Scientists have warned that the Thwaites Glacier in West Antarctica – known as the 'doomsday glacier' – is "holding on by its fingernails".
The glacier could result in a sea level rise of up to six feet if it triggers a runaway collapse, researchers have previously warned.
That study, based on scans of the seafloor that showed how fast the glacier had retreated in the past, revealed that catastrophic changes could come to the glacier in the very near future.
Robert Larter, from the British Antarctic Survey, said: "Thwaites is really holding on today by its fingernails.
"We should expect to see big changes over small timescales in the future – even from one year to the next – once the glacier retreats beyond a shallow ridge in its bed."
Thwaites Glacier is 74,000 square miles, the size of Great Britain, and is thought to be particularly susceptible to climate change.
Over the past 30 years, the amount of ice flowing out of Thwaites and its neighbouring glaciers has nearly doubled.
Even now, ice draining from Thwaites into the Amundsen Sea accounts for about 4% of global sea-level rise as it dumps 50 billion tonnes of ice into the ocean each year.
If it collapses, it could raise sea levels by about 65cm (25.5in) as it melts, but it could trigger a runaway collapse across the western half of Antarctica that could lead to a sea level rise of up to 6ft, scientists told the Financial Times.
A new study in Nature Geoscience, led by marine geophysicist Alastair Graham at the University of South Florida's College of Marine Science, adds cause for concern.
For the first time, scientists mapped in high-resolution a critical area of the seafloor in front of the glacier that gives them a window into how fast Thwaites retreated and moved in the past.
The team documented more than 160 parallel ridges that were created, like a footprint, as the glacier’s leading edge retreated and bobbed up and down with the daily tides.
"It's as if you are looking at a tide gauge on the seafloor," Graham said. "It really blows my mind how beautiful the data are."
To understand Thwaites' past retreat, the team analysed the rib-like formations submerged just under half a mile beneath the polar ocean and factored in the tidal cycle for the region, as predicted by computer models, to show that one rib must have been formed every single day.
At some point in the last 200 years, over a duration of less than six months, the front of glacier lost contact with a seabed ridge and retreated at a rate of more than 1.3 miles per year – twice the rate documented using satellites between 2011 and 2019.
Earlier this year, scientists speaking to the BBC warned that dramatic changes could occur within 10 or even five years. They said that a floating section of Thwaites Glacier could "shatter like a car windscreen".
Professor Ted Scambos, the US lead co-ordinator for the International Thwaites Glacier Collaboration (ITGC), said: "There is going to be dramatic change in the front of the glacier, probably in less than a decade. Both published and unpublished studies point in that direction.
"This will accelerate the pace (of Thwaites) and widen, effectively, the dangerous part of the glacier."
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In December, Paul Cutler, programme director for Antarctic glaciology at America’s National Science Foundation, said: "[Thwaites] is a keystone for the other glaciers around it in West Antarctica ... If you remove it, other ice will potentially start draining into the ocean too."
Cutler said the Thwaites glacier was losing ice faster and faster, and that the process seemed to be accelerating.
He said: "The big question is how quickly it becomes unstable. It seems to be teetering at the edge."
The South Pole, the most remote place on the planet, has warmed three times faster than other areas over the past three decades, researchers have said.
Watch: Doomsday glacier could raise sea levels by several feet