Abstract
Several supraglacial ponds are developing and increasing in size and number in the Himalayan region. They are the precursors of large glacial lakes and may become potential for glacial lake outburst floods (GLOFs). Recently, GLOF events originating from supraglacial ponds were recorded; however, the spatial, temporal, and seasonal distributions of these ponds are not well documented. We chose 23 debris-covered glaciers in the Everest region, Nepal, to study the development of supraglacial ponds. We used historical Landsat images (30-m resolution) from 1989 to 2017, and Sentinel-2 (10-m resolution) images from 2016 to 2018 to understand the long-term development and seasonal variations of these ponds. We also used fine-resolution (0.5–2 m) WorldView and GeoEye imageries to reveal the high-resolution inventory of these features and these images were also used as references for accuracy assessments. We observed a continuous increase in the area and number of ponds from 1989–2017, with minor fluctuations. Similarly, seasonal variations were observed at the highest ponded area in the pre- and postmonsoon seasons, and lowest ponded area in the winter season. Substantial variations of the ponds were also observed among glaciers corresponding to their size, slope, width, moraine height, and elevation. The persistency and densities of the ponds with sizes >0.005 km2 were found near the glacier terminuses. Furthermore, spillway lakes on the Ngozompa, Bhote Koshi, Khumbu, and Lumsamba glaciers were expanding at a faster rate, indicating a trajectory towards large lake development. Our analysis also found that Sentinel-2 (10-m resolution) has good potential to study the seasonal changes of supraglacial ponds, while fine-resolution (<2 m) imagery is able to map the supraglacial ponds with high accuracy and can help in understanding the surrounding morphology of the glacier.
Highlights
High Mountain Asian glaciers are the perennial sources of water for approximately 1.4 billion people [1]
We presented an extensive application of multiresolution satellite imageries to study the historical development and seasonal variations in the Everest region
Our results show that supraglacial ponds are widely distributed on glaciers in the Everest region, and show the rapid increase in their area and number from 1989–2017
Summary
High Mountain Asian glaciers are the perennial sources of water for approximately 1.4 billion people [1]. Supraglacial ponds are known for meltwater storage [16], progressively buffering the runoff regimes of the glacier-originated river in increased projections of debris cover [12]. They play an important role in the ablation of debris-covered glaciers [17,18] through absorbing atmospheric energy [19,20]. The majority of absorbed atmospheric energy leaves the pond system through englacial conduits [16,20,21], and hydraulic connection of pond to englacial water level exerts a key control on whether the pond contributes to longer-term terminus disintegration [10] This process enlarges the englacial conduits which can collapse the roof of the conduits, leading to the formation of ice cliffs and new ponds [20,22,23]. Ponds are highly recurrent and persistent with high interannual variability [19], but small ponds have the potential to expand rapidly [25]
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