A comparison of glacier melt on debris-covered glaciers in the northern and southern Caucasus

The 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

Late-20th-century changes in glacier extent in the Caucasus Mountains, Russia/Georgia

Glaciers occupy an area of ∼1600 km2 in the Caucasus Mountains. There is widespread evidence of retreat since the Little Ice Age, but an up-to-date regional assessment of glacier change is lacking. In this paper, satellite imagery (Landsat Thematic Mapper and Enhanced Thematic Mapper Plus) is used to obtain the terminus position of 113 glaciers in the central Caucasus in 1985 and 2000, using a manual delineation process based on a false-colour composite (bands 5, 4, 3). Measurements reveal that 94% of the glaciers have retreated, 4% exhibited no overall change and 2% advanced. The mean retreat rate equates to ∼8 m a−1, and maximum retreat rates approach ∼38 m a−1. The largest (>10 km2) glaciers retreated twice as much (∼12 m a−1) as the smallest (<1 km2) glaciers (∼6 m a−1), and glaciers at lower elevations generally retreated greater distances. Supraglacial debris cover has increased in association with glacier retreat, and the surface area of bare ice has reduced by ∼10% between 1985 and 2000. Results are compared to declassified Corona imagery from the 1960s and 1970s and detailed field measurements and mass-balance data for Djankuat glacier, central Caucasus. It is concluded that the decrease in glacier area appears to be primarily driven by increasing temperatures since the 1970s and especially since the mid-1990s. Continued retreat could lead to considerable changes in glacier runoff, with implications for regional water resources

Geodetic mass balance of Azarova glacier, Kodar mountains, eastern Siberia, and its links to observed and projected climatic change

The Kodar mountains in eastern Siberia accommodate 30 small, cold-based glaciers with a combined surface area previously estimated at 19 km2. Very little is known about these glaciers, which were first surveyed in the late 1950s. In this paper, we use terrestrial photogrammetry to calculate changes in the surface area, elevation, volume and geodetic mass balance of 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 the surface lowered by an average of 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 0.0368 C a–1 between 1979 and 2007, and the 1980–2007 period was on average 18 C warmer than 1938–79. In comparison to the 1961–90 period, regional climate projections for the A2 and B2 CO2 emission scenarios developed using the PRECIS regional climate model indicate that summer temperatures will increase by 2.6–4.7°C and 4.9–6.2°C, respectively, during the 2071–2100 period. The annual total of solid precipitation will increase by 20% under the B2 scenario but is projected to decline by 3% under the A2 scenario. Azarova glacier exhibits high sensitivity to climatic warming due to its low elevation and exposure to comparatively high summer temperatures. Further summer warming and a decline in solid precipitation projected under the A2 scenario will force Azarova glacier to retreat further, but the impact of an increase in solid precipitation projected under the B2 scenario is more uncertain and requires further investigation before a more conclusive prediction can be made

Debris cover and surface melt at a temperate maritime alpine glacier: Franz Josef Glacier, New Zealand

Melt rates on glaciers are strongly influenced by the presence of supraglacial debris, which can either enhance or reduce ablation relative to bare ice. Most recently, Franz Josef Glacier has entered into a phase of strong retreat and downwasting, with the increasing emergence of debris on the surface in the ablation zone. Previously at Franz Josef Glacier, melt has only been measured on bare ice. During February 2012, a network of 11 ablation stakes was drilled into locations of varying supraglacial debris thickness on the lower glacier. Mean ablation rates over 9 days varied over the range 1.2–10.1 cm d−1, and were closely related to debris thickness. Concomitant observations of air temperature allowed the application of a degree-day approach to the calculation of melt rates, with air temperature providing a strong indicator of melt. Degree-day factors (d f) varied over the range 1.1–8.1 mm d−1 °C−1 (mean of 4.4 mm d−1 °C−1), comparable with rates reported in other studies. Mapping of the current debris cover revealed 0.7 km2 of the 4.9 km2 ablation zone surface was debris-covered, with thicknesses ranging 1–50 cm. Based on measured debris thicknesses and d f, ablation on debris-covered areas of the glacier is reduced by a total of 41% which equates to a 6% reduction in melt overall across the entire ablation zone. This study highlights the usefulness of a short-term survey to gather representative ablation data, consistent with numerous overseas ablation studies on debris-covered glaciers

О влиянии поверхностной морены на состояние ледника Джанкуат (Центральный Кавказ) к 2025 г.

