Parkachik glacier's melting may form three lakes: what does this mean for Ladakh?

In a recent study by scientists at the Wadia Institute of Himalayan Geology, an autonomous institute of the Indian Government's Department of Science and Technology (DST), startling revelations have come to light about the Parkachik Glacier in the Ladakh Himalayas. Rapid ice melt is likely to form three glacial lakes around Parkachik Glacier in Ladakh, as found by the study.

The study, recently published in the prestigious Annals of Glaciology of Cambridge University, sheds light on the dynamic changes and morphological evolution of the glacier during the last five decades.

The findings suggest that the glacier is retreating rapidly, with potential implications for regional climate change and the development of glacial lakes. The research represents a vital step towards understanding the behavior of Himalayan glaciers and their response to ongoing climate warming.

The Parkachik Glacier, situated in Kargil, Ladakh, India, majestically descends from the Nun-Kun slopes. Ice chunks break off its towering front wall, forming a stunning ice-fall into the Suru River. Visitors can cross a suspension footbridge for a closer view.

Mountaineers use this glacier to access the challenging north face route of Mt Nun. The upper Suru Valley provides picturesque camping areas, and nearby Panikhar is another attractive destination. Accessible from Kargil, located 90 km north.

Himalayan glaciers

Himalayan glaciers have been under close scrutiny for over a century due to their sensitivity and role as direct indicators of regional climate change. Numerous studies, combining field investigations and state-of-the-art remote sensing techniques, have been conducted to monitor these glaciers.

The region has witnessed accelerated glacial melt and mass loss since the 1990s, leading to significant alterations in glacier hydrology, river runoff, and contributing to sea level rise.

Parkachik glacier

The study, led by Dr. Manish Mehta and his team, used a combination of medium-resolution satellite imagery from 1971 to 2021, field surveys between 2015 and 2021, and ground-penetrating radar techniques to estimate ice thickness.

The scientists used the Himalayan Glacier Thickness Mapper (HIGTHIM), a semi-automated approach based on the sheet flow method, to infer the depth, water volume of potential lakes, and identify the glacier bed topography for overdeepening sites.

The results of the study are alarming. Remote sensing data reveals that the Parkachik Glacier experienced an average retreat rate of around 2 meters per year between 1971 and 1999. However, between 1999 and 2021, this retreat rate increased dramatically to around 12 meters per year. More worrisome, field observations indicate an even higher rate of retreat of approximately 20.5 meters per year between 2015 and 2021.

Dr. Mehta said, "Global warming and increasing temperatures in the region are the first reason for the rapid melting of the glacier, and the second reason is that it is at a lower altitude than other glaciers in the Zanskar region."

Scientists found alarming results in the ablation and accumulation in the glacier, Mehta said. The top of a glacier indicates the accumulation of snow. The glacier's lower half, where melting typically takes place, indicates ablation.

Geospatial analysis, satellite images, field surveys, glacier changes

A major contributor to the rapid retreat of the glacier is the detachable nature of its margin and the development of a proglacial lake. Since 2015, a proglacial lake has formed at an elevation of about 3,600 meters above sea level, which is expanding rapidly due to the receding glacier. This development of new glacial lakes and the expansion of existing ones pose the risk of Glacial Lake Flash Floods (GLOFs), with potentially serious consequences for downstream communities.

In this study, geospatial techniques were used to analyze multispectral and multi-temporal satellite scenes from various sources: CORONA KH-4 (1971), Landsat 7 ETM+ (1999–2000, 2002, and 2009), Operational Land Imager (OLI) (2020–2021), and Sentinel-2A (2021).

The satellite images were co-registered using projective transformation, and the glacier outlines were manually digitized based on false color composite images. The length changes of the glacier were quantified using the parallel line method, and the glacier boundaries and frontal positions were validated during field surveys.

Field surveys were conducted annually on the Parkachik Glacier since 2015 using a differential global positioning system (GPS) to monitor frontal position and area changes. In situ measurements of glacier surface lowering, debris thickness, and frontal changes were observed from 2015 to 2021. The surface ice velocity was calculated using optical image correlation techniques based on Landsat images for two consecutive years (1999–2000 and 2020–2021).

Himalayan Glacier Thickness Mapper

Ice thickness estimation was done using the Himalayan Glacier Thickness Mapper (HIGTHIM) tool, which utilized glacier boundary, flowlines, moraines, and contour polygons in vector format, along with digital elevation models (DEMs) and glacier surface ice velocity in raster format. The ice thickness estimates were obtained by manually digitized flowlines interpolated over the entire glacier area.

The study also estimated uncertainties associated with various parameters, such as frontal retreat, surface ice velocity, and ice thickness, based on previous studies and data sources used in the analysis.

The results showed that the Parkachik Glacier experienced significant frontal retreat over the past five decades, with an overall retreat of -210 ± 88 meters between 1971 and 2021, with an accelerated rate after 2009. The glacier also showed fluctuations in frontal retreat, including an anomalous advancement between 1999 and 2002, likely caused by subglacial cavity collapse and lateral spreading of ice.

The surface ice velocity of the glacier decreased over time, with a reduction from 45.18 ± 1.78 m/a in 1999–2000 to 32.28 ± 0.80 m/a in 2020–2021. The study also provided insights into the ice thickness distribution, with the average ice thickness estimated to be 115 ± 16 meters, varying from the terminus to the accumulation zone.

The study identified potential overdeepening sites for lake formation on the glacier at different elevations, with estimated mean depths ranging from 34 to 84 meters.

Implications for Regional Climate Change

The accelerating retreat of the Parkachik Glacier serves as a visible indicator of ongoing climate change in the region. The glacier's behavior mirrors similar trends seen on other Himalayan glaciers, raising concerns about the consequences for water resources and downstream populations.

Understanding the thickness and distribution of ice is essential to understanding the behavior of Himalayan glaciers. However, existing remote sensing approaches cannot directly estimate the thickness of glaciers. Only a few studies, using ground-penetrating radar, have been conducted on the thickness of glaciers in the Indian Himalayas.

The application of the Himalayan Glacier Thickness Mapper (HIGTHIM) tool represents an important step forward in estimating ice thickness and volume, critical to assessing the overall health of the glacier and its response to climate change.

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