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1.
In recent years, ground‐penetrating radar (GPR) has been increasingly used for characterization of subglacial and englacial environments at polythermal glaciers. The geophysical method is able to exploit the dielectric difference between water, air, sediment and ice, allowing delineation of subsurface hydrological, thermal and structural conditions. More recent GPR research has endeavoured to examine temporal change in glaciers, in particular the distribution of the cold ice zone at polythermal glaciers. However, the exact nature of temporal change that can be identified using GPR has not been fully examined. This research presents the results of three GPR surveys conducted over the course of a summer ablation season at a polythermal glacier in the Canadian Arctic. A total of approximately 30 km of GPR profiles were collected in 2002 repeatedly covering the lower 2 km of Stagnation Glacier, Bylot Island (72°58′ N 78°22′ W). Comparison between profiles indicated changes in the radar signature, including increased noise, appearance and disappearance of englacial reflections, and signal attenuation in the latter survey. Further, an area of chaotic returns in up‐glacier locations, which was interpreted to be a wet temperate ice zone, showed marked recession over the course of the ablation season. Combining all the temporal changes that were detected by GPR, results indicate that a polythermal glacier may exhibit strongly seasonal changes in hydrological and thermal characteristics throughout the ice body, including the drainage of 17 000 m3 of temporarily stored intra‐glacial meltwater. It is also proposed that the liquid water content in the temperate ice zone of polythermal glaciers can be described as a fraction of a specific retention capacity. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

2.
To improve our understanding of the interactions between hydrology and dynamics in mostly cold glaciers (in which water flow is limited by thermal regime), we analyse short‐term (every two days) variations in glacier flow in the ablation zone of polythermal John Evans Glacier, High Arctic Canada. We monitor the spatial and temporal propagation of high‐velocity events, and examine their impacts upon supraglacial drainage processes and evolving subglacial drainage system structure. Each year, in response to the rapid establishment of supraglacial–subglacial drainage connections in the mid‐ablation zone, a ‘spring event’ of high horizontal surface velocities and high residual vertical motion propagates downglacier over two to four days from the mid‐ablation zone to the terminus. Subsequently, horizontal velocities fall relative to the spring event but remain higher than over winter, reflecting channelization of subglacial drainage but continued supraglacial meltwater forcing. Further transient high‐velocity events occur later in each melt season in response to melt‐induced rising supraglacial meltwater inputs to the glacier bed, but the dynamic response of the glacier contrasts with that recorded during the spring event, with the degree of spatial propagation a function of the degree to which the subglacial drainage system has become channelized. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

3.
Rock glaciers are slowly flowing mixtures of debris and ice occurring in mountains. They can represent a reservoir of water, and melting ice inside them can affect surface water hydrochemistry. Investigating the interactions between rock glaciers and water bodies is therefore necessary to better understand these mechanisms. With this goal, we elucidate the hydrology and structural setting of a rock glacier–marginal pond system, providing new insights into the mechanisms linking active rock glaciers and impounded surface waters. This was achieved through the integration of waterborne geophysical techniques (ground penetrating radar, electrical resistivity tomography and self‐potentials) and heat tracing. Results of these surveys showed that rock glacier advance has progressively filled the valley depression where the pond is located, creating a dam that could have modified the level of impounded water. A sub‐surface hydrological window connecting the rock glacier to the pond was also detected, where an inflow of cold and mineralised underground waters from the rock glacier was observed. Here, greater water contribution from the rock glacier occurred following intense precipitation events during the ice‐free season, with concomitant increasing electrical conductivity values. The outflowing dynamic of the pond is dominated by a sub‐surface seepage where a minor fault zone in bedrock was found, characterised by altered and highly‐fractured rocks. The applied approach is evaluated here as a suitable technique for investigating logistically‐complex hydrological settings which could be possibly transferred to wider scales of investigation. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