Current 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.Преобладание отрицательных значений баланса массы ледника Джанкуат за минувшие полтора столетия привело к значительному накоплению моренного материала на его поверхности. Поверхностная морена искажает структуру теплового баланса и влияет на изменение баланса массы ледника. В настоящее время поверхностная морена перекрывает 13% площади ледника и на 93% этой площади оказывает бронирующее воздействие. На основании климатической модели HadCM3 установлено, что к 2025 г. забронированные мореной участки языка будут понижаться на 7–15 м (или на 42–45%) медленнее, чем участки открытого льда. Ныне поверхностная морена играет в эволюции ледника роль, соизмеримую с климатическим фактором

Об обратной связи доли лавинного питания с аккумуляцией ледника

Releases 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 (&lt; 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.На основе полевых измерений и вычислений по оригинальной методике рассчитана доля лавинного питания ледника Джанкуат за 15 сезонов. Вклад снежных лавин в приход вещества варьирует от 1,8 до 10,0% и в среднем составляет 4,7%. Установлено, что доля лавинной подпитки и абсолютные объёмы лавинной аккумуляции связаны обратной зависимостью с фоновой снежностью зимы и общим объёмом накопившегося на леднике зимнего снега

Лавинное питание ледника Джанкуат

In 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. Лавинное питание относится к основным компонентам приходной статьи вещественного баланса ледника. Для ледников, на которых возможны прямые наземные масс-балансовые измерения, предлагается расчётная схема, позволяющая выделить из всей массы накопившегося сезонного снега объём лавинного питания, поступающего из-за пределов ледника. Методика основана на результатах построения поля аккумуляции по итогам проведения снегомерной съёмки на дату максимума сезонного снегонакопления. Одновременно картографируются зоны транзита и конусы выноса лавин (раздельно – зарождающиеся на леднике и приходящие извне). Распознавать точки со снеголавинными отложениями можно на ощупь зондами непосредственно при снегомерном профилировании. Превышение снегозапаса в лавинных точках против норм аккумуляции в морфологических аналогах ледниковой поверхности, находящихся вне зон лавинного воздействия, трактуется и численно параметризуется как привнос лавинного снега. Отмечены недостатки и неоднозначности предлагаемой схемы, а также возможные погрешности количественной оценки доли лавинного питания. Экспериментальный алгоритм был получен на леднике Джанкуат в сезон 1998/99 г., когда аккумуляция минимально отличалась от своего медианного значения за весь 46-летний ряд наблюдений. Доля лавинного питания составила 2,8%, что почти на порядок меньше значений, которые предполагались ранее.

Including debris cover effects in a distributed model of glacier ablation

Distributed glacier melt models generally assume that the glacier surface consists of bare exposed ice and snow. In reality, many glaciers are wholly or partially covered in layers of debris that tend to suppress ablation rates. In this paper, an existing physically based point model for the ablation of debris-covered ice is incorporated in a distributed melt model and applied to Haut Glacier d’Arolla, Switzerland, which has three large patches of debris cover on its surface. The model is based on a 10 m resolution digital elevation model (DEM) of the area; each glacier pixel in the DEM is defined as either bare or debris-covered ice, and may be covered in snow that must be melted off before ice ablation is assumed to occur. Each debris-covered pixel is assigned a debris thickness value using probability distributions based on over 1000 manual thickness measurements. Locally observed meteorological data are used to run energy balance calculations in every pixel, using an approach suitable for snow, bare ice or debris-covered ice as appropriate. The use of the debris model significantly reduces the total ablation in the debris-covered areas, however the precise reduction is sensitive to the temperature extrapolation used in the model distribution because air near the debris surface tends to be slightly warmer than over bare ice. Overall results suggest that the debris patches, which cover 10% of the glacierized area, reduce total runoff from the glacierized part of the basin by up to 7%

