top of page

Larsen C's 'Delaware-size' iceberg breaks free

The countdown – you could think of it as a death watch – had been going on for weeks, months and years in the case of glaciologists and avid climate change and Antarctica experts and geeks.

It was complete with all but an on-screen CNN-type minute-by-minute countdown clock. That would be impossible given the relative imprecision of the “hours, days, or weeks” best estimates of precisely when the closely-watched Larsen C ice shelf would rip free and be cast aside. (Rhode Island got off easy this time, with popular size comparison references in this case pointing not to the “Ocean State” but to the “First State” of Delaware.)

The end itself, inevitable for all but lacking the exact ETD (expected time of departure) was first announced in early morning East Coast time July 12, as officially determined by the Project MIDASUnited Kingdom-based research group most closely tracking the Larsen C ice shelf’s calving of “one of the largest icebergs on record.”

Popular network and cable news programs and organizations like the National Geographic Society for the better part of a year have been flying over and watching intently: the large crack formed in the surface of the Larsen C ice shelf; it kept moving toward the north and then somewhat toward the northeast, snail-like at times, occasionally picking up the pace, but always resolutely.

Scientists were of course the first to recognize the final calving as a matter of “when” and not of “if.” And with the calving now behind them, they turn to “What’s next?” It’s not a matter of short-term sea-level rise they’re expecting at this point.

As that calving process was under way, Yale Climate Connections regular contributor and independent videographer Peter Sinclair interviewed scientists to gain insights into the process of this historic calving – and what it tells us about climate change.

As background, Larsen C is the largest of several ice shelves on the Antarctic Peninsula to have undergone major changes in the last two-plus decades. Larsen A broke up in 1995. Even larger, the Larsen B spectacularly disintegrated in 2002, an event recorded in a widely publicized series of satellite images. Both A and B are north of Larsen C.

“It’s pretty clear that we’re losing mass. It’s pretty clear that we’re almost certainly accelerating in our mass loss,” says Jeremy Bassis, a glacier expert at the University of Michigan. “Starting in the nineties and early two-thousands, we saw some pretty spectacular changes.”

In the case of Larsen B, Bassis points out, “Here’s an ice sheet that had been sitting there, stable for 10,000 years, and it’s gone.” It all happened over just six weeks.

That may or may not be the pattern for Larsen C, says Bassis. He explains that the situation is “less clear” on whether the Larsen C calving is “the beginning of the end, or just part of its usual cycle.” When Larsen B calved, the iceberg “all of a sudden started to disintegrate completely.” A similar disintegration may or may not occur, and may well occur only more gradually with Larsen C. Scientists will now be closely monitoring and keeping a close watch.

The floating ice tongues like the Larsen shelves buttress and support – in effect, hold-back – large masses of ice further-up on the ice sheet. So the shelves themselves serve as roadblocks to the would-be calving that leads to increased sea-level rise.

“When you lose that buttressing force, you allow the upstream glaciers to flow faster,” says Kelly Brunt, of NASA’s Goddard Space Flight Center.

That faster flow, says Bassis, is what accelerates sea-level rise.

Now scientists are watching to find out if Larsen C will proceed in the direction of rapidly disintegrating, as did the A and B shelves.

“We seem to have an evolution in that direction right now with the Larsen C ice shelf,” says Eric Rignot of the NASA Jet Propulsion Laboratory.

But it’s important to note that Larsen C is closer to the South Pole, and colder than the A and B shelves.

That might mean it could take a while, even a decade or more of warmer summers, for Larsen C to fully go the way of A and B, according to Ted Scambos of the National Snow and Ice Data Center in Boulder, Co.

An important mechanism in determining that progression will be water on the surface of the shelf. When ice melts and forms lakes on the surface, that water can force its way deep into the interior of the ice, a process called “hydro-fracking.” When that happens extensively, as it did on Larsen B, “eventually, you have an ice shelf that is essentially a rubble field,” says Bassis.

“Is this just part of the regular cycle of icebergs occasionally breaking off? We’re not really sure for Larsen C. It’s the place where people are looking most closely for one of these next big events.”

Time will tell. So maybe it’s time to re-set the countdown clocks.

Editor’s note: Peter Sinclair and Bud Ward collaborated closely on the text accompanying this video. Sinclair was in Greenland at the time of the actual calving of Larsen C and did not participate directly in the completion of the actual text.

bottom of page