scholarly journals The ice thickness distribution of a debris-covered glacier: Tasman Glacier, New Zealand

2021 ◽  
Author(s):  
◽  
Rory Hart
Keyword(s):  
Mass Flux ◽  
Dynamic Models ◽  
Thickness Distribution ◽  
Geophysical Methods ◽  
Three Dimensional ◽  
Gravity Models ◽  
Ice Thickness ◽  
Model Studies ◽  
Flux Model ◽  
Thickness Measurements

<p>The ice thickness distribution of mountain valley glaciers is an important physical constraint for modelling their flow. Ice thickness measurements are used to calculate the geometry and ultimately the driving stress of a glacier. This information is all required if realistic models are to forecast the response of glaciers to climate forcings. For New Zealand's Tasman Glacier, two factors complicate its response to climate: 1) A layer of insulative rocky debris covers the lower half of the glacier, retarding surface melt, and 2) the glacier has recently entered a period of iceberg calving into a proglacial lake, introducing complex mechanical processes. These complications, along with the uncertainty of the current bed topography of the Tasman Glacier, make future predictions of its retreat behaviour difficult. The bed of the Tasman Glacier has not been fully imaged but ice thickness measurements obtained through seismic and gravity surveys have provided constraints for parts of the glacier. This study applies a range of geophysical methods (gravity and refraction seismics) to measure and model the ice thickness distribution of the lower Tasman Glacier. We surveyed orthogonal to glacier flow to obtain 12 transects within the lower 5 km of the glacier. Two-dimensional and three-dimensional gravity models generally indicate a U-shaped valley with ice thicknesses of 92-722 m from the present day terminus to the most upstream transect respectively. These results were used as input data to a simple mass flux model to assess its performance in estimating ice thickness and volume for the Tasman Glacier. The mass-flux model estimated a volume of 14.96 km3 for the Tasman Glacier, but generally underestimated ice thickness with an RMSE of 148 m between the modelled and the gravity-derived ice thickness. This discrepancy could be reduced by constraining ice thickness for a larger area of the glacier and providing a more recent DEM to the mass flux model. Studies such as this highlight the importance of constraining ice thickness in order to improve glacio-dynamic models and global volume estimates.</p>

scholarly journals The ice thickness distribution of a debris-covered glacier: Tasman Glacier, New Zealand

2021 ◽  
Author(s):  
◽  
Rory Hart
Keyword(s):  
Mass Flux ◽  
Dynamic Models ◽  
Thickness Distribution ◽  
Geophysical Methods ◽  
Three Dimensional ◽  
Gravity Models ◽  
Ice Thickness ◽  
Model Studies ◽  
Flux Model ◽  
Thickness Measurements

<p>The ice thickness distribution of mountain valley glaciers is an important physical constraint for modelling their flow. Ice thickness measurements are used to calculate the geometry and ultimately the driving stress of a glacier. This information is all required if realistic models are to forecast the response of glaciers to climate forcings. For New Zealand's Tasman Glacier, two factors complicate its response to climate: 1) A layer of insulative rocky debris covers the lower half of the glacier, retarding surface melt, and 2) the glacier has recently entered a period of iceberg calving into a proglacial lake, introducing complex mechanical processes. These complications, along with the uncertainty of the current bed topography of the Tasman Glacier, make future predictions of its retreat behaviour difficult. The bed of the Tasman Glacier has not been fully imaged but ice thickness measurements obtained through seismic and gravity surveys have provided constraints for parts of the glacier. This study applies a range of geophysical methods (gravity and refraction seismics) to measure and model the ice thickness distribution of the lower Tasman Glacier. We surveyed orthogonal to glacier flow to obtain 12 transects within the lower 5 km of the glacier. Two-dimensional and three-dimensional gravity models generally indicate a U-shaped valley with ice thicknesses of 92-722 m from the present day terminus to the most upstream transect respectively. These results were used as input data to a simple mass flux model to assess its performance in estimating ice thickness and volume for the Tasman Glacier. The mass-flux model estimated a volume of 14.96 km3 for the Tasman Glacier, but generally underestimated ice thickness with an RMSE of 148 m between the modelled and the gravity-derived ice thickness. This discrepancy could be reduced by constraining ice thickness for a larger area of the glacier and providing a more recent DEM to the mass flux model. Studies such as this highlight the importance of constraining ice thickness in order to improve glacio-dynamic models and global volume estimates.</p>

scholarly journals Measuring and inferring the ice thickness distribution of four glaciers in the Tien Shan, Kyrgyzstan

