Abstract
This study assesses changes in glacier area, velocity and geodetic mass balance for the glaciers in the Manaslu region of Nepal, a previously undocumented region of the Himalayas. We studied changes between 1970 (for select glaciers), 2000, 2005 and 2013 using freely available Landsat satellite imagery, the SRTM Digital Elevation Model (DEM) and a DEM based on Worldview imagery. Our results show a complex pattern of mass changes across the region, with glaciers lowering on average by -0.25 ± 0.08 m a-1 between 2000 and 2013 which equates to a negative geodetic mass balance of -0.21 ± 0.16 m w.e.a-1. Over approximately the same time period (1999 to 2013) the glaciers underwent a -16.0% decrease in mean surface velocity over their debris-covered tongues as well as a reduction in glacier area of -8.2%. The rates of glacier change appear to vary between the different time periods, with glacier losses increasing in most cases. The glaciers on Manaslu itself underwent a change in surface elevation of -0.46 ± 0.03 m a-1 between 1970 and 2000 and -0.99 ± 0.08 m a-1 between 2000 and 2013. Rates of glacier area shrinkage for the same glaciers increased from -0.36 km2 a-1 between 1970 and 2001 to -2.28 km2 a-1 between 2005 and 2013. Glacier change varies across the region and seems to relate to a combination of glacier hypsometry, glacier elevation range and the presence and distribution of supraglacial debris. Lower-elevation, debris-free glaciers with bottom-heavy hypsometries are losing most mass. As the glaciers in the Manaslu region continue to stagnate, an accumulation and thickening of the debris-cover is likely, thereby insulating the glacier and further complicating future glacier responses to climate.
Highlights
High Mountain Asia contains the largest concentration of glacier ice outside of the polar areas
Given the large time period between these datasets, and the image distortions associated with Corona data, these deviations are acceptable, ∼5 m higher than the standard deviations found by Bolch et al (2011) and Pieczonka et al (2013)
This study presents varied and complex glacier changes in the Manaslu region of Nepal
Summary
High Mountain Asia contains the largest concentration of glacier ice outside of the polar areas. Existing in-situ glacier mass balance data in the Himalayas is extremely limited and biased toward accessible small to medium sized and debris-free glaciers (Bolch et al, 2012; Gardelle et al, 2013). Within the Himalayas, remote sensing has permitted large scale investigations of glacier area (Bajracharya et al, 2014; 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). The Nepali Himalayas have seen some pioneering studies on ice-cliffs and supraglacial ponds on debris-covered glaciers, with ice cliffs found to ablate by between six and 10 times the mean glacier ablation rate (Immerzeel et al, 2014; Brun et al, 2016) and contribute up to 20% of the total glacier ablation (Sakai et al, 2000)
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