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1
Temovski, Marjan, Balázs Madarász, Zoltán Kern, Ivica Milevski, and Zsófia Ruszkiczay-Rüdiger. "Glacial Geomorphology and Preliminary Glacier Reconstruction in the Jablanica Mountain, Macedonia, Central Balkan Peninsula." Geosciences 8, no. 7 (July 23, 2018): 270. http://dx.doi.org/10.3390/geosciences8070270.
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Although glacial landforms on the Balkan Peninsula have been studied since the 19th century, only scarce data are available about the extent of the former glaciations in the Central Balkan Peninsula, the transition zone between the Mediterranean and Central Europe. Glacial features of the Jablanica Mt. were mapped, described and classified into morphostratigraphic units. A revised glacio-geomorphological map was produced and glacial landforms were assigned to six morphostratigraphic units. Ten primary and two secondary cirques were identified in the upper parts of the studied valleys, while downstream the valleys were steep and glacially shaped with several glacial steps and thresholds. Cirque and valley morphology indicate that subglacial deepening was limited within the cirques and was more intensive in the valley sections during more extensive glacial phases. The largest reconstructed glaciers were 4.6–7 km long, while the last cirque glaciers were only a few hundred meters long. Using morphostratigraphic data, a glacier reconstruction was carried out for the largest mapped glacial extent. On the basis of glacial geomorphology, a former equilibrium-line altitude (ELA) of ~1800 m and glacier cover of 22.6 km2 were estimated during this stage. The local ELA values were compared to the regional ELA record and enabled to tentatively attribute a MIS 6 age for the reconstructed maximum ice extent in the study area.
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Cortés-Ramos, J., and H. Delgado-Granados. "The recent retreat of Mexican glaciers on Citlaltépetl Volcano detected using ASTER data." Cryosphere Discussions 6, no. 4 (August 6, 2012): 3149–76. http://dx.doi.org/10.5194/tcd-6-3149-2012.
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Abstract. Satellite imagery and net radiation data collected between 2001 and 2007 for Citlaltépetl Volcano confirm the dramatic shrinkage of Glaciar Norte and the elimination of Jamapa and Chichimeco glacier tongues. The Glaciar Norte rapidly retreated between 2001 and 2002 while for 2007 this retreat decreases considerably. Jamapa and Chichimeco tongues disappeared by 2001 as compared to the geometry shown for 1958. The Glaciar Norte lost about 72% of its surface area between 1958 and 2007. Recently, the ice loss appears to be accelerating as evidenced by the 33% areal loss in just 6 yr between 2001 and 2007. At this shrinkage rate the glaciers would be gone from the volcano by the year 2020, which is decades earlier than previously estimated. The net radiation from ASTER images and the energy fluxes calculated via the meteorological data at the glacial surface show the close relationship between glacial shrinkage and surface energy balance. The magnitude of changes in the net radiation balance allows improved understanding of glacial retreat in Mexico.
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Steinemann, Olivia, Alicia Martinez, Vincenzo Picotti, Christof Vockenhuber, and Susan Ivy-Ochs. "Glacial Erosion Rates Determined at Vorab Glacier: Implications for the Evolution of Limestone Plateaus." Geosciences 11, no. 9 (August 24, 2021): 356. http://dx.doi.org/10.3390/geosciences11090356.
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Understanding how fast glaciers erode their bedrock substrate is one of the key elements in reconstructing how the action of glaciers gives mountain ranges their shape. By combining cosmogenic nuclide concentrations determined in glacially abraded bedrock with a numerical model, we quantify glacial erosion rates over the last 15 ka. We measured cosmogenic 36Cl in fourteen samples from the limestone forefield of the Vorab glacier (Eastern Alps, Switzerland). Determined glacial erosion rates range from 0.01 mm a−1 to 0.16 mm a−1. These glacial abrasion rates differ quite markedly from rates measured on crystalline bedrock (>1 mm a−1), but are similarly low to the rates determined on the only examined limestone plateau so far, the Tsanfleuron glacier forefield. Our data, congruent with field observations, suggest that the Vorab glacier planed off crystalline rock (Permian Verrucano) overlying the Glarus thrust. Upon reaching the underlying strongly karstified limestone the glacier virtually stopped eroding its bed. We attribute this to immediate drainage of meltwater into the karst passages below the glacier, which inhibits sliding. The determined glacial erosion rates underscore the relationship between geology and the resulting landscape that evolves, whether high elevation plateaus in limestone terrains or steep-walled valleys in granitic/gneissic areas.
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Koppes, Michèle, Bernard Hallet, and John Anderson. "Synchronous acceleration of ice loss and glacial erosion, Glaciar Marinelli, Chilean Tierra del Fuego." Journal of Glaciology 55, no. 190 (2009): 207–20. http://dx.doi.org/10.3189/002214309788608796.
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AbstractTo contribute to the understanding of the influence of climate on glacial erosion and on orogenic processes, we report contemporary glacial erosion rates from a calving glacier in the Southern Andes and elucidate the influence of ice dynamics on erosion. Using seismic profiles of sediments collected in a proglacial fjord and a documented history of retreat, we determine the time-varying sediment flux of Glaciar Marinelli as a measure of basin-wide erosion rates, and compare these rates with the annual ice budget reconstructed using NCEP–NCAR reanalysis climate data from 1950 to 2005. The rate of erosion of the largest tidewater glacier in Tierra del Fuego averaged 39 ± 16 mm a−1 during the latter half of the 20th century, with an annual maximum approaching 130 mm a−1 following a decade of rapid retreat. A strong correlation emerges between the variable rate of ice delivery to the terminus and the erosion rate, providing quantitative insight into the relationship between ice fluxes and glacial erosion rates. For Glaciar Marinelli, as for other calving glaciers for which suitable data exist, the marked retreat and thinning over the past 50 years have resulted in a period of accelerated basal sliding and unusually rapid erosion.
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Glasser, Neil F., and Matthew R. Bennett. "Glacial erosional landforms: origins and significance for palaeoglaciology." Progress in Physical Geography: Earth and Environment 28, no. 1 (March 2004): 43–75. http://dx.doi.org/10.1191/0309133304pp401ra.
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Glacial inversion modelling of continental-scale palaeo-ice sheets is now recognized as an important tool in palaeoglaciology. Existing palaeoglaciological reconstructions of the dimensions, geometry and dynamics of former ice sheets are based mainly on glacial depositional, as opposed to glacial erosional, landforms. Part of the reason for this is a lack of detailed understanding of the origin and significance of glacial erosional landforms. Here we review recent developments in our understanding of the processes and landforms of glacial erosion and consider their value in palaeoglaciology. Glacial erosion involves the removal and transport of bedrock and/or sediment by glacial quarrying, glacial abrasion and glacial meltwater. These processes combine to create a suite of landforms that are frequently observed in areas formerly occupied by ice sheets and glaciers, and which can be used in palaeoglaciological reconstructions. For example, all landforms of glacial erosion provide evidence for the release of subglacial meltwater and the existence of warm-based ice. Landforms of glacial quarrying such as roches moutonnées, rock basins and zones of areal scouring are created when cavities form between an ice sheet and its bed and therefore are indicative of low effective basal pressures (0.1-1 MPa) and high sliding velocities that are necessary for ice-bed separation. Fluctuations in basal water pressure also play an important role in the formation of glacially quarried landforms. Landforms of glacial abrasion include streamlined bedrock features (‘whalebacks’), some ‘p-forms’, striae, grooves, micro-crag and tails, bedrock gouges and cracks. Abrasion can be achieved by bodies of subglacial sediment sliding over bedrock or by individual clasts contained within ice. Although abrasion models depend critically on whether clasts are treated as dependent or independent of subglacial water pressure, it appears that abrasion is favoured in situations where effective basal pressures are greater than 1 MPa and where there are low sliding velocities. Consequently, landforms dominated by glacial abrasion are created when there is no ice-bed separation. Landforms of glacial meltwater erosion include both subglacial and ice-marginal meltwater channels. Investigations of the relationship between glacial meltwater channels and other aspects of the subglacial drainage system, such as areas of ice-bed contact, areas of ice-bed separation and precipitate-filled depressions, enable inferences to be made concerning former subglacial water pressure-drainage relationships, effective pressures and glacier velocities. Meltwater palaeovelocity and palaeodischarge can also be calculated from measurements of channel shape, channel width and the size of material transported within former glacial meltwater channels. We surmize that glacial erosional landforms offer insight into former glacio-logical conditions at both the landform- and landscape-scale within palaeoglaciology. Exposure-age dating techniques, including cosmogenic isotope dating of bedrock surfaces, will be important in increasing our understanding of the age and chronological significance of landforms of glacial erosion. We conclude that landforms of glacial erosion are of great value in ice mass reconstruction and speculate that these landforms will achieve greater recognition within palaeoglaciology in line with improvements in exposure-age dating techniques.
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Shangguan, Donghui, Da Li, Yongjian Ding, Jun Liu, Muhammad Naveed Anjum, Yaojun Li, and Wanqin Guo. "Determining the Events in a Glacial Disaster Chain at Badswat Glacier in the Karakoram Range Using Remote Sensing." Remote Sensing 13, no. 6 (March 18, 2021): 1165. http://dx.doi.org/10.3390/rs13061165.
