Supraglacial pond evolution in the Everest region, central Himalaya, 2015–2018

Abstract. Supraglacial ponds are characteristic of debris-covered glaciers and greatly enhance local melt rates. They can grow rapidly and coalesce to form proglacial lakes, which represent a major hazard. Here, we use Sentinel-2A satellite imagery (10 m) to quantify the spatiotemporal changes of 6,425 supraglacial ponds for 10 glaciers in the Everest region, Nepal, between 2015 and 2018. During the study period, ponded area increased on all glaciers, but showed substantial temporal and spatial variation, and the rate of pond growth increased substantially relative to 2000–2015 (Watson et al., 2016). Both Imja and Spillway Lake expanded and Khumbu Glacier developed a chain of connected ponds. 54 % of ponds were associated with an ice-cliff, but the proportion of ponds with cliffs decreased during the study period. Pond location generally corresponded to lower surface velocity, but this relationship was not ubiquitous. Ponds are now predominantly found at mid-elevations on our study glaciers, suggesting that conditions conducive to pond formation have advanced up-glacier compared to general theory. Results demonstrate the need to utilize high-resolution imagery (< 10 m), as using Landsat (30 m) would miss 55–86 % of the total ponds. Glaciers were classified by stage of development (Komori, 2008; Robertson, 2012). Two glaciers transitioned between stages between 2015 and 2018, suggesting that lakes in the region are evolving rapidly. Some study glaciers displayed characteristics of multiple classes, so we propose an adapted classification system. Overall, our results demonstrate rapid pond expansion in the Everest region and highlight the need for continued monitoring for hazard assessment.