Recent slowdown and thinning of debris-covered glaciers in south-eastern Tibet

Abstract

Recent large-scale remote sensing studies have shown that glacier mass loss in southeastern Tibet, specifically in the eastern Nyainqêntanglha Range exceeds the average in High Asia. However, detailed studies at individual glaciers are scarce and the drivers behind the observed rapid changes are poorly constrained to date. Employing feature tracking techniques on TerraSAR-X data for the periods 2008/2009, 2012/2013 and 2013/2014 we found measurable surface velocities through to the glacier terminus positions of five debris-covered glacier tongues. This is contrary to debris-covered glaciers in other parts of High Asia, where stagnant glacier tongues are common. Our feature tracking results for the 2013/2014 period suggest an average deceleration of 51% when compared with published Landsat velocities for the period 1999/2003. Further, we estimated surface elevation changes for the five glaciers from recently released one arc second resolution elevation data obtained during the Shuttle Radar Topography Mission in 2000 and an interferometrical derived TanDEM-X elevation model for the year 2014. With an average rate of-0.83±0.57 m a −1 we confirm strong surface lowering in the region, despite the widely discussed insulation effect of debris cover. Beside the influence of thermokarst processes and delayed response times of debris-covered glaciers, we highlight that abundant monsoonal summer rainfall might contribute significantly to the pronounced negative mass balances

Can ice-cliffs explain the debris-cover anomaly? New insights from Changri Nup Glacier, Nepal, Central Himalaya

“…10). Additionally, there are evidences 20 of slowing down of debris-covered tongues and detachment from their accumulations area, both leading to reduction in ice flux and consequently in w e (Neckel et al, 2017). In conclusion, this term "debris-cover anomaly" comes from a confusion between thinning rates and net ablation and in turn we recommend to abandon the term.…”

Spatial Variability in Patterns of Glacier Change across the Manaslu Range, Central Himalaya

“…Remote sensing data allows systematic monitoring of glaciers over decadal scales. Within the Himalayas, remote sensing has permitted large scale investigations of glacier area Nuimura et al, 2014;Robson et al, 2015), glacier velocities (Copland et al, 2009;Heid and Kääb, 2012b;Dehecq et al, 2015), and geodetic mass balances (Bolch et al, 2011;Gardelle et al, 2012b;Kääb et al, 2012;Maurer and Rupper, 2015;Neckel et al, 2017). Landsat imagery has been used to establish that the Nepali Himalayas contain a total of 3808 glaciers with a total area of 3902 km 2 as of 2010 (Bajracharya, 2014).…”

A Combined Approach for Filtering Ice Surface Velocity Fields Derived from Remote Sensing Methods

“…This limits the use of the smooth segment filter in these regions. However, it has been shown previously, that filters based on local variance within a moving search window or a directional threshold are capable to remove many outliers in such areas [22][23][24][25]. We therefore argue, that even if the smooth segment filter fails in these areas, robust results might be obtained by employing the median filter and the directional filter.…”