Structure and evolution of the drainage system of a Himalayan debris-covered glacier, and its relationship with patterns of mass loss

Abstract

Abstract. We provide the first synoptic view of the drainage system of a Himalayan debris-covered glacier and its evolution through time, based on speleological exploration and satellite image analysis of Ngozumpa Glacier, Nepal. The drainage system has several linked components: (1) a seasonal subglacial drainage system below the upper ablation zone; (2) supraglacial channels, allowing efficient meltwater transport across parts of the upper ablation zone; (3) submarginal channels, allowing long-distance transport of meltwater; (4) perched ponds, which intermittently store meltwater prior to evacuation via the englacial drainage system; (5) englacial cut-and-closure conduits, which may undergo repeated cycles of abandonment and reactivation; and (6) a "base-level" lake system (Spillway Lake) dammed behind the terminal moraine. The distribution and relative importance of these elements has evolved through time, in response to sustained negative mass balance. The area occupied by perched ponds has expanded upglacier at the expense of supraglacial channels, and Spillway Lake has grown as more of the glacier surface ablates to base level. Subsurface processes play a governing role in creating, maintaining, and shutting down exposures of ice at the glacier surface, with a major impact on spatial patterns and rates of surface mass loss. Comparison of our results with observations on other glaciers indicate that englacial drainage systems play a key role in the response of debris-covered glaciers to sustained periods of negative mass balance.

Heterogeneous water storage and thermal regime of supraglacial ponds on debris‐covered glaciers

“…In the upper ablation zone of debris‐covered glaciers, observations of increased summer velocities on Lirung and Ngozumpa Glaciers, suggest that basal‐sliding is promoted where surface meltwater is routed the glacier bed (e.g. via crevasses) (Kraaijenbrink et al ., ; Benn et al ., ). Seasonal velocity observations are lacking for Khumbu Glacier; however, it is likely that surface‐bed hydrological connections play a similar role.…”

Large drainages from short-lived glacial lakes in the Teskey Range, Tien Shan Mountains, Central Asia

“…This drainage process seems similar to the closure and opening (connection) of an englacial conduit for a supraglacial lake on a debris-covered glacier (Benn et al, 2001;Gulley and Benn, 2007;Gulley et al, 2009). Supraglacial lakes have a seasonal variability and can be transient or recurring, depending on the connectivity to englacial network (Miles et al, 2017a, b;Benn et al, 2017;Narama et al, 2017). The formation and sudden drainage of supraglacial ponds have also occurred in the Cordillera Blanca, Peru (Emmer et al 2015).…”

“…After drainage, vertical subsidence occurs along the subsurface channel in the debris landform. Such short-lived glacial lake types recur when their ice tunnel closes, similar to that on a supraglacial lake on a glacier or on a debris-covered glacier (Kropáček, et al, 2015;Benn et al, 2017;Narama et al, 2017). For example, at Angisay Glacier in the Teskey Range (Fig.…”

“…At the Kashkasuu lake in 2007, a debris landform containing ice was found at the glacier front. The ice rich debris landforms are also called moraine complex (Shatravin, 2007;Janský et al, 2010;Bolch et al, 2014). The debris landform, composed of debris and ice, remained from glacier shrinkage.…”

Quantification of different flow components in a high-altitude glacierized catchment (Dudh Koshi, Nepalese Himalaya)

“…However, an analysis of the diurnal 5 cycle (Figure 14) showed that DHSVM-GDM responds too rapidly to the ice melt production and that the representation of the water storage within the glaciers needs to be improved. Further improvements should be based on studies that analyze the mechanisms of glaciers drainage systems in the Khumbu region and their influence on glaciers outflow (e.g., Gulley et al, 2009;Benn et al, 2017). These studies show that englacial conduits and supraglacial channels, ponds and lakes play a key role in the response of glaciers: DHSVM-GDM could thus be upgraded by implementing a parameterization of such systems and 10 delay the response of glacierized areas, as successfully proposed, for instance, in the model developed by Flowers and Clarke (2002).…”