What causes an iceberg to overturn?

Icebergs — the floating giants scattered across the North Atlantic, Antarctic, and other oceans — may appear stable. After all, only a small portion, about one-tenth, is visible above the water’s surface, with the majority submerged.

Yet occasionally, even massive icebergs, as large as cities with towering peaks hundreds of feet high, can topple over.

Icebergs are created when a piece of ice breaks away from a glacier, ice shelf, or another iceberg. For example, ice shelves form in cold regions like Greenland, where the glacier’s edge extends over land and into the water, causing the ice to crack.

An iceberg is most likely to flip during its early stages. When a chunk detaches, it's called calving. After separating from the parent, these large, icy pieces can be irregular in shape and often tip and roll as gravity pulls much of their mass below the water's surface.

Justin Burton, an assistant professor of physics at Emory University, compares the breaking away of ice shelves to squeezing toothpaste from a tube. 'A small amount of toothpaste comes out, then it breaks off, and more follows, breaking off again. This creates thin pieces of ice that flip over right after breaking off.'

In other cases, the melting of ice can destabilize an iceberg. Since fresh water is less dense than salt water, and icebergs are made of fresh water, their weight distribution shifts as they melt.

Burton mentioned that climate change is leading to more icebergs flipping, though it's still uncommon for people to witness such an event.

When icebergs flip over, they can appear quite different from the snow-covered peaks we typically envision. Filmmaker Alex Cornell observed a flipped iceberg that resembled a large blue-green gemstone, as reported by Smithsonian magazine. The ice was probably ancient and highly compressed, forcing out the small air pockets that make ice appear white. As a result, the ice absorbs some red light, giving it a blue hue when the light is reflected.