Structural evolution triggers a dynamic reduction in active glacier length during rapid retreat: Evidence from Falljökull, SE Iceland
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Abstract Over the past two decades Iceland's glaciers have been undergoing a phase of accelerated retreat set against a backdrop of warmer summers and milder winters. This paper demonstrates how the dynamics of a steep outlet glacier in maritime SE Iceland have changed as it adjusts to recent significant changes in mass balance. Geomorphological evidence from Falljökull, a high‐mass turnover temperate glacier, clearly shows that between 1990 and 2004 the ice front was undergoing active retreat resulting in seasonal oscillations of its margin. However, in 2004–2006 this glacier crossed an important dynamic threshold and effectively reduced its active length by abandoning its lower reaches to passive retreat processes. A combination of ice surface structural measurements with radar, lidar, and differential Global Navigation Satellite Systems data are used to show that the upper active section of Falljökull is still flowing forward but has become detached from and is being thrust over its stagnant lower section. The reduction in the active length of Falljökull over the last several years has allowed it to rapidly reequilibrate to regional snowline rise in SE Iceland over the past two decades. It is possible that other steep, mountain glaciers around the world may respond in a similar way to significant changes in their mass balance, rapidly adjusting their active length in response to recent atmospheric warming.Keywords:
Glacier mass balance
Tidewater glacier cycle
Glacier terminus
Glacier ice accumulation
Glacier morphology
Glacier terminus
Glacier ice accumulation
Glacier morphology
Tidewater glacier cycle
Accumulation zone
Glacier mass balance
Cirque glacier
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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.
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Interactions between glacier dynamics, ice structure, and climate at Fjallsjökul, south-east Iceland
Over recent decades, the number of outlet glaciers terminating in lakes in Iceland has increased in line with climate warming. The mass-balance changes of these lake-terminating outlet gla-ciers are sensitive to rising air temperatures, due to altered glacier dynamics and increased surface melt. This study aims to better understand the relationship between proglacial lake development, climate, glacier dynamics and glacier structure at Fjallsjökull, a large, lake-terminating outlet glacier in south-east Iceland. We used satellite imagery to map glacier terminus position and lake extent between 1973 and 2016, and a combination of aerial and satellite imagery to map the structural architecture of the glacier's terminus in 1982, 1994 and 2011. The temporal evolution of ice surface velocities between 1990 and 2018 was calculated using feature tracking. Statistically significant increases in the rate of terminus retreat and lake expansion were identified in 2001, 2009 and 2011. Our surface velocity and structural datasets revealed the development of localised flow 'corridors' over time, which conveyed relatively faster flow towards the glacier's terminus. We attribute the overall changes in dynamics and structural architecture at Fjallsjökull to rising air temperatures, but argue that the spatial complexities are driven by glacier specific factors, such as basal topography.
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Feature tracking
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Glacier terminus
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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.
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Abstract. The Little Ice Age maximum extent of glaciers in Iceland was reached about 1890 AD and most glaciers in the country have retreated during the 20th century. A model for the surface mass balance and the flow of glaciers is used to reconstruct the 20th century retreat history of Hoffellsjökull, a south-flowing outlet glacier of the ice cap Vatnajökull, which is located close to the southeastern coast of Iceland. The bedrock topography was surveyed with radio-echo soundings in 2001. A wealth of data are available to force and constrain the model, e.g. surface elevation maps from ~1890, 1936, 1946, 1989, 2001, 2008 and 2010, mass balance observations conducted in 1936–1938 and after 2001, energy balance measurements after 2001, and glacier surface velocity derived by kinematic and differential GPS surveys and correlation of SPOT5 images. The approximately 20% volume loss of this glacier in the period 1895–2010 is realistically simulated with the model. After calibration of the model with past observations, it is used to simulate the future response of the glacier during the 21st century. The mass balance model was forced with an ensemble of temperature and precipitation scenarios derived from 10 global and 3 regional climate model simulations using the A1B emission scenario. If the average climate of 2000–2009 is maintained into the future, the volume of the glacier is projected to be reduced by 30% with respect to the present at the end of this century. If the climate warms, as suggested by most of the climate change scenarios, the model projects this glacier to almost disappear by the end of the 21st century. Runoff from the glacier is predicted to increase for the next 30–40 yr and decrease after that as a consequence of the diminishing ice-covered area.
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Recent studies indicate that widespread wastage of glaciers in western China has happened since the late 1970s, but diverse places under different climate settings have marked regional discrepancy as to the amplitude in glacier shrinkages. In the present study, we investigate the changes of glaciers at the head of Yurungkax river (centered at 35o40'N, 81oE) in the heavily glaciated West Kunlun Mts. by using aerial photos (1970), Landsat TM (1989) and ETM+ (2001) imageries. A comparative analysis performed for glacier length/area variations since 1970 in the West Kunlun Mts. shows that the prevailing characteristic of glacier variation is ice wastage, however, changes in glacier area are very small in this region. Results indicate that a small enlargement of ice extent during 1970-1989 was followed by a reduction of over 0.5% during 1989-2001. It concludes that the enlargement of glaciers during 1970-1989 might be caused by the decrease in air temperature and the increase in precipitation during the 1960s and that glacier shrinkage during 1989-2001 might be reaction to increase in air temperature, but abundant precipitation acts as a role of buffer in variations of surface mass balance of glaciers in the research region.
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