Mystery of glacial lake flooding solved

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Hot water drilling used to drill through the glacier to subglacial lakes. The drill pipe sits hundreds of meters under the ice, suspended from a rubber hose through which hot water is pumped. Credit: Eric Gaidos

A long-standing mystery in the study of glaciers was recently – and by accident – solved by a team led by the University of Hawaii at Mānoa astrobiologist and earth scientist Eric Gaidos. Their results were published this week in the journal Geophysical research letters.

The mystery involves floods or “jokulhlaups” that suddenly and unpredictably emerge from glaciers or ice caps like those in Iceland where volcanic heat melts ice and water collects in lakes beneath glaciers. Scientists have long studied the development of these floods, which are among the largest in the world.

“These floods can affect the movement of some glaciers and pose a significant hazard in Iceland,” said Gaidos, professor at the UH Mānoa School of Ocean and Earth Science and Technology (SOEST). “But the mechanism and timing of these floods was not understood. ”

Then, in June 2015, a series of unexpected events revealed how the flooding started.

That summer, Gaidos and his colleagues drilled a hole in one of Iceland’s lakes to study its microbial life. While collecting samples through the borehole, the team noticed a downdraft, like a tub drain, in the hole.

“The flow was so strong that we almost lost our sensors and our sampling equipment in the hole,” Gaidos said. “We assumed that we accidentally connected a body of water inside the glacier to the lake below. This body of water quickly drained into the lake. “

Illustration of the movement of water that may have triggered the flood of June 2015 (the arrows indicate the direction of flow): the subglacial lake, heated to 4 C by geothermal input, the perched reservoir fed by the summer melt through the layer of fir, a water-filled system of crevices and conduits (mills), our borehole and the exit under the ice dam. Credit: Gaidos, et al. (2020)

A few days later, after the team left the glacier, the lake drained in a flood. Fortunately, the flooding was low and the Icelanders have an elaborate early warning system on their rivers, so that no one was injured or infrastructure damaged in this event, Gaidos assured.

The researchers used a computer model of the draining of the flow through the hole, and its effect on the lake, to show that this could have triggered the flooding.

“We discovered that the glacier can hold smaller bodies of water above lakes fed by the summer melt,” Gaidos said. “If this body of water is hydraulically connected to the lake, the pressure in the lake increases and this allows water to start flowing under the glacier. “

Mystery of glacial lake flooding solved

In June 2015, a team led by Gaidos used hot water to melt a hole through 250 meters of ice to sample a lake under a glacier in Iceland. Credit: Eric Gaidos

While the team made an artificial connection to the lake in 2015, natural connections can form when water from rain or slush collects in crevices and pressure eventually forces a crack through. the glacier to the lake. This discovery provides a better understanding of how these floods can start and how it depends on the weather and the season.

Collaborators in Iceland are continuing their research into this phenomenon, using radio soundings to search for bodies of water in the ice, as well as to study the larger lake below.


The consequences of shrinking glaciers


More information:
E. Gaidos et al, After Us, the Flood: A Human ‐ Triggered Jökulhlaup from a Subglacial Lake, Geophysical research letters (2020). DOI: 10.1029 / 2020GL089876

Provided by the University of Hawaii at Manoa

Citation: Mystery of glacial lake floods resolved (2020, November 7) retrieved November 7, 2020 from https://phys.org/news/2020-11-mystery-glacial-lake.html

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