Large Differences between Glaciers 3D Surface Extents and 2D Planar Areas in Central Tianshan
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Most glaciers in China lie in high mountainous environments and have relatively large surface slopes. Common analyses consider glaciers’ projected areas (2D Area) in a two-dimensional plane, which are much smaller than glacier’s topographic surface extents (3D Area). The areal difference between 2D planar areas and 3D surface extents exceeds −5% when the glacier’s surface slope is larger than 18°. In this study, we establish a 3D model in the Muzart Glacier catchment using ASTER GDEM data. This model is used to quantify the areal difference between glaciers’ 2D planar areas and their 3D surface extents in various slope zones and elevation bands by using the second Chinese Glacier Inventory (CGI2). Finally, we analyze the 2D and 3D area shrinking rate between 2007 and 2013 in Central Tianshan using glaciers derived from Landsat images by an object-based classification approach. This approach shows an accuracy of 89% when it validates by comparison of glaciers derived from Landsat and high spatial resolution GeoEye images. The extracted glaciers in 2007 also have an agreement of 89% with CGI2 data in the Muzart Glacier catchment. The glaciers’ 3D area is 34.2% larger than their 2D area from CGI2 in the Muzart Glacier catchment and by 27.9% in the entire Central Tianshan. Most underestimation occurs in the elevation bands of 4000–5000 m above sea level (a.s.l.). The 3D glacier areas reduced by 30 and 115 km2 between 2007 and 2013 in the Muzart Glacier catchment and Central Tianshan, being 37.0% and 27.6% larger than their 2D areas reduction, respectively. The shrinking rates decrease with elevation increase.Keywords:
Accumulation zone
Glacier mass balance
Elevation (ballistics)
Glacier morphology
Glacier mass balance
Glacier morphology
Glacier ice accumulation
Accumulation zone
Cirque glacier
Ablation zone
Tidewater glacier cycle
Glacier terminus
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Geospatial visualisation presents us with innovative techniques of assessing uncertainty in digital elevation datasets. It gives the viewer immediate feedback on potential problems and heightens understanding of effects not easily appreciated when dealing with numerical statistics only. This study evaluated the performance of 30-metre resolution SRTM version 3.0 and ASTER GDEM version 2 over Lagos, Nigeria. Both datasets were examined by direct comparison with 176 highly accurate Ground Control Points (GCPs) coordinated by GPS (Global Positioning System) observation. The basis of comparison was on the elevation differences between the Digital Elevation Models (DEMs) and the GCPs at coincident points. The performance of both DEMs was visualised in 2D and 3D space by comparing pixel values and surface models. In the assessment, the absolute vertical accuracies of SRTM v3.0 and ASTER v2 are 4.23m and 28.73m respectively. The accuracy of SRTM for the study site proved to be higher than the value of 16m presented in the original SRTM requirement specification. ASTER did not meet up with its 17m overall accuracy specification.KEYWORDS: Uncertainty, Visualisation, Digital Elevation Model, SRTM, ASTER.
Elevation (ballistics)
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Rock glacier
Glacier mass balance
Glacier morphology
Accumulation zone
Tidewater glacier cycle
Massif
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The Malan Ice Caps are located at the central part of the Kunlun Mountains.In this study,serial RBV,MSS,TM and ETM+ Landsat data from 1973 to 2010 were used to map the glacier extents by applying remote sensing(RS) and visual interpretation.After constructing the glacier maps,the details of glaciers change during the last 37 years were obtained by using GIS tools.The results show that the Malan Ice Caps experienced a general shrinkage,the total glacierized area decreased by 6.8% from 1973 to 2010.The glacier retreat included a fast-slow-fast-slow process,with an insignificant retreat in recent decade,which reflected a transitional period of glacier change.In this retreat period,the glacier shrank 690.4 m in the south-north direction,and 84.29 in the east-west direction.By analyzing the climate records(annual mean temperature,summer mean temperature and annual precipitation) and glacier variation in the research area,it is found that glacier changes are a response to summer temperature increase.Annual precipitation also showed an upward trend,but had not compensated the mass loss due to ablation.Besides,topographic condition and the scale of glacier are key factors for glacier changes as well.
