glacial debris increased on many glaciers. Only a few glaciers in the Caucasus are monitored on a regular basis, while for most areas no continuous field measurements are available. In this study, regional differences of the conditions for glacier melt with a special focus on debris covered glacier tongues in the well-studied Adyl-su basin on the northern slope of the Caucasus Mountains (Russia) is compared with the Zopkhito basin which has similar characteristics but is located on the southern slope in Georgia. The paper focuses on the effect of supra-glacial debris cover on glacier summer melt. There are systematic differences in the distribution and increase of the debris cover on the glaciers of the two basins. In the Adyl-su basin an extensive debris cover on the glacier tongues is common, however, only those glacier tongues that are positioned at the lowest elevations in the Zopkhito basin show a considerable extent of supra-glacial debris. The observed increase in debris cover is considerably stronger in the north. Field experiments show that thermal resistance of the debris cover in both basins is somewhat higher than in other glaciated regions of the world, but there is also a significant difference between the two regions. A simple ablation model accounting for the effect of debris cover on ice melt shows that melt rates are considerably higher in the northern basin despite a wider debris distribution. This difference between the two regions can be attributed to different meteorological conditions which are characterised by more frequent cloud cover and precipitation in the south. Furthermore ablation is strongly influenced by the occurrence of supra-glacial debris cover in both basins, reducing the total amount of melt on the studied glaciers by about 25 %. This effect mitigates glacier retreat in the lower sectors of the ablation zones considerably. The sensitivity to moderate changes in the debris cover, however, is rather small which implies only gradual changes of the melt regime due to debris cover dynamics during the near future
Avalanche feeding of the Djankuat Glacier
Get PDFIn order to evaluate the contribution of snow avalanches, coming from outside the glacier limits, into the seasonal accumulation, an original algorithm is proposed for glaciers with ongoing terrestrial mass balance programme. It was tested on the Djankuat Glacier, Caucasus. A case study was realized for 1998/99 balance year when accumulation value was the closest to its long-term mean over the 46-year-long monitoring period. Snow avalanche feeding turned out to be only 2.8 per cent of total accumulation that is about an order of magnitude smaller than assumed hitherto
Influence of the surface moraine on the state of Djankuat Glacier (Central Caucasus) by 2025
Get PDFCurrent glaciation of the Central Caucasus is in the regressive stage of evolution. Observed long rising of the air temperature in the ablation seasons (almost 1 °C since 1968 on the Djankuat Glacier) together with insignificant growth of winter precipitation caused a long period of the glacier degradation: since 1871 the mass balance of the glacier, with rare exceptions, remained negative. During this time, the glacier has lost about 60 m w.e. mainly by areas of the smallest ice thickness, i.e. the steep slopes of the rocky framing of the fi n basin which become exposing from ice due to conditions of extreme instability. In parallel with the processes of freezing and thawing in cracks, this leads to a signifi ant increase in the frequency of rockfalls. In 2001–2003, huge rockfalls occurred on the glacier from the slopes, which had recently undergone deglaciation. The last one covered 4% of the glacier surface with about 70 000 m3 of clastic products. The marine cover differs significantly from the open ice surface in its thermal characteristics, which affect the structure of the thermal balance and the absolute values of ablation. The temperature inside the moraine is positive throughout the ablation season, even at a depth of 60 cm, but the absolute values of daily maximum melting are five times lower than those on open ice. The influence of the moraine material layer on the ablation is determined not only by its thickness, but also by the structure. The fi ld experiment conducted in 2011 demonstrated that melting under a layer of coarse-grained material (particle diameter 16–17 cm) is four times faster than under a layer of fi e-grained (7–8 cm) material equal in thickness. The study of the influence of the surface moraine and the account of its further growth in thickness and area made it possible to predict changes in the surface of the glacier by 2025. The climatic forecast was made using the HadCM3 model (A2 climate change scenario). Data on air temperature and precipitation were used to construct a predictive fi ld of the mass balance of the Djankuat Glacier for each year until 2025. Th s became possible by the use of a quantitative parameterized relationship between the mass balance of the entire glacier and each of its points, identifi d in the study of the total mass transfer of the glacier, as well as parameterized linear regression equations. The forecast of hypsometry of the Djankuat Glacier made it possible to determine that by 2025 the depression of the tongue areas covered by the moraine will be 7–15 m (or 42–45%) smaller than areas of the open ice. Th s means that at the present stage of the glaciation development the surface moraine plays a role in the evolution of the glacier, commensurable with the climate factor
Influence of Sub-Debris Thawing on Ablation and Runoff of the Djankuat Glacier in the Caucasus
