scholarly journals Analysis of the first jökulhlaup at Blåmannsisen, northern Norway, and implications for future events

2005 ◽  
Vol 42 ◽  
pp. 35-41 ◽  
Author(s):  
Rune Verpe Engeset ◽  
Thomas Vikhamar Schuler ◽  
Miriam Jackson
Keyword(s):  
Water Levels ◽  
Pressure Measurements ◽  
Negative Mass ◽  
Overburden Pressure ◽  
Northern Norway ◽  
Ice Cap ◽  
Lake Volume ◽  
Show Evidence ◽  
Future Events ◽  
Hydropower Reservoir

AbstractThe first known jökulhlaup from the Blåmannsisen ice cap in northern Norway began on 6 September 2001. It lasted 35 hours and emptied the lake Øvre Messingmalmvatn (∼4.0 × 107m3). Before the event, the lake drained steadily via a rock spillway into Sweden. The water from the jökulhlaup drained into the hydropower reservoir Sisovatn, and so was financially beneficial to Norway. Glaciological data show evidence of glacier retreat and thinning during the last four decades. Glacier thickness decreased in the ablation zone, reducing ice-barrier stability. The lake drained at a water level 40 m below that required to equalize the ice overburden pressure. Measurements show an ice-barrier thinning of 3.5 m since the jökulhlaup occurred. Climate scenarios indicate future negative mass balance and further thinning. The lake volume was 82% full 2.5 years after the event, suggesting a probable repeat interval of 3 years. Future jökulhlaups may be triggered at lower water levels and produce lower discharges.

scholarly journals A regression model for the mass-balance distribution of the Vatnajökull ice cap, Iceland

2003 ◽  
Vol 37 ◽  
pp. 189-193 ◽  
Author(s):  
Guðefinna Aðalgeirsdóttir ◽  
G. Hilmar Gudmundsson ◽  
Helgi Björnsson
Keyword(s):  
Linear Regression ◽  
Regression Model ◽  
Mass Balance ◽  
Surface Mass Balance ◽  
Negative Mass ◽  
Equilibrium Line Altitude ◽  
Surface Mass ◽  
Ice Cap ◽  
Maximum Value ◽  
Slope Direction

AbstractA non-linear regression model describing the mass-balance distribution of the whole Vatnajökull ice cap, Iceland, for the years 1992–2000 is presented. All available data from some 40 locations over this 9 year period were used to determine the parameters of the model. The regression model uses six adjustable parameters which all have a clear physical interpretation. They are the slope, direction and the height of the equilibrium-line altitude (ELA) plane, two altitude mass-balance gradients, and a maximum value of the surface mass balance. It is found that the temporal variation of the observed mass-balance distribution can be accurately described through annual shifts of the ELA. Annual shifts in ELA are on the order of 100 m, which is of the same magnitude as the change expected to be caused by the climate variation predicted during the next decades. A slight trend towards a more negative mass balance is detected during this 9 year period.

scholarly journals Helicopter-borne radio-echo sounding of Svartisen, Norway

1993 ◽  
Vol 17 ◽  
pp. 23-26 ◽  
Author(s):  
Michael Kennett ◽  
Tron Laumann ◽  
Cecilie Lund
Keyword(s):  
Low Frequency ◽  
Ice Thickness ◽  
Digital Receiver ◽  
Outlet Glacier ◽  
Northern Norway ◽  
Bed Topography ◽  
Ice Cap ◽  
Radio Echo Sounding ◽  
Depth Sounding ◽  
Ice Radar

A helicopter-mounted low frequency ice-radar has been developed for the depth sounding of temperate glaciers. The radar consists of standard transmitter and digital receiver equipment. The long antennae are supported on a special aluminium and fibreglass construction which hangs 20 m below the helicopter. The radar has been used on Engabreen, an outlet glacier of the Svartisen Ice Cap in northern Norway, where ice thicknesses of up to 350 m were obtained. The results have been used to construct a map of bed topography of the lower part of Engabreen. This map is largely consistent with ice thickness data obtained by drilling.

scholarly journals Direct Measurement of Basal Water Pressures: Progress and Problemss

1979 ◽  
Vol 23 (89) ◽  
pp. 309-319 ◽  
Author(s):  
Steven M. Hodge
Keyword(s):  
Large Scale ◽  
Water Pressure ◽  
Water System ◽  
Water Levels ◽  
Hot Water ◽  
Overburden Pressure ◽  
Well Control ◽  
System A ◽  
Pressure Water ◽  
Internal Change

