Massive Iceberg Finally Breaks Off From Antarctica's Larsen C Ice Shelf

This massive rift in the Larsen C ice shelf, pictured here in November 2016, created a historically large iceberg that calved off from the ice shelf around July 11, 2017. The area to the right of the crack is now afloat in the sea. John Sonntag/NASA

A massive iceberg has broken off from Antarctica, according to scientists from the University of Swansea and the British Antarctic Survey. One of the largest observed in the history of satellite imaging, the new iceberg weighs about 1.1 trillion tons (1 trillion metric tons) and measures approximately 2,240 square miles (5,800 square kilometers). The iceberg is about half the size of Jamaica, or twice the size of Hong Kong.

It's the product of a crack that spread across the Larsen C ice shelf over the past decade, but really picked up speed in the past year, taking a sharp 90-degree turn toward the water in May 2017. Scientists have been waiting for this incident, a breaking-off process called calving, which occurred sometime between July 10 and July 12. The calving was first detected in data from NASA's thermal infrared Aqua MODIS satellite and then confirmed by the space agency's Suomi VIIRS instrument.


antarctica, larsen c, map
This map of Larsen C has been overlaid with a thermal image from July 12, 2017, generated by NASA MODIS satellite data showing the iceberg has calved
MIDAS Project/A. Luckman/Swansea University

In January 2017 scientists from Great Britain's Project MIDAS monitoring the crack predicted the ice shelf would lose about 10 percent of its area when the massive iceberg calved — current measurements of the new iceberg place it at slightly larger than what had been predicted, as around 12 percent. Additionally, the new iceberg was already afloat before breaking off from the shelf, so scientists expect no immediate impact on sea levels.

"We have been anticipating this event for months, and have been surprised how long it took for the rift to break through the final few kilometres of ice," said glaciologist Adrian Luckman, lead investigator of the MIDAS Project, in an announcement of the calving. "We will continue to monitor both the impact of this calving event on the Larsen C Ice Shelf, and the fate of this huge iceberg."

This isn't the first time in recent history we've seen massive Antarctic ice shelves change. The ice shelves named Larsen A and B collapsed in 1995 and 2002, respectively. They were located further north on the Antarctic Peninsula. Following their collapses, glacial flow from inland Antarctica, which otherwise would have deposited ice on the shelves, instead added directly into the ocean, contributing to the rise of sea levels.

"Calving from all Antarctic ice shelves occurs periodically," H. Jay Zwally, a senior research scientist at NASA, told HowStuffWorks in January before the current calving incident. "Some calving is in small icebergs and less frequently is in large tabular icebergs as the one about to calve from Larsen C. This calving occurs to balance the continuous flow of ice into the shelves over the grounding line — i.e. the ground ice sheet on upstream side and floating ice shelf on the ocean-ward side."  

Some scientists are concerned this newly broken-off iceberg could presage the collapse of Larsen C, though predictions are mixed. According to a 2015 study, the calving would likely present "significant risk to stability" of the entire shelf. But a later study conducted by European researchers in 2016 and published in the journal Nature Climate Change concluded at the time that even calving of a vast iceberg from Larsen C "will be unlikely to produce much dynamic change."

As science, like our environment itself, is an ever-evolving field, researchers will need to reassess the situation now that iceberg is no longer connected to the ice shelf. Regardless, an iceberg the size of an island will present issues not just for environmentalists, but also for shipping concerns, especially if it breaks into smaller pieces.

David Vaughan, a glaciologist and director of science at British Antarctic Survey, told Reuters that scientists will need to monitor the ice shelf to see what happens — and whether glacial flow issues similar to those of Larsen A and B in the past will occur.

"If Larsen C now starts to retreat significantly and eventually collapses," he said, "then we will see another contribution to sea level rise."

According to Project Midas' Adrian Luckman, several outcomes are possible for the iceberg, which will likely be named A38. "The iceberg is one of the largest recorded and its future progress is difficult to predict," he said. "It may remain in one piece but is more likely to break into fragments. Some of the ice may remain in the area for decades, while parts of the iceberg may drift north into warmer waters."