Article

Recent evolution of Marmolada glacier (Dolomites, Italy) by means of ground and airborne GPR surveys

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Abstract

A 10-year-long evolution of ice thickness and volume of the Marmolada glacier is presented. Quantitative measurements have been performed by using two different Ground Penetrating Radar (GPR) datasets. A ground-based survey using two different ground-coupled systems equipped with 100 MHz and 35 MHz antennas was performed in 2004. In 2015 the dataset was collected by using a helicopter-borne step frequency GPR equipped with a 100 MHz antenna. Through a critical discussion of the two different methodologies, we show how both approaches are useful to estimate the ice volume within a glacier, as well as its morphological characteristics and changes with time, even if datasets are acquired in different periods of the year. The observed 2004–2014 ice volume reduction of the Marmolada glacier is equal to about 30%, while the area covered by ice decreased by about 22%. The glacier is now splitted in several separated units. It is very likely that the fragmentation of the Marmolada glacier observed in the period 2004–2014 was accelerated due to irregular karst topography. By applying the observed 2004–2014 ice-melting trend for the future although the Marmolada glacier might behave slightly differently compared to glaciers on non-karstic terrains owing to dominant vertical subglacial drainage, it will likely disappear by the year 2050. Only few isolated very small and thin ice patches will eventually survive due to avalanche feeding and shading at the foot of the north-facing cliffs.

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... Some studies Scotti and Brardinoni 2018;Santin et al. 2019) confirm that the smaller is one glacier, the least dependent is it from climate change. Many glaciers in the southern and the eastern Alps have shrunk rapidly throughout the twentieth century, and, when they reached sufficiently small size (e.g. ...
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Conference Paper
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... However, we can hypothesize that, at least in some cases, the combined action of the temperature increase and precipitation decrease that occurred after 1980 influenced the evolution of glaciers. According to the present rate of glacier decline, and according to the observed climatic warming trends, the glaciers in the Italian Alps are expected to disappear by 2050 (Santin et al., 2019). ...
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... The Alpine landscape is rapidly changing due to global warming and larger ice masses continue to disintegrate into smaller ice bodies (e.g., [2,8,9,10]). In the future, alpine glaciers will be likely characterized by a larger number of these very small ice bodies, especially in karstic terrains. ...
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... This depth of penetration was possible due to the extreme aridity of the Moon with an estimated dielectric of 2 (Olhoeft and Strangway, 1975), whereby little energy is lost at the vacuum-lunar surface interface. Glaciology studies using helicopter and fixed-wing aircraft towing GPR system have been commonplace for decades (Evans, 1963;Evans and Robin, 1966;Casassa et al., 2014;Langhammer et al., 2019;Santin et al., 2019). Similar to the Moon, glacier ice has a dielectric of approximately 3.15 which is similar to air (1) and allows the passage of radar waves with minimal reflection loss at the air-ice interface. ...
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Glaciers were common across the Mediterranean mountains during the Little Ice Age. In parts of Turkey some glaciers were several kilometres longer than they are today, whilst in the Pyrenees glaciers were up to several hundred metres longer. In the wettest Mediterranean mountains, such as the Dinaric Alps, many small glaciers and perennial snow patches would have been present. Even in driest and most southerly mountains, such as the High Atlas, small glaciers and perennial snowfields were present. This paper examines the evidence from these two contrasting regions (the western and southern Balkans and the High Atlas) and the climatic significance of glaciers in these areas during the Little Ice Age. Particular focus is given on the climatological controls on glacier mass balance in different climatic conditions. Glaciers in cold and dry climates exhibit different sensitivity to regional climate change compared with glaciers in cold and wet climates. In addition, the factors controlling ablation of glaciers in different climatic regimes can differ considerably, especially the relative contributions and effects of melting and sublimation. All Mediterranean mountain glaciers were strongly controlled by local topoclimatic factors. Avalanche-fed glaciers have proven to be the most resilient to climate change and dramatically increased accumulation from avalanching snow explains the surviving glaciers in the Dinaric Alps and the semi-perennial snow fields of the High Atlas. In addition, geology as well as landscape morphology inherited from Pleistocene glaciations plays a role in explaining the patterns of Little Ice Age glacier distribution and especially the patterns of retreat and survival of these glaciers. The resilience of some of the last remaining Mediterranean glaciers, in the face of warming climate, presents a contradiction and comparisons between glaciers gone and those that remain provides important insight into the future of similar glaciers globally.
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We document the occurrence in December 2015 of unprecedented high monthly mean temperatures in the observational record of mountain sites in the eastern Alps. For the first time in the last 150 years mean December temperature exceeded 0 °C at elevations between 2100 and 2500 m, with December mean anomalies exceeding 6.5 °C with respect to the 1971–2000 mean. Along with the absence of snow cover, such temperatures might have lead to unprecedented winter ablation of glaciers in this elevation range. Smaller temperature anomalies occurred in surrounding low elevation sites, highlighting the key role of topography in this event. Specifically, strong inversions associated with the very stable synoptic conditions during the month amplified the anomalies at the high elevations of the mountain glacier sites. We analyze the processes underlying this exceptional event and place this anomaly within the context of future warming scenarios over the region.
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Glacier mass balance is a key variable for the monitoring strategies of the Earth climate system, but the continuation of long-term observations is now endangered by the impending extinction of several monitored glaciers. It is therefore advisable to start new observations on neighbouring glaciers that are more likely to survive into the next few decades. These glaciers will be located at higher altitude, have larger elevation range, thus preserving an accumulation area and have good spatial representativeness. Glaciers with these characteristics may pose some problems and are more demanding for mass-balance measurements and calculations, due to their size and presence of remote and inaccessible areas, further complicated by the complex morphology and high-lateral gradients of mass balance. I present the new mass-balance series for La Mare Glacier, started in 2003 to replace the long-term monitored and rapidly vanishing Careser Glacier in the Ortles-Cevedale Group (Eastern Italian Alps). Direct glaciological mass-balance observations have been complemented by measurements with the hydrological method and, as recommended by the World Glacier Monitoring Service, validated using the geodetic method. The collected data are useful for testing and optimising two techniques proposed in the literature for extrapolating measurements to inaccessible areas.