2020 ◽  
pp. 1-18
Author(s):  
Lander Van Tricht ◽  
Philippe Huybrechts ◽  
Jonas Van Breedam ◽  
Johannes J. Fürst ◽  
Oleg Rybak ◽  
...  
Keyword(s):  
Cross Validation ◽  
Thickness Distribution ◽  
Tien Shan ◽  
Ice Thickness ◽  
Ice Volume ◽  
In Situ Data ◽  
Radio Echo Sounding ◽  
Thickness Measurements ◽  
Tien Shan Mountains

Abstract Glaciers in the Tien Shan mountains contribute considerably to the fresh water used for irrigation, households and energy supply in the dry lowland areas of Kyrgyzstan and its neighbouring countries. To date, reconstructions of the current ice volume and ice thickness distribution remain scarce, and accurate data are largely lacking at the local scale. Here, we present a detailed ice thickness distribution of Ashu-Tor, Bordu, Golubin and Kara-Batkak glaciers derived from radio-echo sounding measurements and modelling. All the ice thickness measurements are used to calibrate three individual models to estimate the ice thickness in inaccessible areas. A cross-validation between modelled and measured ice thickness for a subset of the data is performed to attribute a weight to every model and to assemble a final composite ice thickness distribution for every glacier. Results reveal the thickest ice on Ashu-Tor glacier with values up to 201 ± 12 m. The ice thickness measurements and distributions are also compared with estimates composed without the use of in situ data. These estimates approach the total ice volume well, but local ice thicknesses vary substantially.

Ice thickness, volume and subglacial relief of Ashuu-Tor, Bordu, Kara-Batkak and Golubina glaciers (Central-Asia) derived from GPR measurements and different approaching methods

2020 ◽  
Author(s):  
Lander Van Tricht ◽  
Philippe Huybrechts ◽  
Jonas Van Breedam ◽  
Johannes Fuerst ◽  
Oleg Rybak ◽  
...  
Keyword(s):  
Central Asia ◽  
Thickness Distribution ◽  
Mass Conservation ◽  
Tien Shan ◽  
Ice Age ◽  
Ice Thickness ◽  
Mountain Range ◽  
Lake Formation ◽  
Ground Penetrating ◽  
Thickness Measurements

&lt;p&gt;Glaciers in the Tien Shan (Central-Asia) mountains contribute a considerable part of the freshwater used for irrigation and households in the dry lowland areas of Kyrgyzstan and its neighbouring countries. Since the Little Ice Age, the total ice mass in this mountain range has been decreasing significantly. However, accurate measurements of the current ice volume and ice thickness distribution in the Tien Shan remain scarce, and accurate data is largely lacking at the local scale. In 2016, 2017 and 2019, we organized 1-month field campaigns in Central-Asia to sound the ice thickness of four different glaciers in the Tien Shan using a Narod ground penetrating radar (GPR) system.&lt;/p&gt;&lt;p&gt;Here, we present and discuss our in-situ ice thickness measurements of the four glaciers. We performed in total more than 1000 GPR soundings. We found a maximum ice thickness of 200 meters in the central part of the southern facing Ashuu-Tor glacier. On both Bordu and Golubina, we measured ice thicknesses up to 140 meters. Kara-Batkak was found to have the thinnest ice which is in agreement to the large average slope of this glacier. We extended all the ice thickness measurements to the entire glacier surfaces using three different methods based on the assumption of plastic flow (method 1) and the principle of mass conservation (method 2 &amp; 3) and assessed their differences.&lt;/p&gt;&lt;p&gt;In this research, we show a detailed ice thickness distribution of Ashuu-Tor, Bordu, Golubina and Kara-Batkak glaciers. This can be used for glaciological modelling and assessing ice and water storage. We also point out the locations of potential lake formation in bedrock overdeepenings as a succession of glacier retreat.&lt;/p&gt;

scholarly journals Ice thickness measurements and volume estimates for glaciers in Norway