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The Karakoram mountain range is prone to natural disasters such as glacial surging and glacial lake outburst flood (GLOF) events. In this study, we aimed to document and reconstruct the sequence of events caused by glacial debris flows that dammed the Immit River in the Hindu Kush Karakoram Range on 17 July 2018. We used satellite remote sensing and field data to conduct the analyses. The order of the events in the disaster chain were determined as follows: glacial meltwater from the G2 glacier (ID: G074052E36491N) transported ice and debris that dammed the meltwater at the snout of the G1 glacier (ID: G074103E36480N), then the debris flow dammed the Immit River and caused Lake Badswat to expand. We surveyed the extent of these events using remote sensing imagery. We analyzed the glaciers’ responses to this event chain and found that the glacial debris flow induced G1 to exhibit accelerating ice flow in parts of the region from 25 July 2018 to 4 August 2018. According to the records from reanalysis data and data from the automatic weather station located 75 km from Lake Badswat, the occurrence of this disaster chain was related to high temperatures recorded after 15 July 2018. The chains of events caused by glacially related disasters makes such hazards more complex and dangerous. Therefore, this study is useful not only for understanding the formation of glacial disaster chains, but also for framing mitigation plans to reduce the risks for vulnerable downstream/upstream residents.
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Kotlyakov, V. M., L. P. Chernova, T. Ye Khromova, and N. M. Zverkova. "Glacier surges and glacial disasters." Doklady Earth Sciences 472, no. 1 (January 2017): 57–61. http://dx.doi.org/10.1134/s1028334x17010056.
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Yagol, P., A. Manandhar, P. Ghimire, RB Kayastha, and JR Joshi. "Identification of Locations for Potential Glacial Lakes Formation using Remote Sensing Technology." Journal on Geoinformatics, Nepal 12 (October 31, 2013): 10–16. http://dx.doi.org/10.3126/njg.v12i0.9068.
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In past Nepal has encountered a number of glacial lake outburst flood (GLOF) events causing loss of billions of rupees. Still there are a number of glacial lakes forming and there are chances of new glacial lake formation. Hence there is intense need to monitor glaciers and glacial lakes. The development on remote sensing technology has eased the researches on glacier and glacial lakes. Identification of locations of potential glacial lakes through the use of remote sensing technology has been proven and hence is opted for identification of locations of potential glacial lake in Khumbu Valley of Sagarmatha Zone, Nepal. The probable sites for glacial lake formation are at Ngojumpa, Lobuche, Khumbu, Bhotekoshi, Inkhu, Kyasar, Lumsumna, etc. As per study, the biggest glacial lake could form at Ngozumpa glacier. Even in other glaciers potential supra-glacial lakes could merge together to form lakes that occupy significant area. Nepalese Journal on Geoinformatics -12, 2070 (2013AD): 10-16
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Allen, R., M. J. Siegert, and A. J. Payne. "Reconstructing glacier-based climates of LGM Europe and Russia – Part 3: Comparison with GCM and pollen-based climate reconstructions." Climate of the Past Discussions 3, no. 5 (October 26, 2007): 1199–233. http://dx.doi.org/10.5194/cpd-3-1199-2007.
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Abstract. Understanding past climates using GCM models is critical to confidently predicting future climate change. Although previous analysis of GCM simulations have shown them to under predicted European glacial temperature anomalies (the difference between modern and glacial temperatures) such analyses have focused primarily on results from glacial simulations alone. Here we compare glacial maximum GCM results with the palaeoenvironment derived from glacier-climate modelling. The comparison confirms that GCM anomalies are under predicted, and that this is due to modern conditions that are modelled too cold and glacial temperatures that are too warm. The result is that CGM results, if applied to a glacier mass balance model, over predict the extent of glaciers today, and under predict their extent at the last glacial (as depicted in glacial geological reconstructions). Effects such as seasonality and model parameterisation change the magnitude of the under prediction but still fail to match expected glacial conditions.
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Cauvy-Fraunié, S., T. Condom, A. Rabatel, M. Villacis, D. Jacobsen, and O. Dangles. "Technical Note: Glacial influence in tropical mountain hydrosystems evidenced by the diurnal cycle in water levels." Hydrology and Earth System Sciences 17, no. 12 (December 4, 2013): 4803–16. http://dx.doi.org/10.5194/hess-17-4803-2013.
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Abstract. Worldwide, the rapid shrinking of glaciers in response to ongoing climate change is modifying the glacial meltwater contribution to hydrosystems in glacierized catchments. Determining the influence of glacial runoff to streams is therefore of critical importance to evaluate potential impact of glacier retreat on water quality and aquatic biota. This task has challenged both glacier hydrologists and ecologists over the last 20 yr due to both structural and functional complexity of the glacier–stream system interface. Here we propose quantifying the diurnal cycle amplitude of the streamflow to determine the glacial influence in glacierized catchments. We performed water-level measurements using water pressure loggers over 10 months at 30 min time steps in 15 stream sites in 2 glacier-fed catchments in the Ecuadorian Andes (> 4000 m a.s.l.) where no perennial snow cover is observed outside the glaciers. For each stream site, we performed wavelet analyses on water-level time series, determined the scale-averaged wavelet power spectrum at 24 h scale and defined three metrics, namely the power, frequency and temporal clustering of the diurnal flow variation. The three metrics were then compared to the percentage of the glacier cover in the catchments, a metric of glacial influence widely used in the literature. As expected, we found that the diurnal variation power of glacier-fed streams decreased downstream with the addition of non-glacial tributaries. We also found that the diurnal variation power and the percentage of the glacier cover in the catchment were significantly positively correlated. Furthermore, we found that our method permits the detection of glacial signal in supposedly non-glacial sites, thereby revealing glacial meltwater resurgence. While we specifically focused on the tropical Andes in this paper, our approach to determine glacial influence may have potential applications in temperate and arctic glacierized catchments. The measure of diurnal water amplitude therefore appears as a powerful and cost-effective tool to understand the hydrological links between glaciers and hydrosystems better and assess the consequences of rapid glacier shrinking.
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Allen, R., M. J. Siegert, and A. J. Payne. "Reconstructing glacier-based climates of LGM Europe and Russia – Part 3: Comparison with previous climate reconstructions." Climate of the Past 4, no. 4 (November 13, 2008): 265–80. http://dx.doi.org/10.5194/cp-4-265-2008.
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Abstract. Understanding past climates using GCM models is critical to confidently predicting future climate change. Although previous analysis of GCM simulations have shown them to under calculate European glacial temperature anomalies (the difference between modern and glacial temperatures) such analyses have focused primarily on results from glacial simulations alone. Here we compare glacial maximum GCM results with the palaeoenvironment derived from glacier-climate modelling. The comparison confirms that GCM anomalies are not large enough, and that this is due to modern conditions that are modelled too cold and glacial temperatures that are too warm. The result is that GCM results, if applied to a glacier mass balance model, over predict the extent of glaciers today, and under calculate their extent at the last glacial (as depicted in glacial geological reconstructions). Effects such as seasonality and model parameterisation change the magnitude of the under calculation but still fail to match expected glacial conditions.
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Hughes, Philip D., and Philip L. Gibbard. "Global glacier dynamics during 100 ka Pleistocene glacial cycles." Quaternary Research 90, no. 1 (June 4, 2018): 222–43. http://dx.doi.org/10.1017/qua.2018.37.
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AbstractIce volume during the last ten 100 ka glacial cycles was driven by solar radiation flux in the Northern Hemisphere. Early minima in solar radiation combined with critical levels of atmospheric CO2drove initial glacier expansion. Glacial cycles between Marine Isotope Stage (MIS) 24 and MIS 13, whilst at 100 ka periodicity, were irregular in amplitude, and the shift to the largest amplitude 100 ka glacial cycles occurred after MIS 16. Mountain glaciers in the mid-latitudes and Asia reached their maximum extents early in glacial cycles, then retreated as global climate became increasingly arid. In contrast, larger ice masses close to maritime moisture sources continued to build up and dominated global glacial maxima reflected in marine isotope and sea-level records. The effect of this pattern of glaciation on the state of the global atmosphere is evident in dust records from Antarctic ice cores, where pronounced double peaks in dust flux occur in all of the last eight glacial cycles. Glacier growth is strongly modulated by variations in solar radiation, especially in glacial inceptions. This external control accounts for ~50–60% of ice volume change through glacial cycles. Internal global glacier–climate dynamics account for the rest of the change, which is controlled by the geographic distributions of glaciers.
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Gíslason, Gísli Már, Jón S. Ólafsson, and Hákon Adalsteinsson. "Life in Glacial and Alpine Rivers in Central Iceland in Relation to Physical and Chemical Parameters." Hydrology Research 31, no. 4-5 (August 1, 2000): 411–22. http://dx.doi.org/10.2166/nh.2000.0025.
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The characteristics of stream and river ecosystems in arctic and alpine areas are determined mainly by the relative contribution of glacial meltwater, snowmelt, rainfall and groundwater. Each source generates a particular seasonal hydrological signature, affecting physical and chemical properties, and hence biological communities. The relative contribution of each source is sensitive to climate change. The study was concentrated on the glacial River W-Jökulsá and some non-glacial rivers in the central highlands of Iceland. The water in the glacial river was entirely glacial meltwater at the glacier margin, but the glacial contribution was about 20% 40 km downstream. However, its tributaries and non-glacial reference rivers were mainly springfed. The invertebrate fauna was confined to Chironomidae of the genus Diamesa close to the glacier, but other taxa (species and groups of species) occupied the river further downstream, where their diversity was close to that found in the reference rivers.