4.
In extensively glaciarized permafrost areas such as Northern Victoria Land, rock glaciers are quite common and are considered postglacial cryotic landforms. This paper reveals that two rock glaciers in Northern Victoria Land (at Adélie Cove and Strandline) that are located close to the Italian Antarctic Station (Mario Zucchelli Station) should have the same origin, although they were previously mapped as Holocene periglacial landforms and subsequently considered ice‐cored and ice‐cemented rock glaciers, respectively. In fact, by integrating different geophysical investigations and borehole stratigraphy, we show that both landforms have similar internal structures and cores of buried glacier ice. Therefore, this kind of rock glacier is possibly related to the long‐term creep of buried ice rather than to permafrost creep alone. This interpretation can be extended to the larger part of the features mapped as rock glaciers in Antarctica. In addition, a high‐reflective horizon sub‐parallel to the topographic surface was detected in Ground Probing Radar (GPR) data over a large part of the study area. Combining all the available information, we conclude that it cannot be straightforwardly interpreted as the base of the active layer but rather represents the top of a cryo‐lithological unit characterized by ice lenses within sediments that could be interpreted as the transition zone between the active layer and the long‐term permafrost table. More generally, knowledge of the subsurface ice content and, in particular, the occurrence of massive ice and its depth is crucial to make realistic and affordable forecasts regarding thermokarst development and related feedbacks involving GHG emissions, especially in the case of cryosoils rich in carbon content. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

5.
Various parameters of the most recent surge of the polythermal glacier Comfortlessbreen in northwest Svalbard, have been assessed through a combination of remote sensing and ground observations. Analysis of a digital elevation model time‐series shows a marked change in the geometry of the glacier from quiescence (1990 and earlier) into the late surge phase (2009). The transfer of 0.74 km3 of ice caused up to 80 m of surface drawdown in the reservoir area, above the equilibrium line, whilst ice built up in a spatially concentrated manner in the receiving zone, below the equilibrium line. A ramp of ice, c. 100 m above quiescent level, developed in the lower reaches of the glacier late in the surge. Also in the lower reaches of the glacier, structures attributable to the passage of a kinematic wave are identified and the migration of a surge front on the glacier is thus inferred. In a conceptual model, we consider that a bend in the valley, in which the glacier resides, and convergence with tributary glaciers, to be significant factors in the style of surge evolution. Their flow‐restrictive interference results in slow initial mass‐transfer and the growth of a surge front within 3–4 km of the terminus. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

6.
Glaciological controls on debris cover formation are investigated from the perspective of primary dispersal of supraglacial debris across a melting ice surface. This involves the migration of angled debris septa outcrops across a melting, thinning glacier ablation zone. Three measures of a glacier's ability to evacuate supraglacial debris are outlined: (1) a concentration factor describing the focusing of englacial debris into specific supraglacial mass loads; (2) the rate of migration of a septum outcrop relative to the local ice surface; and (3) a downstream velocity differential between a slower septum outcrop and the faster ice surface velocity. Measures (1) and (2) are inversely related, while measure (3) increases down‐glacier to explain why slow‐moving, thinning ice rapidly becomes debris covered. Data from Glacier d'Estelette (Italian Alps) are used to illustrate these processes, and to explore the potential for debris cover formation and growth in different glaciological environments. The transition from a ‘clean’, transport‐dominated to a debris‐covered ablation‐dominated glacier is explained by the melting out of more closely‐spaced debris septa, in combination with the geometric interactions of angled septa and ice surface in a field of reducing flow and increasing ablation. The growth and shrinkage of debris covers are most sensitive to glaciological changes at glaciers with gently‐dipping debris‐bearing foliation, but less sensitive at high‐compression glaciers whose termini are constrained by moraine dams and other forms of obstruction. These findings show that a variety of debris‐covered glacier types will show a spectrum of response characteristics to negative mass balance. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

7.
Kuannersuit Glacier, a valley glacier on Disko Island in west Greenland, experienced a major surge from 1995 to 1998 where the glacier advanced 10·5 km and produced a ～65 m thick stacked sequence of debris‐rich basal ice and meteoric glacier ice. The aim of this study is to describe the tectonic evolution of large englacial thrusts and the processes of basal ice formation using a multiproxy approach including structural glaciology, stable isotope composition (δ18O and δD), sedimentology and ground‐penetrating radar. We argue that the major debris layers that can be traced in the terminal zone represent englacial thrusts that were formed early during the surge. Thrust overthrow was at least 200–300 m and this lead to a 30 m thick repetition of basal ice at the ice margin. It is assumed that the englacial thrusting was initiated at the transition between warm ice from the interior and the cold snout. The basal debris‐rich ice was mainly formed after the thrusting phase. Two sub‐facies of stratified basal ice have been identified; a lower massive ice facies (SM) composed of frozen diamict enriched with heavy stable isotopes overlain by laminated ice facies (SL) consisting of millimetre thick lamina of alternating debris‐poor and debris‐rich ice. We interpret the stratified basal ice as a continuum formed mainly by freeze‐on processes and localized regelation. First laminated basal ice is formed and as meltwater is depleted more sediment is entrained and finally the glacier freezes to the base and massive diamict is frozen‐on. The increased ability to entrain sediments may partly be associated with higher basal freezing rates enhanced by loss of frictional heat from cessation of fast flow and conductive cooling through a thin heavily crevassed ice during the final phase of the glacier surge. The dispersed basal ice facies (D) was mainly formed by secondary processes where fine‐grained sediment is mobilized in the vein system of ice. Our results have important implications for understanding the significance of basal ice formation and englacial thrusting beneath fast‐flowing glaciers and it provides new information about the development of landforms during a glacier surge. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

