Ice Cliff Dynamics of Debris-Covered Trakarding Glacier in the Rolwaling Region, Nepal Himalaya

Yota Sato,Akiko Sakai,Rijan B Kayastha,Hiroshi Inoue,Rakesh Kayastha,Koji Fujita,Evgeny A Podolskiy,Sojiro Sunako,Akane Tsushima

doi:10.3389/feart.2021.623623

Abstract

Ice cliffs can act as “hot spots” for melt on debris-covered glaciers and promote local glacier mass loss. Repeat high-resolution remote-sensing data are therefore required to monitor the role of ice cliff dynamics in glacier mass loss. Here we analyze high-resolution aerial photogrammetry data acquired during the 2007, 2018, and 2019 post-monsoon seasons to delineate and monitor the morphology, distribution, and temporal changes of the ice cliffs across the debris-covered Trakarding Glacier in the eastern Nepal Himalaya. We generate an ice cliff inventory from the 2018 and 2019 precise terrain data, with ice cliffs accounting for 4.7 and 6.1% of the debris-covered area, respectively. We observe large surface lowering (&gt;2.0 m a−1) where there is a denser distribution of ice cliffs. We also track the survival, formation, and disappearance of ice cliffs from 2018 to 2019, and find that ∼15% of the total ice cliff area is replaced by new ice cliffs. Furthermore, we observe the overall predominance of northwest-facing ice cliffs, although we do observe spatial heterogeneities in the aspect variance of the ice cliffs (ice cliffs face in similar/various directions). Many new ice cliffs formed across the stagnant middle sections of the glacier, coincident with surface water drainage and englacial conduit intake observations. This spatial relationship between ice cliffs and the glacier hydrological system suggests that these englacial and supraglacial hydrological systems play a significant role in ice cliff formation.

Highlights

Glaciers in High Mountain Asia have been shrinking in recent decades (e.g., Bolch et al, 2012; Brun et al, 2017; Shean et al, 2020)
We initially focused on the 2018 photogrammetry dataset since the aerial photogrammetry coverage area in 2018 extended to the offglacier terrain; we extracted 78 ground control points (GCPs) from the shifted Pléiades-digital elevation models (DEMs) and ortho-image (Ground Control Points) to create the 2018 ortho-image and DEM
Our ice cliff coverage ratios are larger than the 0.2–3.9% values obtained for individual glaciers in the Langtang catchment, and our ice cliff length densities are higher than the highest ice cliff length density of 7.4 × 10−3 m−1 on Lhotse Shar Glacier, Khumbu region, in May 2009

Summary

INTRODUCTION

Glaciers in High Mountain Asia have been shrinking in recent decades (e.g., Bolch et al, 2012; Brun et al, 2017; Shean et al, 2020). Brun et al (2018) combined in situ measurements, UAV photogrammetry, and satellite data to estimate the ice cliff mass loss across the debris-covered area of the Changri Nup Glacier in the Khumbu region, Nepal. The ortho-image and processed SfM-DEM data (hillshade, aspect, and slope) were analyzed in ArcGIS, with edge polylines and slope polygons manually created on the ridges and slope sections of the ice cliffs, respectively (Supplementary Figure S4). We estimated the decadal (2007–2018) and annual (2018–2019) surface elevation changes of the debris-covered area by differentiating the generated SfM-DEMs. We modified the glacier area from the GAMDAM Glacier Inventory (Nuimura et al, 2015; Sakai, 2019) using the glacier boundary and calving front that were derived from the ortho-images for the surface elevation change analysis. We adopted the spatial distribution of the thermal resistance across the surface of Trakarding Glacier using nine ASTER images that were acquired between October 2004 and February 2008 (Fujita and Sakai, 2014)

RESULTS

DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT