scholarly journals Geophysical constraints on the properties of a subglacial lake in northwest Greenland

2021 ◽  
Vol 15 (7) ◽  
pp. 3279-3291
Author(s):  
Ross Maguire ◽  
Nicholas Schmerr ◽  
Erin Pettit ◽  
Kiya Riverman ◽  
Christyna Gardner ◽  
...  
Keyword(s):  
Glacial Ice ◽  
Bed Topography ◽  
Subglacial Lake ◽  
Impedance Contrast ◽  
Lake Formation ◽  
Lake Bottom ◽  
Lake Bottom Sediments ◽  
A Site ◽  
Ground Penetrating

Abstract. In this study, we report the results of an active-source seismology and ground-penetrating radar survey performed in northwestern Greenland at a site where the presence of a subglacial lake beneath the accumulation area has previously been proposed. Both seismic and radar results show a flat reflector approximately 830–845 m below the surface, with a seismic reflection coefficient of −0.43 ± 0.17, which is consistent with the acoustic impedance contrast between a layer of water and glacial ice. Additionally, in the seismic data we observe an intermittent lake bottom reflection arriving between 14–20 ms after the lake top reflection, corresponding to a lake depth of approximately 10–15 m. A strong coda following the lake top and lake bottom reflections is consistent with a package of lake bottom sediments although its thickness and material properties are uncertain. Finally, we use these results to conduct a first-order assessment of the lake origins using a one-dimensional thermal model and hydropotential modeling based on published surface and bed topography. Using these analyses, we narrow the lake origin hypotheses to either anomalously high geothermal flux or hypersalinity due to local ancient evaporite. Because the origins are still unclear, this site provides an intriguing opportunity for the first in situ sampling of a subglacial lake in Greenland, which could better constrain mechanisms of subglacial lake formation, evolution, and relative importance to glacial hydrology.

scholarly journals A multi-level strategy for anticipating future glacier lake formation and associated hazard potentials

2010 ◽  
Vol 10 (2) ◽  
pp. 339-352 ◽  
Author(s):  
H. Frey ◽  
W. Haeberli ◽  
A. Linsbauer ◽  
C. Huggel ◽  
F. Paul
Keyword(s):  
Swiss Alps ◽  
Bed Topography ◽  
Aster Gdem ◽  
Digital Elevation ◽  
Lake Formation ◽  
Level 3 ◽  
Multi Level ◽  
Four Levels ◽  
Elevation Model

Abstract. In the course of glacier retreat, new glacier lakes can develop. As such lakes can be a source of natural hazards, strategies for predicting future glacier lake formation are important for an early planning of safety measures. In this article, a multi-level strategy for the identification of overdeepened parts of the glacier beds and, hence, sites with potential future lake formation, is presented. At the first two of the four levels of this strategy, glacier bed overdeepenings are estimated qualitatively and over large regions based on a digital elevation model (DEM) and digital glacier outlines. On level 3, more detailed and laborious models are applied for modeling the glacier bed topography over smaller regions; and on level 4, special situations must be investigated in-situ with detailed measurements such as geophysical soundings. The approaches of the strategy are validated using historical data from Trift Glacier, where a lake formed over the past decade. Scenarios of future glacier lakes are shown for the two test regions Aletsch and Bernina in the Swiss Alps. In the Bernina region, potential future lake outbursts are modeled, using a GIS-based hydrological flow routing model. As shown by a corresponding test, the ASTER GDEM and the SRTM DEM are both suitable to be used within the proposed strategy. Application of this strategy in other mountain regions of the world is therefore possible as well.

scholarly journals Geophysical constraints on the properties of a subglacial lake in northwest Greenland

2020 ◽  
Author(s):  
Ross Maguire ◽  
Nicholas Schmerr ◽  
Erin Pettit ◽  
Kiya Riverman ◽  
Christyna Gardner ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
High Salinity ◽  
Radar Data ◽  
Airborne Radar ◽  
Field Site ◽  
Subglacial Lake ◽  
Lake Bottom ◽  
Lateral Extent ◽  
Ground Penetrating ◽  
Geothermal Flux

