Photos of the sample locations on Khumbu Glacier and Lobuche Glacier.
Moraines are heaps of debris accumulated by glaciers around their edges, which are left behind when glaciers retreat. This figure shows perspective photographs of the moraines from which samples were collected for Be-10 exposure-age dating, and the ages produced (in ka) for each sample for (top) Khumbu Glacier and (bottom) Lobuche Glacier. Colored lines show various generations of moraine crests identified in this study (see key). Credit: Hornsey et al. [2022], Figure 4(a,c)
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Earth Surface

Glaciers are vulnerable to climate change, in particular in the monsoon-influenced Himalaya. Retreating glaciers pose serious risks, including risks associated with glacial lake outburst floods (GLOFs) and challenges in managing water resources for the communities living downstream. To understand how glaciers will respond to climate change in the future, we need to understand how they responded to climate change in the past.

In the Holocene (past 12,000 years of the Earth’s history), the Earth experienced a succession of warming and cooling periods. When glaciers retreat, usually during warming periods, they leave behind heaps of debris that had accumulated around their edges, named moraines. Glaciers in the Khumbu area have left a series of well-developed moraines, which Hornsey et al. [2022] dated using Beryllium-10 (Be-10).

Be-10 is a cosmogenic nuclide, that is, a type of atom that does not exist in rocks at depth. As soon as a rock is brought to the surface, cosmogenic nuclides start accumulating in the rock due to interactions between the atoms that make up the rocks and the cosmic rays that continually bombard the surface of the Earth. The longer a rock is exposed at the surface of the Earth, the greater its concentration in cosmogenic nuclides. Cosmogenic nuclides can therefore be used like a stopwatch to date when a rock fragment has been brought to the surface of the Earth, for example, when a glacier retreated and left previously buried fragments behind.

The new ages show that glaciers in the Khumbu area have responded to past climate warming in a rapid and predictable way, leaving behind complete evidence of their advance and retreat at known times of cooling and warming, respectively. This work will help scientists better understand and predict the response of Himalayan glaciers to ongoing unprecedented climate change.

Citation: Hornsey, J., Rowan, A. V., Kirkbride, M. P., Livingstone, S. J., Fabel, D., Rodes, A., et al. (2022). Be-10 dating of ice-marginal moraines in the Khumbu Valley, Nepal, Central Himalaya, reveals the response of monsoon-influenced glaciers to Holocene climate change. Journal of Geophysical Research: Earth Surface, 127, e2022JF006645. https://doi.org/10.1029/2022JF006645

—Mikael Attal, Editor, Journal of Geophysical Research: Earth Surface

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