As increased warming in Antarctica causes glaciers to retreat and shed their increasingly-unstable shelves, towering walls of ice are left looming high above the sea. But how tall these rugged cliffs actually grow before they come crashing down has been a question for glacial scientists—and one that has important implications for sea-level rise.
“There’s a theory out there that says ice is only so strong, so it can only ever reach a certain height before it breaks apart,” says WHOI assistant scientist Catherine Walker, who studies the dynamics of ice on Earth and in space. “In the case of ice cliffs, the general assumption has been that a cliff can only grow to roughly one-hundred meters—just slightly higher than the Statue of Liberty—before it collapses under its own weight and falls into the ocean.”
The theory, it turns out, stems from research that University of Michigan professor Jeremy Bassis and Walker conducted a decade ago. They had come up with some relatively straightforward calculations and combined those with estimated heights of ice cliffs that had been observed in existing ice shelves to settle on the 100-meter figure.
Surprisingly, no one has ever actually surveyed the height of ice cliffs around the continent, according to Walker. Yet, sea-level rise models, and predictions for how high seas will rise, are largely based on this 100-meter threshold figure.
“In reality, we don’t actually know when an ice cliff will collapse,” says Walker. “It’s currently one of the biggest sources of uncertainty in sea-level predictions.”
In Antarctica, these magnificent cliffs collar the edges of the ice sheet. Paired with floating ice shelves, they hold in all the ice sitting in the middle of the continent like a cork that keeps it from flowing into the ocean. If, in the near future, ice cliffs begin to collapse rapidly, the interior of the ice sheet will start to get eaten away faster and faster (called runaway collapse), which could contribute as much as six feet of sea-level rise by 2100, according to some models.
“This is where a lot of the scary news reports come from that talk about what could happen if all of West Antarctica suddenly disintegrated,” says Walker.