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Cauvy-Fraunié, S., T. Condom, A. Rabatel, M. Villacis, D. Jacobsen, and O. Dangles. "Technical Note: Using wavelet analyses on water depth time series to detect glacial influence in high-mountain hydrosystems." Hydrology and Earth System Sciences Discussions 10, no. 4 (April 5, 2013): 4369–95. http://dx.doi.org/10.5194/hessd-10-4369-2013.
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Abstract. Worldwide, the rapid shrinking of glaciers in response to ongoing climate change is currently modifying the glacial meltwater contribution to hydrosystems in glacierized catchments. Assessing the contribution of glacier run-off to stream discharge is therefore of critical importance to evaluate potential impact of glacier retreat on water quality and aquatic biota. This task has challenged both glacier hydrologists and ecologists over the last 20 yr due to both structural and functional complexity of the glacier-stream system interface. Here we propose a new methodological approach based on wavelet analyses on water depth time series to determine the glacial influence in glacierized catchments. We performed water depth measurement using water pressure loggers over ten months in 15 stream sites in two glacier-fed catchments in the Ecuadorian Andes (> 4000 m). We determined the global wavelet spectrum of each time series and defined the Wavelet Glacier Signal (WGS) as the ratio between the global wavelet power spectrum value at a 24 h-scale and its corresponding significance value. To test the relevance of the WGS we compared it with the percentage of the glacier cover in the catchments, a metric of glacier influence often used in the literature. We then tested whether one month data could be sufficient to reliably determine the glacial influence. As expected we found that the WGS of glacier-fed streams decreased downstream with the increasing of non-glacial tributaries. We also found that the WGS and the percentage of the glacier cover in the catchment were significantly positively correlated and that one month data was sufficient to identify and compare the glacial influence between two sites, provided that the water level time series were acquired over the same period. Furthermore, we found that our method permits to detect glacial signal in supposedly non-glacial sites, thereby evidencing glacial meltwater infiltrations. While we specifically focused on the tropical Andes in this paper, our approach to determine glacier influence would be applicable to temperate and arctic glacierized catchments. The WGS therefore appears as a powerful and cost effective tool to better understand the hydrological links between glaciers and hydrosystems and assess the consequences of rapid glacier melting.
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Jamšek Rupnik, Petra, Manja Žebre, and Giovanni Monegato. "Late Quaternary evolution of the sedimentary environment in Modrejce near Most na Soči (Soča Valley, Julian Alps)." Geologija 63, no. 2 (December 7, 2020): 295–309. http://dx.doi.org/10.5474/geologija.2020.022.
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Geomorphological and geological mapping have long been used to study the glacial history of the Slovenian Alps, but many uncertainties remain regarding the time and extent of Pleistocene glaciations there. Glacial landforms and undisturbed glacial deposits are rare in the areas of the former glacier terminus, especially in the Soča Valley, where large discrepancies in the interpretation of the extent of the former Soča Glacier have been reported. Early studies proved inconclusive as to whether one or two glaciations extended into the Soča Valley as far as Most na Soči. In order to answer this question, the Quaternary sedimentary succession and landforms in the Modrejce Valley near Most na Soči were investigated. New geological and geomorphological field data allow the interpretation of the sedimentary environment and the stratigraphic relationships between different units. In response to glacial dynamics, the sedimentation developed from glaciofluvial and glaciolacustrine to fully glacial environments, followed by slope deposition. At higher altitudes lateral moraines are preserved, while the staircase-like slope below has been carved into older glacial, glaciofluvial and glaciolacustrine deposits by glacial and post-glacial processes, including fluvial erosion and slope dynamics. We conclude that the succession studied here was deposited over the course of two different glacial advances – LGM and pre-LGM. Our study thus suggests that the Soča Glacier extended as far as the area of Most na Soči twice over the course of the late Quaternary.
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Richardson, Cecilia, and Per Holmlund. "Glacial cirque formation in northern Scandinavia." Annals of Glaciology 22 (1996): 102–6. http://dx.doi.org/10.3189/1996aog22-1-102-106.
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Passglaciären is a small cirque glacier in the Kebnekaise massif, northern Sweden. It is frozen to its bed over more than 70% of its area, and under present climatic conditions has little effect on cirque formation. More favourable conditions for cirque glacier erosion during the Holocene are of short duration. Assuming similar conditions during previous interglacials, it is suggested that forms such as the Passglaciären cirque developed mainly during the initial phases of glacials when they were part of networks of large valley glaciers or of a small warm-based mountain-centred ice sheet. Passglaciären has been examined in order to evaluate its erosive capacity and its association with the subglacial cirque morphology. The methods used are radar surveys and direct ice-temperature measurements. Erosion is restricted to a small section of the glacier bed, at present resulting in only partial deepening of the cirque and erosion of the backwall. In cold, arid regions with extensive permafrost, small cirque glaciers are largely frozen to the bed, and therefore cannot contribute significantly to cirque formation. In such regions glacial erosion by larger temperate glaciers is more likely to be the major cause of cirque excavation.
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Richardson, Cecilia, and Per Holmlund. "Glacial cirque formation in northern Scandinavia." Annals of Glaciology 22 (1996): 102–6. http://dx.doi.org/10.1017/s0260305500015275.
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Passglaciären is a small cirque glacier in the Kebnekaise massif, northern Sweden. It is frozen to its bed over more than 70% of its area, and under present climatic conditions has little effect on cirque formation. More favourable conditions for cirque glacier erosion during the Holocene are of short duration. Assuming similar conditions during previous interglacials, it is suggested that forms such as the Passglaciären cirque developed mainly during the initial phases of glacials when they were part of networks of large valley glaciers or of a small warm-based mountain-centred ice sheet. Passglaciären has been examined in order to evaluate its erosive capacity and its association with the subglacial cirque morphology. The methods used are radar surveys and direct ice-temperature measurements. Erosion is restricted to a small section of the glacier bed, at present resulting in only partial deepening of the cirque and erosion of the backwall. In cold, arid regions with extensive permafrost, small cirque glaciers are largely frozen to the bed, and therefore cannot contribute significantly to cirque formation. In such regions glacial erosion by larger temperate glaciers is more likely to be the major cause of cirque excavation.
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Menounos, Brian, Lyssa Maurer, John J. Clague, and Gerald Osborn. "Late Holocene fluctuations of Stoppani Glacier, southernmost Patagonia." Quaternary Research 95 (March 3, 2020): 56–64. http://dx.doi.org/10.1017/qua.2019.87.
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AbstractSome lateral moraines contain a rich record of Holocene glacial expansion. Previous workers have used such evidence to document glacial fluctuations in western Canada, Alaska, and the U.S. Pacific Northwest, but similar studies in Patagonia are uncommon. Here we report on the late Holocene behavior of Stoppani Glacier, a 75 km2 glacier sourced in the Cordillera Darwin, southernmost Patagonia. Based on radiocarbon-dated wood and organic material contained in the glacier's northeast lateral moraine, we infer that Stoppani Glacier advanced shortly before 3.8–3.6, at 3.2–2.8, 2.3–2.1, and 0.3–0.2, and possibly sometime before 1.4–1.3 and 0.8–0.7 cal ka BP. These advances culminated at 0.3–0.2 cal ka BP, when the glacier constructed a prominent end moraine, marking its greatest extent of the past 4000 years. Although the timing of several of the advances overlap with the age range of glacial expansion recognized elsewhere in Patagonia, some do not. Asynchronous behavior observed in the glacial record may arise from the type of evidence (e.g., lateral stratigraphy vs. end moraine) used to document glacial fluctuations or variations in climate or glacial response times. A significant difference between the Stoppani record and some other Patagonian records is that the former indicates general expansion of ice over the last 4000 years, whereas the latter indicate a net decrease in extent over that period.
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Tielidze, Levan G., Tobias Bolch, Roger D. Wheate, Stanislav S. Kutuzov, Ivan I. Lavrentiev, and Michael Zemp. "Supra-glacial debris cover changes in the Greater Caucasus from 1986 to 2014." Cryosphere 14, no. 2 (February 13, 2020): 585–98. http://dx.doi.org/10.5194/tc-14-585-2020.
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Abstract. Knowledge of supra-glacial debris cover and its changes remain incomplete in the Greater Caucasus, in spite of recent glacier studies. Here we present data of supra-glacial debris cover for 659 glaciers across the Greater Caucasus based on Landsat and SPOT images from the years 1986, 2000 and 2014. We combined semi-automated methods for mapping the clean ice with manual digitization of debris-covered glacier parts and calculated supra-glacial debris-covered area as the residual between these two maps. The accuracy of the results was assessed by using high-resolution Google Earth imagery and GPS data for selected glaciers. From 1986 to 2014, the total glacier area decreased from 691.5±29.0 to 590.0±25.8 km2 (15.8±4.1 %, or ∼0.52 % yr−1), while the clean-ice area reduced from 643.2±25.9 to 511.0±20.9 km2 (20.1±4.0 %, or ∼0.73 % yr−1). In contrast supra-glacial debris cover increased from 7.0±6.4 %, or 48.3±3.1 km2, in 1986 to 13.4±6.2 % (∼0.22 % yr−1), or 79.0±4.9 km2, in 2014. Debris-free glaciers exhibited higher area and length reductions than debris-covered glaciers. The distribution of the supra-glacial debris cover differs between the northern and southern and between the western, central and eastern Greater Caucasus. The observed increase in supra-glacial debris cover is significantly stronger on the northern slopes. Overall, we have observed up-glacier average migration of supra-glacial debris cover from about 3015 to 3130 m a.s.l. (metres above sea level) during the investigated period.