8.
A numerical simulation of electromagnetic propagation through a multilayered medium is performed in order to explain and interpret the signal received from the radar sounding of a temperate glacier. During the winter of 1990, several radar profiles were obtained on the Mont-de-Lans glacier in the French Alps with a ground penetrating radar which uses a phase modulation of the transmitted pulse by coded sequences. The pulse compression is obtained by applying the matched filter to the received signal, which provides a range-resolution of about 8 m in the ice. The profiles recorded on the temperate glacier do not show a single clear reflection from the ice-bedrock interface, but they exhibit widely distributed energy decreasing with depth. This may be due to the inhomogeneous inner structure of the temperate glacier and we use a simple model of a layered medium to compute a simulation of the propagation. Thus, partial reflection at each layer and scattering from a rough basal interface may explain the observed signal. A computer-based technique is used to locate on the data the bottom of the glacier in order to estimate the ice thickness. The results from the different radar profiles are consistent and are a good fit to the thickness which has been determined by other geophysical methods.  相似文献   

9.
Cold‐based glaciers exist in low temperature and low humidity environments in which shortwave radiation is the largest source of energy to the glacier surface and the energy budget is very sensitive to the surface albedo. Consequently, the presence of relatively low volumes of debris on glacier surfaces has a significant impact on the timing, magnitude and rate of ablation at the surface. The aim of this study is to understand how the presence of sediment on the glacier surface at the start of the melt season can affect meltwater generation and delivery on a cold‐based glacier. A combination of field measurements, energy balance modelling and chemical mixing modelling were used on the Wright Lower Glacier, McMurdo Dry Valleys, Antarctica, between October 2005 and January 2006 to address this aim. In this system, sediment was transported onto the glacier surface during the winter months (March–October) by foehn winds, which reduced surface albedo at the start of the summer melt season. The areas of the glacier on which sediment accumulated began to melt earlier than other parts of the glacier and experienced a longer melt season. Over the study period, the total ablation on the dirty surfaces was nine times greater than for clean ice. Ablation on the dirty surfaces is dominated by melting, whereas sublimation dominates the clean ice. As the sediment was unevenly distributed over the glacier surface, the variation in melt amount and timing drove the development of a cryoconite hole system. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

10.
Abstract

A mathematical model of the flow and temperature distribution of polythermal glaciers or ice sheets is deduced. Cold ice is treated as a non-linear viscous heat conducting fluid, while temperate ice is regarded as a binary mixture of ice and water. The simplest mixture concept with two balance laws of mass but only one balance law of momentum and energy is proposed. The field equations for the ice and water content and the boundary conditions which must hold at the free surface, at the ice-water interface, at the cold-temperature transition surface and at the rock-bed are deduced. In particular it is shown that an earlier formulation of polythermal ice due to Fowler and Larson (1978) is inconsistent. No boundary value problems are solved as the emphasis is on the physical motivation and justification of the principles.  相似文献   