AbstractIn 1975 and 1977, 24 bore holes were drilled to the bed of South Cascade Glacier, Washington, U.S.A., using both electrothermal and hot-water drills. Only two holes connected directly with the basal water system, a significant decrease from the four to five such connections in 13 holes drilled in 1973 and 1974 (Hodge, 1976). Most of the bed, possibly as much as 90%, appears to be hydraulically inactive and isolated from a few active subglacial conduits. Bore holes which penetrate these inactive areas initially should connect eventually with the active basal water system due to bed pressurization by the water standing in the bore hole, provided there is a sufficient supply of water available to form and maintain the connection passageway. These sealed-off areas probably consist of the sub-sole drift and permeability barriers found recently at the bed of Blue Glacier by Engelhardt and others (1978); an increase in the area of bed covered by these features probably caused the decrease in chance of bore-hole connection. This apparently was not due to any external cause but rather was the result of a real internal change in the subglacial hydraulic system which occurred between 1974 and 1975.If most of the area of a glacier bed is hydraulically isolated sub-sole drift, or something similar, such features may well control large-scale glacier sliding changes, since changes in the amount of water having access to the glacier bed will take considerable time to affect the interstitial water pressure in the more widespread sub-sole drift.Water pressures in the active part of the basal water system of South Cascade Glacier are generally in the range of 50–75% of the ice overburden pressure. Water levels in a connected bore hole are probably representative over an area of the bed 100 m or more in extent. A correlation of bore-hole water levels with changes in surface motion supports the idea that the sliding of a temperate glacier is controlled largely by the basal water pressure.

scholarly journals Remote sounding of Greenland supraglacial melt lakes: implications for subglacial hydraulics

2007 ◽  
Vol 53 (181) ◽  
pp. 257-265 ◽  
Author(s):  
Jason E. Box ◽  
Kathleen Ski
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Lake Depth ◽  
Cross Sectional ◽  
Overburden Pressure ◽  
Ice Dynamics ◽  
Subglacial Environment ◽  
Lake Volume ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Lake Drainage

AbstractA supraglacial lake-depth retrieval function is developed, based on the correspondence between moderate-resolution imaging spectroradiometer (MODIS) reflectance and water depth measured during raft surveys. Individual lake depth, area and volume statistics, including short-term temporal changes for Greenland’s southwestern ablation region, were compiled for 2000–05. The maximum area of an individual lake was found to be 8.9 km2, the maximum volume 53.0 × 106 m3 and the maximum depth 12.2 m, sampling over 0.0625 km2 pixel areas. The total lake volume reaches >1 km3 in this region by July each year. The importance of melt lake reservoirs to Greenland ice-sheet flow may be a feedback between abrupt lake drainage events and ice dynamics. Lake-outburst volumes up to 31.5 × 106 m3 d−1 are capable of providing sufficient water via moulins to hydraulically pressurize the subglacial environment. Since the overburden pressure at the base of a flooded moulin is greater than that provided by ice, lake-outburst events seem capable of exerting sufficient upward force to lift the ice sheet locally, if water flow in the subglacial environment is constrained laterally. Considering a moulin with a 10 m2 cross-sectional area, basal pressurization can be maintained over lake-outburst episodes lasting hours to days.

scholarly journals Filling and drainage of a subglacial lake beneath the Flade Isblink ice cap, northeast Greenland

2022 ◽  
Author(s):  
Qi Liang ◽  
Wanxin Xiao ◽  
Ian Howat ◽  
Xiao Cheng ◽  
Fengming Hui ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Aquifer Storage ◽  
Subglacial Lake ◽  
Ice Cap ◽  
Lake Volume ◽  
Basin Surface ◽  
Multi Temporal ◽  
Lake Drainage ◽  
Subglacial Lakes

Abstract. The generation, transport, storage and drainage of meltwater beneath the ice sheet play important roles in the Greenland ice sheet (GrIS) system. Active subglacial lakes, common features in Antarctica, have recently been detected beneath GrIS and may impact ice sheet hydrology. Despite their potential importance, few repeat subglacial lake filling and drainage events have been identified under Greenland Ice Sheet. Here we examine the surface elevation change of a collapse basin at the Flade Isblink ice cap, northeast Greenland, which formed due to sudden subglacial lake drainage in 2011. We estimate the subglacial lake volume evolution using multi-temporal ArcticDEM data and ICESat-2 altimetry data acquired between 2012 and 2021. Our long-term observations show that the subglacial lake was continuously filled by surface meltwater, with basin surface rising by up to 55 m during 2012–2021 and we estimate 138.2 × 106 m3 of meltwater was transported into the subglacial lake between 2012 and 2017. A second rapid drainage event occurred in late August 2019, which induced an abrupt ice dynamic response. Comparison between the two drainage events shows that the 2019 drainage released much less water than the 2011 event. We conclude that multiple factors, e.g., the volume of water stored in the subglacial lake and bedrock relief, regulate the episodic filling and drainage of the lake. By comparing the surface meltwater production and the subglacial lake volume change, we find only ~64 % of the surface meltwater successfully descended to the bed, suggesting potential processes such as meltwater refreezing and firn aquifer storage, need to be further quantified.

