Solved the mystery of the glacial lake floods

A long-standing mystery in the study of glaciers was recently – and by accident – solved by a team led by astrobiologist and earth scientist Eric Gaidos of the University of Hawai’i in Mānoa. Their findings were published this week in the journal Geophysical Research Letters.

The mystery involves floods or “jokulhlaups” that suddenly and unpredictably emerge from glaciers or polar ice caps such as those of Iceland, where volcanic heat melts ice and water accumulates in lakes under glaciers. Scientists have long studied the development of these floods, which are among the largest on Earth.

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

Then, in June 2015, an unexpected series of events revealed how these floods begin.

That summer, Gaidos and colleagues drilled a hole in one of Iceland’s lakes to study its microbial life. While collecting samples through the well, the team noticed a downward current, like a bathtub drain, in the hole.

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

A few days later, after the team left the glacier, the lake dried up in flood. Fortunately, the flooding was small and Icelanders have an elaborate early warning system on the rivers so that no people were injured, nor did the infrastructure damaged in this event, Gaidos assured.

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

“We found that the glacier may contain smaller bodies of water above the 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 the water to start flowing under the glacier.”

While the team established an artificial connection to the lake in 2015, natural connections can form when water from rain or melting snow builds up in crevasses and the pressure eventually forces a crack across the glacier to the lake. This discovery provides new insight into how these floods can start and how this depends on the weather and the season.

Collaborators in Iceland are continuing to research this phenomenon by using radio echo to search for bodies of water within the ice, as well as studying the larger lake below.