No full textSuperficial moraines grew in size during the entire 32-year-long period of direct monitoring of water and ice balance of the Djankuat Glacier in the Caucasus. The total area of debris cover on the glacier increased from 0.104 km2 (3% of the entire glacier surface) in 1968 to 0.266 km2 (8% of the glacier) in 1996. Such rapid dynamics of moraine formation greatly influences the ablation rate and distorts fields of mass-balance components. Sub-debris thawing can be calculated by means of a model, which describes the role of debris cover for the thermal properties of a glacier. Its meltwater equivalent depends mainly on debris thickness. In 1983 and 1994 the debris cover was repeatedly mapped over the whole glacier portion that was covered with morainic material. Sub-moraine ablation increases (vs. pure ice surface) under the thin, less than ca. 7-8 cm, debris layer, whereas the thicker debris cover reduces the liquid runoff due to its shielding effect. Zones differing due to their hydrological effect are depicted on the glacier map and the degree of debris influence on ablation is estimated quantitatively. As a whole runoff from debris-covered parts of the Djankuat Glacier has diminished due to the dominant shielding effect. Variation of the terminus is also shown to be dependent on the evolution of superficial moraine.</jats:p
On a feedback of the share of avalanche alimentation with a glacier accumulation
Get PDFReleases of avalanches are an important factor of snow accumulation for many mountain glaciers. However, the quantitative estimate of the share of avalanche snow in the incoming part of the mass balance has not yet been standardized due to the lack of a universal methodological scheme for the calculation and collection of actual material. In rare cases, e.g. for the Djankuat Glacier in the Caucasus, this problem is partly solved. Here, the conceptual basis of the required calculations is created, and the input information has been supplied for many years by the route snow-measuring profling performed in the spring close to the date of the maximum of seasonal snow reserves and accompanied by direct feld mapping. Annually, avalanche deposits attributed to additional snow income from outside the glacier are recorded in all high-altitude morphological zones, with the exception of the lowest (< 2850 m) hypsometric belt, although in the half-century history of monitoring there were cases when snow avalanches reached it. Te volume of avalanche deposits was calculated for 15 years afer 1991/92, and each time it correlated with the gross snow accumulation of the corresponding balance year. Te contribution of snow avalanches to the income of substances on the glacier varies from 1.8 to 10.0% and averages 4.7%. Paradoxical (but only at frst glance) conclusion based on the analysis of data on volumes of avalanche and total accumulation is the feedback of these indicators (r = -0.58). It should be noted that the share of avalanche contribution to alimentation of the glacier has a more convincing feedback with accumulation and background snow content of winter (r = -0.72). Probably, the revealed tendency of increasing role of the additional avalanche alimentation in low-snow years (and vice versa) is not limited by the only reference object, and it is true for any glacier prone to the avalanche influence
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Geodetic mass balance of Azarova glacier, Kodar Mountains, eastern Siberia, and its links to observed and projected climatic change
Get PDFThe Kodar Mountains in eastern Siberia accommodate 30 small, cold-based glaciers with a combined surface area of about 19 km2. Very little is known about these glaciers, with the first survey conducted in the late 1950s. In this paper, we use terrestrial photogrammetry to calculate changes in surface area, elevation, volume and geodetic mass balance of the Azarova Glacier between 1979 and 2007 and relate these to meteorological data from nearby Chara weather station (1938-2007). The glacier surface area declined by 20±6.9% and surface lowered on average by 20±1.8 m (mean thinning: 0.71 m a-1) resulting in a strongly negative cumulative and average mass balance of -18±1.6 m w.e. and -640±60 mm w.e.a-1 respectively. The July-August air temperature increased at a rate of 0.036oC a-1 between 1979 and 2007 and the 1980-2007 period was, on average, around 1oC warmer than 1938-1979. The regional
climate projections for A2 and B2 CO2 emission scenarios developed using PRECIS regional climate model indicate that summer temperatures will increase in 2071–2100 by 2.6-4.7°C and 4.9-6.2°C respectively in comparison with 1961–1990. The annual total of solid precipitation will increase by 20% under B2 scenario but decline by 3% under A2 scenario. The length of the ablation season will extend from July–August to June-September. The Azarova Glacier exhibits high sensitivity to climatic warming due to its low elevation, exposure to comparatively high summer temperatures, and
the absence of a compensating impact of cold season precipitation. Further summer warming and decline of solid precipitation projected under the A2 scenario will force
Azarova to retreat further while impacts of an increase in solid precipitation projected under the B2 scenario require further investigation
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A glacier inventory for the Buordakh Massif, Cherskiy Range, northeast Siberia, and evidence for recent glacier recession
