scholarly journals Growth and drainage of supraglacial lakes on debris-mantled Ngozumpa Glacier, Khumbu Himal, Nepal

2001 ◽  
Vol 47 (159) ◽  
pp. 626-638 ◽  
Author(s):  
D. I. Benn ◽  
S. Wiseman ◽  
K. A. Hands
Keyword(s):  
Mass Balance ◽  
Rapid Growth ◽  
Drainage System ◽  
Lateral Moraine ◽  
Limited Growth ◽  
Water Line ◽  
Ablation Area ◽  
Supraglacial Lakes ◽  
Lake Formation ◽  
Dammed Lake

AbstractAblation of debris-mantled glaciers in Nepal has resulted in the formation of several potentially unstable moraine-dammed lakes, some of which constitute serious hazards. Ngozumpa Glacier, Khumbu Himal, has undergone significant downwasting in recent decades, and is believed to lie close to the threshold for moraine-dammed lake formation. The debris-mantled ablation area of the glacier is studded with numerous supraglacial lakes, the majority of which occupy closed basins with no perennial connections to the englacial drainage system (“perched lakes”). Perched lakes can undergo rapid growth by subaerial and water-line melting of exposed ice faces, and calving. Subaerial and subaqueous melting beneath thick (>1 m) debris mantles is comparatively insignificant. Although lake expansion can contribute substantially to ablation of the glacier, perched lakes cannot continue to grow indefinitely, but are subject to rapid drainage once a connection is made to englacial conduits. The level of one of the lakes on the Ngozumpa, however, is controlled by the altitude of a spillway through the lateral moraine of the glacier. This lake underwent only limited growth in the period 1998–2000, but is likely to experience monotonic growth ifglacier mass balance continues to be negative.

scholarly journals Unravelling the evolution of Zmuttgletscher and its debris cover since the end of the Little Ice Age

2019 ◽  
Vol 13 (7) ◽  
pp. 1889-1909 ◽  
Author(s):  
Nico Mölg ◽  
Tobias Bolch ◽  
Andrea Walter ◽  
Andreas Vieli
Keyword(s):  
Mass Balance ◽  
Ice Age ◽  
Aerial Photographs ◽  
Dynamic Interactions ◽  
Glacier Surface ◽  
Ablation Area ◽  
Debris Cover ◽  
Historic Maps ◽  
Length And Area ◽  
Flow Velocities

Abstract. Debris-covered glaciers generally exhibit large, gently sloping, slow-flowing tongues. At present, many of these glaciers show high thinning rates despite thick debris cover. Due to the lack of observations, most existing studies have neglected the dynamic interactions between debris cover and glacier evolution over longer time periods. The main aim of this study is to reveal such interactions by reconstructing changes of debris cover, glacier geometry, flow velocities, and surface features of Zmuttgletscher (Switzerland), based on historic maps, satellite images, aerial photographs, and field observations. We show that debris cover extent has increased from ∼13 % to ∼32 % of the total glacier surface since 1859 and that in 2017 the debris is sufficiently thick to reduce ablation compared to bare ice over much of the ablation area. Despite the debris cover, the glacier-wide mass balance of Zmuttgletscher is comparable to that of debris-free glaciers located in similar settings, whereas changes in length and area have been small and delayed by comparison. Increased ice mass input in the 1970s and 1980s resulted in a temporary velocity increase, which led to a local decrease in debris cover extent, a lowering of the upper boundary of the ice-cliff zone, and a strong reduction in ice-cliff area, indicating a dynamic link between flow velocities, debris cover, and surface morphology. Since 2005, the lowermost 1.5 km of the glacier has been quasi-stagnant, despite a slight increase in the surface slope of the glacier tongue. We conclude that the long-term glacier-wide mass balance is mainly governed by climate. The debris cover governs the spatial pattern of elevation change without changing its glacier-wide magnitude, which we explain by the extended ablation area and the enhanced thinning in regions with thin debris further up-glacier and in areas with abundant meltwater channels and ice cliffs. At the same time rising temperatures lead to increasing debris cover and decreasing ice flux, thereby attenuating length and area losses.

