Abstract
Moraine-dammed lakes at debris-covered glaciers are becoming increasingly common and pose significant outburst flood hazards if the dam is breached. While moraine subsurface structure and internal processes are likely to influence dam stability, only few sites have so far been investigated. We conducted electrical resistivity tomography (ERT) surveys at two sites on the terminal moraine complex of the Ngozumpa Glacier, Nepal, to aid assessment of future terminus stability. The resistivity signature of glacier ice at the site (100–15 kΩ m) is more consistent with values measured from cold glacier ice and while this may be feasible, uncertainties in the data inversion introduce ambiguity to this thermal interpretation. However, the ERT data does provide a significant improvement to our knowledge of the subsurface characteristics at these sites, clearly showing the presence (or absence) of glacier ice. Our interpretation is that of a highly complex latero-terminal moraine, resulting from interaction between previous glacier advance, recession and outburst flooding. If the base-level Spillway Lake continues to expand to a fully formed moraine-dammed glacial lake, the degradation of the ice core could have implications for glacial lake outburst risk.
Highlights
Moraine-dammed lakes at debris-covered glaciers are becoming increasingly common and pose significant outburst flood hazards if the dam is breached
Figure 3. 2-D inversion results for the three electrical resistivity tomography (ERT) profiles acquired at site B, plotted in a 3-D grid
As little is known about the subsurface characteristics at Ngozumpa, negating the use of a priori information, we develop a synthetic resistivity data model (See Methods)
Summary
Moraine-dammed lakes at debris-covered glaciers are becoming increasingly common and pose significant outburst flood hazards if the dam is breached. Both observations and theoretical considerations indicate that ‘permafrost-frozen avalanche material’ is not present near the terminus of Ngozumpa and due to the comparable signature at Profile 13, where ground truth exists (Fig. 4a), the high resistivity values (>100 kΩ m) at Site A (Fig. 2) are interpreted as glacier ice (see Methods).
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