Dangerous cracks developing across Antarctica’s Brunt Ice Shelf are due to unleash a massive iceberg twice the size of New York City, according to NASA researchers who warn when it breaks, it could destabilize the entire shelf.

NASA recently released images acquired by Landsat satellites of Antarctica’s Brunt Ice Shelf, where a rift is visibly slicing through the shelf. Researchers said the crack had been stable for more than three decades, but since, has been moving north at about 2.5 miles per year.

“The near-term future of Brunt Ice Shelf likely depends on where the existing rifts merge relative to the McDonald Ice Rumples,” said Joe MacGregor, a glaciologist at NASA’s Goddard Space Flight Center. “If they merge upstream (south) of the McDonald Ice Rumples, then it’s possible that the ice shelf will be destabilized.”

The rift is moving toward another fissure, as known as Halloween crack, that is located 3 miles away. Halloween crack was first discovered in 2016, continues to move east, and when the two rifts intersect in the very near term, an iceberg is formed measuring 660 square miles.

“We don’t have a clear picture of what drives the shelf’s periods of advance and retreat through calving,” said NASA/UMBC glaciologist Chris Shuman. “The likely future loss of the ice on the other side of the Halloween Crack suggests that more instability is possible."

Researchers are puzzled on what drives this process, known as calving, could mean the health of the shelf is in immediate danger.

“At worst, this calving could destabilize the remainder of the Brunt Ice Shelf leading to its complete collapse,” Dominic Hodgson, a senior scientist at the British Antarctic Survey, told NBC News Tuesday in an email. “This would then likely be followed by an acceleration of ice in the upstream glaciers, increasing their contribution to sea level.”

Calving is a natural part of the life cycle of ice shelves, but recent rifts forming in the region are unusual. The edge of the Brunt Ice Shelf has evolved since Ernest Shackleton surveyed the coast in 1915, but in the last several years, the speed of its transformation has been accelerated.

The risk of the 660 square mile shelf breaking off has prompted safety concerns for researchers working in the area, particularly researchers at the British Antarctic Survey’s Halley Station, a major base for Earth, atmospheric, and space science research typically operates year-round, but has recently closed operations due to unpredictable changes in the ice.

If the converging cracks destabilize the ice shelf even further, a massive iceberg twice the size of New York City could soon be soon floating in the South Atlantic Ocean.