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When do glacial ponds become glacial lakes at risk of outburst floods?
Two young UK geographers are on a mission to the Everest to study the melting of glaciers into ponds, and eventually lakes. This process can increase glacial melt, a climate change issue in the Himalayas, and increase the risk of floods downhill.
Cameron Watson and Owen King from the University of Leeds are studying how ice cliffs and ponds spread on top of glaciers melt across time. While packing up, Watson told me he looked forward to his trip to the Himalayas, “home to some of the hardest working and welcoming people.” He climbs mountains back home and in the Alps, and loves trail runs.
King, another trail runner, will be repeating a photographic survey of the valley. The team will create high resolution 3D models of the Khumbu glacier, comparing the scale of glacial ice loss over the recent past.
There is a lot of concern about how melting snow and ice will change the seasonal distribution of meltwater for downstream areas in decades to come. “An additional worry is the amount of surface water some of these glaciers are storing, and the potential for them to develop into large glacial lakes,” said Prof. Duncan Quincey, the doctoral supervisor of Watson and King at Leeds.
Earlier Watson, Quincey and colleagues used satellite imagery to study changes more than 9,000 ponds on top of nine glaciers in the Everest region. Six glaciers showed a net increase in ponded area, even when they drained, expanded and shrank seasonally and yearly.
The stagnating, low gradient, thinning, debris-covered Himalayan glaciers such as Khumbu, Nuptse, Lhotse Nup, Lhotse, and Lhotse Shar showed more and more smaller ponds in the study. As pond water absorbs and passes on the sun’s heat to the underlying ice, they contribute to further melting and receding of glaciers. In the Khumbu Glacier, a chain of ponds its the low-altitude area – where the ice melts, calves and erodes – indicated the development of a large lake, warranting monitoring.
Still, for now Quincey would call these water bodies ponds. “I’d stick with ‘pond’ for now,” he said. “Quite where the division between pond and lake lies I’m not sure, but the latter does tend to ring alarm bells which we’re trying to avoid.”
“Yes, there is a possibility that the ponds may develop to such a size where we would be concerned about an outburst, but would stress that this is not currently the case, “ Quincey said. “We have seen elsewhere in the region that large lakes start as a series of ponds that become hydrologically connected (as is now the case at Khumbu) and then eventually coalesce to become a single lake. This might happen over a decade or more (from now). Equally, the ponds that are currently in existence may find an escape route between now and then (through or beneath the moraine); if so no lake will develop.”
The Khumbu Glacier is predicted to lose eight to ten per cent of its volume by 2100, with its debris-covered tongue detaching from the active glacier in 150 years, as another study by University of Sheffield researcher Dr Ann Rowan, Quincey and colleagues showed.
Watson and King have been preparing over the Spring for the trip. “The altitude slows everything down, especially when hauling kit around; the unstable glacier surface cause flash floods downstream,” Watson said.
King has been running up a few more hills than usual. He counts of the goodwill of the local people, introduced by the Himalayan Research Expeditions. “Like Scott (Watson), the first thing I think of is the Nepali people. They're very accommodating and generous, and they make the trip up to the Khumbu valley very enjoyable! They're all very keen to share their knowledge and stories.”
Max Martin is a researcher at the Sussex University Geography Department and the Institute of Development Studies, in the UK. His work focuses on people's responses to climate- and environment-related hazards.
