The world's largest iceberg, roughly four times the size of New York City, has run aground after crashing into the southern tip of South America. As the New York Times reports, the event is an early warning sign of what's still to come as global warming is causing major changes in the Antarctic Peninsula.

A23a weighs nearly a trillion metric tons, making it the world’s largest active iceberg. It calved from Antarctica in 1986, making it the world’s oldest berg. And now, after drifting for half a decade, A23a has grounded itself about 56 miles (90 kilometers) south of South Georgia.

A massive superberg, four times as big as New York City, has halted east of the southern tip of South America.