30 Apr 2020 | Cryosphere

New study finds that crevasses in Himalayan glaciers can play a key role in influencing ice temperature

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The research team surveying Rikha Samba Glacier with GPR in 2015 (Photo: Tenzing Chogyal Sherpa/ICIMOD)

Glaciers in cold and arid climates, such as in High Mountain Asia, can warm up much faster than expected because atmospheric warming is resulting in meltwater moving into glaciers through surface crevasses.

Temperate ice is at the pressure melting point, which is the melting temperature of ice at a given pressure, and contains water. Glaciers in high mountains are often considered to consist only of cold ice (ice temperature below pressure melting point). A 2020 study published in The Cryosphere by ICIMOD and its partners shows that Rikha Samba Glacier in the Himalaya is polythermal, meaning that it consists of both temperate and cold ice. In the study, the team found that the transition period from cold to temperate ice in high-altitude mountain glaciers could be much shorter than earlier assumed.

“We found that the basal ice in the upper part of Rikha Samba Glacier could switch from cold to temperate in 50–60 years instead of the expected 100–150 years without the crevasse effect”, says Adrien Gilbert, lead author of the study from the University of Oslo, Oslo, Norway.

The research team combined field measurements made on Rikha Samba Glacier, a benchmark glacier monitored in Nepal, with remote sensing and numerical modelling to better understand the thermal structure of high-altitude mountain glaciers.

Originally, the team conducted ground-penetrating radar (GPR) surveys to estimate the ice volume of Rikha Samba Glacier. “To our surprise, in addition to the ice thickness, we saw large amounts of temperate ice within the glacier in the radar data”, explains Tika Gurung, ICIMOD, one of the authors of the paper.

A 4.5 km GPR profile of Rikha Samba Glacier shows bedrock topography and large temperate ice zones within the glacier. (Source: Gilbert et al., 2020)

The team linked the temperate ice zones within the glacier with locations of surface crevasse fields. Numerical modelling demonstrated that deep water movement into the glacier through surface crevasses plays a crucial role in influencing the thermal structure of Rikha Samba Glacier. This indicates that similar processes apply elsewhere as well.

Rikha Samba Glacier is one of the benchmark glaciers being monitored as part of the Cryosphere Monitoring Programme in Nepal, being implemented by ICIMOD in collaboration with the Department of Hydrology and Meteorology, Government of Nepal; Kathmandu University; Tribhuvan University; and the Water and Energy Commission Secretariat.