Thermal Stresses near the Surface of a Glacier

1978 ◽  
Vol 20 (83) ◽  
pp. 257-283 ◽  
Author(s):  
T. J. O. Sanderson
Keyword(s):  
Strain Rate ◽  
Thermal Stresses ◽  
Overburden Pressure ◽  
Ice Cap ◽  
Short Period ◽  
Thermal Origin ◽  
Fourier Theory ◽  
Flow Law ◽  
Set Up ◽  
Strain Rate Field

AbstractStresses occur in the uppermost 10 m of a glacier as a result of temperature fluctuations at the surface. A model is set up of a typical year's surface temperature variation, and the progress of temperature waves through the glacier is calculated using Fourier theory of heat conduction. Short-period fluctuations are rapidly attenuated, and at 10 m depth the annual cycle is reduced to 5% of its surface amplitude. As the temperature of the ice varies it undergoes small volume changes; stresses are calculated on the assumption that any tendency of the ice to expand or contract laterally results in the creation of just enough stress to cause the ice to remain unstrained. It is found that in the top 2 or 3 m stresses of thermal origin are generally in excess of those due to gross deformation or overburden pressure. For the case of high-density ice Glen's flow law is used, and conditions are found to be favourable for the formation of surface rumples of wavelength about 10 m. For the case of firm or snow a Newtonian flow law is assumed, and it is found that under cold conditions fracture under tension can occur. Cracks of thermal origin may be responsible for the initial formation of crevasses, and they also provide an explanation for background noise encountered when seismic shooting at low temperatures. Calculations are made of the strain-rate field surrounding a crack and it is found that thermal effects can lead to appreciable Strain-rate anomalies for strain-rate measurements near cracks. The magnitude of the effect is easily sufficient to account for anomalous fluctuating strain-rates found by workers using wire strainmeters on the Barnes Ice Cap.

scholarly journals Analysis of Salt Lake Volume Dynamics Using Sentinel-1 Based SBAS Measurements: A Case Study of Lake Tuz, Turkey

2021 ◽  
Vol 13 (14) ◽  
pp. 2701
Author(s):  
Burhan Baha Bilgilioğlu ◽  
Esra Erten ◽  
Nebiye Musaoğlu
Keyword(s):  
Water Level ◽  
Salt Lake ◽  
Good Alternative ◽  
Water Levels ◽  
Wet Season ◽  
Interferometric Technique ◽  
Lake Volume ◽  
Environmental Protection Area ◽  
Protection Area ◽  
Small Baseline

As one of the largest hypersaline lakes, Lake Tuz, located in the middle of Turkey, is a key waterbird habitat and is classified as a Special Environmental Protection Area in the country. It is a dynamic lake, highly affected by evaporation due to its wide expanse and shallowness (water depth <40 cm), in addition to being externally exploited by salt companies. Monitoring the dynamics of its changes in volume, which cause ecological problems, is required to protect its saline lake functions. In this context, a spatially homogeneous distributed gauge could be critical for monitoring and rapid response; however, the number of gauge stations and their vicinity is insufficient for the entire lake. The present study focuses on assessing the feasibility of a time-series interferometric technique, namely the small baseline subset (SBAS), for monitoring volume dynamics, based on freely available Sentinel-1 data. A levelling observation was also performed to quantify the accuracy of the SBAS results. Regression analysis between water levels, which is one of the most important volume dynamics, derived by SBAS and levelling in February, April, July and October was 67%, 80%, 84%, and 95% respectively, for correlation in the range of 10–40 cm in water level, and was in line with levelling. Salt lake components such as water, vegetation, moist soil, dry soil, and salt, were also classified with Sentinel-2 multispectral images over time to understand the reliability of the SBAS measurements based on interferometric coherence over different surface types. The findings indicate that the SBAS method with Sentinel-1 is a good alternative for measuring lake volume dynamics, including the monitoring of water level and salt movement, especially for the dry season. Even though the number of coherent, measurable, samples (excluding water) decrease during the wet season, there are always sufficient coherent samples (>0.45) over the lake.

scholarly journals Helicopter-borne radio-echo sounding of Svartisen, Norway

1993 ◽  
Vol 17 ◽  
pp. 23-26 ◽  
Author(s):  
Michael Kennett ◽  
Tron Laumann ◽  
Cecilie Lund
Keyword(s):  
Low Frequency ◽  
Ice Thickness ◽  
Digital Receiver ◽  
Outlet Glacier ◽  
Northern Norway ◽  
Bed Topography ◽  
Ice Cap ◽  
Radio Echo Sounding ◽  
Depth Sounding ◽  
Ice Radar

