Glacier Thickness Research Articles

Bias-corrected estimates of glacier thickness in the Columbia River Basin, Canada

AbstractSeveral global datasets of glacier thickness exist, but the number of observations from western Canada are sparse and spatially biased. To supplement these limited observations, we measured ice thickness with ice penetrating radar on five glaciers in the Columbia Mountains, Canada. Our radar surveys, when combined with previous surveys for two glaciers in the Rocky Mountains, total 182 km of transects that represent 34 672 point measurements of ice thickness. Our measurements are, on average, 38% thicker than previous surface inversion model estimates of glacier thickness. Using our measurements within a cross-validation scheme, we model ice thickness with the Open Global Glacier Model (OGGM) driven with recent observations of surface mass balance and glacier elevation. We calibrated OGGM ice thickness by optimizing the ice creep parameter in the model. The optimized OGGM yields an ice volume for Columbia Basin of 122.5 ± 22.4 km3for the year 2000, which is 23% greater than the range of previous estimates. At current rates of glacier mass loss for this region, glaciers would disappear from the basin in about 65–80 years. Disappearance of these glaciers will negatively affect the basin's surface hydrology, freshwater availability and aquatic ecosystems.

The satellite observed glacier mass changes over the Upper Indus Basin during 2000\u20132012

Decadal glacier thickness changes over the Upper Indus Basin in the Jammu and Kashmir Himalaya were estimated using the TanDEM-X and SRTM-C Digital Elevation Models (DEMs) from 2000 to 2012. In the study area 12,243 glaciers having 19,727 ± 1,054 km2 area have thinned on an average of − 0.35 ± 0.33 m a−1 during the observation period. The highest thinning of − 1.69 ± 0.60 m a−1 was observed in the Pir Panjal while as the marginal thinning of − 0.11 ± 0.32 m a−1 was observed for the glaciers in the Karakoram. The observed glacier thickness changes indicated a strong influence of the topographic parameters. Higher thickness reduction was observed on the glaciers situated at lower altitudes (− 1.40 ± 0.53 m a−1) and with shallower slopes (− 1.52 ± 0.40 m a−1). Significantly higher negative thickness changes were observed from the glaciers situated on the southern slopes (− 0.55 ± 0.37 m a−1). The thickness loss was higher on the debris-covered glaciers (− 0.50 ± 0.38 m a−1) than on the clean glaciers (− 0.32 ± 0.33 m a−1). The cumulative glacier mass loss of − 70.32 ± 66.69 Gt was observed during the observation period, which, if continued, would significantly affect the sustainability of water resources in the basin.

Glacial geomorphology and recent glacial recession of the Harmukh Range, NW Himalaya

A comprehensive description of the glaciation and glacial geomorphology of the Harmukh range, northwest Himalaya is reported first time in this study. The geomorphic system of the range is dominated by glaciation and provides an excellent opportunity to assess the glacial fluctuations from the Late Quaternary to the present. Using a time series of the satellite data from 1992 to 2018, the glacier area, snout and equilibrium line altitude (ELA) changes of the existing glaciers in the Harmukh Range were estimated. The glacier cover has receded from 7.47 ± 0.58 km2 in 1992 to 6.24 ± 0.62 km2 in 2018, a deglaciation of 16.46 ± 0.24%. The glaciers showed an upward shift in ELA from 47 m to 80 m during the last two and a half decade. The observations revealed that, other than the climatic factors, the ELA change and glacier recessions are influenced by the glacier size, mean altitude, and the aspect of the glaciers. Further, the high-resolution Google Earth images, supplemented by field observations, were used for mapping various glacial-geomorphic landforms. The nature of glacial grooves, overdeepenings, the height of the lateral moraine deposits and trimlines indicated appreciable thickness of the former glaciers. The pattern of the glaciated valleys revealed that the area has predominantly experienced alpine type of glaciation with most of the glaciers centred on the Harmukh peak. Based on the shape and the number of lateral moraine ridges present, it is suggested that the area has witnessed three major glacial advances. By tracing the outer limits of the glacial valleys, moraine boulders, and ice scoured terrain, it was estimated that the glaciers in the range covered 629 km2 during the glacial maxima. The presence of numerous rock glaciers and debris-free cirque glaciers on the north-eastern slopes of the range indicated a strong climatic and topographical control on the pattern, situation and extent of glaciers. However, there is a need for detailed field-based mapping of the glacial-geomorphology and geochronological study in order to better understand the nature and extent of paleo-glaciation, the observed glacier recession and the past climatic variations in this hitherto understudied glaciated region of the Kashmir Himalaya.