Реконструкция баланса массы ледника Сары-Тор по метеорологическим данным

Mass balance bn is the most important indicator of a glacier evolution. However, after the decay of the USSR direct measurements of bn performed in 1985–1989 in the Inner Tien Shan, including the Sary-Tor Glacier in Ak-Shiyrak Massif, had been desisted. As a result the available series of the data were limited 1989. Measurements in this area were renewed only in 2015. This paper is devoted to restoring the continuity of the mass-balance series over the period of the gap in measurements and extending this series down to 1929, i.e. to the beginning of regular meteorological observations on the reference HMS Tien Shan (3660 m a.m.s.l.). Accumulation was reconstructed using a linear relationship of bn with the air temperature and precipitation sum. Reconstruction of ablation was based on its cubic relationship with the temperature (modified Krenke– Khodakov formula) or on two-parameter linear approximation using the air temperature and wind velocity. Thereby, the decade of direct instrumental measurements (1984/85–1988/89 and 2014/15–2018/19) resulted in deriving and analyzing continuous 90-year-long series of annual values of bn and its constituents, analytical type of referent glacio-meteorological equations being assumed unchanged in time. Reconstruction for the Sary-Tor Glacier reveals a dominant trend towards the mass loss with rare and short-time episodes of retarding the negative tendencies. The comparison made with the long series of mass balance of other glaciers in Asia indicates a certain degree of synchronicity, which is slightly disturbed in recent years: the degradation of Sary Tor Glacier tends to progress more intensively. Conclusions about its evolution are particularly relevant in connection with the assumption about the impact of the Kyrgyz-Canadian gold mining company «Kumtor Gold Company» on local ecosystems against the background of its interest in expanding the mining zone to the bowels of the Earth under the tongue of this glaciological object.По длинным рядам метеоданных ГМС Тянь-Шань восстановлены годовые значения аккумуляции, абляции и баланса массы долинного ледника Сары-Тор в массиве Ак-Шийрак. В основе поиска зависимостей – прямые гляциологические измерения в 1980-е и 2010-е годы. Реконструкция позволила заполнить пробел между этими периодами и продлить ряд до 1930 г. Результаты сравниваются с более ранними реконструкциями, а также с длинными балансовыми рядами опорных ледников Азии

Толщина, объём льда и подлёдный рельеф ледника Джанкуат (Центральный Кавказ)

In this paper we present and discuss results of radio-echo sounding and modelling of ice thickness of the Djankuat Glacier. This glacier is the reference one for the Central Caucasus and was earlier studied comprehensively, but direct ice thickness measurements survey were not made so far. In 2012–2013, more than 20 km of ice-thickness measurement profiles were obtained using monopulse ground radar VIRL-6 with its central frequency of 20 MHz. Standard error of the ice-thickness measurement was 2.5%. Detailed maps of the ice-thickness and the bedrock topography based on these direct measurements were constructed for the first time. Its average ice-thickness is 31 m with the maximum of 105 m. Djankuat Glacier ice volume is 0.077±0.002 km3 when Djantugan plateau is not taken into account. Ice thickness map was supplemented by results of the ice thickness modelling using the GlabTop model. It was shown that the model reproduces the ice thickness distribution correctly, and a special approach was developed to correct model parameters using ice thickness measurements. Further on, we plan to use corrected GlabTop model for estimation glaciations of the Caucasus as well as to carry out ground radar sounding of the Djantugan plateau.Анализируются результаты радиолокационных измерений и моделирования толщины льда опорного для Центрального Кавказа ледника Джанкуат. Несмотря на всестороннюю изученность, площадная инструментальная съёмка толщины льда на этом леднике до сих пор не проводилась. В 2012–2013 гг. на леднике Джанкуат при помощи моноимпульсного радиолокатора ВИРЛ-6 с центральной частотой 20 МГц пройдено более 20 км профилей, перекрывающих основную часть ледника. Стандартная ошибка измерений составила 2,5% измеряемой величины. Впервые были построены детальные карты толщины льда и подлёдного рельефа ледника, основанные на фактических данных. Максимальная измеренная толщина ледника составляет 105 м при средней толщине 31 м. Объём ледника Джанкуат без учёта Джантуганского плато, согласно данным инструментальных измерений, составил 0,077±0,002 км3. Карты толщины льда, построенные на основе радиолокационных измерений, дополнены результатами моделирования толщины льда с помощью модели GlabTop. Показано, что модель достоверно воспроизводит распределение толщины льда. Предложен и реализован подход, позволяющий корректировать параметры модели по данным прямых измерений