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The variability of glacier response to atmospheric temperature rise in different topo-climatic settings is still matter of debate. To address this question in the Central Italian Alps we compile a post-LIA (Little Ice Age) multitemporal glacier inventory (1860-1954-1990-2003-2007) along a latitudinal transect that originates north of the continental divide in the Livigno mountains, and extends south through the Disgrazia and Orobie ranges, encompassing continental-to-maritime climatic settings. In these sub-regions we examine area change of 111 glaciers. Overall, total glacierized area has declined from 34.1 to 10.1 km2, with a substantial increase in the number of small glaciers due to fragmentation. Average annual decrease (AAD) in glacier area has risen of about an order of magnitude from 1860–1990 (Livigno: 0.45; Orobie: 0.42; and Disgrazia: 0.39 % a−1) to 1990–2007 (Livigno: 3.08; Orobie: 2.44; and Disgrazia: 2.27 % a−1). This ranking changes when considering glaciers
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Proglacial icings accumulate in front of many High Arctic glaciers during the winter months, as water escapes from englacial or subglacial storage. Such icings have been interpreted as evidence for warm-based subglacial conditions, but several are now known to occur in front of cold-based glaciers. In this study, we investigate the drainage system of Tellbreen, a 3.5 km long glacier in central Spitsbergen, where a large proglacial icing develops each winter, to determine the location and geometry of storage elements. Digital elevation models (DEMs) of the glacier surface and bed were constructed using maps, differential GPS and ground penetrating radar (GPR). Rates of surface lowering indicate that the glacier has a long-term mass balance of −0.6 ± 0.2 m/year. Englacial and subglacial drainage channels were mapped using GPR, showing that Tellbreen has a diverse drainage system that is capable of storing, transporting and releasing water year round. In the upper part of the glacier, drainage is mainly via supraglacial channels. These transition downglacier into shallow englacial "cut and closure" channels, formed by the incision and roof closure of supraglacial channels. Below thin ice near the terminus, these channels reach the bed and contain stored water throughout the winter months. Even though no signs of temperate ice were detected and the bed is below pressure-melting point, Tellbreen has a surface-fed, channelized subglacial drainage system, which allows significant storage and delayed discharge.
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Glacier mass balance is measured with the direct or the geodetic method. In this study, the geodetic mass balances of six Austrian glaciers in 19 periods between 1953 and 2006 are compared to the direct mass balances in the same periods. The mean annual geodetic mass balance for all periods is −0.5 m w.e./year. The mean difference between the geodetic and the direct data is −0.7 m w.e., the minimum −7.3 m w.e. and the maximum 5.6 m w.e. The accuracy of geodetic mass balance resulting from the accuracy of the DEMs ranges from 2 m w.e. for photogrammetric data to 0.002 m w.e. for LIDAR data. Basal melt, seasonal snow cover and density changes of the surface layer contribute up to 0.7 m w.e. for the period of 10 years to the difference to the direct method. The characteristics of published data of Griesgletscher, Gulkana Glacier, Lemon Creek glacier, South Cascade, Storbreen, Storglaciären, and Zongo Glacier is similar to these Austrian glaciers. For 26 analyzed periods with an average length of 18 years the mean difference between the geodetic and the direct data is −0.4 m w.e., the minimum −7.2 m w.e. and the maximum 3.6 m w.e. Longer periods between the acquisition of the DEMs do not necessarily result in a higher accuracy of the geodetic mass balance. Specific glaciers show specific trends of the difference between the direct and the geodetic data according to their type and state. In conclusion, geodetic and direct mass balance data are complementary, but differ systematically.
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It is well known that small glaciers of mid latitudes and especially those located at low altitude respond suddenly to climate changes both on local and global scale. For this reason their monitoring as well as evaluation of their extension and volume is essential. We present a ground penetrating radar (GPR) dataset acquired on September 23 and 24, 2013 on the Triglav glacier to identify layers with different characteristics (snow, firn, ice, debris) within the glacier and to define the extension and volume of the actual ice. Computing integrated and interpolated 3D using the whole GPR dataset, we estimate that at the moment of data acquisition the ice area was 3800 m2 and the ice volume 7400 m3. Its average thickness was 1.95 m while its maximum thickness was slightly more than 5 m. Here we compare the results with a previous GPR survey acquired in 2000. A critical review of the historical data to find the general trend and to forecast a possible evolution is also presented. Between 2000 and 2013, we observed relevant changes in the internal distribution of the different units (snow, firn, ice) and the ice volume reduced from about 35,000 m3 to about 7400 m3. Such result can be achieved only using multiple GPR surveys, which allow not only to assess the volume occupied by a glacial body, but also to image its internal structure and the actual ice volume. In fact, by applying one of the widely used empirical volume-area relations to infer the geometrical parameters of the glacier, a relevant underestimation of ice-loss would be achieved.
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We evaluate the applicability and the effectiveness of GPR attribute analysis for high-resolution glacier imaging and characterization, testing this approach on 4-D GPR multi-frequency data collected in a small glacier in the Eastern Alps, by repeating the acquisition along the same profiles in four different periods of the year 2013. The main objectives are to image and characterize the glacier's inner structure and to quantitatively monitor the seasonal thawing of near-surface frozen materials (snow/firn). A multi-attribute approach is used to characterize the subsurface through different attribute categories, including instantaneous, and textural attributes considering not only amplitude-, phase- and frequency-related attributes, but also other more complex and integrated parameters. We combine information from more than one attribute into a single image with composite displays, using overlays or mixed displays. The results demonstrate that the developed GPR attribute analysis can provide significant improvements in the discrimination of GPR signals, and obtain enhanced and more constrained data interpretations.
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Using Landsat Images and GIS to Assess the Changes of Mer de Glace and Marmolada Glaciers, in the Last Three Decades. We have demonstrated that Mer de Glace Glacier (GL) and Marmolada GL are in continuous retreat. The changes in size and status of terminus points were estimated in various time intervals by satellite images (SIs) and Geographic Information Systems (GIS) techniques, during the last three decades. The aim of the research was to found the value of the ice melting areas of Mer de Glace GL and Marmolada GL and to calculate the decline rate for both GLs. A large number of GLs have lost ice mass all over the world. Often glaciologists monitor the GLs movements under climate changes and they express their opinions about the ocean level rise, ecosystem challenges and the future implications of GLs decline. The analysed information to quantify the Mer de Glace GL and Marmolada GL areas derived from SIs. By manual vectorization we obtained the outlines of GLs in different years. For 1984, 1999, 2013 we defined the limits for Mer de Glace GL and for 1986, 1999, 2013 we defined the limits for Marmolada GL. These vector layers were compared in order to observe the melting area and to establish the withdrawal rate. The first results indicate that Mer de Glace GL area declined by 2.365 km² between 1984 and 2013 and a mean melting rate of 0.082 km²/year was obtained. Marmolada GL decreased by 1.035 km² between 1986 and 2013 and a mean melting rate of 0.038 km²/year was calculated. We believe that these results represent significant quantitative data about GLs movements regarding two different areas in the Alps Range and may provide knowledge for hydrology, geomorphology and environmental sciences.