A helicopter-mounted low frequency ice-radar has been developed for the depth sounding of temperate glaciers. The radar consists of standard transmitter and digital receiver equipment. The long antennae are supported on a special aluminium and fibreglass construction which hangs 20 m below the helicopter. The radar has been used on Engabreen, an outlet glacier of the Svartisen Ice Cap in northern Norway, where ice thicknesses of up to 350 m were obtained. The results have been used to construct a map of bed topography of the lower part of Engabreen. This map is largely consistent with ice thickness data obtained by drilling.

scholarly journals Deglaciation-enhanced mantle CO2 fluxes at Yellowstone imply positive climate feedback

2021 ◽  
Author(s):  
Fiona Clerc ◽  
Mark Behn ◽  
Brent Minchew
Keyword(s):  
Co2 Flux ◽  
Climate Feedback ◽  
Mantle Melting ◽  
West Antarctica ◽  
Positive Feedbacks ◽  
Active Systems ◽  
Ice Cap ◽  
Volatile Release ◽  
Show Evidence ◽  
Positive Climate

The generation of mantle melts in response to decompression by glacial unloading has been linked to enhanced volcanic activity and volatile release in Iceland and in global eruptive records. However, it is unclear whether this process is also important in magmatically-active systems that do not show evidence of enhanced eruption rates. For example, the deglaciation of the Yellowstone ice cap did not observably enhance volcanism, yet Yellowstone may still have released large volumes of CO2 to the surface due to the crystallization of melts at depth. Here we develop models to simulate mantle melt production and volatile release associated with the deglaciation of Yellowstone and Iceland. In agreement with previous work, we find mantle melt production in Iceland is enhanced 33-fold during deglaciation, generating an additional 3728 km3 of melt and releasing an additional 31–51 Gt of CO2. Beneath Yellowstone, we find mantle melt production is comparably enhanced 19-fold during deglaciation, generating an additional 815 km3 of melt, though thicker lithosphere may prevent the transport of this melt to the surface. These melts segregate an additional 135–230 Gt of CO2 from the mantle, representing a ~23–39% increase of the global volcanic CO2 flux (if degassed during deglaciation). Our results suggest deglaciation-enhanced mantle melting is important in continental settings with partially molten mantle (potentially Greenland and West Antarctica) and may result in positive feedbacks between deglaciation and climate warming.

scholarly journals Development of a subglacial lake monitored with radio-echo sounding: Case study from the Eastern Skaftá Cauldron in the Vatnajökull ice cap, Iceland

2021 ◽  
Author(s):  
Eyjólfur Magnússon ◽  
Finnur Pálsson ◽  
Magnús T. Gudmundsson ◽  
Thórdís Högnadóttir ◽  
Cristian Rossi ◽  
...  
Keyword(s):  
Lake Area ◽  
Ice Cap ◽  
Lake Volume ◽  
Digital Elevation ◽  
Geothermal Activity ◽  
Before And After ◽  
Radio Echo Sounding ◽  
Water Volumes ◽  
Elevation Model ◽  
Echo Sounding

Abstract. We present repeated radio-echo sounding (RES, 5 MHz) on a profile grid over the Eastern Skaftá Cauldron (ESC) in Vatnajökull ice cap, Iceland. The ESC is ~3 km wide and 50–150 m deep ice cauldron created and maintained by subglacial geothermal activity of ~1 GW. Beneath the cauldron and 200–400 m thick ice, water accumulates in a lake and is released semi-regularly in jökulhlaups. The RES record consists of annual surveys with 200–400 m between profiles in early summers of 2014–2020. Comparison of the RES surveys (2D migrated profiles) reveals variable lake area (0.5–4.1 km2) and enables traced reflections from the lake roof to be distinguished from bedrock reflections. This allows construction of a digital elevation model (DEM) of the bedrock in the area, further constrained by two borehole measurements at the cauldron centre. It also allows creation of lake thickness maps and an estimate of lake volume at the time of each survey, which we compare with lowering patterns and released water volumes obtained from surface DEMs obtained before and after jökulhlaups. The estimated lake volume is 250 × 106 m3 in June 2015 but 320 ± 20 × 106 m3 drained from the cauldron in October 2015. In June 2018, RES profiles reveal a lake volume of 185 × 106 m3 while 220 ± 30 × 106 m3 was released in a jökulhlaup in August 2018. Considering the water accumulation over the periods between RES surveys and jökulhlaups, this indicates 10–20 % uncertainty in the RES-derived volumes at times when significant jökulhlaups may be expected.

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