Abstract. We report the first ground-based observations of a subglacial lake in Greenland, confirming previous work base on airborne radar data. Here, we perform an active source seismology and ground penetrating radar survey in northwest Greenland where Palmer et al. (2013) first proposed the presence of a subglacial lake. From reflections of both the lake top and lake bottom, we observe a subglacial lake underlying approximately 845 m of ice, and constrain its depth to be between 10–15 m. Additionally, using previously reported estimates of the lake's lateral extent, we estimate the total volume of liquid water to be 0.15 km3 (0.15 Gt of water). Thermal and hydropotential modeling both suggest that the lake should not exist unless it either sits over a localized geothermal flux high or has high salinity due to significant evaporite source in the bedrock. Our study indicates that this field site in northwestern Greenland is a good candidate for future investigations aimed at understanding lake properties and origins or for direct lake sampling via drilling.

Assessment of glacier lakes development in Central Caucasus

2020 ◽  
Author(s):  
Ivan Lavrentiev ◽  
Dmitry Petrakov ◽  
Stanislav Kutuzov ◽  
Andrey Smirnov
Keyword(s):  
Growth Potential ◽  
Ice Thickness ◽  
Topographic Map ◽  
Model Errors ◽  
Bed Topography ◽  
Subglacial Lake ◽  
Flow Formation ◽  
Lake Formation ◽  
Central Caucasus ◽  
Rfbr Grant

<p>Glacier mass loss and consequent termini retreat lead to formation and growth of glacier lakes. In the Mt. Elbrus region, outbursts of lakes formed in recent decades have led to human casualties and significant damage. Building codes of Russian Federation on engineering surveys do not regulate the possibility of glacier lake formation in front of retreating glaciers, which can lead to errors in the future engineering design. Using ground based and airborne GPR data, as well as global ice thickness models, we have identified areas of potential lake formation on glacier bed for a number of glaciers in the Mt. Elbrus region. The method was tested by retrospective modeling for Bolshoy Azau and Djikiugankez glaciers bed topography on the base of 1957 topographic map. In the areas where glaciers disappeared by 2017, out of 13 simulated closed bed depressions 7 existing lakes were predicted by the hydraulic potential. 6 closed depressions on Djikiugankez glacier bed as of 1957 are currently absent, which might be related to the model uncertainties and the original DEMs errors, as well as to possible filling of lakes by sediments. Retrospective modeling of the Bashkara glacier bed topography based on SRTM DEM (2000) showed significant growth potential of the lake Lapa. Retrospective modeling of the Kaayarty glacier bed topography has not provided a clear answer about the possibility if subglacial lake outburst flood was a trigger for catastrophic debris flow formation during the summer of 2000.</p><p>In case of total disappearance of Bolshoy Azau, Djikiugankez and Bashkara glaciers at least 11 new lakes with total area of about 1.7 km<sup>2</sup> and an average depth of 8 m will form. While the deepest lake will appear in ablation zone of Bolshoy Azau glacier (at elevation 3100-3400 m a.s.l.) the largest in area (1 km<sup>2</sup>) glacial lake will be formed at the Djikiugankez snout with maximum depth of 40 m and mean depth of 7.2 m. The simulation also showed that in the present conditions, glacier bed lakes of different number and size may also exist under studied glaciers. Our estimates may contain uncertainties due to low resolution of airborne GPR data and the lack of GPR data for Kaayarty glacier, DEM and ice thickness model errors. Detailed ground-based radar survey planned for the summer 2020 will enable the assessment of the size and volume of the potential lakes under Bolshoy Azau glacier.</p><p>This work was funded by RFBR grant No. 18-05-00520.</p>

scholarly journals Ice thickness distribution of all Swiss glaciers based on extended ground-penetrating radar data and glaciological modeling

2021 ◽  
pp. 1-19
Author(s):  
Melchior Grab ◽  
Enrico Mattea ◽  
Andreas Bauder ◽  
Matthias Huss ◽  
Lasse Rabenstein ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Thickness Distribution ◽  
Radar Data ◽  
Tourism Industry ◽  
Swiss Alps ◽  
Ice Thickness ◽  
Hazard Management ◽  
Bed Topography ◽  
Ice Volume ◽  
Ground Penetrating