Area and Mass Changes of Glaciers in the West Kunlun Mountains Based on the Analysis of Multi-Temporal Remote Sensing Images and DEMs from 1970 to 2018

Most of the world’s glaciers have retreated significantly against the background of recent climate warming, while reports have indicated that the glaciers in the West Kunlun Mountains (WKL) may be in a relatively stable state, although there are some gaps in previous research. Based on Landsat series data, topographic maps, SRTM and TanDEM-x data, this paper extracts detailed glacial area information and glacial mass balance during different time periods from 1970 to 2018. We found that, the total area of glaciers in the WKL decreased by 8.0 km2 from 1972 to 2018. The area decreased by 12.0 km2 from 1972 to 1991 and increased by 4.7 km2 from 2010 to 2018. Glacier surface elevation change results in the WKL showed that the overall glacier thickness slightly decreased from 1970 to 2016, with an average of 1.9 ± 1.0 m. The glaciers thinned by approximately 2.5 ± 1.0 m from 1970 to 2000, while from 2000 to 2016, the glaciers thickened approximately by 0.6 ± 1.0 m. Overall, the glaciers in the WKL showed very slight retreat. In addition, the mass changes of glaciers were affected by glacial surging.

Modeling ice thickness distribution and storage volume of glaciers in Chandra Basin, western Himalayas

This article reports modeled ice thickness distribution and total ice volume of the 65 selected glaciers (>0.5 km2) of Chandra basin, located in the Western Himalayas. This is a first-of-its-kind study that gives detailed insights about the current ice thickness distribution at an individual glacier level in the Western Himalayas. The estimates are obtained using an optimally parameterized GlabTop2_IITB [Glacier Bed Topography Indian Institute of Technology Bombay (IITB) version] model with highresolution Digital Elevation Model (DEM) as an input. The total estimated volume of all the 65 selected glaciers is about 55.32 km3 covering a total area of about 591.03 km2. Using hypsometric analysis, it is found that the maximum amount of ice volume, i.e., about 12.79 km3 is currently residing at the elevation range of 5200–5400 m a.s.l. Ice thickness estimates obtained in the current study are compared with the ensemble estimates obtained in the Global Glacier Thickness Initiative (G2TI) project for three large glaciers, namely, Bada Shigri, Samudra Tapu, and Gepang Gath glaciers. The obtained results indicate that the difference between both the studies is marginal in terms of mean ice thickness and maximum ice thickness estimates except Samudra Tapu glacier. Moreover, the uncertainty of the estimated glacier ice volume from this study is about ±15% whereas, from the G2TI project, it is about 25%. The main reasons for the difference could be the quality of the inputs used, model structure, model parameterization as well as the time stamp of the input used. The obtained results from this study indicate that the use of appropriate shape factor and better DEM would result in more reliable glacier ice thickness estimates even by using a simple slope-dependent model like GlabTop2_IITB.

