A giant iceberg in the western part of Antarctica has disintegrated.

Researchers from the British Antarctic Survey have discovered that a 100-square mile iceberg that was calving from Antarctica’s Pine Island Glacier (PIG) has disintegrated into several smaller icebergs.

“What we’re witnessing on Pine Island Glacier is worrying,” Robert Larter, Ph.D., a marine geophysicist at British Antarctic Survey, who flew over the PIG rift last season during his research cruise with the German Alfred Wegener Institute, said in a statement. “We’re now seeing changes in the calving behavior of the ice shelf, when for 68 years we saw a pattern of advance and retreat resulting in the calving of a single large iceberg which left the ice front to approximately the same place.”

In September, satellite images showed an open-water gap emerging between the ice shelf and the iceberg—which is about 103 square miles.

While scientists anticipated after discovering the iceberg in September that the iceberg would drift far out into the Southern Ocean before breaking up, the iceberg ultimately got stuck, likely impeded by a thick sea ice, before it started to disintegrate.

Larter compared the current situation with calving episodes of the 2001, 2007 and 2013.

“Each calving event returned the ice front to more or less the same position and the ice shelf flowed into the sea again,” he said. “But with continuing thinning it was clear that sooner or later there would have to be a change to this pattern–and this is what we are witnessing now.

“What’s both interesting and of concern is the lines along which the iceberg has broken follow the pattern of crevasses developed in the ice shelf that it calved from,” he added. “This change of behavior might reflect the crevasses within the ice shelf having an increasing influence on the spacing and pattern of iceberg calving as a result of the thinning that has taken place over the past few decades.”

Pine Island Glacier is considered the fastest melting glacier in Antarctica and is responsible for around 45 billion tons of ice loss each year.

While the ice shelf has been thinning in recent decades, until two years ago there had been no systematic retreat of the ice front since it was first observed in 1947.

“If the ice shelf continues to thin and the ice front continues to retreat, its buttressing effect on PIG will diminish, which is likely to lead to further dynamic thinning and retreat of the glacier,” Larter said. “PIG already makes the largest contribution to sea-level rise of any single Antarctic glacier and the fact that its bed increases in depth upstream for more than 200 km means there is the possibility of runway retreat that would result in an even bigger contribution to sea level.”

In July, R&D Magazine reported that a 5,800 square km, one trillion-ton iceberg broke free of the Larsen C ice shelf on the edge of the Antarctic Peninsula.