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On the basis of a large data set, comprising approximately 1200 km of profile lines acquired with different helicopterborne ground-penetrating radar (GPR) systems over temperate glaciers in the western Swiss Alps, we have analyzed the possibilities and limitations of using helicopter-borne GPR surveying to map the ice-bedrock interface. We have considered data from three different acquisition systems including (1) a low-frequency pulsed system hanging below the helicopter (BGR), (2) a stepped frequency system hanging below the helicopter (Radar Systemtechnik GmbH [RST]), and (3) a commercial system mounted directly on the helicopter skids (Geophysical Survey Systems Incorporated [GSSI]). The systems showed considerable differences in their performance. The best results were achieved with the BGR system. On average, the RST and GSSI systems yielded comparable results, but we observed significant site-specific differences. A comparison with ground-based GPR data found that the quality of helicopter-borne data is inferior, but the compelling advantages of airborne surveying still make helicopter-borne data acquisition an attractive option. Statistical analyses concerning the bedrock detectability revealed not only large differences between the different acquisition systems but also between different regions within our investigation area. The percentage of bedrock reflections identified (with respect to the overall profile length within a particular region) varied from 11.7% to 68.9%. Obvious factors for missing the bedrock reflections included large bedrock depths and steeply dipping bedrock interfaces, but we also observed that internal features within the ice body may obscure bedrock reflections. In particular, we identified a conspicuous "internal reflection band" in many profiles acquired with the GSSI system. We attribute this feature to abrupt changes of the water content within the ice, but more research is required for a better understanding of the nature of this internal reflection band.
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Despite their importance as freshwater reservoirs for downstream river systems, few glaciers in central Chile have been comprehensively surveyed. This study presents ground-penetrating radar (GPR) and field-based observations for characterizing the englacial and basal conditions of Glaciar Olivares Alfa (33°11 0 S, 70°13 0 W), central Chilean Andes. Using a 50 MHz radar mounted onto a helicopter platform, data were collected covering large portions of the glacier accumulation and ablation zones. The radar data revealed boundaries of a temperate-ice layer at the base of the eastern body of Glaciar Olivares Alfa which appears to be covered by colder ice that extends throughout large parts of the glacier. The thickness of the temperate ice layer is highly variable across the glacier, being on average 40% of the total ice thickness. Radar data analyses reveal regions of cold ice at the bottom/ base of the glacier and also patterns of highly saturated sediments beneath the glacier. Using GPR data, this study represents the most exhaustive analysis of glacier ice structure performed in the central Chilean Andes. The results will enable improved estimations of the glacier's mass balance and ice dynamics, helping us to understand its further development and its impact on water availability.
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Alpine glaciers store large amounts of fresh water contributing to groundwater recharge during warmer periods, but the interactions between glaciers and aquifers have rarely been investigated in detail. The Tsanfleuron-Sanetscharea, Switzerland, is an ideal test site to study glacier-aquifer interactions. It consists of a rapidly retreating glacier (2.8 km 2) overlying a karst aquifer drained by a spring (mean discharge 600-700 L/s) used for drinking water supply and irrigation. The geometry and structure of the glacier were assessed by means of geophysical surveys, using radiomagnetotellurics (RMT). The estimated ice volume is 1.0 × 10 8 m 3 (0.92 × 1010 8 m 3 water equivalent), but the glacier currently loses 1.5 m ice thickness per year. Field observations, flow measurements and tracer tests allowed characterisation of glacier drainage and aquifer recharge. Three recharge pathways have been identified: 1) The main glacial stream sinks into the aquifer via swallow holes 3 km downstream of the glacier mouth; 2) Numerous small meltwater streams sink underground shortly below the glacier front; 3) Subglacial meltwaters and supraglacial streams sink into the glacier via moulins and contribute to aquifer recharge throughfractures and swallow holes underneaththe glacier. Recharge and spring discharge display strong diurnal and seasonal variability, witha general high-flow period during snow and glacier melt from spring to autumn. Preliminary predictions of the future availability of spring water after disappearance of the glacier suggest that the discharge may decrease by 20-30%. Nearly all of this loss will occur in summer and autumn, presumably resulting in temporary water shortage.
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The response of glaciers to atmospheric warming has become a key issue in scientific as well as public and even political discussions about human impacts on the climate system. The predominant tendency of continued worldwide glacier shrinkage may indeed constitute one of the clearest indications in nature of rapid climate change at a global scale. More than a century of systematic and internationally coordinated observations provide quantitative documentation of this development and a basis for model developments in view of possible future scenarios. Mountain ranges at lower latitudes have lost large percentages of their glacier areas and volumes since the end of the Little Ice Age. Many of them may even become largely to even completely de-glaciated already during the coming decades. Such changes have the potential to profoundly affect environmental conditions in and around cold mountain chains. Sea-level rise, changing seasonality in water supply, and local formation of new lakes reflect changes in the water cycle at global, continental, and regional to local scales. They are accompanied by rather marked changes in landscape appearance, slope stability, erosion/sedimentation, and hazard conditions. The monitoring of glaciers itself faces difficult challenges of vanishing glaciers with long-term mass-balance observations. Modern techniques of spatial modeling increasingly help with integrated analysis of observed phenomena and early anticipation of possible developments.
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Austre Lovenbreen is a 4.6 km(2) glacier on the Archipelago of Svalbard (79 degrees N) that has been surveyed over the last 47 years in order to monitor in particular the glacier evolution and associated hydrological phenomena in the context of nowadays global warming. A three-week field survey during April 2010 allowed for the acquisition of a dense mesh of ground-penetrating radar (GPR) data with an average of 14 683 points per km2 (67 542 points total) on the glacier surface. The profiles were acquired using Main equipment with 100 MHz antennas, towed slowly enough to record on average every 0.3 m, a trace long enough to sound down to 189 m of ice. One profile was repeated with a 50 MHz antenna set to improve electromagnetic wave propagation depth in scattering media observed in the cirques closest to the slopes. The GPR was coupled to a GPS system to position traces. Each profile was manually edited using standard GPR data processing including migration, to pick the reflection arrival time from the ice-bedrock interface. Snow cover was evaluated through 42 snow drilling measurements regularly spaced to cover the entire glacier. These data were acquired at the time of the GPR survey and subsequently spatially interpolated using ordinary kriging. Using a snow velocity of 0.22 m/ns, the snow thickness was converted to electromagnetic wave traveltimes and subtracted from the picked traveltimes to the ice-bedrock interface. The resulting traveltimes were converted to ice thickness using a velocity of 0.17 m/ns. The velocity uncertainty is discussed from a common midpoint profile analysis. A total of 67 542 geo-referenced data points with GPR-derived ice thicknesses, in addition to a glacier boundary line derived from satellite images taken during summer, were interpolated over the entire glacier surface using kriging with a 10 m grid size. Some uncertainty analyses were carried out and we calculated an averaged ice thickness of 76 m and a maximum depth of 164 m with a relative error of 11.9%. The volume of the glacier is derived as 0.3487 +/- 0.041 km(3). Finally a 10 m grid map of the bedrock topography was derived by subtracting the ice thicknesses from a dual-frequency GPS-derived digital elevation model of the surface. These two data sets are the first step for modelling thermal evolution of a glacier and its bedrock, as well as the main hydrological network.