The Surge of the Hispar Glacier, Central Karakoram: SAR 3‐D Flow Velocity Time Series and Thickness Changes

AbstractThe Hispar Glacier is a useful site for studying surge mechanisms. Prior to this study, only two‐dimensional (2‐D) flow velocities having low temporal resolution were available for this glacier, providing inadequate information about its surge evolution. In this study, 139 synthetic aperture radar (SAR) images from Sentinel‐1A were used to obtain 3‐D flow velocity time series for the Hispar Glacier during the recent surge (2014–2016). The 3‐D flow velocities were sampled at an interval of 11 days, which is much greater than in previous studies. Besides, the Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) and two TanDEM‐X images were used to determine glacier thickness changes prior to and following the recent surge. Combining the results and geomorphologic features, we deduced that the recent surge was because of saturated basal water pressure in the Yutmaru tributary. The mass from the Yutmaru tributary squeezed into the trunk and rapidly flowed downslope along the northern margin, generating strong normal pressure to the trunk mass. Pushed by the Yutmaru tributary, the trunk began to surge in September 2014. The flow velocity reached a first peak in May 2015 and then decreased in October 2015, as part of the basal meltwater ran off. However, basal meltwater accumulated again during the following 4 months, and correspondingly, the trunk accelerated again after October 2015. Finally, as kinetic energy was released and resisting force increased, the trunk became almost stagnant in August 2016. The surge mass was blocked downstream in the trunk by the mass transferred from the Kunyang tributary, and consequently, the glacier did not advance.

Towards Bedmap Himalayas: development of an airborne ice-sounding radar for glacier thickness surveys in High-Mountain Asia

AbstractThe thickness of glaciers in High-Mountain Asia (HMA) is critical in determining when the ice reserve will be lost as these glaciers thin but is remarkably poorly known because very few measurements have been made. Through a series of ground-based and airborne field tests, we have adapted a low-frequency ice-penetrating radar developed originally for Antarctic over-snow surveys, for deployment as a helicopter-borne system to increase the number of measurements. The manoeuvrability provided by helicopters and the ability of our system to detect glacier beds through thick, dirty, temperate ice makes it well suited to increase greatly the sample of measurements available for calibrating ice thickness models on the regional and global scale. The Bedmap Himalayas radar-survey system can reduce the uncertainty in present-day ice volumes and therefore in projections of when HMA's river catchments will lose this hydrological buffer against drought.

Traces of late quaternary glaciations and paleoclimatic interpretation of Mount Akdağ (Alanya, 2451 m), Southwest Turkey

Mount Akdag, located 25 km northeast of Alanya (2451 m above sea level a.s.l.), and largely made up of carbonates, is one of the mountains exposed to Late Quaternary glaciation in the Western Taurus Mountains. Although today, there are no modern glaciers, the traces of the Late Quaternary glaciers and rock glaciers are still fresh. In this study, geomorphological features related to the glaciations in Mount Akdag, which were not previously reported in the literature, were first identified from satellite images, and then verified by field studies. The geomorphological development of Mount Akdag during the Quaternary was explained by considering its climatic and karstic characteristics. For this purpose, spatial data obtained from field studies, unmanned aerial vehicles and meteorological stations were analysed using geographic information systems. Akdag is directly open to humid air masses coming from the SW sector over the Mediterranean Sea, resulting in heavy orographic precipitation that encouraged the growth of glaciers. In addition, glacier reconstruction and pELA estimates have been made to contribute to the interpretation of glacial geomorphology. The pELA in Mount Akdag was calculated with the AABR ratio of 1.69, and was found to be around 2030 m a.s.l. More than 15 cirques and a 6.5 km long glacial valley in Mount Akdag indicate the presence of glaciers. Reconstruction of the paleoglaciers shows that the lowest altitude reached was 1410 m a.s.l. At their maximum extent glaciers covered an area of ~ 14 km2, with a volume of ~ 1 km3 and had an average thickness of 60 m with a maximum glacier thickness of ~ 200 m.