2015 ◽  
Vol 61 (228) ◽  
pp. 763-775 ◽  
Author(s):  
L.M. Andreassen ◽  
M. Huss ◽  
K. Melvold ◽  
H. Elvehøy ◽  
S.H. Winsvold
Keyword(s):  
Water Resource Management ◽  
Thickness Distribution ◽  
Distributed Model ◽  
Ice Thickness ◽  
Ice Caps ◽  
Glacier Changes ◽  
Physically Based ◽  
Detailed Assessment ◽  
Volume Estimates ◽  
Thickness Measurements

AbstractGlacier volume and ice thickness distribution are important variables for water resource management in Norway and the assessment of future glacier changes. We present a detailed assessment of thickness distribution and total glacier volume for mainland Norway based on data and modelling. Glacier outlines from a Landsat-derived inventory from 1999 to 2006 covering an area of 2692 ± 81 km2 were used as input. We compiled a rich set of ice thickness observations collected over the past 30 years. Altogether, interpolated ice thickness measurements were available for 870 km2 (32%) of the current glacier area of Norway, with a total ice volume of 134 ± 23 km3. Results indicate that mean ice thickness is similar for all larger ice caps, and weakly correlates with their total area. Ice thickness data were used to calibrate a physically based distributed model for estimating the ice thickness of unmeasured glaciers. The results were also used to calibrate volume–area scaling relations. The calibrated total volume estimates for all Norwegian glaciers ranged from 257 to 300 km3.

scholarly journals Ice volume estimates for the Himalaya–Karakoram region: evaluating different methods

2013 ◽  
Vol 7 (5) ◽  
pp. 4813-4854 ◽  
Author(s):  
H. Frey ◽  
H. Machguth ◽  
M. Huss ◽  
C. Huggel ◽  
S. Bajracharya ◽  
...  
Keyword(s):  
Thickness Distribution ◽  
Critical Evaluation ◽  
Estimation Method ◽  
Ice Thickness ◽  
Distribution Models ◽  
Glacier Inventory ◽  
Ice Volume ◽  
Sensitivity Assessment ◽  
Volume Estimates ◽  
Thickness Measurements

Abstract. Ice volume estimates are crucial for assessing water reserves stored in glaciers. A variety of different methodologies exist but there is a lack of systematic comparative analysis thereof. Due to its large glacier coverage, such estimates are of particular interest for the Himalayan-Karakoram (HK) region. Here, three volume–area (V–A) relations, a slope-dependent estimation method, and two ice-thickness distribution models are applied to a complete glacier inventory of the HK region. An uncertainty and sensitivity assessment is performed to investigate the influence of the input glacier areas, and model approaches and parameters on the resulting total ice volumes. Results of the two ice-thickness distribution models are validated with local ice-thickness measurements at six glaciers. The resulting ice volumes for the entire HK region range from 2955 km3 to 6455 km3, depending on the approach. Results from the ice thickness distribution models and the slope-dependent thickness estimations agree well with measured local ice thicknesses while V–A relations show stronger deviations. The study provides evidence on the significant effect of the selected method on results and underlines the importance of a careful and critical evaluation. More ice-thickness measurements are needed to improve models and results in the future.

scholarly journals The feasibility of imaging subglacial hydrology beneath ice streams with ground-based electromagnetics

