Radar images capture new Antarctic mega-iceberg

TerraSAR-X pictured the new berg at 23:12 GMT on Saturday

Radar satellites got their first good look at Antarctica’s new mega-iceberg over the weekend.

The EU’s Sentinel-1 and Germany’s TerraSAR-X spacecraft both had passes over the 1,270-sq-km (490-sq-mile) block, informally named “A74”.

Their sensors showed the berg to have moved rapidly away from the Brunt Ice Shelf – the floating platform from which it calved on Friday.

The good news is that no disturbance was felt at the UK’s nearby base.

The Halley research station is sited just over 20km from the line of fracture, but GPS stations installed around the facility reported continued stability.

“We didn’t think there would be a reaction simply because, glaciologically speaking, the ice around Halley is slightly separated from the area that produced A74; there’s not a good way for stress to be transmitted across to the ice under the station,” explained Dr Oliver Marsh from the British Antarctic Survey (BAS).

“Since Friday’s calving, we’ve had a lot more high-precision GPS data that measures centimetre changes in strain along a whole range of baselines, and none of these show anything different from what was happening before the calving,” he told BBC News.

Halley is currently mothballed. In part, that’s because of Covid; very little Antarctic science is being undertaken at present. But it’s also because BAS has been waiting to see how the Brunt Ice Shelf would behave when bergs started to calve from the platform.

A74 was the result of multiple cracks that have been developing in the Brunt – some over many years, some very recently. Friday’s calving could well be the first in a series of breakaways during the coming days and weeks.

Of particular interest now is the section of the Brunt directly west of Halley. This is almost completely cut through by several wide chasms and rifts, and is only held in place by a very thin stretch of ice that’s pinned to the sea floor at a location known as the McDonald Ice Rumples.

If this gives way, there might well be a reaction near Halley, with the ice under the station moving seaward at an accelerated rate.

But whether this section will actually calve is anyone’s guess.

“I don’t think there’s been a major calving there since Halley was set up in the late 1950s. Smaller pieces have come off but essentially the ice front was a lot farther back than it is now,” said Dr Marsh.

A small team briefly went into Halley in January and early February to do essential maintenance, and to check over the station’s automated instruments, including its spectrophotometer which measures the behaviour of Earth’s ozone “hole”.

One of the group’s jobs was to raise the Brunt’s GPS units above the fallen snow. Two of these now find themselves travelling with the new berg as it drifts out to sea.

Indeed, it was this pair’s data that first alerted BAS to the calving on Friday when they reported their positions as having moved by about 100m in an hour between 08:00 and 09:00 GMT. Previously, the ice had been moving by only about 8m per day.

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