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Seguinot, Julien, and Ian Delaney. "Last-glacial-cycle glacier erosion potential in the Alps." Earth Surface Dynamics 9, no. 4 (August 3, 2021): 923–35. http://dx.doi.org/10.5194/esurf-9-923-2021.
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Abstract. The glacial landscape of the Alps has fascinated generations of explorers, artists, mountaineers, and scientists with its diversity, including erosional features of all scales from high-mountain cirques to steep glacial valleys and large overdeepened basins. Using previous glacier modelling results and empirical inferences of bedrock erosion under modern glaciers, we compute a distribution of potential glacier erosion in the Alps over the last glacial cycle from 120 000 years ago to the present. Despite large uncertainties pertaining to the climate history of the Alps and unconstrained glacier erosion processes, the resulting modelled patterns of glacier erosion include persistent features. The cumulative imprint of the last glacial cycle shows a very strong localization of erosion potential with local maxima at the mouths of major Alpine valleys and some other upstream sections where glaciers are modelled to have flowed with the highest velocity. The potential erosion rates vary significantly through the glacial cycle but show paradoxically little relation to the total glacier volume. Phases of glacier advance and maximum extension see a localization of rapid potential erosion rates at low elevation, while glacier erosion at higher elevation is modelled to date from phases of less extensive glaciation. The modelled erosion rates peak during deglaciation phases, when frontal retreat results in steeper glacier surface slopes, implying that climatic conditions that result in rapid glacier erosion might be quite transient and specific. Our results depict the Alpine glacier erosion landscape as a time-transgressive patchwork, with different parts of the range corresponding to different glaciation stages and time periods.
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Fan, Jinghui, Qun Wang, Guang Liu, Lu Zhang, Zhaocheng Guo, Liqiang Tong, Junhuai Peng, et al. "Monitoring and Analyzing Mountain Glacier Surface Movement Using SAR Data and a Terrestrial Laser Scanner: A Case Study of the Himalayas North Slope Glacier Area." Remote Sensing 11, no. 6 (March 14, 2019): 625. http://dx.doi.org/10.3390/rs11060625.
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The offset tracking technique based on synthetic aperture radar (SAR) image intensity information can estimate glacier displacement even when glacier velocities are high and the time interval between images is long, allowing for the broad use of this technique in glacier velocity monitoring. Terrestrial laser scanners, a non-contact measuring system, can measure the velocity of a glacier even if there are no control points arranged on a glacier. In this study, six COSMO-SkyMed images acquired between 31 July and 22 December 2016 were used to obtain the glacial movements of five glaciers on the northern slope of the central Himalayas using the offset tracking approach. During the period of image acquirement, a terrestrial laser scanner was used, and point clouds of two periods in a small area at the terminus of the Pingcuoliesa Glacier were obtained. By selecting three fixed areas of the point clouds that have similar shapes across two periods, the displacements of the centers of gravity of the selected areas were calculated by using contrast analyses of feature points. Although the overall low-density point clouds data indicate that the glacial surfaces have low albedos relative to the wavelength of the terrestrial laser scanner and the effect of its application is therefore influenced in this research, the registration accuracy of 0.0023 m/d in the non-glacial areas of the scanner’s measurements is acceptable, considering the magnitude of 0.072 m/d of the minimum glacial velocity measured by the scanner. The displacements from the point clouds broadly agree with the results of the offset tracking technique in the same area, which provides further evidence of the reliability of the measurements of the SAR data in addition to the analyses of the root mean squared error of the velocity residuals in non-glacial areas. The analysis of the movement of five glaciers in the study area revealed the dynamic behavior of these glacial surfaces across five periods. G089972E28213N Glacier, Pingcuoliesa Glacier and Shimo Glacier show increasing surface movement velocities from the terminus end to the upper part with elevations of 1500 m, 4500 m, and 6400 m, respectively. The maximum velocities on the glacial surface profiles were 31.69 cm/d, 62.40 cm/d, and 42.00 cm/d, respectively. In contrast, the maximum velocity of Shie Glacier, 50.60 cm/d, was observed at the glacier’s terminus. For each period, Glacier G090138E28210N exhibited similar velocity values across the surface profile, with a maximum velocity of 39.70 cm/d. The maximum velocities of G089972E28213N Glacier, Pingcuoliesa Glacier, and Shie Glacier occur in the areas where the topography is steepest. In general, glacial surface velocities are higher in the summer than in the winter in this region. With the assistance of a terrestrial laser scanner with optimized wavelengths or other proper ground-based remote sensing instruments, the offset tracking technique based on high-resolution satellite SAR data should provide more reliable and detailed information for local and even single glacial surface displacement monitoring.
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Molnia, Bruce F., Austin Post, and Paul R. Carlson. "20th-century glacial-marine sedimentation in Vitus Lake, Bering Glacier, Alaska, U. S. A." Annals of Glaciology 22 (1996): 205–10. http://dx.doi.org/10.3189/1996aog22-1-205-210.
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Vitus Lake, the ice-marginal basin at the southeastern edge of Bering Glacier, Alaska, U.S.A., is a site of modern, rapid, glacial-marine sedimentation. Rather than being a fresh-water lake, Vitus Lake is a tidally influenced, marine to brackish embayment connected to the Pacifie Ocean by an inlet, the Seal River. Vitus Lake consists of five deep bedrock basins, separated by interbasinal highs. Glacial erosion has cut these basins as much as 250 m below sea level. High-resolution seismic reflection surveys conducted in 1991 and 1993 of four of Vitus Lake’s basins reveal a complex, variable three-component acoustic stratigraphy. Although not fully sampled, the stratigraphy is inferred to be primarily glacial-marine units of (1) basal contorted and deformed glacial-marine and glacial sediments deposited by basal ice-contact processes and submarine mass-wasting; (2) acoustically well-stratified glacial-marine sediment, which unconformably overlies the basal unit and which grades upward into (3) acoustically transparent or nearly transparent glacial-marine sediment. Maximum thicknesses of conformable glacial-marine sediment exceed 100 m. All of the acoustically transparent and stratified deposits in Vitus Lake are modern in age, having accumulated between 1967 and 1993. The basins where these three-part sequences of “present-day” glacial-marine sediment are accumulating are themselves cut into older sequences of stratified glacial and glacial-marine deposits. These older units outcrop on the islands in Vitus Lake.In 1967, as the result of a major surge, glacier ice completely filled all five basins. Subsequent terminus retreat, which continued through August 1993, exposed these basins, providing new locations for glacial-marine sediment accumulation. A correlation of sediment thicknesses measured from seismic profiles at specific locations within the basins, with the year that each location became ice-free, shows that the sediment accumulation at some locations exceeds 10 m year−1.
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Molnia, Bruce F., Austin Post, and Paul R. Carlson. "20th-century glacial-marine sedimentation in Vitus Lake, Bering Glacier, Alaska, U. S. A." Annals of Glaciology 22 (1996): 205–10. http://dx.doi.org/10.1017/s0260305500015433.
Full textAbstract:
Vitus Lake, the ice-marginal basin at the southeastern edge of Bering Glacier, Alaska, U.S.A., is a site of modern, rapid, glacial-marine sedimentation. Rather than being a fresh-water lake, Vitus Lake is a tidally influenced, marine to brackish embayment connected to the Pacifie Ocean by an inlet, the Seal River. Vitus Lake consists of five deep bedrock basins, separated by interbasinal highs. Glacial erosion has cut these basins as much as 250 m below sea level. High-resolution seismic reflection surveys conducted in 1991 and 1993 of four of Vitus Lake’s basins reveal a complex, variable three-component acoustic stratigraphy. Although not fully sampled, the stratigraphy is inferred to be primarily glacial-marine units of (1) basal contorted and deformed glacial-marine and glacial sediments deposited by basal ice-contact processes and submarine mass-wasting; (2) acoustically well-stratified glacial-marine sediment, which unconformably overlies the basal unit and which grades upward into (3) acoustically transparent or nearly transparent glacial-marine sediment. Maximum thicknesses of conformable glacial-marine sediment exceed 100 m. All of the acoustically transparent and stratified deposits in Vitus Lake are modern in age, having accumulated between 1967 and 1993. The basins where these three-part sequences of “present-day” glacial-marine sediment are accumulating are themselves cut into older sequences of stratified glacial and glacial-marine deposits. These older units outcrop on the islands in Vitus Lake.In 1967, as the result of a major surge, glacier ice completely filled all five basins. Subsequent terminus retreat, which continued through August 1993, exposed these basins, providing new locations for glacial-marine sediment accumulation. A correlation of sediment thicknesses measured from seismic profiles at specific locations within the basins, with the year that each location became ice-free, shows that the sediment accumulation at some locations exceeds 10 m year−1.
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Lai, Jingtao, and Alison M. Anders. "Climatic controls on mountain glacier basal thermal regimes dictate spatial patterns of glacial erosion." Earth Surface Dynamics 9, no. 4 (August 2, 2021): 845–59. http://dx.doi.org/10.5194/esurf-9-845-2021.
