Recent time-lapse images and GPS data from the George VI Ice Shelf show that numerous meltwater lakes on the Larsen B Ice Shelf may have been one of the reasons for its sudden breakup 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 a few days, most of the ice sheet had disintegrated – an area of 3,250 square kilometers. A research team led by the Cooperative Institute for Environmental Sciences (CIRES) at the University of Colorado Boulder provides new insights into the causes with its new study, published in May. Journal of Clasticology.
Their study shows for the first time by observing that ice shelves not only bend but also fracture under the weight of meltwater lakes. As warming continues and melting rates increase, the accumulation of meltwater can cause ice shelves to collapse relatively abruptly, allowing inland glaciers to flow into the ocean, contributing to sea-level rise.
Because the Larsen B Ice Shelf was covered in meltwater lakes months before its collapse, it drained within weeks, a connection to its rapid decline has long been suspected. Modeling studies have already shown that the sheer weight of thousands of meltwater lakes and their drainage has caused the Larsen B ice shelf to bend and break, leading to its collapse. However, there is no evidence based on observational data.
„Scientists have predicted and modeled that surface meltwater loading could break up ice shelves, but until now no one had observed this process in the field,” Alison Banwell, a scientist at CIRES and lead author of the study, said in a press release. Release from the company.
So Alison Banwell and her team wanted to investigate the effects of meltwater on the ice shelves in more detail. On the George VI Ice Shelf off the west coast of the Antarctic Peninsula, they observed a depression, or doline, over several months during the summer of 2019/2020 – a record melting season. In the past, meltwater had already collected there and flowed back.
In November 2019, they installed a time-lapse camera system that takes photos of the ice surface and meltwater lakes every 30 minutes, high-precision GPS stations to measure minimal elevation changes in the ice surface, and water pressure sensors to measure lake depth.
From the GPS data, the researchers were able to read that the ice at the center of the meltwater lake had sunk by about 30 centimeters due to the weight of the water. The team also found that the horizontal distance between the edge and center of the coastal basin increased by more than 30 centimeters. They suspect this is most likely caused by the formation of circular cracks around the meltwater lake, which the images show over time.
„It’s an amazing discovery,” says Alison Banwell. „We believe these types of circular fractures were important in the chain-reaction-style lake drainage process that helped break up the Larson B ice shelf.”
Currently, the Thwaites Glacier ice shelf in West Antarctica and the Brunt Ice Shelf in the Weddell Sea are particularly at risk, from which several large glaciers have broken off in recent times. The extent to which these two are disrupted by meltwater lakes remains to be seen.
Julia Hager, Polar Journal Ag
