TanDEM-X digital elevation models and surface velocities of Columbia Glacier, Alaska during 2011-2016

Alaskan glaciers are among the largest contributors to sea-level rise outside the polar ice sheets. The contributions include dynamic discharge from marine-terminating glaciers which depends on the seasonally variable ice velocity. Columbia Glacier is a large marine-terminating glacier located in Southcentral Alaska that has been exhibiting pronounced retreat since the early 1980s. Since 2010, the glacier has split into two branches, main branch and west branch.

We derived a 5-year record of surface velocity, mass flux (ice discharge), surface elevation and changes in front position using a dense time series of TanDEM-X synthetic aperture radar data (2011-2016). We observed distinct seasonal velocity patterns at both branches. At the main branch, the surface velocity peaked during late winter to midsummer but reached a minimum between late summer and fall. Its near-front velocity reached up to 14 m/day in May, 2015 and dropped to 1 m/day in October, 2012. Mass flux via the main branch was strongly controlled by the seasonal and interannual fluctuations of its velocity. The west branch also exhibited seasonal velocity variations with comparably lower magnitudes. The role of subglacial hydrology on the ice velocities of Columbia Glacier is already known from the published field measurements during summers of 1987. Our observed variability in its ice velocities on a seasonal basis also suggest that they are primarily controlled by the seasonal transition of the subglacial drainage system from an inefficient to an efficient and channelized drainage networks. However, abrupt velocity increase events for short periods (2014-2015 and 2015-2016 at the main branch, and 2013-2014 at the west branch) appear to be associated with strong near-front thinning and frontal retreat. This needs further investigations on the role of other potential controlling mechanisms. On the technological side, this study demonstrates the potential of high-resolution X-band SAR missions with a short revisit interval to examine glaciological variables and controlling processes.

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Elevation change rates of glaciers in the Lahaul-Spiti (Western Himalaya, India) during 2000-2012 and 2012-2013

Previous studies have shown contrasting glacier elevation and mass changes in the sub-regions of high-mountain Asia. However, the elevation changes on an individual catchment scale can be potentially influenced by supraglacial debris, ponds, lakes and ice cliffs besides regionally driven factors. Here, we present a detailed study on elevation changes of glaciers in the Lahaul-Spiti region derived from TanDEM-X and SRTM C-/X-band DEMs during 2000-2012 and 2012-2013.

We observe three elevation change patterns during 2000-2012 among glaciers with different extent of supraglacial debris. The first pattern (< 10 % debris cover, type-1) indicates maximum thinning rates at the glacier terminus and is observed for glacier with no or very low debris cover. In the second pattern (> 10 % debris cover, type-2), maximum thinning is observed up-glacier instead of glacier terminus. This is interpreted as the insulating effect of a thick debris cover. A third pattern, high elevation change rates near the terminus despite high debris cover (> 10 % debris cover, type-3) is most likely associated with either thinner debris thickness or enhanced melting at supraglacial ponds and lakes as well as ice cliffs. We empirically determined the SRTM C- and X-band penetration differences for debris-covered ice, clean ice/firn/snow and correct for this bias in our elevation change measurements. We show that this penetration bias, if uncorrected, underestimates the region-wide elevation change and geodetic mass balance by 20 %. After correction, the region-wide elevation change (1712 sqkm) was estimated to be -0.65±0.43 m/yr during 2000-2012. Due to the short observation period, elevation change measurements from TanDEM-X for selected glaciers in the period 2012-2013 are subject to large uncertainties. However, similar spatial patterns were observed during 2000-2012 and 2012-2013, but at different magnitudes. This study reveals that the thinning patterns of debris-covered glaciers cannot be generalized and spatially detailed mapping of glacier elevation change is required to better understand the impact of different surface types under changing climatic conditions.

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Snow depth from GNSS reflectometry (WP H3)

Snow storage dynamics is essential to predict floods, to quantify water resources for human use and irrigation, and to assess the risk of avalanches. Recently, Global Navigation Satellite System (GNSS) ground stations have been successfully used to continuously estimate snow depth at an intermediate scale of about 1.000 m2 around the stations. This dataset contains snow depth time series derived from the GNSS signal-to-noise ratio (SNR) at the station Wettzell, Germany,. The data coverthe time period from July 1, 2012 to July 1, 2015 and givean average snow depth over an area of about 150 by 30 m.

Data Publication

Vey, Sibylle; Güntner, Andreas; Wickert, Jens; Blume, Theresa; Thoss, Heiko; Ramatschi, Markus (2016): Supplement to: Monitoring snow depth by GNSS reflectometry in built-up areas: A case study for Wettzell, Germany. GFZ Data Services. doi:10.5880/GFZ.1.1.2016.001.

Cryosphere > Land Ice / Snow

Land Ice / Snow

TanDEM-X digital elevation models and surface velocities of Columbia Glacier, Alaska during 2011-2016

Data Publication

Related Journal Article

Elevation change rates of glaciers in the Lahaul-Spiti (Western Himalaya, India) during 2000-2012 and 2012-2013

Snow depth from GNSS reflectometry (WP H3)

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