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Abstract. Climate has been viewed as a primary control on the rates and patterns of glacial erosion, yet our understanding of the mechanisms by which climate influences glacial erosion is limited. We hypothesize that climate controls the patterns of glacial erosion by altering the basal thermal regime of glaciers. The basal thermal regime is a first-order control on the spatial patterns of glacial erosion. Polythermal glaciers contain both cold-based portions that protect bedrock from erosion and warm-based portions that actively erode bedrock. In this study, we model the impact of various climatic conditions on glacier basal thermal regimes and patterns of glacial erosion in mountainous regions. We couple a sliding-dependent glacial erosion model with the Parallel Ice Sheet Model (PISM) to simulate the evolution of the glacier basal thermal regime and glacial erosion in a synthetic landscape. We find that both basal thermal regimes and glacial erosion patterns are sensitive to climatic conditions, and glacial erosion patterns follow the patterns of the basal thermal regime. Cold temperature leads to limited glacial erosion at high elevations due to cold-based conditions. Increasing precipitation can overcome the impact of cold temperature on the basal thermal regime by accumulating thick ice and lowering the melting point of ice at the base of glaciers. High precipitation rates, therefore, tend to cause warm-based conditions at high elevations, resulting in intensive erosion near the peak of the mountain range. Previous studies often assessed the impact of climate on the spatial patterns of glacial erosion by integrating climatic conditions into the equilibrium line altitudes (ELAs) of glaciers, and glacial erosion is suggested to be maximal around the ELA. However, our results show that different climatic conditions produce glaciers with similar ELAs but different patterns of basal thermal regime and glacial erosion, suggesting that there might not be any direct correlation between ELAs and glacial erosion patterns.
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Goodwin, Ian D., and John Hellstrom. "Glacio-lacustrine aragonite deposition, meltwater evolution and glacial history during isotope stage 3 at Radok Lake, Amery Oasis, northern Prince Charles Mountains, East Antarctica." Antarctic Science 19, no. 3 (June 29, 2007): 365–72. http://dx.doi.org/10.1017/s0954102007000466.
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AbstractThe late Quaternary glacial history of the Amery Oasis, and Prince Charles Mountains is of significant interest because about 10% of the total modern Antarctic ice outflow is discharged via the adjacent Lambert Glacier system. A glacial thrust moraine sequence deposited along the northern shoreline of Radok Lake between 20–10 ka bp, overlies a layer of thin, aragonite crusts which provide important constraints on the glacial history of the Amery Oasis. The modern Radok Lake is fed by the terminal meltwaters of the alpine Battye Glacier. The aragonite crusts were deposited in shallow water of ancestral Radok Lake 53 ka bp, during the A3 warm event in Isotope Stage 3. Oxygen isotope (δ18O) analysis of the last glacial-age aragonite crusts indicates that they precipitated from freshwater with a δ18OSMOW composition of -36%, which is 8% more depleted than the present water (-28%) in Radok Lake. A regional oxygen isotope (δ18O) and elevation relationship for snow is used to determine the source of meltwater and glacial ice in Radok Lake during the A3 warm event. This relationship indicates that Radok Lake received meltwater from the confluence of both Battye Glacier ice and an expansion of grounded western Lambert Glacier ice in the Amery embayment.
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Varliero, Gilda, Alexandra Holland, Gary L. A. Barker, Marian L. Yallop, Andrew G. Fountain, and Alexandre M. Anesio. "Glacier clear ice bands indicate englacial channel microbial distribution." Journal of Glaciology 67, no. 265 (March 22, 2021): 811–23. http://dx.doi.org/10.1017/jog.2021.30.
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AbstractDistant glacial areas are interconnected by a complex system of fractures and water channels which run in the glacier interior and characterize the englacial realm. Water can slowly freeze in these channels where the slow freezing excludes air bubbles giving the ice a clear aspect. This ice is uplifted to the surface ablation zone by glacial movements and can therefore be observed in the form of clear surface ice bands. We employed an indirect method to sample englacial water by coring these ice bands. We were able, for the first time, to compare microbial communities sampled from clear (i.e. frozen englacial water bands) and cloudy ice (i.e. meteoric ice) through 16S rRNA gene sequencing. Although microbial communities were primarily shaped and structured by their spatial distribution on the glacier, ice type was a clear secondary factor. One area of the glacier, in particular, presented significant microbial community clear/cloudy ice differences. Although the clear ice and supraglacial communities showed typical cold-adapted glacial communities, the cloudy ice had a less defined glacial community and ubiquitous environmental organisms. These results highlight the role of englacial channels in the microbial dispersion within the glacier and, possibly, in the shaping of glacial microbial communities.
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Riedel, Jon L., John J. Clague, and Brent C. Ward. "Timing and extent of early marine oxygen isotope stage 2 alpine glaciation in Skagit Valley, Washington." Quaternary Research 73, no. 2 (March 2010): 313–23. http://dx.doi.org/10.1016/j.yqres.2009.10.004.
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Twenty-two new radiocarbon ages from Skagit valley provide a detailed chronology of alpine glaciation during the Evans Creek stade of the Fraser Glaciation (early marine oxygen isotope stage (MIS) 2) in the Cascade Range, Washington State. Sediments at sites near Concrete, Washington, record two advances of the Baker valley glacier between ca. 30.3 and 19.5 cal ka BP, with an intervening period of glacier recession about 24.9 cal ka BP. The Baker valley glacier dammed lower Skagit valley, creating glacial Lake Concrete, which discharged around the ice dam along Finney Creek, or south into the Sauk valley. Sediments along the shores of Ross Lake in upper Skagit valley accumulated in glacial Lake Skymo after ca. 28.7 cal ka BP behind a glacier flowing out of Big Beaver valley. Horizontally laminated silt and bedded sand and gravel up to 20 m thick record as much as 8000 yr of deposition in these glacially dammed lakes. The data indicate that alpine glaciers in Skagit valley were far less extensive than previously thought. Alpine glaciers remained in advanced positions for much of the Evans Creek stade, which may have ended as early as 20.8 cal ka BP.
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Menkovic, Ljubomir, and Milovan Milivojevic. "Glacial morphology of the Sara Mountains." Glasnik Srpskog geografskog drustva 101, no. 1 (2021): 1–29. http://dx.doi.org/10.2298/gsgd2101001m.
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The paper defines and presents the forms of glacial relief formed, most likely, during the last Pleistocene glacial maximum (LGM). A graphic and textual presentation of almost all glacial forms is given on the entire territory of the Sara Mountains, on both sides of their main ridge, from Ljuboten in the NE to the source tributaries of the Radika River in the SW. Based on the height position and spatial development of glacial forms, the height of the snow line (ELA) was determined, glacier types were determined and defined, which is shown on two overview maps representing Pleistocene glacial morphology and reconstructed Pleistocene glaciers referring to the last Pleistocene glacial (MIS-2). Since these are the youngest glacial morphological traces on the Sara Mountains, they are the best preserved today.
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Coulthard, Bethany, Dan J. Smith, and Terri Lacourse. "Dendroglaciological investigations of mid- to late-Holocene glacial activity in the Mt. Waddington area, British Columbia Coast Mountains, Canada." Holocene 23, no. 1 (September 18, 2012): 93–103. http://dx.doi.org/10.1177/0959683612455537.
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Dendroglaciological investigations near Mt. Waddington in the central British Columbia Coast Mountains provide an enhanced perspective of Holocene glacial activity. Field investigations at Confederation, Franklin, and Jambeau glaciers led to the discovery of subfossil wood mats encased in glacial deposits and glacially sheared stumps buried beneath till. Radiocarbon-dated wood collected from valley-bottom and lateral moraine sites at Confederation Glacier suggest that an early-Holocene advance occurred at c. 5665 cal. yr BP, followed by succeeding intervals of glacier expansion at c. 3700 and 3500 cal. yr BP. At Jambeau Glacier detrital wood mats buried close to the contemporary lateral moraine crests document glacier expansion at c. 3000 cal. yr BP. Detrital subfossil wood buried in lateral moraines at the confluence of Confederation and Franklin glaciers records distinct episodes of ‘Little Ice Age’ glacier expansion as early as c. 1212 cal. yr ad, and suggests the glacier surface continued to thicken until at least c. 1330–1410 cal. yr ad. An interval of downwasting and retreat followed, before late ‘Little Ice Age’ advances such as those at Jambeau Glacier were overwhelming valley-bottom forests by c. 1740 cal. yr ad. With the exception of the previously unrecognized advance of Confederation Glacier at c. 3700 cal. yr BP, our dendroglaciological findings corroborate the emerging record of Holocene glacier activity in the British Columbia Coast Mountains.
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Broster, Bruce E. "Glacitectonic Deformation in Sediment and Bedrock, Hat Creek, British Columbia." Géographie physique et Quaternaire 45, no. 1 (December 13, 2007): 5–20. http://dx.doi.org/10.7202/032841ar.
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ABSTRACT A variety of deformation structures attributed to glacial overriding occur in rock and sediment of an intermontane valley at Hat Creek, British Columbia. Sediments exposed in vertical outcrops along Hat Creek, display contrasting styles of deformation involving fluidization, as well as brittle and ductile deformations that appear to have been formed concurrently. Typical structures include: joints, faults, infillings, and clastic dikes comprising; fluid-escape structures, glacigenic injections, as well as fluidal and viscous hydraulic expulsions. A model is presented for the glacitectonic formation of hydraulic expulsions during compression of underlying partially saturated unfrozen sediments. Bedrock exposed in excavations at higher elevations displays joints, faults and wedge fillings possibly associated with subglacial freezing during glacial advance. Orientation of the structures are correlative with directions of glacier flow as inferred from fabric, striae and geomorphology. The structures are believed to have been the product of several interrelated factors, including: glacial dynamics, engineering properties of the glacier bed material, subglacial relief, and the variation between coalescing glaciers. Correlation with directions of glacial movement, association with glacial faciès and infilling by glacial sediments, are conditions considered to be glacigenic signatures useful in differentiation of glacial from nonglacial (e.g. earthquake) origins for similar structures elsewhere.
