<img class="styles__noscript__2rw2y" src="https://dsx.weather.com//util/image/w/imrs_0.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0" srcset="https://dsx.weather.com//util/image/w/imrs_0.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 400w, https://dsx.weather.com//util/image/w/imrs_0.jpg?v=ap&w=980&h=551&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 800w" > Large rift near the Pine Island Glacier tongue, West Antarctica, as seen during an IceBridge flight on Nov. 4, 2016. (NASA/Nathan Kurtz) (NASA/Nathan Kurtz)

At a Glance This wasn't the first time this happened. In 2015, a nearly 225-square-mile iceberg broke off from the glacier, one of the largest in West Antarctica.

Pine Island loses an estimated 45 billion tons of ice each year to the ocean, which amounts to 1 millimeter of global sea level rise every eight years.

A massive chunk of ice has broken off from a key Antarctic glacier, creating an iceberg four and a half times the size of Manhattan.

The iceberg that broke from the Pine Island Glacier in western Antarctica on Saturday measures some 100 square miles. It is the second time in two years the glacier has lost such a large piece and scientists are concerned that the latest break signifies a considerable change in the behavior of the glacier.

Stef Lhermitte, a satellite observation specialist at the Delft University of Technology in the Netherlands, posted a satellite image to Twitter Saturday showing that the glacier had calved.

In 2015, a nearly 225-square-mile iceberg broke off from the glacier , one of the largest in West Antarctica.

Greenhouse gas emissions-driven global warming is being blamed for an incredible amount of ice lost each year in Antartica.

Pine Island loses an estimated 45 billion tons of ice each year to the ocean, which amounts to 1 millimeter of global sea level rise every eight years.

Last year, a study led by Seongsu Jeong and Ian Howat of Ohio State University found that Pine Island Glacier was “breaking up from the inside out .”

The researchers noted that the ice shelf had developed a new way of losing ice, rifts were forming in the center of the huge glacier rather than along its edges, suggesting the warmer waters reaching the base of the glacier is undermining it.

“Rifts usually form at the margins of an ice shelf, where the ice is thin and subject to shearing that rips it apart,” said study leader Ian Howat , associate professor of earth sciences at Ohio State. “However, this latest event in the Pine Island Glacier was due to a rift that originated from the center of the ice shelf and propagated out to the margins. This implies that something weakened the center of the ice shelf, with the most likely explanation being a crevasse melted out at the bedrock level by a warming ocean.”

With each break, the glacier becomes more and more unstable, possibly leading to a runaway retreat in ice.

Howat noted in 2016 that it's "no longer a question of whether the West Antarctic Ice Sheet will melt, it’s a question of when."

"This kind of rifting behavior provides another mechanism for rapid retreat of these glaciers, adding to the probability that we may see significant collapse of West Antarctica in our lifetimes,” Howat said.

Studies suggest that the West Antarctic Ice Sheet could collapse within the next 100 years, leading to a sea rise of nearly 10 feet. That would result in widespread flooding to major U.S. cities like New York and Miami and the displacement of 150 million people living on coasts worldwide, the researchers note.

Lhermitte noted in a subsequent tweet that Saturday's break is "the fifth large calving event since 2000."

“This one and 2015, they were much further inland than the previous ones. So there has been a retreat of the calving front, specifically between 2011 and 2015,” he added.

Howat told the Washington Post that new cracks on the glacier could indicate that another calving event could happen “very soon.”

(More: One of the Largest Icebergs Ever Recorded Breaks Off From Antarctica )

Knut Christianson, a glaciologist at the University of Washington in Seattle who studies Pine Island, told the Post that calving is normal and to be expected, but the "mode of calving of Pine Island Glacier appears to be shifting.”

Like Howat, Christianson suggests that calving from the interior of the glacier from warmer waters undermining the glacier's base indicates that more frequent calving will occur.

“This results in smaller but more-frequent calving events,” he continued. “The persistence and net effect of this shift in calving behavior has yet to be determined as it has only occurred during the past two years, but it clearly merits continued observation.”

Saturday's calving comes just 2 months after the largest ever-recorded iceberg broke from Antarctica's Larsen C ice shelf.

The iceberg that was observed by a U.S. satellite in July covers an area greater than 2,300 square miles, larger than the state of Delaware, and is more than 650 feet thick.