Seen in stunning pictures from either of Earth’s Poles, icebergs are most often white-blue objects. But like an artist willing to experiment with whatever resources are available, nature is also capable of creating startlingly green icebergs, and they can be found only in Antarctica.

Although the scientific literature is full of reports of these emerald ice blocks going back more than a century, no one could adequately explain where they were coming from. Now, a team of researchers may have finally cracked the case.

According to their work, the unusual hue seems to be a combination of two distinct processes. First, bubble-free icebergs need to form at the bases of ice shelves jutting out into the Southern Ocean. At the same