Get PDFThe Buordakh Massif, in the Cherskiy Range of northeast Siberia, contains mountains over 3000 in and, despite its and climate, numerous glaciers. This paper presents a glacier inventory for the region and documents some 80 glaciers, which range in size from 0.1 to 10.4 km(2) (total glacierized area is ca. 70 km(2)). The inventory is based on mapping derived from Landsat 7 ETM+ satellite imagery from August 2001, augmented with data from field investigations obtained at that time. The glaciers in this region are of the 'firn-less,' cold, continental type, and their mass balance relies heavily on the formation of superimposed ice. The most recent glacier maximum extents have also been delineated, and these are believed to date from the Little Ice Age (ca. A.D. 1550-1850). Glacier areal extent has reduced by some 14.8 km(2) (ca. 17%) since this most. recent maximum. Of the 80 glaciers catalogued, 49 have undergone a measurable retreat from their most recent maximum extent
Role of Debris Cover in the Thermal Physics of Glaciers
No full textAbstractA mathematical model is presented of non-stationary melting processes of ice including particles of morainic material. The problem is treated as a Stephen-type one with the phase boundary of ice melting being located under the debris cover. The main terms of the heat-balance equation for a glacier surface are solar radiation and convective heat transfer. The quantitative relationships characterizing the effect of glacier run-off augmentation from under a thin layer of debris cover are obtained for different bulk moraine concentrations inside the ice. The concept of equivalent time is introduced. It is defined as the time elapsed until the moment the sub-moraine ice-ablation rate becomes equal to the ablation rate of clean ice. This moment signifies the beginning of the shielding stage. Thus, a glacier can be considered as a self-controlling system with respect to its summer run-off. A series of numerical tests for Djankuat glacier, Central Caucasus, has been carried out. The dynamics of moraine-cover growth and alterations of seasonal ablation rate under debris show perfect agreement between the computed data and the results of 14 years of direct observations. Some practical recommendations concerning artificial blackening of a glacier surface for augmentation of liquid run-off are presented. Conditions promoting increase of run-off are: relatively high albedo, relatively low summer air temperature, and relatively small convective heat transfer between the air and the ice surface. The method of artificially blackening a glacier surface is by means of a durable thin dark polymer film. In conclusion, some further aspects of the problem are discussed.</jats:p
Role of Debris Cover in the Thermal Physics of Glaciers
No full textAbstractA mathematical model is presented of non-stationary melting processes of ice including particles of morainic material. The problem is treated as a Stephen-type one with the phase boundary of ice melting being located under the debris cover. The main terms of the heat-balance equation for a glacier surface are solar radiation and convective heat transfer. The quantitative relationships characterizing the effect of glacier run-off augmentation from under a thin layer of debris cover are obtained for different bulk moraine concentrations inside the ice. The concept of equivalent time is introduced. It is defined as the time elapsed until the moment the sub-moraine ice-ablation rate becomes equal to the ablation rate of clean ice. This moment signifies the beginning of the shielding stage. Thus, a glacier can be considered as a self-controlling system with respect to its summer run-off. A series of numerical tests for Djankuat glacier, Central Caucasus, has been carried out. The dynamics of moraine-cover growth and alterations of seasonal ablation rate under debris show perfect agreement between the computed data and the results of 14 years of direct observations. Some practical recommendations concerning artificial blackening of a glacier surface for augmentation of liquid run-off are presented. Conditions promoting increase of run-off are: relatively high albedo, relatively low summer air temperature, and relatively small convective heat transfer between the air and the ice surface. The method of artificially blackening a glacier surface is by means of a durable thin dark polymer film. In conclusion, some further aspects of the problem are discussed.</jats:p
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An Assessment of the Recent Past and Future Climate Change, Glacier Retreat, and Runoff in the Caucasus Region Using Dynamical and Statistical Downscaling and HBV-ETH Hydrological Model
No full textThe paper discusses the observed and projected warming in the Caucasus region and its implications for glacier melt and runoff. A strong positive trend in summer air temperatures of 0.05 degrees C a(-1) is observed in the high-altitude areas providing for a strong glacier melt and continuous decline in glacier mass balance. A warming of 4-7 degrees C and 3-5 degrees C is projected for the summer months in 2071-2100 under the A2 and B2 emission scenarios respectively, suggesting that enhanced glacier melt can be expected. The expected changes in winter precipitation will not compensate for the summer melt and glacier retreat is likely to continue. However, a projected small increase in both winter and summer precipitation combined with the enhanced glacier melt will result in increased summer runoff in the currently glaciated region of the Caucasus (independent of whether the region is glaciated at the end of the twenty-first century) by more than 50% compared with the baseline period
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