Bayesian inversion of joint SH seismic and seismoelectric data to infer glacier system properties

ABSTRACTIn glacial studies, properties such as glacier thickness and the basement permeability and porosity are key to understand the hydrological and mechanical behaviour of the system. The seismoelectric method could potentially be used to determine key properties of glacial environments. Here we analytically model the generation of seismic and seismoelectric signals by means of a shear horizontal seismic wave source on top of a glacier overlying a porous basement. Considering a one‐dimensional setting, we compute the seismic waves and the electrokinetically induced electric field. We then analyse the sensitivity of the seismic and electromagnetic data to relevant model parameters, namely depth of the glacier bottom, porosity, permeability, shear modulus and saturating water salinity of the glacier basement. Moreover, we study the possibility of inferring these key parameters from a set of very low noise synthetic data, adopting a Bayesian framework to pay particular attention to the uncertainty of the model parameters mentioned above. We tackle the resolution of the probabilistic inverse problem with two strategies: (1) we compute the marginal posterior distributions of each model parameter solving multidimensional integrals numerically and (2) we use a Markov chain Monte Carlo algorithm to retrieve a collection of model parameters that follows the posterior probability density function of the model parameters, given the synthetic data set. Both methodologies are able to obtain the marginal distributions of the parameters and estimate their mean and standard deviation. The Markov chain Monte Carlo algorithm performs better in terms of numerical stability and number of iterations needed to characterize the distributions. The inversion of seismic data alone is not able to constrain the values of porosity and permeability further than the prior distribution. In turn, the inversion of the electric data alone, and the joint inversion of seismic and electric data are useful to constrain these parameters as well as other glacial system properties. Furthermore, the joint inversion reduces the uncertainty of the model parameters estimates and provides more accurate results.

Investigating the Recent Surge in the Monomah Glacier, Central Kunlun Mountain Range with Multiple Sources of Remote Sensing Data

Several glaciers in the Bukatage Massif are surge-type. However, previous studies in this region focused on glacier area and length changes, and more information is needed to support the deep analysis of glacier surge. We determined changes in glacier thickness, motion, and surface features in this region based on TanDEM-X, ALOS/PRISM, Sentinel-1A, and Landsat images. Our results indicated that the recent surge of the Monomah Glacier, the largest glacier in the Bukatage Massif, started in early 2009 and ceased in late 2016. From 2009 to 2016, its area and length respectively increased by 6.27 km2 and 1.45 km, and its ice tongue experienced three periods of changes: side broadening (2009–2010), rapid advancing (2010–2013), and slow expansion (2013–2016). During 2000–2012, its accumulation zone was thinned by 50 m, while its ice tongue was thickened by 90 m. During 2015–2017, its flow velocity reduced from 1.2 to 0.25 m/d, and the summer velocities were much higher than winter velocities. We conclude that the recent Monomah Glacier surge is thermal-controlled. The subglacial temperature rose to the pressure-melting point because of substantial mass accumulation, and then the increased basal meltwater caused the surge.

Strong changes in englacial temperatures despite insignificant changes in ice thickness at Dôme du Goûter glacier (Mont Blanc area)

Abstract. The response of very-high-elevation glaciated areas on Mont Blanc to climate change has been analysed using observations and numerical modelling over the last 2 decades. Unlike the changes at low elevations, we observe very low glacier thickness changes, of about −2.6 m on average since 1993. The slight changes in horizontal ice flow velocities and submergence velocities suggest a decrease of about 10 % in ice flux and surface mass balance. This is due to less snow accumulation and is consistent with the precipitation decrease observed in meteorological data. Conversely, measurements performed in deep boreholes since 1994 reveal strong changes in englacial temperature reaching a 1.5 ∘C increase at a depth of 50 m. We conclude that at such very high elevations, current changes in climate do not lead to visible changes in glacier thickness but cause invisible changes within the glacier in terms of englacial temperatures. Our analysis from numerical modelling shows that glacier near-surface temperature warming is enhanced by increasing melt frequency at high elevations although the impact on surface mass balance is low. This results in a non-linear response of englacial temperature to currently rising air temperatures. In addition, borehole temperature inversion including a new dataset confirms previous findings of similar air temperature changes at high and low elevations in the Alps.