Article
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The response of glaciers to atmospheric warming has become a key issue in scientific as well as public and even political discussions about human impacts on the climate system. The predominant tendency of continued worldwide glacier shrinkage may indeed constitute one of the clearest indications in nature of rapid climate change at a global scale. More than a century of systematic and internationally coordinated observations provide quantitative documentation of this development and a basis for model developments in view of possible future scenarios. Mountain ranges at lower latitudes have lost large percentages of their glacier areas and volumes since the end of the Little Ice Age. Many of them may even become largely to even completely de-glaciated already during the coming decades. Such changes have the potential to profoundly affect environmental conditions in and around cold mountain chains. Sea-level rise, changing seasonality in water supply, and local formation of new lakes reflect changes in the water cycle at global, continental, and regional to local scales. They are accompanied by rather marked changes in landscape appearance, slope stability, erosion/sedimentation, and hazard conditions. The monitoring of glaciers itself faces difficult challenges of vanishing glaciers with long-term mass balance observations. Modern techniques of spatial modeling increasingly help with integrated analysis of observed phenomena and early anticipation of possible developments.
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Volume-area power law scaling, one of a set of analytical scaling techniques based on principals of dimensional analysis, has become an increasingly important and widely used method for estimating the future response of the world’s glaciers and ice caps to environmental change. Over 60 papers since 1988 have been published in the glaciological and environmental change literature containing applications of volume-area scaling, mostly for the purpose of estimating total global glacier and ice cap volume and modeling future contributions to sea level rise from glaciers and ice caps. The application of the theory is not entirely straightforward, however, and many of the recently published results contain analyses that are in conflict with the theory as originally described by Bahr et al. (1997). In this review we describe the general theory of scaling for glaciers in full three-dimensional detail without simplifications, including an improved derivation of both the volume-area scaling exponent γ and a new derivation of the multiplicative scaling parameter c. We discuss some common misconceptions of the theory, presenting examples of both appropriate and inappropriate applications. We also discuss potential future developments in power law scaling beyond its present uses, the relationship between power law scaling and other modeling approaches, and some of the advantages and limitations of scaling techniques.
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To forecast rock glacier movements, it is necessary to have dependable information on their internal structures and physical properties. A first attempt to expand our knowledge of a rock glacier in the Swiss Alps involved acquiring ground-based ground-penetrating radar (GPR) data along numerous profiles using different acquisition systems and antennae with different nominal frequencies. Images derived from these ground-based data were inconsistent and unreliable. For our second attempt, we recorded GPR data using a helicopter-mounted system. The helicopter GPR sections were surprisingly good, with consistent images along adjacent and intersecting profiles. Internal shear horizons, ice-rich and ice-poor regions and the bedrock interface were well delineated on the helicopter GPR images. Besides providing excellent-quality images, the helicopter GPR system allowed areas of the rock glacier to be surveyed that would have been difficult or impossible to access for a ground-based study. Because near-surface heterogeneity does not seem to have a major effect on helicopter GPR data acquired across a rugged rock glacier, we suggest that helicopter GPR surveying might be useful for investigating many terrains covered by heterogeneous loose material, including debris avalanches, scree slopes and rockfalls. Copyright © 2015 John Wiley & Sons, Ltd.
Conference Paper
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In order to assess the seasonal changes of the topography, the inner structure and the physical properties of a small glacier in the Eastern Alps, we performed a 4-D multi frequency GPR survey by repeating the same data acquisition in four different periods of the year 2013. The usual glacier mass balance estimation encompasses only topographic variations, but the real evolution is much more complex and includes surface melting and refreezing, snow metamorphism, and basal melting. We analyzed changes in both the imaged geometrical-morphological structures and the densities, estimated from GPR data inversion. The inversion algorithm uses reflection amplitudes and traveltimes to extract the electromagnetic velocities in the interpreted layers and the densities of the frozen materials through empirical relations. The obtained results have been compared and validated with direct measures like snow thickness surveys, density logs within snow pits and ablation stakes. This study demonstrates that GPR techniques are a fast and effective tool not only for glacial qualitative studies, but also for detailed glacier monitoring and accurate quantitative analyses of crucial glaciological parameters like density distribution and water runoff.
Article
Full-text available
Volume-area power law scaling, one of a set of analytical scaling techniques based on principals of dimensional analysis, has become an increasingly important and widely-used method for estimating the future response of the world's glaciers and ice caps to environmental change. Over sixty papers since 1988 have been published in the glaciological and environmental change literature containing applications of volume-area scaling, mostly for the purpose of estimating total global glacier and ice cap volume and modeling future contributions to sea level rise from glaciers and ice caps. The application of the theory is not entirely straightforward, however, and many of the recently published results contain analyses that are in conflict with the theory as originally described by Bahr et al. [1997]. In this review we describe the general theory of scaling for glaciers in full three-dimensional detail without simplifications, including an improved derivation of both the volume-area scaling exponent γ and a new derivation of the multiplicative scaling parameter c. We discuss some common misconceptions of the theory, presenting examples of both appropriate and inappropriate applications. We also discuss potential future developments in power-law scaling beyond its present uses, the relationship between power-law scaling and other modeling approaches, and some of the advantages and limitations of scaling techniques.
Article
Full-text available
The variability of glacier response to atmospheric temperature rise in different topo-climatic settings is still a matter of debate. To address this question in the Central Italian Alps, we compile a post-LIA (Little Ice Age) multitemporal glacier inventory (1860–1954–1990–2003–2007) along a latitudinal transect that originates north of the continental divide in the Livigno Mountains and extends south through the Disgrazia and Orobie ranges, encompassing continental-to-maritime climatic settings. In these sub-regions, we examine the area change of 111 glaciers. Overall, the total glacierized area has declined from 34.1 to 10.1 km2, with a substantial increase in the number of small glaciers due to fragmentation. The average annual decrease (AAD) in glacier area has risen by about 1 order of magnitude from 1860–1990 (Livigno: 0.45; Orobie: 0.42; and Disgrazia: 0.39 % a−1) to 1990–2007 (Livigno: 3.08; Orobie: 2.44; and Disgrazia: 2.27 % a−1). This ranking changes when considering glaciers smaller than 0.5 km2 only (i.e., we remove the confounding caused by large glaciers in Disgrazia), so that post-1990 AAD follows the latitudinal gradient and Orobie glaciers stand out (Livigno: 4.07; Disgrazia: 3.57; and Orobie: 2.47 % a−1). More recent (2007-2013) field-based mass balances in three selected small glaciers confirm post-1990 trends showing the consistently highest retreat in continental Livigno and minimal area loss in maritime Orobie, with Disgrazia displaying transitional behavior. We argue that the recent resilience of glaciers in Orobie is a consequence of their decoupling from synoptic atmospheric temperature trends, a decoupling that arises from the combination of local topographic configuration (i.e., deep, northfacing cirques) and high winter precipitation, which ensures high snow-avalanche supply, as well as high summer shading and sheltering. Our hypothesis is further supported by the lack of correlations between glacier change and glacier attributes in Orobie, as well as by the higher variability in ELA0 positioning, post-LIA glacier change, and interannual mass balances, as we move southward along the transect.
