Reconstructing Holocene Glacier Fluctuations in the Khumbu Himal, Nepal, using Be-10 exposure-age dating

Abstract:

Many glaciers in the Himalaya have undergone rapid mass loss in recent years. The mass loss experienced by debris-covered glaciers is evidenced through surface lowering driven by differential ablation and dynamics, highlighted by ice-marginal moraines which are left high above the glacier surface. The combination of large latero-frontal moraines and thick debris cover causes the glacier to become pinned at the terminus, and as such recession is limited. Whilst there is an increasing body of literature highlighting the rapid mass loss experienced by these high-elevation glaciers over the last 40 years, it is less clear how debris-covered Himalayan glaciers have responded to longer-term Holocene climate change and limited understanding of the processes driving current and future glacier change.

This study uses geomorphological mapping of ice-marginal moraines combined with Terrestrial Cosmogenic Nuclide (TCN) exposure-age dating using Be-10 to reconstruct the behaviour of four glaciers in the Everest region of Nepal—Khumbu Glacier and its former tributary glaciers; Lobuche, Changri Nup, and Changri Shar Glaciers. By mapping the substantial moraines surrounding these glaciers, patterns of glacier response to Holocene climate events such as the Little Ice Age (LIA) are reconstructed. Moraine building events at 7.19 ± 0.63 ka and 1.37 ± 0.15 ka at Khumbu Glacier, in conjunction with moraine patterns, indicate that the debris cover on Khumbu Glacier developed during the early Holocene. In contrast, Changri Nup and Changri Shar Glaciers exhibit a response only to one event in the Holocene, with moraines dated to the LIA (0.27 ± 0.05 ka). The multiple, and different, landform-building events between glaciers indicate geometric controls on glacier behaviour and suggests that there are multiple drivers of glacier change and debris cover development in this region.