Glacier mass balance
Accumulation zone
Glacier morphology
Glacier ice accumulation
Tidewater glacier cycle
Ablation zone
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A low-altitude rock glacier associated with two small come glaciers on the Lyngen Peninsula is described on the basis of aerial-photographic interpretation. It is argued that a rock glacier originated when rock-fall debris from the corrie headwall covered the gently-sloping lower part of the two coalesced glaciers during the 19th century. Continued glacier wastage resulted in the separation of the glacier from the rock glacier. The rock glacier has experienced markedly differential flow; one part, by 1954, had advanced as a narrow lobe beyond the Neoglacial moraine ridges into the valley bottom. Some theoretical implications of rock glaciers cored by glacier ice are considered: the relationship of debris accumulation to ice mass balance on such a thin corrie glacier appears to be critical, and if the ablation is effectively, reduced by a debris cover, then a rock glacier can form. It is proposed that such a rock glacier's ice core can be replenished by a much-reduced ice mass gain to the upper corrie glacier and that a healthy rock glacier can exist where debris-free glaciers in the vicinity are retreating. In the present case, however, the separation of the rock glacier from its ice source has resulted in its ultimate stagnation.
Rock glacier
Tidewater glacier cycle
Glacier morphology
Glacier mass balance
Cirque glacier
Glacier ice accumulation
Accumulation zone
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<p>Glaciers in High Mountain Asia have been shrinking in the recent decades. They are a valuable indicator of climate change, and their meltwater plays an important role for regional water resources. Debris-covered glaciers, which are prevalent throughout the Himalayas, exhibit complex melt processes due to their heterogeneous surface.&#160; Previous studies have demonstrated that ice cliffs disproportionally contribute to glacier melt, but their importance at the glacier scale has been quantified for only a few sites. In this study, we exploit measurements taken since 2016 on the lake-terminating Trakarding Glacier (27.9&#176;N, 86.5&#176;E; 2.9 km<sup>2</sup> spanning 4,500&#8211;5,000 m a.s.l.; ~5% ice cliff cover), eastern Nepal Himalaya, to investigate the importance of cliffs for debris-covered ice melt at the glacier scale from a remote-sensing inversion and energy-balance modeling. We generated super-high-resolution (0.2 m) terrain data from aerial photographs (UAV and helicopter-borne photogrammetry) during 2018-2019 and manually delineated ~500 ice cliffs to derive surface velocity, elevation change, and specific mass balance, providing an observational estimate of ablation across the debris-covered tongue and attributable to ice cliffs. Further we employed a process-based 3D-backwasting model to estimate continuous ice cliff mass-loss over the study period. The model calculates the energy balance of ice cliff surfaces and reproduces their evolutions (cliff expansion, shrinkage, and reburial), based on the characteristics of the glacier surface and location of individual ice cliffs. This method, forced with in-situ meteorological and terrain data and evaluated against the observed changes, provides ice cliff mass-loss from the scale of individual features to the entire Trakarding Glacier.</p>
Glacier mass balance
Cliff
Glacier ice accumulation
Meltwater
Glacier morphology
Tidewater glacier cycle
Accumulation zone
Cirque glacier
Ice tongue
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During the expeditions to Mt.Nyainqentanglha in the summer of 1999 and 2007,glacier termini had been surveyed using GPS technology for five glaciers around the mount.Comparing the terminus positions surveyed by the two GPS with those surveyed in 1970 reveal that five glaciers have retreated since 1970.The retreat rate of glacier termini is around 10.0 m·a-1 for the Lanong and Zhadang Glaciers in the northern slopes of the mount and the Panu Glacier in the southern slope during 1970-2007.However,retreat of the Xibu Glacier is dramatic with a rate of 38.9 m·a-1,while a small high-elevation glacier(5O270C0049) in the Panu basin has a low retreat rate of 4.8 m·a-1.A stream was observed in the 1970′s firn basin of the Panu Glacier,indicating that not only the glacier termini are retreating dramatically but also the ablation areas are expanding around the mount.
Glacier mass balance
Tidewater glacier cycle
Glacier terminus
Accumulation zone
Cirque glacier
Glacier morphology
Firn
Glacier ice accumulation
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Glacier mass balance
Cirque glacier
Glacier morphology
Accumulation zone
Glacier terminus
Little ice age
Glacier ice accumulation
Tidewater glacier cycle
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Glacier mass balance
Tidewater glacier cycle
Glacier morphology
Cirque glacier
Accumulation zone
Glacier ice accumulation
Glacier terminus
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