pine island glacier antarctica

Since 2011, wary scientists have kept an especially close watch on West Antarctica’s Pine Island Glacier, the fastest-melting region of the threatened continent. On Saturday, satellite specialists at Delft University of Technology in the Netherlands saw what researchers had long feared: Pine Island had calved again, releasing a rectangular 103-square-mile mass of frozen ice into the rapidly warming sea.

According to Stef Lhermitte, the satellite observation specialist who broke the news on Twitter, this is Pine Island’s fifth large calving event since 2000. Most recently, an ice mass estimated at 225 square miles (580 square kilometers) tore off the main glacier in 2015.

It’s likely that this will only continue; some scientists believe that Pine Island represents the “weak underbelly” of the entire West Antarctic ice sheet, and scientists who published a 2016 study in Geophysical Research Letters wrote that the glacier’s acceleration, retreat, and thinning suggests “that irreversible retreat has already begun.”

The chunk of ice that already broke off on Saturday is estimated to contain 1.7 feet of potential global sea level rise, according to the Washington Post.

We can take small comfort in the fact that, for now, the chunks of ice that have already broken off of Pine Island Glacier won’t contribute directly to sea level rise. Pine Island Glacier is already floating (as opposed to being part of the main West Antarctic ice sheet land mass), and so if chunks of it break off or melt they’re not going to take up any more volume in the sea.

The parts of Pine Island that have calved from the main glacier over the past several decades have begun to form a barrier in the Amundsen Sea, which will hopefully prevent future wedges of ice — some of which won’t come from already-floating parts of Antarctica — from being released into the warming ocean.

However, ice barriers are by no means permanent. As ice continues to calve off the continent, it’s certainly possible they will break through and drift into the sea.

pine island glacier crack
NASA first caught a glimpse of the massive crack across the Pine Island Glacier in mid-October 2011.

While it’s not unusual for ice to calve off of Antartica, the particular way in which Pine Island Glacier is calving is not common and highly concerning, according to a 2016 Geophysical Research Letters study. Most Antarctic ice cracks on the edges of the continent, but satellite imagery has shown that Pine Island rifts, in particular, extend far into the center of the glacier, indicating a degree of instability that is far from natural. The glacier, the researchers wrote in a release, is “breaking up from the inside out.”

If the entire West Antarctic ice sheet collapses and drifts into the ocean — and studies suggest it could happen within the next century — scientists estimate it will lead to a 10-foot rise in sea level, which would completely submerge major coastal cities like New York, Miami, and Los Angeles.

Photos via NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team