11.
An analysis of temporal variability in proglacial suspended sediment concentration is undertaken using time series data collected from three Svalbard basins which include one largely cold-based glacier (Austre Brøggerbreen), one largely warm-based glacier (Finsterwalderbreen) and one intermediate polythermal glacier (Erdmannbreen). The temporal variability in proglacial suspended sediment concentration is analysed using multiple regression techniques in which discharge is supplemented by other predictors acting as surrogates for variability in sediment supply at diurnal, medium-term and seasonal timescales. These multiple regression models improve upon the statistical explanation of suspended sediment concentration produced by simple sediment rating curves but need to account for additional stochastic elements within the time series before they may be considered successful. An interpretation of the physical processes which are responsible for the regression model characteristics is offered as a basis for comparing the different arctic glaciofluvial suspended sediment transport systems with that of their better known temperate glaciofluvial counterparts. It is inferred that the largely warm-based glacier is dominated by sediment supply from subglacial reservoirs which evolve in a similar manner to temperate glaciers and which cause a pronounced seasonal exhaustion of suspended sediment supply. The largely cold-based glacier, however, is dominated by sediment supply from marginal sources which generate a responsive system at short time scales but no significant seasonal pattern. The intermediate polythermal glacier basin, which was anticipated to be similar to the warm-based glacier, instead shows a highly significant seasonal increase in suspended sediment supply from an unusual subglacial reservoir emerging under pressure in the glacier foreland. The temperate model of glaciofluvial suspended sediment transport is therefore found to be of limited use in an arctic context. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

12.
We present an investigation of changes taking place on the Columbia Glacier, a lake-terminating outlet of the Columbia Icefield in the Canadian Rockies. The Columbia Icefield is the largest, and one of the most important, ice bodies in the Canadian Rockies. Like other ice masses, it stores water as snow and ice during the winter and releases it during warmer summer months, sustaining river flows and the ecosystems that rely on them. However, the Columbia Glacier and Icefield is shrinking. We use Landsat and Sentinel-2 imagery to show that the Columbia Glacier has retreated increasingly rapidly in recent years, and suggest that this looks set to continue. Importantly, we identify a previously undocumented process that appears to be playing an important role in the retreat of this glacier. This process involves the ‘detachment’ of the glacier tongue from its accumulation area in the Columbia Icefield. This process is important because the tongue is cut off from the accumulation area and there is no replenishment of ice that melts in the glacier's ablation area by flow from upglacier. As a consequence, for a given rate of ablation, the ice in the tongue will disappear much faster than it would if the local mass loss by melting/calving was partly offset by mass input by glacier flow. Such a change would alter the relationship between rates of surface melting and rates of glacier frontal retreat. We provide evidence that detachment has already occurred elsewhere on the Columbia Icefield and that it is likely to affect other outlet glaciers in the future. Modelling studies forecast this detachment activity, which ultimately results in a smaller ‘perched’ icefield without active outlets. © 2019 John Wiley & Sons, Ltd.  相似文献   

13.
Debris cover on glaciers is an important component of glacial systems as it influences climate–glacier dynamics and thus the lifespan of glaciers. Increasing air temperatures, permafrost thaw and rock faces freshly exposed by glacier downwasting in accumulation zones result in increased rockfall activity and debris input. In the ablation zone, negative mass balances result in an enhanced melt-out of englacial debris. Glacier debris cover thus represents a clear signal of climate warming in mountain areas. To assess the temporal development of debris on glaciers of the Eastern Alps, Austria, we mapped debris cover on 255 glaciers using Landsat data at three time steps. We applied a ratio-based threshold classification technique and analysed glacier catchment characteristics to understand debris sources better. Across the Austrian Alps, debris cover increased by more than 10% between 1996 and 2015 while glaciers retreated in response to climate warming. Debris cover distribution shows significant regional variability, with some mountain ranges being characterised by mean debris cover on glaciers of up to 75%. We also observed a general rise of the mean elevation of debris cover on glaciers in Austria. The debris cover distribution and dynamics are highly variable due to topographic, lithological and structural settings that determine the amount of debris delivered to and stored in the glacier system. Despite strong variation in debris cover, all glaciers investigated melted at increasing rates. We conclude that the retarding effects of debris cover on the mass balance and melt rate of Austrian glaciers is strongly subdued compared with other mountain areas. The study indicates that, if this trend continues, many glaciers in Austria may become fully debris covered. However, since debris cover seems to have little impact on melt rates, this would not lead to prolonged existence of debris-covered ice compared with clean ice glaciers.  相似文献   

14.
冰川作为地球系统中重要的组成部分,是全球气候变化的敏感指示器和调节器.冰川运动的遥感监测也是进行冰川研究的重要内容.本文主要采用偏移追踪的方法,利用2003-2010年期间7对雷达单视复数数据监测了青藏高原珠穆朗玛峰地区的卓琼冰川运动情况.经验证,本研究获得的冰川流速结果可靠.卓琼冰川的流向自西向东,流速自冰川末端向上游积累区逐渐增加,流速大小主要来自距离向的贡献.研究结果显示,卓琼冰川在2003-2005年期间流速较大,最大流速达到45 m·a~(-1),而在2005-2010年期间流速有所降低,最大流速在35~40 m·a~(-1)范围内波动;卓琼冰川年际间流速变化基本一致,冰川中部存在流速突变情况,突变幅度为3~7 m·a~(-1),但该尺度的突变并不会影响卓琼冰川的总体运动趋势.此外,本文还分析了气象以及地理位置因素对卓琼冰川运动的影响.  相似文献   

