Surface and subsurface hydrology of debris-covered Khumbu Glacier, Nepal, revealed by dye tracing

Katie E Miles,Bryn Hubbard,Duncan J Quincey,Evan S Miles,Tristram D.L Irvine-Fynn,Ann V Rowan

doi:10.1016/j.epsl.2019.02.020

Katie E Miles, Bryn Hubbard + Show 4 more

Open Access

https://doi.org/10.1016/j.epsl.2019.02.020

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Abstract

While the supraglacial hydrology of debris-covered glaciers is relatively well studied, almost nothing is known about how water is transported beneath the glacier surface. Here, we report the results of sixteen fluorescent dye tracing experiments conducted in April–May 2018 over the lowermost 7 km of the high-elevation, debris-covered Khumbu Glacier, Nepal, to characterise the glacier's surface and subsurface drainage system. Dye breakthroughs indicated a likely highly sinuous and channelised subsurface hydrological system draining water from the upper part of the ablation area. This flowpath was distinct from the linked chain of supraglacial ponds present along much of the glacier's lower ablation area, through which water flow was extremely slow (∼0.003 ms−1), likely reflecting the study's timing during the pre-monsoon period. Subsurface drainage pathways emerged at the glacier surface close to the terminus, and flowed into small near-surface englacial reservoirs that typically delayed meltwater transit by several hours. We observed rapid pathway changes resulting from surface collapse, indicating a further distinctive aspect of the drainage of debris-covered glaciers. We conclude that the surface and subsurface drainage of Khumbu Glacier is both distinctive and dynamic, and argue that further investigation is needed to refine the characterisation and test its regional applicability to better understand future Himalayan debris-covered glacier meltwater delivery to downstream areas.

Highlights

Meltwater from Himalayan glaciers and snow feeds some of Earth’s largest river systems, influencing the supply of water to ∼1.4 billion people (Barnett et al, 2005; Bolch, 2017; Immerzeel et al, 2010)
We propose that Khumbu Glacier’s drainage system across the ablation area initiates supraglacially in the clean-ice region beneath the ice fall above DIP8
This study reports the first successful dye tracing experiments at a debris-covered glacier in the Nepal Himalaya and the first dye tracing-based investigation exploring the intricacies of debris-covered glacier hydrology, both at and beneath the surface

Summary

Introduction

Meltwater from Himalayan glaciers and snow feeds some of Earth’s largest river systems, influencing the supply of water to ∼1.4 billion people (Barnett et al, 2005; Bolch, 2017; Immerzeel et al, 2010). Melt rates are disproportionately high at pond margins due to the continued horizontal and vertical incision (Miles et al, 2016; Sakai et al, 2000), and recent studies have found that supraglacial ponds are expanding to cover an increasing proportion of the surface of debris-covered glaciers (Gardelle et al, 2012; Watson et al, 2016). This has implications for greater meltwater production and water storage, since ponds moderate diurnal glacier runoff (Irvine-Fynn et al, 2017)

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