German satellite on 'berg watch'

The German radar satellite TerraSAR-X is on "PIG watch".

The spacecraft, which circles the globe at an altitude of 500km, is returning regular images of the Pine Island Glacier (PIG) ice shelf.

Scientists expect its observations to alert them to the birth of a monster iceberg covering some 750 sq km.

A huge crack in the shelf was first noticed in TerraSAR-X data back on 13 October. A Nasa aeroplane also got photographic confirmation the next day.

The crack seems to have propagated in two main steps - the first break tearing a 24km-long gash in the shelf; the second, just a few days later, opening up the fracture to 28km in length.

A few more km and the tabular block of ice will be floating free of the shelf.
"These are brittle failures, not ductile failures," explained Prof Angelika Humbert from the University of Hamburg. "When they break, they break really quite fast - typically, at one third the speed of sound."

That means the initial gap in the shelf would have opened up along its full length nearly instantaneously.

Prof Humbert has been describing the TerraSAR-X monitoring effort here at the European Geosciences Union (EGU) meeting in Vienna, Austria.


The German Space Agency (DLR) satellite returns a picture of the PIG shelf about every third day, although it is 11 days before it gets exactly the same viewing angle.

Being a radar mission, TerraSAR-X sees right through cloud and so is guaranteed to catch the "calving" event - once it has happened - on its next pass.

"I'd bet a single malt it will go in the next six months," Prof Humbert told BBC News.

"We'll probably be the first to see it go. I hope so, but that's not so important.

"What's important here is that we acquire the data. We study calving laws - for small-scale calving, which is perhaps not so interesting to the public, but also for these big events."  (BBC.co.uk)