Antarctic ice shelves can break under the weight of meltwater lakes
Recent time-lapse images and GPS data from the George VI Ice Shelf show that the numerous meltwater lakes on the Larsen B ice shelf may have been one of the causes of its sudden disintegration in 2002.
The sudden collapse of the Larsen B Ice Shelf on the east coast of the Antarctic Peninsula in 2002 is still a mystery: Within just a few days, most of the ice shelf disintegrated – an area of 3,250 square kilometers. A research team led by the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder provides new insights into the causes with its new study, which was published in May in the Journal of Glaciology.
Their study shows for the first time through observation that ice shelves not only bend under the weight of meltwater lakes, but also fracture. As warming continues and melt rates increase, the accumulation of meltwater could cause vulnerable ice shelves to collapse relatively suddenly, making way for inland glaciers to flow into the ocean, which in turn contributes to sea level rise.
As the Larsen B Ice Shelf was covered with meltwater lakes in the months before its disintegration, which drained within a few weeks, a connection with its rapid collapse has long been suspected. Modeling studies have already shown that the immense weight of thousands of meltwater lakes and their drainage caused the Larsen B Ice Shelf to bend and fracture, leading to its collapse. However, there was no evidence based on observational data.
“Scientists have predicted and modeled that surface meltwater loading could cause ice shelves to fracture, but no one had observed the process in the field, until now,” said Alison Banwell, a scientist at CIRES and lead author of the study, in a press release from the institute.
Alison Banwell and her team therefore wanted to investigate the effects of meltwater on ice shelves in more detail. On the George VI Ice Shelf on the west coast of the Antarctic Peninsula, they observed a depression, or doline, over several months in the summer of 2019/2020 – a record melt season. Melt water had already collected there in the past and had run off again.
In November 2019, they installed a time-lapse camera system that took photos of the ice surface and meltwater lakes every 30 minutes, high-precision GPS stations to measure minimal height changes on the ice surface, and water pressure sensors to measure lake depth.
From the GPS data, the researchers were able to read that the ice in the center of the meltwater lake had sunk about 30 centimeters due to the weight of the water. The team also found that the horizontal distance between the edge and the center of the meltwater basin had increased by more than 30 centimeters. They suspect that this is most likely due to the formation of circular cracks around the meltwater lake, which the time-lapse images show.
“This is an exciting discovery,” says Alison Banwell. “We believe these types of circular fractures were key in the chain reaction style lake drainage process that helped to break up the Larsen B Ice Shelf.”
Currently, the ice shelf of the Thwaites Glacier in West Antarctica and the Brunt Ice Shelf in the Weddell Sea are particularly at risk, from which several large icebergs have broken off in the recent past. The extent to which these two are also destabilized from above by meltwater lakes remains to be seen.
Julia Hager, Polar Journal AG
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