Abstract
There have been rapid increases in both the number and expansion of the proglacial lakes across High Mountain Asia. However, the relationship between proglacial lakes and glacier dynamics remains unclear in the Himalayan region. Here we present the surface elevation, flow velocity changes, and proglacial lake expansion of Thorthormi and Lugge glaciers in the Lunana region, Bhutanese Himalaya, during the 2000–2018 period using photogrammetry and GPS survey data. The lake expansion and surface lowering rates, and flow velocity field of Lugge Glacier, a lake-terminating glacier, have remained approximately constant since 2000. Conversely, there has been accelerated proglacial lake expansion and a two-fold increase in the thinning rate of Thorthormi Glacier since 2011, as well as a considerable speed-up in the flow velocity field (> 150 m a−1). We reveal that the lake formation and transition of Thorthormi Glacier from a land- to lake-terminating glacier have triggered glacier speed-up and rapid thinning via a positive (compressive) to negative (extensional) change in the emergence velocities. This study provides the first evidence of dynamic glacier changes that are associated with proglacial lake formation across the Himalayan region.
Highlights
20 A recent deglacial trend has been reported for numerous glaciers across High Mountain Asia (HMA; e.g., Brun et al, 2019; Maurer et al, 2019; Shean et al, 2020), with these glaciers exhibiting spatially heterogeneous thinning patterns (Bolch et al, 2012; Kääb et al, 2012; Brun et al, 2017)
We presented the surface elevation and velocity changes, and proglacial lake expansion of lake-terminating Thorthormi and Lugge glaciers in the Lunana region, Bhutanese Himalaya
We analysed satellite/photogrammetry data and compared our 310 results with those in previous studies to reveal the recent glacier and proglacial lake changes of Thorthormi Glacier, which are associated with the transition from land- to lake-terminating conditions
Summary
20 A recent deglacial trend has been reported for numerous glaciers across High Mountain Asia (HMA; e.g., Brun et al, 2019; Maurer et al, 2019; Shean et al, 2020), with these glaciers exhibiting spatially heterogeneous thinning patterns (Bolch et al, 2012; Kääb et al, 2012; Brun et al, 2017). There has been a rapid increase in both the number and expansion of the proglacial lakes across HMA owing to this deglacial trend (Zhang et al, 2015; Nie et al, 2017; Shugar et al, 2020), which has been pronounced across the eastern Himalayas (e.g., Gardelle et al, 2011; Chen et al, 2021). The increasing number and evolution of proglacial lakes have led to a rise in the hazardous potential of glacial lake outburst floods (GLOFs). GLOF hazards can be triggered by either unstable terminal moraines or snow/rock avalanches (e.g., Fujita et al, 2008; Westoby et al, 2014), and can cause significant damage to hydropower stations, bridges and buildings that exist downstream of 30 proglacial lakes (Richardson and Reynolds, 2000).
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