The Thwaites Glacier in Antarctica.

The Thwaites Glacier’s fractures were identified in satellite imagery.Credit: NASA

Giant fractures in the floating ice of Antarctica’s massive Thwaites Glacier — a fast-melting formation that has become an icon of climate change — could shatter part of the shelf within five years, research suggests. If that happens, in what had been considered a relatively stable part of Thwaites, the glacier could release an armada of icebergs and begin flowing much faster into the ocean, funnelling ice that had been resting on land into the sea, where it would contribute to sea-level rise.

For decades, scientists have carefully tracked changes in the Thwaites Glacier, which already loses around 50 billion tonnes of ice each year and causes 4% of global sea-level rise. The recently identified fractures are deep, fast-moving cracks in Thwaites’s eastern ice shelf (see ‘Cracking up’). They have appeared in satellite images over the past few years and their growth seems to be accelerating.

“I visualize it somewhat similar to that car window where you have a few cracks that are slowly propagating, and then suddenly you go over a bump in your car and the whole thing just starts to shatter in every direction,” said Erin Pettit, a glaciologist at Oregon State University in Corvallis, on 13 December at the American Geophysical Union (AGU) meeting. If Thwaites’s eastern ice shelf collapses, ice in this region could flow up to three times faster into the sea, Pettit says. And if the glacier were to collapse completely, it would raise sea levels by 65 centimetres.

Cracking up: Map of Antartica showing the location of Thwaites Glacier.

Brink of change

Pettit will describe the work on 15 December at the AGU meeting, which is being held in New Orleans, Louisiana. It is the latest finding from the five-year, US$50-million International Thwaites Glacier Collaboration, an initiative funded by the US and UK governments to study how Thwaites might contribute to rising sea levels in a warming world, and to understand the threat that this might pose.

“We have been expecting that ice shelf to fail, and that’s one of the reasons that there has been such a coordinated international effort to study Thwaites — it’s big and important, but it’s also been clearly poised on the brink of change,” says Kirsty Tinto, a geophysicist at the Lamont-Doherty Earth Observatory in Palisades, New York, who has studied the glacier. The latest work, she says, reveals more about how ice shelves fail. “Understanding those processes helps us to understand not just Thwaites, but also all the rest of Antarctica — past, present and future,” she says.

Mountain brace

Thwaites flows off the Antarctic continent into the Southern Ocean. At 120 kilometres across, it is the world’s widest glacier. Across about two-thirds of that expanse, ice flows relatively quickly into the ocean. The remaining one-third is the eastern ice shelf, where ice had been flowing more slowly1. In part, that’s because the ice grinds to a halt when it reaches an underwater mountain about 40 kilometres offshore. The submerged mountain holds back the ice flow like a cork in a bottle.

Earlier this year, members of the Thwaites collaboration reported that the glacier is becoming unstuck from that mountain, causing cracking and fracturing across other parts of the ice shelf2,3. Previous studies4,5 have also shown hints of instability across Thwaites’s eastern ice shelf. “It’s been something to keep an eye on for a long time,” says Matthew Siegfried, a glaciologist at the Colorado School of Mines in Golden.

The fractures caught the attention of Pettit and her colleagues two years ago, as they were looking through satellite images to work out where to set up camp for the season. One crack, nicknamed ‘the dagger’, was even heading straight towards the proposed camp site. It wasn’t moving fast enough for the scientists to relocate their work, but “we actually all just had to take a pause”, said Pettit. “It still was hugely surprising to me that this was changing that fast.”

The fractures are propagating through the ice at speeds of several kilometres per year. They are heading into weaker and thinner ice, where they could accelerate and lead to the demise of this part of the ice shelf within five years, Pettit estimates.

“There’s going to be a dramatic change in the front of the glacier,” said Ted Scambos, a glaciologist at the Cooperative Institute for Research in Environmental Sciences in Boulder, Colorado. “It will accelerate the pace and effectively widen the dangerous part of the glacier.”

Warm-water flows

How exactly the changes might happen isn’t clear, says Siegfried, because many factors influence how ice shelves fall apart. They include how rapidly warm water melts the bottom of the floating part of the glacier, and the geometry of how ice, land and water interact.

One of the collaboration’s recent discoveries is that ocean tides cause Thwaites’s floating part to rise up at high tide and drop down at low tide. That up-and-down ‘tidal pumping’ — long suspected but rarely observed in detail — causes the glacier to flex farther upstream, including in the region where it flows off land and into the water. Seismic and radar data have shown that because of this flexing, warm water might be able to intrude beneath the glacier more easily, said Lizzy Clyne, a glaciologist at Lewis & Clark College in Portland, Oregon. “The existence and possible rapid formation of these features could have implications for the long-term stability of the ice shelf,” they said.

The Thwaites collaboration completed its most extensive field-research season in 2019–20, before the COVID-19 pandemic interrupted the project. This Antarctic summer, which is under way, several research teams are again descending onto the ice to take measurements at various locations across the glacier. And a major research cruise in February aboard the US icebreaker Nathaniel B. Palmer will study the ocean directly in front of the glacier’s floating edge.

Each visit underscores how fast Thwaites is changing. Seeing this huge ice shelf moving towards you at about a mile every year is unsettling, said Scambos. “And all by itself, this one glacier is big enough to impact sea level significantly.”