scholarly journals Present-Day Glaciation in the South Shetland Islands

1982 ◽  
Vol 3 ◽  
pp. 233-238 ◽  
Author(s):  
Olav Orheim ◽  
L.S. Govorukha
Keyword(s):  
Mass Balance ◽  
Regional Climate ◽  
Equilibrium Line ◽  
South Shetland Islands ◽  
King George Island ◽  
Deception Island ◽  
Shetland Islands ◽  
Ablation Area ◽  
Livingston Island ◽  
Annual Balance

This paper presents mass-balance results from Deception Island for 1968–69 to 1973–74, from King George Island for the balance years 1969–70 and 1970–71, and from Livingston Island from 1971–72 to 1973–74. The accumulation areas of all localities are in the soaked fades, with a firn/ice transition at King George Island at 12 to 20 m depth. Of the glaciers studied, only “Gl” on Deception Island terminates wholly on land and has a relatively large ablation area. The mass-balance curves are similar for King George Island and Livingston Island, with equilibrium lines at around 150 m elevation. “Gl“ on Deception Island has more negative summer balances, and the equilibrium line ranged from 275 to 370 m during the six balance years. Here, there were no years of positive net mass balance, and large negative net values during the 1970–71 to 1972–73 balance years. This resulted from a lowered albedo caused by ash from the August 1970 eruption. Ash layers from the Deception Island eruptions are also observed on Livingston Island and King George Island, where they form stratigraphic markers in the accumulation areas of the glaciers. Annual balance variations from 1957–58 to 1970–71, based on stratigraphic studies at Deception Island and King George Island, show good correlations, indicating that the variations reflect changes in regional climate.

Controls on the formation and sudden drainage of glacier-impounded lakes: implications for jökulhlaup characteristics

1999 ◽  
Vol 23 (1) ◽  
pp. 79-110 ◽  
Author(s):  
Fiona S. Tweed ◽  
Andrew J. Russell
Keyword(s):  
Current Knowledge ◽  
Schematic Model ◽  
The Past ◽  
Lake Formation ◽  
Potential Impact ◽  
Dammed Lake ◽  
Lake Drainage ◽  
Discharge Estimation ◽  
Trigger Mechanisms ◽  
Published Research

Over the past few years there has been an increase in understanding of glacier-impounded or ‘ice-dammed’ lake behaviour. The spectacular jökulhlaup (catastrophic flood) from Grímsvötn, Iceland in November 1996 has both raised the profile of such events and emphasized the need for awareness of the processes involved. This review summarizes the extent of current knowledge of ice-dammed lakes, highlighting key developments and outlining areas of study still subject to difficulties. Controls on ice-dammed lake formation and persistence are identified, and cycles of jökulhlaup activity are related to glacier fluctuations. Ice-dammed lake drainage trigger mechanisms are reviewed and recent progress in the understanding of such mechanisms is emphasized. Controls on jökulhlaup routing and the development and character of jökulhlaup conduits are discussed and recent advances in jökulhlaup prediction, hydrograph modelling and peak discharge estimation are assessed. A process-based schematic model, drawing on published research, links ice-dammed lake occurrence and drainage to jökulhlaup characteristics. It is demonstrated that ice-dammed lake and ice-dam characteristics ultimately control seven key jökulhlaup attributes which determine the potential impact of jökulhlaups on both landscape and human activity in glaciated regions.

Local infiltration devices at parking sites – Experimental assessment of temporal changes in hydraulic and contaminant removal capacity

2007 ◽  
Vol 55 (4) ◽  
pp. 193-200 ◽  
Author(s):  
S. Achleitner ◽  
C. Engelhard ◽  
U. Stegner ◽  
W. Rauch
Keyword(s):  
Mass Balance ◽  
Drainage System ◽  
Life Time ◽  
Point Of View ◽  
Traffic Load ◽  
Worst Case ◽  
Parking Lots ◽  
Removal Capacity ◽  
Operational Life ◽  
Chemical Conditions

On site infiltration of stormwater is a common practice in order to avoid hydraulic overload of the urban drainage system. If hydrological conditions allow on-site infiltration – this is even mandatory from a legal point of view. Focus in this work is on surface infiltration of stormwater from parking lots. Proper operation of those devices is assumed to be appr. 15 years, as permits granted are limited to this time. Questions are raised whether this considered life expectancy is feasible. One apprehension is a possible clogging effect reducing the hydraulic capacity of the swale. The second aim was to identify magnitudes of accumulated pollutant loads with respect to limitations onto lifetime. The experimental investigation covered infiltration swales of different ages from eleven supermarket parking lots in Tyrol. Hydraulic permeabilities were assessed as well as chemical conditions of the soil material regarding hydrocarbon index (HI) and heavy metals (Cu, Zn, Pb and Cd). Further mass balance of contaminants has been performed in order to assess the operational life time based on pollutant load consideration. Calculations were based on load estimations using literature based minima and maxima concentrations from surface flows. Testing the correlation of hydraulic and pollutant measurements against site specific parameters (age, traffic load) revealed no distinct relation. In general all measured pollutants were found under limit concentrations. Mass balance calculations showed that limit concentrations are not exceeded either for worst case loading and considering 15 years of operation.