Post-20th century near-steady state of Batura Glacier: observational evidence of Karakoram Anomaly

Stable or marginal mass loss dominating in Karakoram has been reported widely through satellite and ground investigations. This work aimed to verify the variation in glacier mass by collecting ground-based data. By tracking profiles from the first survey by China–Pakistan Batura Glacier Investigation Group in 1974–1975, we revisited Batura Glacier and conducted an updated comparable measurement of the glacier surface elevation and ice thickness of this large valley glacier of Karakoram, in August 2017. Results of ground penetrating radar (GPR) measurement were used to improve the accuracy of an ice thickness distribution model (GlabTop2). The model calculation agreed reasonably with the measurement when the optimal basal shear stress (100 kPa for clean ice to 140 kPa for heavy debris cover) and shape factor (0.9) were used. We then used a glacier bed topographies map to calculate the ice flux. By subtracting the glacier surface topographies from the remote-sensing measurements, we observed a marginal thinning in Batura during 2000–2016, with a rate of variation in glacier surface elevation of −0.12 ± 0.27 m a−1. It indicated that the mass gain in the accumulation area nearly compensated the mass loss in the ablation area. In addition, both ground and satellite remote measurement reveal a steady rate of decrease in surface of the Batura tongue, implying an absence of significant variation during the past 40 years. Moreover, the mass conservation equation was applied to the Batura tongue, in combination with surface elevation variation and ice flux evolution. The tongue-averaged mass balance diminished by more than half from the 1970s to the 2010s. In summary, we inferred a near-steady state of Batura Glacier post 2000 based on the above-mentioned evidence of “Karakoram Anomaly”.

Early twentieth century evolution of Ferdinand glacier, Svalbard, based on historic photographs and structure-from-motion technique

ABSTRACTGlaciers in central Svalbard are retreating since their Little Ice Age maximum, dated in the area to around 1900. Past areal extent of glaciers can confidently be reconstructed based on end moraine position. However, reconstructions of thickness and volume of glaciers remain relatively more complicated and uncertain. In this study, past changes in thickness and volume of the Ferdinand Glacier was reconstructed based on Structure-from-Motion techniques and field dGPS measurements in combination with analysis of historic photos from 1908 and aerial photos from 1938. According to the comparison of the historic and recent photograph, the 1908 glacier front height was estimated to 50 m and the glacier volume to 91.5 mil m3 and the 1938 glacier volume estimated to 76.1 mil m3, in comparison to 6.29 mil m3 in 2014. This means more than 90% loss of volume since 1938. Melting of the glacier in the first half of the twentieth century resulted in thinning and lowering of the glacier surface together with substantial ice volume loss, whereas the areal extent was almost not affected. Considering the 2014 mean ice thickness, together with ongoing climate warming, it is likely that the Ferdinand Glacier will completely disappear within the next 30 years.

Genesis of the pleistocene hummocky moraines in the Moracke Planine Mountains (Montenegro)

The Moracke Planine Mountains, situated in the central part of Montenegro, were the center of intensive Pleistocene glaciation. Specific type of moraines - hummocky ones, which have not been recorded in the southeastern Dinarides up to now, were recently identified and investigated in western part of the Moracke Planine Mts. Moraine material accumulated on limestone basement, where several tens of irregularly distributed hummocks and similar number of bowl-shaped dolines have been carved already. The hummocky moraines formed in the glaciokarst landscape where the well-developed karst morphology has been shaped before glaciation. Pre-glacial karst morphology determined the direction of glacier movement as well as its main morphological characteristics (thickness and width). During the most intensive glaciation phase (?IS 12) the Lukavicko-lukovski Glacier, spread out from the central part of mountain towards west, reaching a length of 16.5 km. Due to uneven glacier thickness, the deglaciation process led to its breaking and separation of the lower and shorter part from the rest of the icy mass. Stagnant state of the icy mass led to specific accumulation of moraine material in a form of numerous hummocks, whose melting produced a bowl-shaped dolinas in-between. The paleogeographic significance of hummocky moraines lies in the possibilities of more detailed studies of the Pleistocene glaciers specifics that arise from their evolution in glacio-karst conditions.