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We propose an integrated methodology to image the internal structure, evaluate the volume and estimate the densities of different units within ice bodies, useful for more precise mass estimation of very small glaciers. The procedure encompasses light detection and ranging (LiDAR) and ground penetrating radar (GPR) common offset data. The case study is the Canin Eastern Glacieret (CEG), a very small and maritime glacier in the Eastern Alps, and one of the lowermost glaciers of the European Alps. We calculate both volumetric and mass variations of the analysed ice body by integrating GPR measurements with LiDAR surveys acquired in different years (2006 and 2011). Between 2006 and 2011, the area of the glacieret increased from 8,510 to 17,530 m2 with a gain of 9,016 m2. The observed volume increase has been estimated in 96,350 m3 (+97 %), which corresponds to a positive mass balance of 3.89 m w.e.. This quite unusual finding in the present global warming behaviour is mainly due to the above-average winter accumulation (cw) in the considered period. Moreover, the winter season 2008–2009 represented an exceptional event with a cw equal to 13.38 m, the highest of the available record. Thanks to density estimation, we infer the total mass of the CEG at the time of the geophysical surveys, comparing such results with the ones obtained with available empirical equations, observing an important mass gain in the 5 years considered.
Article
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Very small glaciers (area <0.1 km2) have received increased scientific attention during recent years, both for their rapid responses to the climate forcing and because they are characterized by microclimatic conditions, often marginal to glacier formation. They are particularly sensitive to climate changes and characterized by a great mass turnover, particularly evident in maritime areas with high precipitation. Here we consider the evolution from 1920 of the ‘Canin Eastern Glacier’ (Italian Southeastern Alps) in order to correlate its evolution to the precipitation–temperature trends. We reconstructed a precipitation–temperature record at the altitude of the glacier, filling a lack of knowledge in this alpine sector. We observed a decrease in the mean annual precipitation of 10% in 90 years and a warming trend of 0.1∘C decade−1 since 1851, and of 0.7∘C decade−1 in the last 20 years. An inverse correlation between precipitation and mean air temperature during summer and ablation periods was also observed. Glacier dynamics revealed a phase of stability between 1945 and 1985 that seems to be a peculiar characteristic of this area. Moreover, through a general regression model the glacial terminus variations seem to be statistically influenced only by winter precipitation. This fact opens interesting perspectives for the possible future evolution of this small glacier and, more in general, to other small glaciers in maritime areas in regard to climate change scenarios.
Article
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Three very small Alpine glaciers in the Julian Alps are presented: the Eastern and the Western Canin glaciers in Italy and the Triglav glacier in Slovenia. The history of measurements using a measuring tape and via geodetic means on Canin glaciers is presented in brief; the majority of the paper deals with the acquisition of glacier boundaries from archive non-metrical images. The acquisition is based on interactive orientation method (mono-plotting) using lidar DTM. Seven archive non-metrical images of Mount Canin from 1893 to the mid-1970s and two aero-photogrametric images from periodic aerial photogrammetric surveys of Slovenia from 2000 and 2011 were used to determine the glaciers’ areas. In addition, a map of Canin glaciers from 1908 was geo-referenced. Five archive non-metrical images of Triglav glacier from 1897 to 1962 were used to determine the glacier area. Problems with obstructed areas are presented, and possible solutions are also given for deriving areas behind the obstructions. The usefulness of archival imagery for long-time monitoring of glaciers is presented, and the importance of old mountaineering publications as a source of such images is emphasized.
Article
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During spring 2013, we performed 500 MHz, helicopter-borne impulsive ground-penetrating radar surveys of several glaciers and glacier forelands in south-central Alaska, USA. These surveys were designed to obtain spatially distributed measurements of snow accumulation spanning a broad range of continental and maritime climatic zones. Visual assessment of radar images shows that data quality varied with the terrains and was optimal for snow that covered smooth glacier ice and firn, smooth debris-covered areas and moraines, freshwater lake and river ice, tundra, and taiga. Conversely, returns from the base of the snowpack were unrecognizable over rough debris-covered glacier termini, icefalls and some high-altitude accumulation basins. Optimal flying speed was 15–20 ms–1 (30–40 kt). At these speeds, which are two to three times faster than previously reported for such surveys, we could still identify snow-depth data with confidence, at a point spacing of ∼1.5–2.0 m. Data quality on glaciers decreased with increased air speed, though useful echoes from the base of the snowpack were still obtained at 40–45 ms–1 (87 kt; data point spacing of 6–8 m). Similar high-speed surveys over non-glacial terrains were unsuccessful, as basal reflections were no longer recognizable.
Article
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We estimate the glacier mass balance of a 9.5 km2 mountain glacier using three approaches for balance years 2009, 2010 and 2011. The photogrammetric, GPS and glaciological methods yielded sampling densities of 100, 5 and 2 points km–2, with measurement precisions of ±0.40, ±0.10 and ±0.10 m w.e. respectively. Our glaciological measurements likely include a positive bias, due to omission of internal and basal mass balance, and uncertainty in determining the interface between snow and firn with a probe (±0.10 m w.e.). Measurements from our photogrammetric method include a negative bias introduced by the manual operator and our temperature index model used to correct for different dates of imaging (0.15 m w.e.), whereas GPS measurements avoid these biases. The photogrammetric and GPS methods are suitable for estimating glacier-wide annual mass balance, and thus provide a valuable measure that complements the glaciological method. These approaches, however, cannot be used to estimate mass balance at a point or mass-balance profiles without a detailed understanding of the vertical component of ice velocity.
Article
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We show that geophysical methods offer an effective means of quantifying snow thickness and density. Opportunistic (efficient but non-optimized) seismic refraction and ground-penetrating radar (GPR) surveys were performed on Storglaciären, Sweden, co-located with a snow pit that shows the snowpack to be 1.73 m thick, with density increasing from ∼120 to ∼500 kg m–3 (with a +50 kg m–3 anomaly between 0.73 and 0.83 m depth). Depths estimated for two detectable GPR reflectors, 0.76±0.02 and 1.71±0.03 m, correlate extremely well with ground-truth observations. Refraction seismic predicts an interface at 1.90±0.31 m depth, with a refraction velocity (3730±190 m s–1) indicative of underlying glacier ice. For density estimates, several standard velocity–density relationships are trialled. In the best case, GPR delivers an excellent density estimate for the upper snow layer (observed = 321±74 kg m–3, estimated = 319±10 kg m–3) but overestimates the density of the lower layer by 20%. Refraction seismic delivers a bulk density of 404±22 kg m–3 compared with a ground-truth average of 356±22 kg m–3. We suggest that geophysical surveys are an effective complement to mass-balance measurements (particularly for controlling estimates of snow thickness between pits) but should always be validated against ground-truth observations.