Automated mapping of Antarctic supraglacial lakes and streams using machine learning

2020 ◽  
Author(s):  
Mariel Dirscherl ◽  
Andreas Dietz ◽  
Celia Baumhoer ◽  
Christof Kneisel ◽  
Claudia Kuenzer
Keyword(s):  
Machine Learning ◽  
Mass Balance ◽  
Antarctic Peninsula ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Antarctic Ice Sheet ◽  
Supraglacial Lakes ◽  
The Antarctic ◽  
Sentinel 2

<p>Antarctica stores ~91 % of the global ice mass making it the biggest potential contributor to global sea-level-rise. With increased surface air temperatures during austral summer as well as in consequence of global climate change, the ice sheet is subject to surface melting resulting in the formation of supraglacial lakes in local surface depressions. Supraglacial meltwater features may impact Antarctic ice dynamics and mass balance through three main processes. First of all, it may cause enhanced ice thinning thus a potentially negative Antarctic Surface Mass Balance (SMB). Second, the temporary injection of meltwater to the glacier bed may cause transient ice speed accelerations and increased ice discharge. The last mechanism involves a process called hydrofracturing i.e. meltwater-induced ice shelf collapse caused by the downward propagation of surface meltwater into crevasses or fractures, as observed along large coastal sections of the northern Antarctic Peninsula. Despite the known impact of supraglacial meltwater features on ice dynamics and mass balance, the Antarctic surface hydrological network remains largely understudied with an automated method for supraglacial lake and stream detection still missing. Spaceborne remote sensing and data of the Sentinel missions in particular provide an excellent basis for the monitoring of the Antarctic surface hydrological network at unprecedented spatial and temporal coverage.</p><p>In this study, we employ state-of-the-art machine learning for automated supraglacial lake and stream mapping on basis of optical Sentinel-2 satellite data. With more detail, we use a total of 72 Sentinel-2 acquisitions distributed across the Antarctic Ice Sheet together with topographic information to train and test the selected machine learning algorithm. In general, our machine learning workflow is designed to discriminate between surface water, ice/snow, rock and shadow being further supported by several automated post-processing steps. In order to ensure the algorithm’s transferability in space and time, the acquisitions used for training the machine learning model are chosen to cover the full circle of the 2019 melt season and the data selected for testing the algorithm span the 2017 and 2018 melt seasons. Supraglacial lake predictions are presented for several regions of interest on the East and West Antarctic Ice Sheet as well as along the Antarctic Peninsula and are validated against randomly sampled points in the underlying Sentinel-2 RGB images. To highlight the performance of our model, we specifically focus on the example of the Amery Ice Shelf in East Antarctica, where we applied our algorithm on Sentinel-2 data in order to present the temporal evolution of maximum lake extent during three consecutive melt seasons (2017, 2018 and 2019).</p>

scholarly journals Structure and evolution of the drainage system of a Himalayan debris-covered glacier, and its relationship with patterns of mass loss

2017 ◽  
Vol 11 (5) ◽  
pp. 2247-2264 ◽  
Author(s):  
Douglas I. Benn ◽  
Sarah Thompson ◽  
Jason Gulley ◽  
Jordan Mertes ◽  
Adrian Luckman ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Balance ◽  
Satellite Image ◽  
Drainage System ◽  
Ablation Zone ◽  
Negative Mass ◽  
Long Distance ◽  
Glacier Surface ◽  
Base Level ◽  
Englacial Drainage

