‘Detachment’ of icefield outlet glaciers – catastrophic thinning and retreat of the Columbia Glacier (Canada)

We present an investigation of changes taking place on the Columbia Glacier – a lake-terminating outlet of the Columbia Icefield in the Canadian Rockies. The Columbia Icefield is the largest, and one of the most important, ice bodies in the Canadian Rockies. Like other ice masses, it stores water as snow and ice during the winter and releases it during warmer summer months, sustaining river flows and the ecosystems that rely on them. However, the Columbia Glacier and Icefield is shrinking. We use Landsat and Sentinel-2 imagery to show that the Columbia Glacier has retreated increasingly rapidly in recent years, and suggest that this looks set to continue. Importantly, we identify a previously undocumented process that appears to be playing an important role in the retreat of this glacier. This process involves the ‘detachment’ of the glacier tongue from its accumulation area in the Columbia Icefield. This process is important because the tongue is cut off from the accumulation area and there is no replenishment of ice that melts in the glacier's ablation area by flow from upglacier. As a consequence, for a given rate of ablation, the ice in the tongue will disappear much faster than it would if the local mass loss by melting/calving was partly offset by mass input by glacier flow. Such a change would alter the relationship between rates of surface melting and rates of glacier frontal retreat. We provide evidence that detachment has already occurred elsewhere on the Columbia Icefield and that it is likely to affect other outlet glaciers in the future. Modelling studies forecast this detachment activity, which ultimately results in a smaller ‘perched’ icefield without active outlets

Flow and structure in a dendritic glacier with bedrock steps

Sherpa Romeo green journal. Open access article. Creative Commons Attribution 4.0 International (CC BY 4.0) appliesWe analyse ice flow and structural glaciology of Shackleton Glacier, a dendritic glacier with multiple ice falls in the Canadian Rockies. A major tributary-trunk junction allows us to investigate the potential of tributaries to alter trunk flow and structure, and the formation of bedrock steps at confluences. Multi-year velocity-stake data and structural glaciology up-glacier from the junction were assimilated with glacier-wide velocity derived from Radarsat-2 speckle tracking. Maximum flow speeds are 65 m a−1 in the trunk and 175 m a−1 in icefalls. Field and remote-sensing velocities are in good agreement, except where velocity gradients are high. Although compression occurs in the trunk up-glacier of the tributary entrance, glacier flux is steady state because flow speed increases at the junction due to the funnelling of trunk ice towards an icefall related to a bedrock step. Drawing on a published erosion model, we relate the heights of the step and the hanging valley to the relative fluxes of the tributary and trunk. It is the first time that an extant glacier is used to test and support such model. Our study elucidates the inherent complexity of tributary/trunk interactions and provides a conceptual model for trunk flow restriction by a tributary in surge-type glaciers.Ye

Dynamics throughout a complete surge of Iceberg Glacier on western Axel Heiberg Island, Canadian High Arctic

This study provides the first comprehensive reconstruction of the dynamics of Iceberg Glacier, located on western Axel Heiberg Island, and reveals detailed observations of a complete surge for the first time in the Canadian Arctic. Historical aerial photographs, declassified intelligence satellite photographs, optical satellite imagery and synthetic aperture radar data were used to quantify changes in terminus position, ice velocity and glacier thickness since the 1950s. A surge initiated at the terminus in 1981 and terminated in 2003, suggesting a 22-year active phase. High surface velocities, reaching ~2300 m a−1 in 1991, were accompanied by a maximum terminus advance of >7 km and a large transfer of mass down-glacier, causing significant median trunk-wide surface elevation changes attaining >3 ± 1 m a−1. We suggest that the retreat from a pinning point, flotation of the terminus, the removal of sea-ice from the ice front, and an increase in subglacial meltwater availability from relatively high air temperatures in 1981 likely contributed to surge initiation. The ensuing quiescent period has seen a continual decrease in surface flow rates to an average centreline velocity of 11.5 m a−1 in 2020–21, a gradual steepening of the glacier surface and a > 2.5 km terminus retreat

Glacier velocities and dynamic ice discharge from the Queen Elizabeth Islands, Nunavut, Canada

Recent studies indicate an increase in glacier mass loss from the Canadian Arctic Archipelago as a result of warmer summer air temperatures. However, no complete assessment of dynamic ice discharge from this region exists. We present the first complete surface velocity mapping of all ice masses in the Queen Elizabeth Islands and show that these ice masses discharged ~2.6 ± 0.8 Gt a−1 of ice to the oceans in winter 2012. Approximately 50% of the dynamic discharge was channeled through non surge-type Trinity and Wykeham Glaciers alone. Dynamic discharge of the surge-type Mittie Glacier varied from 0.90 ± 0.09 Gt a−1 during its 2003 surge to 0.02 ± 0.02 Gt a−1 during quiescence in 2012, highlighting the importance of surge-type glaciers for interannual variability in regional mass loss. Queen Elizabeth Islands glaciers currently account for ~7.5% of reported dynamic discharge from Arctic ice masses outside Greenland.We thank NSERC, Canada Foundation for Innovation, Ontario Research Fund, ArcticNet, Ontario Graduate Scholarship, University of Ottawa and the NSERC Canada Graduate Scholarship for funding. RADARSAT-2 data were provided by MacDonald, Dettwiler and Associates under the RADARSAT-2 Government Data Allocation administrated by the Canadian Space Agency. Support to DB is provided through the Climate Change Geosciences Program, Earth Sciences Sector, Natural Resources Canada (ESS Contribution #20130293). We also acknowledge support from U.K NERC for grants R3/12469 and NE/K004999 to JAD.This is the accepted version of an article published in Geophysical Research Letters. An edited version of this paper was published by AGU. Copyright (2014) American Geophysical Union. The final version is available at http://onlinelibrary.wiley.com/doi/10.1002/2013GL058558/abstract;jsessionid=6A3AD907C4383DA5D4E20C4924D6EC18.f02t02

