The streams of water, some of which are 250m in height and stretch for hundreds of kilometres, could be destabilising parts of the Antarctic ice shelf immediately around them and speeding up melting, researchers said.
However, they added that it remains unclear how the localised effects of the channels will impact on the future of the floating ice sheet as a whole.
The British researchers used satellite images and radar data to measure variations in the height of the Filchner-Ronne Ice Shelf in West Antarctica, which reveal how thick the ice is.
Writing in the Nature Geoscience journal, they described finding large rivers of meltwater beneath the floating ice shelf which had not previously been identified.
These channels lined up with areas where similar flows of water are thought to exist under the ice sheet, the ice formation which sits on solid ground, at the point where the land meets the sea.
The findings indicate that streams of water which form beneath ice on solid land are trickling down to sea and forming channels beneath the floating ice shelf, researchers said.
When the cold meltwater arrives at the ice shelf it causes warmer sea water to plume upwards, which carves large streams into the underside of the ice, they explained.
Previously it had been thought that meltwater which builds up on land would flow into the sea in a thin layer, rather than in concentrated channels, which would have a different effect on ice flow.
Researchers said the formation of water channels “induces large but localised sub-ice-shelf melt rates beneath the ice shelf” and that the drainage patterns “will have an impact” on previous predictions, but emphasised that the full implications for the future of the ice shelf remain unclear.
Dr Anne Le Brocq of the University of Exeter, who led the study, said: “If we are to understand the behaviour of the ice sheet, and its contribution to changes in sea level, we need to fully understand the role of water at the base of the ice sheet.
“The information gained from these newly discovered channels will enable us to understand more fully how the water system works and, hence, how the ice sheet will behave in the future.”
Read article at The Telegraph