15.
In order to assess the annual mass balance of the Mandrone glacier in the Central Alps an energy-balance model was applied, supported by snowpack, meteorological and glaciological observations, together with satellite measurements of snow covered areas and albedo. The Physically based Distributed Snow Land and Ice Model (PDSLIM), a distributed multi-layer model for temperate glaciers, which was previously tested on both basin and point scales, was applied.Verification was performed with a network of ablation stakes over two summer periods. Satellite images processed within the Global Land Ice Measurements from Space (GLIMS) project were used to estimate the ice albedo and to verify the position of the simulated transient snowline on specific dates. The energy balance was estimated for the Mandrone and Presena glaciers in the Central Italian Alps. Their modeled balances (−1439 and −1503 mm w.e. year−1, respectively), estimated over a 15 year period, are in good agreement with those obtained with the glaciological method for the Caresèr glacier, a WGMS (World Glacier Monitoring Service) reference located in the nearby Ortles-Cevedale group.Projections according to the regional climate model COSMO-CLM (standing for COnsortium for Small-scale MOdeling model in CLimate Mode) indicate that the Mandrone glacier might not survive the current century and might be halved in size by 2050.  相似文献   

16.
Rock glaciers and large ice-debris complexes are common in many mountain ranges and are especially prominent in semi-arid mountains such as the Andes or the Tien Shan. These features contain a significant amount of ice but their occurrence and evolution are not well known. Here, we present an inventory of the ice-debris complexes for the Ak-Shiirak, Tien Shan's second largest glacierised massif, and a holistic methodology to investigate two characteristic and large ice-debris complexes in detail based on field investigations and remote sensing analysis using Sentinel-1 SAR data, 1964 Corona and recent high resolution stereo images. Overall, we found 74 rock glaciers and ice-debris complexes covering an area of 11.2 km2 (3.2% of the glacier coverage) with a mean elevation of about 3950 m asl. Most of the complexes are located south-east of the main ridge of Ak-Shiirak. Ground penetrating radar (GPR) measurements reveal high ice content with the occurrence of massif debris-covered dead-ice bodies in the parts within the Little Ice Age glacier extent. These parts showed significant surface lowering, in some places exceeding 20 m between 1964 and 2015. The periglacial parts are characterised by complex rock glaciers of different ages. These rock glaciers could be remnants of debris-covered ice located in permafrost conditions. They show stable surface elevations with no or only very low surface movement. However, the characteristics of the fronts of most rock glacier parts indicate slight activity and elevation gains at the fronts slight advances. GPR data indicated less ice content and slanting layers which coincide with the ridges and furrows and could mainly be formed by glacier advances under permafrost conditions. Overall, the ice content is decreasing from the upper to the lower part of the ice-debris complexes. Hence, these complexes, and especially the glacier-affected parts, should be considered when assessing the hydrological impacts of climate change. © 2018 John Wiley & Sons, Ltd.  相似文献   

17.
In the Tibetan Plateau, many glaciers have extensive covers of supraglacial debris in their ablation zones, which affects glacier response to climate change by altering ice melting and spatial patterns of mass loss. Insufficient debris thickness data make it difficult to analyze regional debris-cover effects. Maritime glaciers of the Mount Gongga have been characterized by a substantial reduction in glacier area and ice mass in recent decades. The thermal property of the debris layer estimated from remotely sensed data reveals that debris-covered glaciers are dominant in this region, on which the proportion of debris cover to total glacier area varies from 1.74% to 53.0%. Using a physically-based debris-cover effect assessment model, we found that although the presence of supraglacial debris has a significant insulating effect on heavily debris-covered glaciers, it accelerates ice melting on ~10.2% of total ablation zone and produces rapid wastage of ~25% of the debris-covered glaciers, leading to the similar mass losses between the debris-covered and debris-free glaciers. Widespread debris cover also facilitates the development of active terminus regions. Regional differences in debris-cover effects are apparent, highlighting the importance of debris cover for understanding glacier mass changes in the Tibetan Plateau and other mountain ranges around the world.  相似文献   

