About a month ago my family and I were privileged to watch the Margerie Glacier in Canada's Glacier Bay calve [click on photo for larger view]. Our cruise ship patrolled about a quarter mile away from Margerie for over an hour and we got to see the birth of a handful of chunks. It was impressive to see pieces the size of large buildings come crashing down into the water and float away as tiny icebergs. First we'd see the iceberg-to-be start to fall and then, a second or two later, we heard the snap, crackle, and pop! The crew of the Holland-America Ryndam served cups of thick, hot split pea soup on deck to celebrate our visit.
The image shows the tongue of the Petermann Glacier prior to separation (31 July). The animation shows separation (4 August) and later after it had moved a few miles away (7 August). [Click CLICK HERE TO SEE HI-RES ANIMATION]
The images were generated using Synthetic Aperture Radar (SAR) an advanced, computer-intensive technology with which I am familiar due to my work on military avionics. It is sometimes called Side-Looking Radar. An aircraft (or satellite) flies in a straight line, and emits radar pulses to the side. The return signals are recorded in memory storage and processed to generate an image with high precision equivalent to a "lens" the length of the flight segment. (As we all know, in optics, the larger the lens the sharper the images, and the equivalent applies to synthetic-aperture radars as well.)
The Petermann Glacier grows about 1 KM (5/8 mile) every year. The piece that just broke off is about 30 KM (19 miles) long and thus represents about 30 years of growth.
Normally, much smaller pieces break off on a regular basis - as we witnessed at Margerie - but every several years a big one lets loose, the last one in 1991. Close examination shows a crack developing that may open up in perhaps ten years, giving birth to what could be up to an 8 KM (5 mile) long iceberg.
For comparison, the most recent Petermann iceberg is about 30 x 14 KM (~19 x 8 miles) while Manhattan Island in New York City is about 20 x 4 KM (~12 x 2 miles).
Read more about this event and see some wonderful images at Watts Up With That and the European Space Agency.
Of course, this giant glacier calving has been interpreted as further proof of the dangers of Global Warming. As regular readers of this Blog know, I am a lukewarmer-skeptic on human-caused warming. I accept that we have been in a warming period for the past 150 years or more (since the Little Ice Age) and that human activity is responsible for perhaps 10% of that warming, while the remainder is due to natural cycles. (see Atmospheric Science Made Simple, and Is the IPCC Process Scientific? and Explaining Away Climategate - 1 and Explaining Away Climategate - 2.)