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Quincey, D. J., R. M. Lucas, S. D. Richardson, N. F. Glasser, M. J. Hambrey, and J. M. Reynolds. "Optical remote sensing techniques in high-mountain environments: application to glacial hazards." Progress in Physical Geography: Earth and Environment 29, no. 4 (December 2005): 475–505. http://dx.doi.org/10.1191/0309133305pp456ra.
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Remote sensing studies have shown that glaciers and their proximal environments exhibit unique temporal, spatial and spectral characteristics that can be analysed to better quantify glacial hazard potential. In this review, the optical remote sensing data sources available to glacial hazard assessors are considered and the range of information on glacial environments that can be derived is analysed. The review shows that the integration of a variety of data sources can provide geoscientists with information regarding glacial lakes and lake development, glacier dynamics, avalanche sources and ice-marginal fluctuations. Such data can be used to complement and, in many cases, improve field-based glacial hazard assessments. The review concludes that aerial photography still remains the main source of data for measuring a number of glacier characteristics, but that fine to moderate spatial resolution satellite sensors (e.g., ASTER, SPOT 5 HRVIR, Landsat ETM) also provide useful information that can be used to support the assessment of hazards in high-mountain glacierized terrain.
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Hussain, Alamgeer, and Dilshad Bano. "Temporal monitoring of Ghamu bar glacial lakes using remote sensing and GIS." International Journal of Advanced Geosciences 7, no. 1 (May 5, 2019): 18. http://dx.doi.org/10.14419/ijag.v7i1.20308.
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The trends of glacial lakes formation and glacial lake outburst flooding events have been increased across Himalayan Karakorum Hindu Kush (HKH) ranges during last decade due to increase in global warming. This research is addressing the temporal monitoring of ghamu bar glacial lakes using remote sensing and GIS. Landsat images of 1990, 2000, 2010 and 2015 were used to map temporal glacial lakes using normalized difference water index (NDWI) index. The results of normalized difference water index were validated through modified normalized difference water index and field photographs. Temporal variability shows that, glacier lake area has been increase from 1990 to 2015. In 1990 total area of lake was 0.052 sq, which further increased 0.0423 in 1995 than it decreases to 0.314 in 2000 due to detached of debris cover moraine from glacier tongue and it reach 0.0846 sq.km in 2005. The area gradually increased up to 0.1296 sq.km in 2010 and it goes up to 0.157 sq.km 2015. The overall increase in area are expanding at an accelerated rate in past two decades, indicating that Darkut glacier is more vulnerable toward climate change through increase in size and volume ofghamu bar glacial lakes. There is need for vigilance in monitoring of ghamu bar glacial lake through high resolution remote sensing data and development of Geo-database enabling more details about past and future lakes behaviors toward climate change impacts.
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Alonso, V. "Mapa geomorfológico del sector sur del Macizo de Las Ubiñas (Cordillera Cantábrica, NO de España)." Trabajos de Geología 34, no. 34 (March 9, 2015): 125. http://dx.doi.org/10.17811/tdg.34.2014.125-132.
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Resumen: Se presenta un mapa geomorfológico de la parte sur del Macizo de las Ubiñas, realizado a escala 1:1000. Este macizo, predominantemente calcáreo, con una dirección aproximada N-S, contiene varios picos de más de 2400 m de altura y ha sido intensamente glaciado. Además de las formas de origen glaciar, destacan en la cartografía los taludes y conos de derrubios, así como numerosos deslizamientos complejos. Una continuación de esta cartografía hacia la parte norte del macizo permitirá la interpretación de la evolución geomorfológica de esta zona.Palabras clave: mapa geomorfológico, modelado glaciar, modelado kárstico, Macizo de la Ubiñas, Cordillera Cantábrica.Abstract: A new geomorphological map of the southern sector of the Ubiñas massif, at a scale of 1:1000, is presented. This massif, a calcareous mountain alignment with an approximate N-S direction and several peaks with altitudes above 2400 m, has been widely glaciated. The main features in the map are glacial forms as well as talus slopes, debris cones and numerous mixed slides. The continuation of this cartography to the north part of the massif will allow the interpretation of the morphological evolution of the zone.Key words: geomorphological map, glacial landscape, karstic landforms, Ubiñas Massif, Cantabrian Mountains.
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Füreder, Leopold, and Georg H. Niedrist. "Glacial Stream Ecology: Structural and Functional Assets." Water 12, no. 2 (January 30, 2020): 376. http://dx.doi.org/10.3390/w12020376.
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High altitude glacier-fed streams are harsh environments inhabiting specialized invertebrate communities. Most research on biotic aspects in glacier-fed streams have focused on the simple relationship between presence/absence of species and prevailing environmental conditions, whereas functional strategies and potentials of glacial stream specialists have been hardly investigated so far. Using new and recent datasets from our investigations in the European Alps, we now demonstrate distinct functional properties of invertebrates that typically dominate glacier-fed streams and show significant relationships with declining glacier cover in alpine stream catchments. In particular, we present and argue about cause-effect relationships between glacier cover in the catchment and temperature, community structure, diversity, feeding strategies, early life development, body mass, and growth of invertebrates. By concentrating on key taxa in glacial and non-glacial alpine streams, the relevance of distinct adaptations in these functional components becomes evident. This clearly demonstrates that further studies of functional characteristics are essential for the understanding of peculiar diversity patterns, successful traits and their plasticity, evolutionary triggered species adaptions, and flexibilities.
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Woolfe, Ken J. "Cycles of erosion and deposition during the Permo-Carboniferous glaciation in the Transantarctic Mountains." Antarctic Science 6, no. 1 (March 1994): 93–104. http://dx.doi.org/10.1017/s095410209400012x.
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At two localities adjacent to Hatherton Glacier, Darwin Mountains, a thick glacio-lacustrine sequence underlies the main diamictite facies of the Darwin Tillite (Metschel Tillite), and at one of these locations a glacio-lacustrine sequence also conformably overlies the diamictite. These deposits record the initial advance and final retreat of the Gondwana ice cap. Other, pro- and periglacial phases within these sequences record several minor advances and retreats of the ice sheet. Carbonaceous sediments above and below the main diamictite phase show that vegetation was established near the ice margin, suggesting that present-day ice margin temperatures are colder than those experienced during the Permo-Carboniferous (Gondwana) glaciation. It appears that there was little or no erosion of the Devonian Taylor Group which underlies the glacial sequence. The apparent erosional nature of the contact between the Permo-Carboniferous glacial sequence and the overlying Permian coal measures is attributed to surface winnowing of unconsolidated tills and locally the units are conformable.
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Phan, Vu Hien, Roderik Lindenbergh, and Massimo Menenti. "Monitoring glacial thickness changes in the Tibetan Plateau derived from ICESat data." Science and Technology Development Journal 19, no. 2 (June 30, 2016): 130–37. http://dx.doi.org/10.32508/stdj.v19i2.677.
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Monitoring glacier changes is essential for estimating the water mass balance of the Tibetan Plateau. Recent research indicates that glaciers at individual regions on the Tibetan Plateau and surroundings are shrinking and thinning during the last decades. Studies considering large regions often ignored however the impact of locally varying weather conditions and terrain characteristics on glacial evolution, i.e. the impact of orographic precipitation and variation in solar radiation. Our hypothesis is therefore that adjacent glaciers of opposite orientation change in a different way. In this study, we exploit Ice Cloud and land Elevation Satellite (ICESat)/ Geoscience Laser Altimetry System (GLAS) data in combination with the NASA Shuttle Radar Topographic Mission (SRTM) digital elevation model (DEM) and the Global Land Ice Measurements from Space (GLIMS) glacier mask to estimate glacial thickness change trends between 2003 and 2009 on the whole Tibetan Plateau. The results show that 90 glacial areas could be distinguished. Most of observed glacial areas on the Tibetan Plateau are thinning, except for some glaciers in the Northwest. In general, glacial elevations on the whole Tibetan Plateau decreased at an average rate of -0.17 ± 0.47 meters per year (m a-1) between 2003 and 2009, taking together glaciers of any size, distribution, and location of the observed glacial area. Moreover, the results show that glacial elevation changes indeed strongly depend on the relative position in a mountain range.
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Peppa, M. V., S. B. Maharjan, S. P. Joshi, W. Xiao, and J. P. Mills. "GLACIAL LAKE EVOLUTION BASED ON REMOTE SENSING TIME SERIES: A CASE STUDY OF TSHO ROLPA IN NEPAL." ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences V-3-2020 (August 3, 2020): 633–39. http://dx.doi.org/10.5194/isprs-annals-v-3-2020-633-2020.
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Abstract. Himalayan glaciers have retreated rapidly in recent years. Resultant glacial lakes in the region pose potential catastrophic threats to downstream communities, especially under a changing climate. The potential for Glacial Lake Outburst Floods (GLOFs) has increased and studies have assessed the risks of those in Nepal and prioritised several glacial lakes for urgent and closer investigation. The risk posed by the Tsho Rolpa Glacial Lake is one of the most serious in Nepal. To investigate the feasibility of high-frequency monitoring of glacial lake evolution by remote sensing, this paper proposes a workflow for automated glacial lake boundary extraction and evolution using a time series of Sentinel optical imagery. The waterbody is segmented and vectorised using bimodal histograms from water indices. The vectorised lake boundary is validated against reference data extracted from rigorous contemporary unmanned aerial vehicle (UAV)-based photogrammetric survey. Lake boundaries were subsequently extracted at four different epochs to evaluate the evolution of the lake, especially at the glacier terminus. The final lake area was estimated at 1.61 km2, significantly larger than the areal extent last formally reported. A 0.99 m/day maximum, and a 0.45 m/day average, horizontal glacier retreat rates were estimated. The reported research has demonstrated the potential of remote sensing time series to monitor glacial lake evolution, which is particularly important for lakes in remote mountain regions that are otherwise difficult to access.