Abstract. We provide the first synoptic view of the drainage system of a Himalayan debris-covered glacier and its evolution through time, based on speleological exploration and satellite image analysis of Ngozumpa Glacier, Nepal. The drainage system has several linked components: (1) a seasonal subglacial drainage system below the upper ablation zone; (2) supraglacial channels, allowing efficient meltwater transport across parts of the upper ablation zone; (3) sub-marginal channels, allowing long-distance transport of meltwater; (4) perched ponds, which intermittently store meltwater prior to evacuation via the englacial drainage system; (5) englacial cut-and-closure conduits, which may undergo repeated cycles of abandonment and reactivation; and (6) a "base-level" lake system (Spillway Lake) dammed behind the terminal moraine. The distribution and relative importance of these elements has evolved through time, in response to sustained negative mass balance. The area occupied by perched ponds has expanded upglacier at the expense of supraglacial channels, and Spillway Lake has grown as more of the glacier surface ablates to base level. Subsurface processes play a governing role in creating, maintaining, and shutting down exposures of ice at the glacier surface, with a major impact on spatial patterns and rates of surface mass loss. Comparison of our results with observations on other glaciers indicate that englacial drainage systems play a key role in the response of debris-covered glaciers to sustained periods of negative mass balance.

scholarly journals Sensitivity of glacier runoff to summer snowfall events

2007 ◽  
Vol 46 ◽  
pp. 309-315 ◽  
Author(s):  
Heidi Escher-Vetter ◽  
Matthias Siebers
Keyword(s):  
Mass Balance ◽  
Air Temperature ◽  
Meteorological Data ◽  
Precipitation Data ◽  
Clear Trend ◽  
Temperature Changes ◽  
Ablation Area ◽  
Glacier Runoff ◽  
Precipitation Type

AbstractIn order to investigate the effect of changing precipitation type on glacier discharge due to air-temperature changes, the relation between summer snowfall and runoff is surveyed for the Vernagtbach basin, Austria, (2640–3630ma.s.l.; ~72% glaciated) for the period 1976–2005. Precipitation data were evaluated for each ablation season with respect to amount and type; the latter derived mainly from daily photographs of the catchment, but validated over 4 years with additional meteorological data. Winter snowfall amounts were determined on the basis of mass-balance measurements. Average ablation period air temperature showed a rise of 1.5 K from 1976 to 2005, and runoff increased from about 1100 mmw.e. to 2200 mmw.e. Snowfall amounts during the ablation period decreased between 1976 and 1991, but increased from 1992 to 2005, indicating a large year-to-year variation. The number of days with snowfall varies even more, with no clear trend discernible. The evolution of runoff is only partly explained by precipitation type during the ablation season, and accumulation amounts during winter deliver a not unambiguous picture. More important is the development of the ablation area from about 20% of glacier size in the 1970s to 100% in 2003.

scholarly journals Mass balance of the Lambert Glacier–Amery Ice Shelf system, East Antarctica: a comparison of computed balance fluxes and measured fluxes

2000 ◽  
Vol 46 (155) ◽  
pp. 561-570 ◽  
Author(s):  
Helen A. Fricker ◽  
Roland C. Warner ◽  
Ian Allison
Keyword(s):  
Mass Balance ◽  
Drainage System ◽  
Radar Altimeter ◽  
Drainage Basins ◽  
Ice Shelf ◽  
Amery Ice Shelf ◽  
Ice Sheet Mass Balance ◽  
Lambert Glacier ◽  
Lambert Glacier Basin

AbstractWe combine European Remote-sensing Satellite (ERS-1) radar altimeter surface elevations (Fricker and others, 2000) with six different accumulation distributions to compute balance fluxes for the Lambert Glacier–Amery Ice Shelf drainage system. These interpolated balance fluxes are compared with fluxes derived from in situ measurements of ice thickness and velocity at 73 stations of the Lambert Glacier basin traverse and at 11 stations further downstream, to assess the system’s state of balance. For the upstream line we obtain a range of imbalance estimates, from −23.8% to +19.9% of the observed flux, reflecting the sensitivity to the accumulation distributions. For some of the accumulation distributions the imbalance estimates vary significantly between different parts of the line. Imbalance estimates for the downstream line range from −17.7% to +70.2%, with four of the estimates exceeding +30%, again reflecting the sensitivity of the result to input accumulation, and strongly suggesting that the mass balance of the region between the two lines is positive. Our results confirm the importance of accurate estimates of accumulation in ice-sheet mass-balance studies. Furthermore, they suggest that it is not possible to accurately determine the state of balance of large Antarctic drainage basins on the basis of currently available accumulation distributions.

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