18.
Many glaciers in alpine regions are currently rapidly receding and thinning at historically unobserved rates causing changes in the velocity field and in normal and shear stresses affecting the surface expression of structures within the ice. We studied the distribution of brittle and ductile structures at the surface of Pasterze Glacier during a 14-year period by analysing orthophotos and digital elevation models of five stages (1998, 2003, 2006, 2009 and 2012). A structural glaciological mapping key was applied. Normal faults, strike-slip faults, en échelon structures (systematic stepping of fractures), thrust faults, and band ogives were distinguished. Results indicate substantial deceleration and glacier thinning in 1998–2012. Glacier thinning was not homogenous over time related to the uneven distribution of supraglacial debris causing differential ablation or the selective ablation effects of subglacial water channels. Peculiar supraglacial features observed are circular collapse structures with concentric crevasses which form when the ice between the surface and the roof of water channels decreases. The total length of brittle structures increased from 38.4 km to 56.9 km whereas the extent of the glacier tongue decreased by 25%. The fracture density doubled from 0.009 to 0.018 m/m2. Areas of the glacier tongue which were up to 100 m away from the nearest brittle structure increased by 16%. The visual appearance of thrust faults shifted upglacier due to decreasing glacier velocity causing horizontal shortening or due to exhumation of faults that did not previously extend to the surface. A large number of brittle structures are progressively independent from glacier motion. Our study suggests that glacier tongues which are in a state of rapid decay and thinning are prone to fracturing due to normal fault formation and glacier disintegration. Water further increases ablation rates substantially if rather large amounts drain through supra-, en- or subglacial water channels. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

19.
We apply the process‐based, distributed TOPKAPI‐ETH glacio‐hydrological model to a glacierized catchment (19% glacierized) in the semiarid Andes of central Chile. The semiarid Andes provides vital freshwater resources to valleys in Chile and Argentina, but only few glacio‐hydrological modelling studies have been conducted, and its dominant hydrological processes remain poorly understood. The catchment contains two debris‐free glaciers reaching down to 3900 m asl (Bello and Yeso glaciers) and one debris‐covered avalanche‐fed glacier reaching to 3200 m asl (Piramide Glacier). Our main objective is to compare the mass balance and runoff contributions of both glacier types under current climatic conditions. We use a unique dataset of field measurements collected over two ablation seasons combined with the distributed TOPKAPI‐ETH model that includes physically oriented parameterizations of snow and ice ablation, gravitational distribution of snow, snow albedo evolution and the ablation of debris‐covered ice. Model outputs indicate that while the mass balance of Bello and Yeso glaciers is mostly explained by temperature gradients, the Piramide Glacier mass balance is governed by debris thickness and avalanches and has a clear non‐linear profile with elevation as a result. Despite the thermal insulation effect of the debris cover, the mass balance and contribution to runoff from debris‐free and debris‐covered glaciers are similar in magnitude, mainly because of elevation differences. However, runoff contributions are distinct in time and seasonality with ice melt starting approximately four weeks earlier from the debris‐covered glacier, what is of relevance for water resources management. At the catchment scale, snowmelt is the dominant contributor to runoff during both years. However, during the driest year of our simulations, ice melt contributes 42 ± 8% and 67 ± 6% of the annual and summer runoff, respectively. Sensitivity analyses show that runoff is most sensitive to temperature and precipitation gradients, melt factors and debris cover thickness. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

20.
Abstract

Aerial photographs of the Cotopaxi Volcano ice cap dating from 1956 to 1997 were used to quantify the evolution of the surface area. Results were obtained using precise stereoscopic methods that give the most accurate information. In addition four specific glacier tongues were investigated in detail to measure the ice mass lost between 1976 and 1997. Surprisingly, the bedrock morphology is shown to be very irregular and this explains a large extent of the variability found in the ice losses. The results show that glaciers stagnated from 1956 to 1976 and lost about 30% of their surface area between 1976 and 1997. Slope exposure did not seem to have any significant effect since all the glaciers of the volcano retreated in the same proportion. In accordance with specific measurements performed on the nearby Antizana 15 Glacier, it is suggested that the strong recession observed after 1976 was associated with increasing melting conditions which have occurred repeatedly during the intense/long-duration warm ENSO phases.  相似文献   

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