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Butler, David R. "GLACIAL HAZARDS IN GLACIER NATIONAL PARK, MONTANA." Physical Geography 10, no. 1 (January 1989): 53–71. http://dx.doi.org/10.1080/02723646.1989.10642367.
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Dobiński, Wojciech, Mariusz Grabiec, and Michał Glazer. "Cold–temperate transition surface and permafrost base (CTS-PB) as an environmental axis in glacier–permafrost relationship, based on research carried out on the Storglaciären and its forefield, northern Sweden." Quaternary Research 88, no. 3 (September 14, 2017): 551–69. http://dx.doi.org/10.1017/qua.2017.65.
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AbstractHere, we present empirical ground penetrating radar (GPR) and electroresistivity tomography data (ERT) to verify the cold-temperate transition surface-permafrost base (CTS-PB) axis theoretical model. The data were collected from Storglaciären, in Tarfala, Northern Sweden, and its forefield. The GPR results show a material relation between the glacial ice and the sediments incorporated in the glacier, and a geophysical relation between the “cold ice” and the “temperate ice” layers. Clearly identifying lateral glacier margins is difficult, as periglacial and glacial environments frequently overlap. In this case, we identified areas showing permafrost aggradation already under the glacier, particularly where the CTS is replaced by the PB surface. This structure appears as a result of the influence of a cold climate over both the glacial and periglacial environments. The results show how these surfaces form a specific continuous environmental axis; thus, both glacial and periglacial areas can be treated uniformly as a specific continuum in the geophysical sense. Similarly, other examples previously described also allow identifying a continuation of permafrost from the periglacial environment onto the glacial base. In addition, the ERT results show the presence of double-layered periglacial permafrost, possibly suggesting a past climatic fluctuation in the study area.
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Wintges, Theodor. "Studies On Crescentic Fractures and Crescentic Gouges with the Help of Close-range Photogrammetry." Journal of Glaciology 31, no. 109 (1985): 340–49. http://dx.doi.org/10.1017/s0022143000006687.
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Abstract Studies on cresceatic fractures and crescentic gouges were carried out in the central part of the Alpine piedmont glaciation and the Quaternary Alpine mountain ice sheet. The test sites were situated in the pro-glacial area of the Hornkees south Berliner Hütte (Oberer Zemmgrund, Zillertal, Tyrol, Austria). This is also the area of the former confluence with another glacier which flowed at about 90° to Hornkees during the late-glacial period. It was therefore possible to make a comparison between different older glacier systems, different flow directions, and different ice thicknesses. About 12 000 minor features were measured by close-range photogrammetry; the result was 240 pairs of stereophotographs which were interpreted on first-order equipment. The single forms were registered point by point by coordinates. It was therefore possible to obtain three-dimensionally registered forms. One important result was that the late-glacial and the post-glacial glaciers of the Zemmgrund produced minor features with a large variation in size. A further result was the definition of possible glacier-flow directions by interpretation of the different directions of crescentic fractures and crescentic gouges. By this means it was possible to obtain several working reconstructions of the late- and post-glacial stream lines of the merged glaciers.
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Wintges, Theodor. "Studies On Crescentic Fractures and Crescentic Gouges with the Help of Close-range Photogrammetry." Journal of Glaciology 31, no. 109 (1985): 340–49. http://dx.doi.org/10.3189/s0022143000006687.
Full textAbstract:
AbstractStudies on cresceatic fractures and crescentic gouges were carried out in the central part of the Alpine piedmont glaciation and the Quaternary Alpine mountain ice sheet. The test sites were situated in the pro-glacial area of the Hornkees south Berliner Hütte (Oberer Zemmgrund, Zillertal, Tyrol, Austria). This is also the area of the former confluence with another glacier which flowed at about 90° to Hornkees during the late-glacial period. It was therefore possible to make a comparison between different older glacier systems, different flow directions, and different ice thicknesses. About 12 000 minor features were measured by close-range photogrammetry; the result was 240 pairs of stereophotographs which were interpreted on first-order equipment. The single forms were registered point by point by coordinates. It was therefore possible to obtain three-dimensionally registered forms. One important result was that the late-glacial and the post-glacial glaciers of the Zemmgrund produced minor features with a large variation in size. A further result was the definition of possible glacier-flow directions by interpretation of the different directions of crescentic fractures and crescentic gouges. By this means it was possible to obtain several working reconstructions of the late- and post-glacial stream lines of the merged glaciers.
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Williams, Haley B., and Michele N. Koppes. "A comparison of glacial and paraglacial denudation responses to rapid glacial retreat." Annals of Glaciology 60, no. 80 (December 2019): 151–64. http://dx.doi.org/10.1017/aog.2020.1.
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AbstractGlacier thinning and retreat drives initial acceleration of glacier sliding and erosion, de-buttressing of steep valley walls, and destabilization of ice-marginal deposits and bedrock, which can lead to massive rock avalanching and accelerated incision of tributary watersheds. A compelling example of these changes occurred in Taan Fjord in SE Alaska due to the rapid thinning and retreat of Tyndall Glacier over the past half century. Increased glacier sliding speeds led to both increased rates of subglacial erosion and the evacuation of subglacially stored sediments into the proglacial basins. The shrinking glacier also exposed proglacial tributary watersheds to rapid incision and denudation driven by >350 m of baselevel fall in a few decades. Moreover, in October 2015 a large tsunamigenic landslide occurred at the terminus of Tyndall Glacier, largely due to thinning exposing oversteepened, unstable slopes. Sediment yields from the glacier, the landslide and the tributary watersheds, measured from surveys of the sediments in the fjord collected in 1999 and 2016, are compared to ongoing changes in glacier and fjord geometry to investigate the magnitude of glacial and paraglacial denudation in Taan Fjord during retreat. In the last 50 years, sediment yields from the glacier and non-glacial tributaries kept pace with the rapid rate of retreat, and were on par with each other. Notably, basin-averaged erosion rates from the paraglacial landscape were twice that from the glacier, averaging 58 ± 9 and 26 ± 5 mm a−1, respectively. The sharp increases in sediment yields during retreat observed from both the glacier and the adjacent watersheds, including the landslide, highlight the rapid evolution of landscapes undergoing glacier shrinkage.
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XU, XIANGKE, BAOLIN PAN, GUOCHENG DONG, CHAOLU YI, and NEIL F. GLASSER. "Last Glacial climate reconstruction by exploring glacier sensitivity to climate on the southeastern slope of the western Nyaiqentanglha Shan, Tibetan Plateau." Journal of Glaciology 63, no. 238 (January 23, 2017): 361–71. http://dx.doi.org/10.1017/jog.2016.147.
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ABSTRACTImprovements in understanding glacial extents and chronologies for the southeastern slope of the western Nyaiqentanglha Shan on the Tibetan Plateau are required to understand regional climate changes during the Last Glacial cycle. A two-dimensional numerical model of mass balance, based on snow–ice melting factors, and of ice flow for mountain glaciers is used to assess the glacier sensitivity to climatic change in a catchment of the region. The model can reproduce valley glaciers, wide-tongued glaciers and a coalescing glacier within step temperature lowering and precipitation increasing experiments. The model sensitivity experiments also indicate that the dependence of glacier growth on temperature and/or precipitation is nonlinear. The model results suggest that the valley glaciers respond more sensitively to an imposed climate change than wide-tongued and coalescing glaciers. Guided by field geological evidence of former glacier extent and other independent paleoclimate reconstructions, the model is also used to constrain the most realistic multi-year mean temperatures to be 2.9–4.6°C and 1.8–2.5°C lower than present in the glacial stages of the Last Glacial Maximum and middle marine oxygen isotope stage 3, respectively.
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Laidre, Kristin L., Twila Moon, Donna D. W. Hauser, Richard McGovern, Mads Peter Heide-Jørgensen, Rune Dietz, and Ben Hudson. "Use of glacial fronts by narwhals ( Monodon monoceros ) in West Greenland." Biology Letters 12, no. 10 (October 2016): 20160457. http://dx.doi.org/10.1098/rsbl.2016.0457.
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Glacial fronts are important summer habitat for narwhals ( Monodon monoceros ); however, no studies have quantified which glacial properties attract whales. We investigated the importance of glacial habitats using telemetry data from n = 15 whales tagged in September of 1993, 1994, 2006 and 2007 in Melville Bay, West Greenland. For 41 marine-terminating glaciers, we estimated (i) narwhal presence/absence, (ii) number of 24 h periods spent at glaciers and (iii) the fraction of narwhals that visited each glacier (at 5, 7 and 10 km) in autumn. We also compiled data on glacier width, ice thickness, ice velocity, front advance/retreat, area and extent of iceberg discharge, bathymetry, subglacial freshwater run-off and sediment flux. Narwhal use of glacial habitats expanded in the 2000s probably due to reduced summer fast ice and later autumn freeze-up. Using a generalized multivariate framework, glacier ice front thickness (vertical height in the water column) was a significant covariate in all models. A negative relationship with glacier velocity was included in several models and glacier front width was a significant predictor in the 2000s. Results suggest narwhals prefer glaciers with potential for higher ambient freshwater melt over glaciers with silt-laden discharge. This may represent a preference for summer freshwater habitat, similar to other Arctic monodontids.