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Deriving glacier outlines from satellite data has become increasingly popular in the past decade. In particular when glacier outlines are used as a base for change assessment, it is important to know how accurate they are. Calculating the accuracy correctly is challenging, as appropriate reference data (e.g. from higher-resolution sensors) are seldom available. Moreover, after the required manual correction of the raw outlines (e.g. for debris cover), such a comparison would only reveal the accuracy of the analyst rather than of the algorithm applied. Here we compare outlines for clean and debris-covered glaciers, as derived from single and multiple digitizing by different or the same analysts on very high- (1 m) and medium-resolution (30 m) remote-sensing data, against each other and to glacier outlines derived from automated classification of Landsat Thematic Mapper data. Results show a high variability in the interpretation of debris-covered glacier parts, largely independent of the spatial resolution (area differences were up to 30%), and an overall good agreement for clean ice with sufficient contrast to the surrounding terrain (differences ∼5%). The differences of the automatically derived outlines from a reference value are as small as the standard deviation of the manual digitizations from several analysts. Based on these results, we conclude that automated mapping of clean ice is preferable to manual digitization and recommend using the latter method only for required corrections of incorrectly mapped glacier parts (e.g. debris cover, shadow).
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This research reveals relationships between climate variables and inter-annual dynamics in the area of the glacieret located in the cirque Golemiya Kazan in the Pirin Mountains. The study period is 1993–2017. The correlations are identified using statistical methods. Also, a statistical model is constructed, including some climate variables as predictors. Despite the evident decrease of the glacieret’s size in the period from the 1950s onwards, the long-term trends for the last decades have been insignificant. The main climatic factors influencing the inter-annual dynamics in the area of the glacieret are air temperature, precipitation, zonal and meridional winds and relative humidity. With respect to the dynamics in the area of the glacieret, the important trends in the different climate variables are those of the warm period air temperatures and zonal (u) wind. They also determine to a great extent its future development by acting in two opposite directions–rising temperatures in the warm period will lead to a rapid decrease of its area by the end of the melting season, while the change of wind direction from west to east in the warm period will increase its area. The influence of the zonal wind in the warm period is explained mainly by the location of the glacieret in the cirque. Generally, the glacieret is tilted downwards from west to east. Thus, westerly winds facilitate blowing away the snow from the surface of the glacieret, assisting its melting in the warm period. Easterly winds do not have such an effect. The combination of the opposite effects of these two most important climate variables leads to the most likely scenario for the future development of the glacieret, according to which by the middle of this century it is expected to turn into a semi-permanent snow patch, which disappears after some summers, and by the end of the century to completely melt every year before the end of the melting season.
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To improve current understanding of ongoing deglaciation dynamics in relation to climatic forcing, it is critical to build long-term series of climate and glacier changes. This task is typically hampered by availability and resolution of Quaternary glacier paleo-reconstructions. To explore opportunities and challenges, we present a case study from Val Viola, which integrates area, volume and ELA changes across a 13k-year time window, including four Younger Dryas–Early Holocene glacier stadials and eight post-LIA periods. Results suggest that relevant shifts in climatic forcing associated with the Pleistocene–Holocene transition and post-LIA deglaciation phases are of comparable magnitude, with an atmospheric temperature increase of about 1.5–2°C. Post-LIA decline in glacierized areas (68.9 ± 6%) is comparable with retreat rates recorded in other Italian glaciers, but is greater than elsewhere in the Alps, where glaciers are comparably larger. Glacier stability in the particularly warm 2007–2015 period testifies to the decoupling attained by small glaciers from synoptic atmospheric conditions. We argue that this is caused by enhanced wind drift and avalanche accumulation, occurred in response to morphological changes on ice surfaces following progressive glacier shrinking. This positive feedback not only could delay glacier extinction in certain physiographic settings but also could introduce bias in paleo-glaciological reconstructions of climatic conditions.
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In order to assess the climate–glacier relationship in the Southern European Alps, two small glaciers in Lombardy, Suretta Sud and Lupo, have been chosen for investigation. GPS profiling in 2016 allowed the determination of elevation changes since 2007 and thus the determination of the glacier mass balance using the geodetic method. Older maps have been digitized to reconstruct mass changes back to 1962. The two glaciers react synchronously and show overall mass losses, but the narrower observation pattern at Suretta Sud reveals positive mass changes from 1970 to 1982. Long-term meteorological series of precipitation and air temperature of representative stations have been analysed, they show highly significant warming trends of 0.32–0.40°C per decade during summer, but no significant trend in winter precipitation. Since 2009/2010, annual mass balance measurements applying the glaciological method were undertaken by the Servizio Glaciologico Lombardo. These annual observations reveal that, despite the decadal mass loss observed by geodetic observations, years with positive mass changes still occur. These years showed below average winter precipitation and below average summer temperatures, indicating that glacier behaviour is influenced by both parameters. Ice thicknesses observed by echo radio sounding allow to calculate glacier volume and the bedrock topography. Maximum ice thicknesses are around 40 m and the cirques are not overdeepened by glacial erosion. Using very simple extrapolations of observed rates of downwasting results in theoretical life expectancies of these glacierets of 50–70 yr.
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The southeastern European Alps represent the spot where mean annual precipitation is at its highest in the entire Alpine chain. Accordingly, the glacial evolution here might have a different spatial and chronological pattern if compared with other alpine areas. This paper discusses geomorphological evidence of three glacial stages from the Krnica Valley in the Julian Alps of Slovenia, and is the first step towards a comprehensive palaeoglaciological studies in this alpine sector. Very well-preserved glacial landforms in the Upper Krnica Valley allowed the reconstruction of glacier surface topographies and corresponding equilibrium line altitudes (ELAs) by means of field-based geomorphological and sedimentological data and by using geospatial analysis. The uppermost frontal moraines belong to the Little Ice Age (LIA) and the corresponding ELA is estimated at 1973 m a.s.l. Other two stages with the ELA depressed by 50 m and 161 m compared to the LIA ELA, suggest early Holocene and Younger Dryas ages of the palaeoglaciers, respectively. This assumption ensues from absolute age datings and related ELA depressions observed elsewhere in the European Alps. The presence of buried ice under the debris in the Krnica cirque, imaged through geophysical investigations, point to peculiar microclimatic conditions able to preserve relict glacier ice. This is favoured by the recursive presence of snow on the ground caused by the extreme summer shading and the significant winter snow-recharge triggered by snowblow and avalanche feeding. The possible evolution of such relict ice under the ongoing climate warming is also discussed.