ESTIMATING THE VOLUME OF ICE LOSS USING LANDSAT IMAGERIES: A CASE STUDY OF RIKHASAMBHA GLACIER, NEPAL

Abstract. Nepal being a part of Hindu Kush Himalayan Region is one of the largest concentration of glaciers. The loss of ice on that region reflects the climate change resulting devastating consequences on billions of people living downstream. This is why regular monitoring of the glaciers on that region is important not only to have insight into the glacier change but also to mitigate the effect of it. The satellite image as an alternate to ground based approach provides much more flexibility for monitoring in a regular basis. Therefore, this research aimed to map the decadal changes in glacier extent followed by estimating volume of ice loss of Rikha Samba Glacier located in Mustang district of Nepal. Multitemporal Landsat satellite images dating back from 1995 to 2015 were utilized in the study. The current research involved the calculation of snow index like NDSI on the radiometrically corrected satellite imageries. An open source GIS software package was used to automatically delineate the boundary of glacier based on the NDSI. It has been revealed that the glacier area shrunk by 2.608 km2 on an average over the period. The ice velocity of the glacier was estimated. Laminar flow approach (Cuffey and Paterson, 2010) was utilized to find the ice thickness of glacier based on the evaluated velocity information. The utilization of thus computed ice thickness gave the volume of ice loss during the study period (i.e. 310000 m3). In addition, 0.69 km glacier retreat was observed over the period.

Solar Activity from the Mid-Second Millennium B.C. to the First Millennium A.D. Based on Radiocarbon Data

The paper reports the results of reconstruction of the heliospheric modulation potential from radiocarbon data for the time interval from the mid-second millennium B.C. to the end of the first millennium A.D. It is known that significant climatic changes took place on the Earth during that time; specifically, the thickness of glaciers in Iceland and Norway were changing. Coincident changes are also observed in the radiocarbon data. The results of calculations show that the heliospheric modulation potential reaches a maximum (~590 MV) on this interval approximately in 1705 B.C. This suggests that solar activity at that moment was highest for the considered interval. Conversely, around 750 and 350 B.C., the smallest values of the modulation potential were observed and, consequently, solar activity could be lowest from the mid-second millennium B.C. to the end of the first millennium A.D.

Impact of frontal ablation on the ice thickness estimation of marine-terminating glaciers in Alaska

Abstract. Frontal ablation is a major component of the mass budget of calving glaciers, strongly affecting their dynamics. Most global-scale ice volume estimates to date still suffer from considerable uncertainties related to (i) the implemented frontal ablation parameterization or (ii) not accounting for frontal ablation at all in the glacier model. To improve estimates of the ice thickness distribution of glaciers, it is thus important to identify and test low-cost and robust parameterizations of this process. By implementing such parameterization into the ice thickness estimation module of the Open Global Glacier Model (OGGM v1.1.2), we conduct a first assessment of the impact of accounting for frontal ablation on the estimate of ice stored in glaciers in Alaska. We find that inversion methods based on mass conservation systematically underestimate the mass turnover and, therefore, the thickness of tidewater glaciers when neglecting frontal ablation. This underestimation can amount to up to 19 % on a regional scale and up to 30 % for individual glaciers. The effect is independent of the size of the glacier. Additionally, we perform different sensitivity experiments to study the influence of (i) a constant of proportionality (k) used in the frontal ablation parameterization, (ii) Glen's temperature-dependent creep parameter (A) and (iii) a sliding velocity parameter (fs) on the regional dynamics of Alaska tidewater glaciers. OGGM is able to reproduce previous regional frontal ablation estimates, applying a number of combinations of values for k, Glen's A and fs. Our sensitivity studies also show that differences in thickness between accounting for and not accounting for frontal ablation occur mainly at the lower parts of the glacier, both above and below sea level. This indicates that not accounting for frontal ablation will have an impact on the estimate of the glaciers' potential contribution to sea-level rise. Introducing frontal ablation increases the volume estimate of Alaska marine-terminating glaciers from 9.18±0.62 to 10.61±0.75 mm s.l.e, of which 1.52±0.31 mm s.l.e (0.59±0.08 mm s.l.e when ignoring frontal ablation) are found to be below sea level.