Characterizing the flow speeds and variability of Trinity and Wykeham Glaciers of the Prince of Wales Icefield, Canadian Arctic using a highly dense record of Synthetic Aperture Radar Data

The Trinity and Wykeham Glacier complex of the Prince of Wales Icefield in the Canadian High Arctic is one of the largest glacier basins within the region. Since 2000, both glaciers have accelerated, increased their discharge and retreated. Recent studies have indicated that this acceleration and retreat has been driven by significant thinning and floatation of glaciers. This acceleration and retreat is also further modulated by each glaciers bed topography. Here, we utilize a highly dense record of TerraSAR-X, Tandem-X, PAZ and Radarsat Constellation Mission data in order to further characterize the recent (since 2021) dynamics of each glacier at ~weekly timescales. This timeseries allows us to investigate variations in glacier flow for both glaciers at an unprecedent resolution. The results of this work will be used as inputs into glacier flow models and will be used to further investigate the dynamic response of a large tidewater terminating glacier to climate warming

Controls on Seasonal and Multi-Year Velocity Variability of South Croker Bay Glacier, Nunavut, Canada from 2015-2020

Velocity records of South Croker Bay Glacier (Devon Ice Cap, Canadian Arctic) obtained from offset tracking of 11-day separated TerraSAR-X image pairs from 2015 to 2020 have captured a significant increase in both ‘winter’ (September-May) and ‘summer’ (June-August) seasons. Winter velocities have increased from 179 m a-1 in 2015 to 251 m a-1 in 2020, with the most significant change identified in 2016/17 increasing from 172 m a-1 to 239 m a-1 in 2018/19. Summer velocities have been following the same upward trend, with velocities of 299 m a-1 observed in 2015, increasing to 397 m a-1 in 2021. The highest velocities are found ~4.5 km up-glacier from the terminus where the bed lies ~50-100 m below sea level. 3D Tomography data from NASA’s Operation IceBridge is used to investigate basal topography as a spatial control on the propagation of faster glacier speeds. Supraglacial lakes are manually delineated from cloud free optical imagery (Sentinel-2 and Landsat-8/9) and are tracked based on their evolution and drainage to help determine the supra-glacial hydrology structure as well as identify when surface water drains to the bed and impacts glacier sliding rates. Sea ice concentrations, as determined from Canadian Ice Service charts at the front of South Croker Bay Glaciers, are used to determine how the observed flow rates of the glacier are linked to changing sea ice conditions. Finally, terminus positions are digitized and measured to assess how the front of the glacier has responded to the variability in ice dynamics over the observation period. Collectively, this work provides one of the most comprehensive records of motion for any glacier in the Canadian High Arctic and allows us to explore how bed topography, sea ice conditions and surface hydrology cause and control variations in flow speeds

Recent velocity observations of Hubbard Glacier: A comparison of RADARSAT Constellation Mission with Sentinel-1, TerraSAR-X and RADARSAT-2 derived velocity maps to determine seasonal flow patterns

Hubbard Glacier is an advancing tidewater glacier in Alaska, with large seasonal variations in flow speeds of 1500 to 5200 m a-1. The large size and fast speeds of Hubbard Glacier caused it to have possibly the largest rates of steady-state discharge of all glaciers outside of Greenland and Antarctica. Previous studies found the fastest flow on Hubbard Glacier to occur between May and June and the slowest flow between September to November. However, we observed a different seasonal pattern when looking at velocities at a higher temporal resolution than used before (image pairs of SAR and optical imagery with a separation in the range of ~4-30 days). In some years, the seasonal flow pattern of Hubbard Glacier changes to having higher velocities in the winter than what is seen in the spring/summer maximums. Here, we show that with the utilization of RADARSAT Constellation Mission (RCM) data, which has a higher temporal resolution than has previously been used to quantify glacier motion on Hubbard Glacier (4-day repeat pass), seasonality can be explored in much greater detail than formally possible. The results of velocities derived from RCM data will be compared to products derived from other SAR sensors (Sentinel-1, TerraSAR-X, and RADARSAT-2) to assess its feasibility in determining velocity patterns of Hubbard Glacier. This comparison provides an example of the improved ability to resolve glacier dynamics using RCM data and provides insight into how this SAR dataset can be used to characterize seasonality on other glaciers within the St. Elias region