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We apply an automated picking and inversion algorithm to ground-based and airborne glaciological GPR surveys, in order to recover the internal stratigraphy, density distribution, and water content of alpine glaciers. Current glacier monitoring techniques encompass topographic mapping, direct measurements, and GPR surveys. However, the resulting models strongly depend on the assumptions made about the glacier's internal EM velocity and density distributions, which are usually set either constant or slow-varying, with the only constraints given by locally sampled values. Our inversion procedure uses amplitudes and timespace positions of the recorded reflections to recover the EM velocity and thickness of each layer by reconstructing the travel path of each reflected wavelet. The internal density distribution of glaciers is then recovered using well-known empirical formulas. The input reflections are automatically picked using an algorithm designed to detect and track any recorded event characterized by lateral phase continuity. Such a procedure is mostly independent of the interpreter and only requires a few input parameters and thresholds. High data densities lead to accurate and statistically sound models, while 4-D GPR surveys allow monitoring of the temporal variations of a glacier and the estimation of its mass balance.
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Interest in brines in extreme and cold environments has recently increased after they have been found on Mars. Those brines can be potential new subsurface habitats for peculiar ecosystems. In the McMurdo Dry Valleys of the Antarctic, the best analogue for Mars conditions, only a few cases of brines have been identified in some perennially frozen lakes and in one case in an underground aquifer. Here, we present the occurrence of pressurized brines in a shallow perennially ice-covered lake south of 70°S in an ice-free area of Victoria Land, Antarctica. For the first time, we also imaged, by means of ground penetrating radar data, the existence of a pingo-like-feature (PLF) formed by the extrusion of brines, which has also been confirmed by borehole evidence. Those brines are fed by an underground talik external to the lake basin, enhancing the possibility of unexploited ecosystems that could find an analogue in Martian environments.
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The Julian Alps (in the southeastern European Alps, Italy and Slovenia) represent an important case study area for the study of small and very small maritime glaciers. High mean annual precipitation results in great snow accumulation during the winter, permitting the presence of ice bodies with the lowest Equilibrium Line Altitudes in the Alps. During the Little Ice Age (LIA) 19 small glaciers (<1 km2) existed, covering a total area of 2.4 km2. By 2012, the glacierized area had shrunk by 84% and only isolated glacierets and ice patches survived, each having a total area less than 0.5 km2. We present here a geomorphological and palaeoglaciological map of 8 sections of the Julian Alps related to the late Holocene distribution of glaciers, at a scale of 1:6000. Glacier topography during the LIA maximum was reconstructed on the basis of well-expressed geomorphological features together with historical archive data. The present-day distribution of ice bodies was inferred from orthophotos and 1 m resolution digital terrain models derived from airborne laser scanning. The past and present areal extent and surface morphology of glaciers permits calculation of volume loss since the LIA, which is estimated at 96%.
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High altitude karstic environments often preserve permanent ice deposits within caves, representing the lesser-known portion of the cryosphere. Despite being not so widespread and easily reachable as mountain glaciers and ice caps, ice caves preserve much information about past environmental changes and climatic evolution. We selected 1111 ice caves from the existing caves inventory, predominantly but not exclusively located in the periglacial domain where permafrost is not dominant (i.e., with mean annual air temperature < 3°C but not in a permafrost environment). The influence of climate and topography on ice caves distribution is also investigated. In order to assess the thickness and the inner structure of the deposits, we selected two exemplary ice caves in the Canin massif (Julian Alps) performing several multifrequency GPR surveys. A strong influence of global and local climate change in the evolution of the ice deposits has been particularly highlighted in the dynamic ice caves type, especially in regards to the role of weather extremes. The natural response of ice caves to a warming climate could lead to a fast reduction of such ice masses. The increased occurrence of weather extremes, especially warmer and more intense precipitation caused by higher mean 0°C-isotherms, could in fact be crucial in the future mass balance evolution of such permanent ice deposits.
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During the summer of 2010 the surface elevation of Storglaciären in northern Sweden was measured using high-precision GNSS and reflectorless Total Station surveys. The DEM created from these data contain less noise than those created from orthophotographic methods over snow covered glaciers and is therefore smoother, with fewer erroneous features in the data. The principal, though not sole, intended use for the DEM is in the calculation of surface mass balance, which has influenced decisions on what constitutes a functional part of a glacier, leading to the exclusion of features such as snow aprons and perennial ice above the bergschrund. Other peripheral features have changed since the previous, aerial survey from 1999 leading to a reduction in size of approximately 0.17 km2.
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The evolution of glaciers and ice patches, as well as the ELA since the LIA maximum were investigated in the Julian Alps (Southeastern European Alps) including ice masses that were previously unreported. Twenty-three permanent firn and ice bodies have been recognized in the 1,853 km2 of this alpine sector, covering a total area in 2012 of 0.385 km2, about one fifth of the area covered during the LIA (2.350 km2). These features were classified as very small glaciers, glacierets or ice patches, with major contribution to the mass balance from avalanches and wind-blown snow. Localized snow accumulation is also enhanced in the area due to the irregular karst topography. The ice masses in the region are at the lowest elevations of any glaciers in the Alpine Chain, and are characterized by low dynamics. The ELAs of the two major LIA glaciers (Canin and Triglav) have been established at 2,275 ± 10 m and 2,486 ± 10 m, respectively, by considering the reconstructed area and digital elevation model (DEM) and using an Accumulation Area Ratio (AAR) of 0.44 ± 0.07, typical of small cirque glaciers. Changes in the ELA and glaciers extension indicate a decoupling from climate. This is most evident in the smallest avalanche-dominated ice bodies, which are currently controlled mainly by precipitation. The damming effect of moraine ridges and pronival ramparts at the snout of small ice bodies in the Julian Alps represents a further geomorphological control on the evolution of such ice masses, which seem to be resilient to recent climate warming instead of rapidly disappearing as should be expected. This article is protected by copyright. All rights reserved.