Proglacial icings as indicators of glacier thermal regime: ice thickness changes and icing occurrence in Svalbard

ABSTRACTProglacial icings (also known as naled or aufeis) are frequently observed in the forefields of polar glaciers. Their formation has been ascribed to the refreezing of upwelling groundwater that has originated from subglacial melt, and thus the presence of icings has been used as evidence of polythermal glacier regime. We provide an updated analysis of icing occurrence in Svalbard and test the utility of icings as an indicator of thermal regime by comparing icing presence with: (1) mean glacier thickness, as a proxy for present thermal regime; and (2) evidence of past surge activity, which is an indicator of past thermal regime. A total of 279 icings were identified from TopoSvalbard imagery covering the period 2008-2012, of which 143 corresponded to icings identified by a previous study of aerial photographs from 1990. Only 46% of icings observed in 2008–2012 were found to occur at glaciers with thicknesses consistent with a polythermal regime, meaning a large proportion were associated with glaciers predicted to be of a cold or transitional thermal regime. As a result, icing presence alone may be an unsuitable indicator of glacier regime. We further found that, of the 279 glaciers with icings, 63% of cold-based glaciers and 64% of transitional glaciers were associated with evidence of surge activity. We therefore suggest that proglacial icing formation in Svalbard may reflect historical (rather than present) thermal regime, and that icings possibly originate from groundwater effusion from subglacial taliks that persist for decades following glacier thinning and associated regime change.

Glacier thickness estimations of alpine glaciers using data and modeling constraints

Abstract. Advanced knowledge of the ice thickness distribution within glaciers is of fundamental importance for several purposes, such as water resource management and the study of the impact of climate change. Ice thicknesses can be modeled using ice surface features, but the resulting models can be prone to considerable uncertainties. Alternatively, it is possible to measure ice thicknesses, for example, with ground-penetrating radar (GPR). Such measurements are typically restricted to a few profiles, with which it is not possible to obtain spatially unaliased subsurface images. We developed the Glacier Thickness Estimation algorithm (GlaTE), which optimally combines modeling results and measured ice thicknesses in an inversion procedure to obtain overall thickness distributions. GlaTE offers the flexibility of being able to add any existing modeling algorithm, and any further constraints can be added in a straightforward manner. Furthermore, it accounts for the uncertainties associated with the individual constraints. Properties and benefits of GlaTE are demonstrated with three case studies performed on different types of alpine glaciers. In all three cases, subsurface models could be found that are consistent with glaciological modeling and GPR data constraints. Since acquiring GPR data on glaciers can be an expensive endeavor, we additionally employed elements of sequential optimized experimental design (SOED) for determining cost-optimized GPR survey layouts. The calculated cost–benefit curves indicate that a relatively large amount of data can be acquired before redundant information is collected with any additional profiles, and it becomes increasingly expensive to obtain further information.

Paleo-glacier reconstruction in southwestern British Columbia, Canada: A glaciovolcanic model

Volcanic rocks erupted within glacial environments offer powerful paleoenvironmental insights. These glaciovolcanoes and their deposits serve as proxies that inform on the paleo-presence, distribution and thickness of past glaciers. We investigate the paleoenvironmental implications of three Mid to Late Pleistocene volcanic deposits in the Garibaldi volcanic belt of southwestern British Columbia, Canada. We use these data to inform a simple geometric model that constrains paleo-glacier distributions in the southern Canadian Cordillera. The three volcanoes are used to recover: i) a coalesced mountain ice sheet in late Marine Isotope Stage (MIS) 4, and possibly into MIS 3 (up to ∼49.1 ± 5.5 ka), ii) major and rapid degradation of glaciers during the late, MIS 6 to 5e transition (by 141 ± 12.9 ka), and, iii) a coalesced mountain ice sheet, or continental ice sheet that existed during MIS 15 (598 ± 7.5 ka).