World's biggest iceberg is about to melt down to nothing

B-15Z in the southern Atlantic Ocean.
B-15Z in the southern Atlantic Ocean. Photo credit: NASA

The remains of what was once the biggest iceberg the world has ever seen are about to melt away.

Iceberg B-15, as it was dubbed, broke off Antarctica's Ross Ice Shelf in 2000. It was 295km long and 37km wide - not only bigger than Jamaica, but six times larger than Stewart Island.

After spending more than a decade drifting around the coast of the southern continent and splitting into smaller pieces, the largest chunk - B-15Z - has made a dart for the equator.

It floated through the Weddell Sea next to the Antarctic Peninsula in May last year, and is now about to hit warm tropical waters in the Atlantic Ocean, photos taken by the crew aboard the International Space Station show.

"When the May 2018 photograph was acquired, the berg was about 150 nautical miles northwest of the South Georgia islands," NASA's Earth Observatory said in a statement on Friday (NZ time).

"Icebergs that make it this far have been known to rapidly melt and end their life cycles here."

Though smaller than the monster iceberg that spawned it, B-15Z is still 18.5km long and 9km wide - about 50 percent larger than Hamilton. In February B-15Z was reported to be 24km long and 11km wide, so it's shrinking fast.

It also has a massive fracture down the middle (kind of like Hamilton) and small pieces are splintering off.

B-15 in 2005, when it split into smaller pieces.
B-15 in 2005, when it split into smaller pieces. Photo credit: Reuters/ESA

As it enters a warmer part of the world, NASA glaciologist Kelly Brunt says it'll disappear pretty quickly.

"They tend to pond with water, which then works its way through the iceberg like a set of knives."

A piece of B-15 were seen off the coast of Timaru in 2006, and in 2011 more pieces were photographed from space about 2400km east of Dunedin. Those bits left the main iceberg years before it started its journey north last year.

When it first calved in 2000, B-15 was the biggest iceberg in recorded history. A chunk that broke off the Larsen C Ice Shelf last year was about the size of Bali - huge, but only half the size of B-15.