2017 ◽  
Vol 63 (241) ◽  
pp. 755-771 ◽  
Author(s):  
KERRY KEY ◽  
MATTHEW R. SIEGFRIED
Keyword(s):  
Geophysical Methods ◽  
Ice Sheet ◽  
Geological Structure ◽  
Ice Thickness ◽  
Ice Streams ◽  
Water Conductivity ◽  
Model Studies ◽  
Seismic Surveying ◽  
Ice Sheet Dynamics ◽  
Ground Penetrating

ABSTRACTSubglacial hydrologic systems in Antarctica and Greenland play a fundamental role in ice-sheet dynamics, yet critical aspects of these systems remain poorly understood due to a lack of observations. Ground-based electromagnetic (EM) geophysical methods are established for mapping groundwater in many environments, but have never been applied to imaging lakes beneath ice sheets. Here, we study the feasibility of passive- and active-source EM imaging for quantifying the nature of subglacial water systems beneath ice streams, with an emphasis on the interfaces between ice and basal meltwater, as well as deeper groundwater in the underlying sediments. We describe a suite of model studies that exam the data sensitivity as a function of ice thickness, water conductivity and hydrologic system geometry for models representative of a subglacial lake and a grounding zone estuary. We show that EM data are directly sensitive to groundwater and can image its lateral and depth extent. By combining the conductivity obtained from EM data with ice thickness and geological structure from conventional geophysical techniques, such as ground-penetrating radar and active seismic surveying, EM data have the potential to provide new insights on the interaction between ice, rock and water at critical ice-sheet boundaries.

scholarly journals Ice volume distribution and implications on runoff projections in a glacierized catchment

2012 ◽  
Vol 9 (6) ◽  
pp. 7507-7541 ◽  
Author(s):  
J. Gabbi ◽  
D. Farinotti ◽  
A. Bauder ◽  
H. Maurer
Keyword(s):  
Thickness Distribution ◽  
Regional Climate ◽  
Accurate Determination ◽  
Annual Runoff ◽  
Ice Thickness ◽  
Volume Distribution ◽  
Ice Volume ◽  
Runoff Decrease ◽  
Ground Penetrating ◽  
Thickness Measurements

Abstract. A dense network of helicopter-based ground penetrating radar (GPR) measurements was used to determine the ice-thickness distribution in the Mauvoisin region. The comprehensive set of ice-thickness measurements was combined with an ice-thickness estimation approach for an accurate determination of the bedrock. A total ice volume of 3.69 ± 0.11 km3 and a maximum ice-thickness of 290 m were found. The ice-thickness values were then employed as input for a combined glacio-hydrological model forced by most recent regional climate scenarios. This model provided glacier evolution and runoff projections. Runoff projections of the measured initial ice volume distribution show an increase in annual runoff of 4% in the next two decades, followed by a persistent runoff decrease until 2100. Finally, we checked the influence of the ice thickness distribution on runoff projections. Our analyses revealed that reliable estimates of the ice volume is essential. Wrong estimations of the total ice volume might even lead to deviations of the predicted general runoff trend.

scholarly journals The bedrock topography of Starbuck Glacier, Antarctic Peninsula, as determined by radio-echo soundings and flow modeling

2014 ◽  
Vol 55 (67) ◽  
pp. 22-28 ◽  
Author(s):  
Daniel Farinotti ◽  
Edward C. King ◽  
Anika Albrecht ◽  
Matthias Huss ◽  
G. Hilmar Gudmundsson
Keyword(s):  
Antarctic Peninsula ◽  
Thickness Distribution ◽  
Flow Speed ◽  
Ice Thickness ◽  
Ice Flow ◽  
Bedrock Topography ◽  
Radio Echo Sounding ◽  
Field Season ◽  
Thickness Measurements