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Phan, V. H., R. C. Lindenbergh, and M. Menenti. "Orientation dependent glacial changes at the Tibetan Plateau derived from 2003–2009 ICESat laser altimetry." Cryosphere Discussions 8, no. 3 (May 12, 2014): 2425–63. http://dx.doi.org/10.5194/tcd-8-2425-2014.
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Abstract. Monitoring glacier changes is essential for estimating the water mass balance of the Tibetan Plateau. Recent research indicated that glaciers at individual regions on the Tibetan Plateau and surroundings are shrinking and thinning during the last decades. Studies considering large regions often ignored however impact of locally varying weather conditions and terrain characteristics on glacial evolution, due to orographic precipitation and variation in solar radiation. Our hypothesis is therefore that adjacent glaciers of opposite orientation change in a different way. In this study, we exploit ICESat laser altimetry data in combination with the SRTM DEM and the GLIMS glacier mask to estimate glacial vertical change trends between 2003 and 2009 on the whole Tibetan Plateau. Considering acquisition conditions of ICESat measurements and terrain surface characteristics, annual glacial elevation trends were estimated for 15 different settings. In the final setting, we only include ICESat elevations acquired over terrain that has a slope of below 20° and a roughness at the footprint scale of below 15 m. Within this setting, 90 glacial areas could be distinguished. The results show that most of observed glacial areas on the Tibetan Plateau are thinning, except for notably glaciers in the Northwest. In general, glacial elevations on the whole Tibetan Plateau decreased at an average rate of −0.17 ± 0.47 m per year (m a−1) between 2003 and 2009, but note that the size, distribution, and representativeness of the observed glacial areas are not taken into account. Moreover, the results show that glacial elevation changes indeed strongly depend on the relative position in a mountain range.
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Wang, Xin, Xiaoyu Guo, Chengde Yang, Qionghuan Liu, Junfeng Wei, Yong Zhang, Shiyin Liu, Yanlin Zhang, Zongli Jiang, and Zhiguang Tang. "Glacial lake inventory of high-mountain Asia in 1990 and 2018 derived from Landsat images." Earth System Science Data 12, no. 3 (September 13, 2020): 2169–82. http://dx.doi.org/10.5194/essd-12-2169-2020.
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Abstract. There is currently no glacial lake inventory data set for the entire high-mountain Asia (HMA) area. The definition and classification of glacial lakes remain controversial, presenting certain obstacles to extensive utilization of glacial lake inventory data. This study integrated glacier inventory data and 668 Landsat TM, ETM+, and OLI images and adopted manual visual interpretation to extract glacial lake boundaries within a 10 km buffer from glacier extent using ArcGIS and ENVI software, normalized difference water index maps, and Google Earth images. The theoretical and methodological basis for all processing steps including glacial lake definition and classification, lake boundary delineation, and uncertainty assessment is discussed comprehensively in the paper. Moreover, detailed information regarding the coding, location, perimeter and area, area error, type, time phase, source image information, and subregions of the located lakes is presented. It was established that 27 205 and 30 121 glacial lakes (size 0.0054–6.46 km2) in HMA covered a combined area of 1806.47±2.11 and 2080.12±2.28 km2 in 1990 and 2018, respectively. The data set is now available from the National Special Environment and Function of Observation and Research Stations Shared Service Platform (China): https://doi.org/10.12072/casnw.064.2019.db (Wang et al., 2019a).
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Chen, Fang. "Comparing Methods for Segmenting Supra-Glacial Lakes and Surface Features in the Mount Everest Region of the Himalayas Using Chinese GaoFen-3 SAR Images." Remote Sensing 13, no. 13 (June 22, 2021): 2429. http://dx.doi.org/10.3390/rs13132429.
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Glaciers and numerous glacial lakes that are produced by glacier melting are key indicators of climate change. Often overlooked, supra-glacial lakes develop in the melting area in the low-lying part of a glacier and appear to be highly variable in their size, shape, and location. The lifespan of these lakes is thought to be quite transient, since the lakes may be completely filled by water and burst out within several weeks. Changes in supra-glacial lake outlines and other surface features such as supra-glacial rivers and crevasses on the glaciers are useful indicators for the direct monitoring of glacier changes. Synthetic aperture radar (SAR) is not affected by weather and climate, and is an effective tool for study of glaciated areas. The development of the Chinese GaoFen-3 (GF-3) SAR, which has high spatial and temporal resolution and high-precision observation performance, has made it possible to obtain dynamic information about glaciers in more detail. In this paper, the classical Canny operator, the variational B-spline level-set method, and U-Net-based deep-learning model were applied and compared to extract glacial lake outlines and other surface features using different modes and Chinese GF-3 SAR imagery in the Mount Everest Region of the Himalayas. Particularly, the U-Net-based deep-learning method, which was independent of auxiliary data and had a high degree of automation, was used for the first time in this context. The experimental results showed that the U-Net-based deep-learning model worked best in the segmentation of supra-glacial lakes in terms of accuracy (Precision = 98.45% and Recall = 95.82%) and segmentation efficiency, and was good at detecting small, elongated, and ice-covered supra-glacial lakes. We also found that it was useful for accurately identifying the location of supra-glacial streams and ice crevasses on glaciers, and quantifying their width. Finally, based on the time series of the mapping results, the spatial characteristics and temporal evolution of these features over the glaciers were comprehensively analyzed. Overall, this study presents a novel approach to improve the detection accuracy of glacier elements that could be leveraged for dynamic monitoring in future research.
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Bolch, T., M. F. Buchroithner, J. Peters, M. Baessler, and S. Bajracharya. "Identification of glacier motion and potentially dangerous glacial lakes in the Mt. Everest region/Nepal using spaceborne imagery." Natural Hazards and Earth System Sciences 8, no. 6 (December 4, 2008): 1329–40. http://dx.doi.org/10.5194/nhess-8-1329-2008.
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Abstract. Failures of glacial lake dams can cause outburst floods and represents a serious hazard. The potential danger of outburst floods depends on various factors like the lake's area and volume, glacier change, morphometry of the glacier and its surrounding moraines and valley, and glacier velocity. Remote sensing offers an efficient tool for displacement calculations and risk assessment of the identification of potentially dangerous glacial lakes (PDGLs) and is especially helpful for remote mountainous areas. Not all important parameters can, however, be obtained using spaceborne imagery. Additional interpretation by an expert is required. ASTER data has a suitable accuracy to calculate surface velocity. Ikonos data offers more detail but requires more effort for rectification. All investigated debris-covered glacier tongues show areas with no or very slow movement rates. From 1962 to 2003 the number and area of glacial lakes increased, dominated by the occurrence and almost linear areal expansion of the moraine-dammed lakes, like the Imja Lake. Although the Imja Lake will probably still grow in the near future, the risk of an outburst flood (GLOF) is considered not higher than for other glacial lakes in the area. Potentially dangerous lakes and areas of lake development are identified. There is a high probability of further lake development at Khumbu Glacier, but a low one at Lhotse Glacier.
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Hunter, Lewis E., Ross D. Powell, and Daniel E. Lawson. "Morainal-bank sediment budgets and their influence on the stability of tidewater termini of valley glaciers entering Glacier Bay, Alaska, U.S.A." Annals of Glaciology 22 (1996): 211–16. http://dx.doi.org/10.1017/s0260305500015445.
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Investigations of grounding-line sedimentation in front of tidewater termini of temperate valley glaciers demonstrate that sediment yields and dynamics provide a second-order control on glacier stability by influencing water depth at the grounding line. Sediment is delivered to the grounding line by two routes: (1) debris transported in, on and beneath the glacier, and (2) sediment transported in glacial outwash streams. Glacial streams in Glacier Bay, Alaska, U.S.A., deliver 106to 107m3year−1of sediment to the grounding lines. The glacial debris flux transports 105to 106m3year−1of debris to the ice cliffs, where approximately 10% is released at the grounding line, the remainder being transported downfjord by iceberg-rafting. An additional 105m3year−1of sediment may be transported to the grounding line by shearing and advection of a deformable bed.
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Just, J., N. Nowaczyk, A. Francke, L. Sagnotti, and B. Wagner. "Climatic control on the occurrence of high-coercivity magnetic minerals and preservation of greigite in a 640 ka sediment sequence from Lake Ohrid (Balkans)." Biogeosciences Discussions 12, no. 16 (August 28, 2015): 14215–43. http://dx.doi.org/10.5194/bgd-12-14215-2015.
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Abstract. The bulk magnetic mineral record from Lake Ohrid, spanning the past ca. 640 ka, shows a strong relationship to environmental conditions on glacial–interglacial and millennial time scales. During extremely cold glacials, a lower accumulation of organic matter and likely enhanced mixing of the water-column coincides with the presence of greigite, whereas greigite is absent in sediments deposited during less severe glacials. Those "non-greigite" glacial sediments are characterized by high concentration of high-coercivity magnetic minerals, which relates to enhanced erosion of soils that had formed during the preceding interglacials. In contrast, magnetite dominated magnetic mineral assemblages characterize interglacial deposits and most likely originate from detrital particles of physically weathered rocks. Superimposed on the glacial–interglacial behavior are millennial scale oscillations in the magnetic mineral composition that parallel variations in summer insolation. Likewise to the process on glacial–interglacial time-scales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock-magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi-level contribution to environmental reconstructions, since the magnetic properties can mirror both, environmental conditions on land and intra-lacustrine processes.