Anyone who saw any of the footage of the devastation wreaked upon Japan by the March 11 earthquake and tsunami - as most of us have done – can have no doubt about the overwhelming power they contained and unleashed. Now researchers have found that the force of the tsunami was so great that it was able to break several pieces of ice, totaling more than twice the size of Manhattan, from an Antarctic ice shelf 8,000 miles from the quake's epicenter.
Writing in the online version of the Journal of Glaciology, Kelly Brunt of NASA's Goddard Space Flight Center and colleagues describe how researchers have long suspected that repeated flexing of an ice shelf as a result of forces from a seismic event could lead to the calving of icebergs, but there had been no observations to confirm the theory. And so, shortly after the March 11 earthquake struck, Brunt and colleagues calculated the likely path the tsunami would follow throughout the Pacific basin in anticipation of such an event occurring.
They focused their attention on the Sulzberger Ice Shelf, on the northeast coast of the Ross Sea south of New Zealand. Remarkably, approximately 18 hours after the tsunami struck Japan, a gap in the clouds above the ice shelf revealed the presence of one large iceberg that had broken off. Recourse to cloud-penetrating radar satellites uncovered the existence of another large iceberg with several smaller ones also breaking away behind them. Brunt and colleagues estimate that by the time the tsunami reached the Antarctic coast, waves were only a foot or so high, but even so, the scientists say the consistency of the swell was enough to cause the icebergs to fracture from an outcrop of ice that had apparently stood unbroken since at least 1965, when it was captured by aerial photographs.
"In the past we've had calving events where we've looked for the source. It's a reverse scenario – we see a calving and we go looking for a source," Brunt said in a press release. "We knew right away this was one of the biggest events in recent history – we knew there would be enough swell. And this time we had a source."
Images by the European Space Agency/Envisat. Video by NASA/Goddard