The influence of water percolation through crevasses on the thermal regime of a Himalayan mountain glacier

Abstract

Abstract. In cold and arid climates, small glaciers with cold accumulation zones are often thought to be entirely cold based. However, scattering in ground-penetrating radar (GPR) measurements on the Rikha Samba Glacier in the Nepal Himalayas suggests a large amount of temperate ice that seems to be influenced by the presence of crevassed areas. We used a coupled thermo-mechanical model forced by a firn model accounting for firn heating to interpret the observed thermal regime. Using a simple energy conservation approach, we show that the addition of water percolation and refreezing in crevassed areas explains these observations. Model experiments show that both steady and transient thermal regimes are significantly affected by latent heat release in crevassed areas. This makes half of the glacier base temperate, resulting in an ice dynamic mainly controlled by basal friction instead of ice deformation. The timescale of thermal regime change, in response to atmospheric warming, is also greatly diminished, with a potential switch from cold to temperate basal ice in 50–60 years in the upper part of the glacier instead of the 100–150 years that it would take without the effect of the crevasses. This study highlights the crucial role of water percolation through the crevasses on the thermal regime of glaciers and validates a simple method to account for it in glacier thermo-mechanical models.

From high friction zone to frontal collapse: dynamics of an ongoing tidewater glacier surge, Negribreen, Svalbard

“…Crevasses have been shown to be able to cause a cycle of positive feedbacks in glacier dynamics by increasing surface melt-water input to the glacier bed, a feedback that was documented in detail during the surge on Basin-3 of Austfonna (Dunse and others, 2015), and has been observed on other glaciers (e.g. Gilbert and others, 2020). Because the accelerating destabilization prior to the active surge probably only lasts for a few seasons on Svalbard tidewater glaciers, high temporal resolution analysis is necessary to understand both how the destabilization begins and further evolves.…”

Borehole‐Based Characterization of Deep Mixed‐Mode Crevasses at a Greenlandic Outlet Glacier

“…Here, it was considered that the crevasses, which possibly initiated in association with band ogives several kilometers upglacier, may have warmed the glacier's full thickness of ∼250-300 m. Such inferences are not limited to the margins of the GrIS. For example, Gilbert et al (2020) suggested that meltwater refreezing in crevasses may be responsible for deep warming, inferred from surface ground-penetrating radar, at Rikha Samba Glacier, Nepal, a process that may also contribute to anomalously warm englacial ice measured in boreholes across the debris-covered tongue of Khumbu Glacier, Nepal (Miles et al, 2018). Second, deep englacially terminating crevasses have also been invoked to explain englacial radar scattering.…”

Hydrology of debris-covered glaciers in High Mountain Asia

“…For example, heat fluxes driven by meltwater conveyance to the englacial and subglacial environments of debris-covered glaciers (i.e. cryo-hydrologic warming (Gilbert et al, 2020;Phillips et al, 2010)), could be explored using numerical models guided by field-based measurements of supraglacial water fluxes and temperatures, along with geophysical and/or borehole-based investigations of englacial temperature fields. Specific loci and timescales of meltwater routing, storage, and release should be determined.…”