Article
Mountainous locations and steep rugged surfaces covered by boulders and other loose debris are the main reasons why rock glaciers are among the most challenging geological features to investigate using ground‐based geophysical methods. Consequently, geophysical surveys of rock glaciers have only ever involved recording data along sparse lines. To address this issue, we acquired quasi‐3‐D ground‐penetrating radar (GPR) data across a rock glacier in the Swiss Alps using a helicopter‐mounted system. Our interpretation of the derived GPR images constrained by borehole information results in a novel “thin‐skinned” rock glacier model that explains a concentration of deformation across a principal shear zone (décollement) and faults across which rock glacier lobes are juxtaposed. The new model may be applicable to many rock glaciers worldwide. We suggest that the helicopter GPR method may be useful for 3‐D surveying numerous other difficult‐to‐access mountainous terrains. First ever quasi‐3‐D helicopter GPR survey of an Alpine rock glacierActive rock glacier units are identified on geophysical imagesNew thin‐skinned rock glacier model is proposed
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Only a few small glaciers survive today in the Mountains of the Mediterranean. Notable examples are found in the Pyrenees, Maritime Alps, Italian Apennines, the Dinaric and Albanian Alps and the mountains of Turkey. Many glaciers disappeared during the 20th Century. Glaciers were much larger and more numerous during the Little Ice Age. Small glaciers even existed as far south as the High Atlas of Morocco and the Sierra Nevada of southern Spain. In more northerly areas, such as the western Balkans, glaciers and permanent snow fields occupied hundreds of cirques on relatively low-lying mountains. In the High Atlas and the Sierra Nevada no glaciers exist today, whilst in the Balkans only a few modern glaciers have been reported (
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Glaciokarst is a landscape which combines karst features and hydrology as well as inherited glacial features. It is a result of glaciation upon a karst geomorphological system. The relationship between glaciers and karst is rather poorly known and inadequately recognised. This research focuses on three distinct karst areas along the Adriatic coast in the southern Dinaric Alps that were affected by the Quaternary glaciations. An insight into specific glaciokarst processes and surface features was provided through the study of the areas of the Lovćen, Orjen and Velež Mountains. A glaciokarst geomorphology is in general well preserved due to the prevailing vertically oriented chemical denudation following deglaciation and almost the entire absence of other surface processes. Typical glacial erosional features are combined by a variety of depressions which are the result of a karstic drainage of subglacial waters. The majority of glacial deposits occur as extensive lateral-terminal moraine complexes, which are often dissected by smaller breach-lobe moraines on the external side of the ridge. Those moraine complexes are likely to be a product of several glacial events, which is supported by complex depositional structures. According to the type of glacial depositional features, the glaciers in the study areas were likely to have characteristics of moraine-dammed glaciers. Due to vertical drainage ice-marginal fluvial processes were unable to evacuate sediment. Fluvial transport between glacial and pro-glacial systems in karst areas is inefficient. Nevertheless, some sediment from the glacier margin is washed away by the pro-glacial streams, filling the karst depressions and forming piedmont-type poljes. This article is protected by copyright. All rights reserved.
Article
The Columbia Icefields are highland ice caps developed upon benchlands of massive platform carbonates in the Main Ranges, Rocky Mountains. Ice is discharged via major valley glaciers, including South Glacier, Castleguard Valley. The karst is developed along the southeast edge of the central icefield, extends beneath it, and drains to springs in Castleguard Valley. Altitudinal range of the karst is 1600 to 2600 m a.s.l. Mean annual temperature is estimated to range from 0 to -7°C over this range. Treeline is at ca. 2100 m. All cirques and valleys were occupied by ice during the late Wisconsinan Glaciation. Modern glaciers are ca. 100 to 300 m in thickness and are receding from well-marked Neoglacial moraines. Periglacial features are prominent on high carbonate surfaces that escaped Neoglacial cover. The principal surface karst features are (1) subglacial precipitates found on newly exposed Neoglacial surfaces; (2) varieties of sinkholes seen on all exposed carbonates above 2000 m; (3) families of springs, most below 2000 m. Castleguard Cave is a major relict system. The first interpretations of the karst, using simple morphological evidences alone, supposed that the Cave was drained by glacial entrenchment during the Wisconsinan Glaciation. Two modern groundwater caves developed beneath it.
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Synoposis: It is suggested that a single electromagnetic pulse having a length in space of the order of a meter can be radiated and received by low-Q (broad-banded) antennas. Rough calculations indicate that peak powers of 100 kw probably can be generated with existing electronic components, capable of producing usable signal returns from large semispecular surfaces at distances of the order of miles. The resulting ¿untuned all-video-radar system¿ would constitute an electromagnetic analogy to the well-known seismic reflection method of geophysical prospecting, in which a single compressional acoustic pulse (under ideal conditions) is emitted isotropically and reflections are received from successive extensive, flat-lying, reflecting surfaces. A single vhf (very-high-frequency) pulse should combine the advantage of good distance resolution with less tendency than microwaves to be absorbed or scattered by the imperfections in natural materials. Preliminary experiments at 125 mc (megacycles) indicate that interfaces less than 60 cm (centimeters) apart could be so resolved. The development and initial application of the method as a rapid air-borne method of profiling the thicknesses of radio-transparent layered materials, such as floating fresh-water ice (for aircraft landing areas) and the polar continental ice sheets. Potential applications in high-speed extraterrestrial communication may also exist.
Conference Paper
The investigation of difficult accessible areas is more and more an important issue for exploration of ore deposits and ground water, glaciology and pipeline mapping. Compared with ground-based GPR measurements, wide areas can be explored faster in a dense grid. In cooperation with the Federal Institute for Geosciences and Natural Resources (BGR), a new helicopter GPR based on gated stepped frequency technology was developed. The paper will describe the development of the stepped frequency radar and the application specific antennas. The first application results of this new GPR will be discussed in order to quantify the performance of the new technology.
Article
Vedretta Piana Glacier is situated in Valle di Trafoi, near Stelvio Pass (Italian Alps). Summer skiing has been a popular sport on this glacier for over seventy years. On this glacier a study for determining its recent evolution was carried out by means of a quantitative, detailed analysis (GPS and GPR surveys) carried out in 1999 and in 2000. The data elaboration shows that the loss of ice and snow during the September 1999 - September 2000 period was equal to 938.920 m3. The specific net mass balance for the 1999/2000 hydrological year thus amounts to -2.138 mm. The glacier's mean thickness proved to be equal to 71 m. The glacier volume proved to be equal to 72.500.000 m3 over a surface area of about 1 km2. The survival time of the glacier is valued of about 35 years. LInk: http://gfdq.glaciologia.it/024_2_06_2001/
Article
We propose a methodology to estimate the density of frozen media (snow, firn and ice) using common offset (CO) GPR data. The technique is based on reflection amplitude analysis to calculate the series of reflection coefficients used to estimate the dielectric permittivity of each layer. We determine the vertical density variations for all the GPR traces by applying an empirical equation. We are thus able to infer the nature of frozen materials, from fresh snow to firn and ice. The proposed technique is critically evaluated and validated on synthetic data and further tested on real data of the Glacier of Mt. Canin (South-Eastern Alps). Despite the simplifying hypotheses and the necessary approximations, the average values of density for different levels are calculated with acceptable accuracy. The resulting large-scale density data are fundamental to estimate the water equivalent (WE), which is an essential parameter to determine the actual water mass within a certain frozen volume. Moreover, this analysis can help to find and locate debris or moraines embedded within the ice bodies.