Abstract Accurate knowledge of the ice thickness distribution and glacier bed topography is essential for predicting dynamic glacier changes and the future developments of downstream hydrology, which are impacting the energy sector, tourism industry and natural hazard management. Using AIR-ETH, a new helicopter-borne ground-penetrating radar (GPR) platform, we measured the ice thickness of all large and most medium-sized glaciers in the Swiss Alps during the years 2016–20. Most of these had either never or only partially been surveyed before. With this new dataset, 251 glaciers – making up 81% of the glacierized area – are now covered by GPR surveys. For obtaining a comprehensive estimate of the overall glacier ice volume, ice thickness distribution and glacier bed topography, we combined this large amount of data with two independent modeling algorithms. This resulted in new maps of the glacier bed topography with unprecedented accuracy. The total glacier volume in the Swiss Alps was determined to be 58.7 ± 2.5 km3 in the year 2016. By projecting these results based on mass-balance data, we estimated a total ice volume of 52.9 ± 2.7 km3 for the year 2020. Data and modeling results are accessible in the form of the SwissGlacierThickness-R2020 data package.

scholarly journals Development of Fragility Curves for Piping and Slope Stability of River Levees

Water ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 738
Author(s):  
Nicola Rossi ◽  
Mario Bačić ◽  
Meho Saša Kovačević ◽  
Lovorka Librić
Keyword(s):  
Slope Stability ◽  
Fragility Curves ◽  
Safety Margin ◽  
Water Levels ◽  
Flood Event ◽  
Soil Parameters ◽  
Design Code ◽  
A Site ◽  
Insight Into

The design code Eurocode 7 relies on semi-probabilistic calculation procedures, through utilization of the soil parameters obtained by in situ and laboratory tests, or by the means of transformation models. To reach a prescribed safety margin, the inherent soil parameter variability is accounted for through the application of partial factors to either soil parameters directly or to the resistance. However, considering several sources of geotechnical uncertainty, including the inherent soil variability, measurement error and transformation uncertainty, full probabilistic analyses should be implemented to directly consider the site-specific variability. This paper presents the procedure of developing fragility curves for levee slope stability and piping as failure mechanisms that lead to larger breaches, where a direct influence of the flood event intensity on the probability of failure is calculated. A range of fragility curve sets is presented, considering the variability of levee material properties and varying durations of the flood event, thus providing crucial insight into the vulnerability of the levee exposed to rising water levels. The procedure is applied to the River Drava levee, a site which has shown a continuous trend of increased water levels in recent years.

scholarly journals Identifying Spatial and Temporal Variations in Concrete Bridges with Ground Penetrating Radar Attributes

2021 ◽  
Vol 13 (9) ◽  
pp. 1846
Author(s):  
Vivek Kumar ◽  
Isabel M. Morris ◽  
Santiago A. Lopez ◽  
Branko Glisic
Keyword(s):  
Compressive Strength ◽  
Ground Penetrating Radar ◽  
Material Properties ◽  
Temporal Variations ◽  
Concrete Bridges ◽  
Spatial And Temporal Variation ◽  
Reflected Waves ◽  
Ground Penetrating ◽  
Over Time

Estimating variations in material properties over space and time is essential for the purposes of structural health monitoring (SHM), mandated inspection, and insurance of civil infrastructure. Properties such as compressive strength evolve over time and are reflective of the overall condition of the aging infrastructure. Concrete structures pose an additional challenge due to the inherent spatial variability of material properties over large length scales. In recent years, nondestructive approaches such as rebound hammer and ultrasonic velocity have been used to determine the in situ material properties of concrete with a focus on the compressive strength. However, these methods require personnel expertise, careful data collection, and high investment. This paper presents a novel approach using ground penetrating radar (GPR) to estimate the variability of in situ material properties over time and space for assessment of concrete bridges. The results show that attributes (or features) of the GPR data such as raw average amplitudes can be used to identify differences in compressive strength across the deck of a concrete bridge. Attributes such as instantaneous amplitudes and intensity of reflected waves are useful in predicting the material properties such as compressive strength, porosity, and density. For compressive strength, one alternative approach of the Maturity Index (MI) was used to estimate the present values and compare with GPR estimated values. The results show that GPR attributes could be successfully used for identifying spatial and temporal variation of concrete properties. Finally, discussions are presented regarding their suitability and limitations for field applications.

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