AbstractA glacier-wide ice-thickness distribution and bedrock topography is presented for Starbuck Glacier, Antarctic Peninsula. The results are based on 90 km of ground-based radio-echo sounding lines collected during the 2012/13 field season. Cross-validation with ice-thickness measurements provided by NASA's IceBridge project reveals excellent agreement. Glacier-wide estimates are derived using a model that calculates distributed ice thickness, calibrated with the radio-echo soundings. Additional constraints are obtained from in situ ice flow-speed measurements and the surface topography. The results indicate a reverse-sloped bed extending from a riegel occurring ~ 5 km upstream of the current grounding line. The deepest parts of the glacier are as much as 500 m below sea level. The calculated total volume of 80.7 ± 7.2 km3 corresponds to an average ice thickness of 312 ± 30 m.

scholarly journals Ice volume distribution and implications on runoff projections in a glacierized catchment

2012 ◽  
Vol 16 (12) ◽  
pp. 4543-4556 ◽  
Author(s):  
J. Gabbi ◽  
D. Farinotti ◽  
A. Bauder ◽  
H. Maurer
Keyword(s):  
Thickness Distribution ◽  
Regional Climate ◽  
Accurate Determination ◽  
Annual Runoff ◽  
Ice Thickness ◽  
Volume Distribution ◽  
Ice Volume ◽  
Runoff Decrease ◽  
Ground Penetrating ◽  
Thickness Measurements

Abstract. A dense network of helicopter-based ground-penetrating radar (GPR) measurements was used to determine the ice-thickness distribution in the Mauvoisin region. The comprehensive set of ice-thickness measurements was combined with an ice-thickness estimation approach for an accurate determination of the bedrock. A total ice volume of 3.69 ± 0.31 km3 and a maximum ice thickness of 290 m were found. The ice-thickness values were then employed as input for a combined glacio-hydrological model forced by most recent regional climate scenarios. This model provided glacier evolution and runoff projections for the period 2010–2100. Runoff projections of the measured initial ice volume distribution show an increase in annual runoff of 4% in the next two decades, followed by a persistent runoff decrease until 2100. Finally, we checked the influence of the ice-thickness distribution on runoff projections. Our analyses revealed that reliable estimates of the ice volume are essential for modelling future glacier and runoff evolution. Wrong estimations of the total ice volume might even lead to deviations of the predicted general runoff trend.

Where shall we measure? Results from the second phase of the Ice Thickness Models Intercomparison eXperiment (ITMIX2)

2021 ◽  
Author(s):  
Daniel Farinotti ◽  
Keyword(s):  
Numerical Models ◽  
Thickness Distribution ◽  
Data Availability ◽  
Ice Thickness ◽  
Test Case ◽  
Second Phase ◽  
Ice Caps ◽  
Direct Measurements ◽  
Thickness Measurements ◽  
Weak Influence

&lt;p&gt;Knowing the ice thickness distribution of glaciers and ice caps is of critical importance for a number of studies. However, since measuring ice thickness directly is difficult and time consuming, the availability of such information is generally scarce. Here, we present results from the Second Phase of the Ice Thickness Models Intercomparison eXperiment (ITMIX2) which had a two-fold objective. First, it aimed at characterizing the capability of numerical models to use sparse thickness measurements to their advantage. Second, it aimed at identifying possible strategies for maximizing the information content gained through direct ice thickness surveys.&lt;/p&gt;&lt;p&gt;The experiment was designed around 23 test cases including both real-world and synthetic glaciers, and comprised a set of 16 different experiments per test case simulating different scenarios of data availability. Based on a total of 2,544 individual solutions submitted by 13 different models, our results show that for locations without direct measurements, the ice thickness can be predicted with typical deviations in the order of 16% of the mean ice thickness. Despite large scatter, even limited sets of ice thickness observations are found to be effective in constraining the glacier total volume, particularly when the thickest part of a glacier is surveyed. Other spatial distributions of the ice thickness observations have only a weak influence on the predicted thickness, although surveys restricted to the lowest glacier elevations often result in an underestimation of the glacier&amp;#8217;s total volume. The response to the various scenarios of data availability is found to be specific to individual models, and while no single best approach emerges, an ensemble-approach based on a combination of models is shown to be beneficial in terms of accuracy and robustness.&lt;/p&gt;

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