125 sq km of ice knocked off Antarctica by Tsunami

ResearchBlogging.orgThe Honshu tsunami of March 11th (the one that caused the Fukushima disaster) caused the otherwise stable Sulzberger Ice Shelf to calve giant hunks of ice. Climate scientists call this "teleconnection." I call it a big whopping bunch of whack knocking off a gigunda chunka stuff. Either way, this is important and interesting.

Scientists figured this out by modeling the movement of the tsunami's energy across the Pacific and correlating this with the calving event observed from s satellite. That sounds easier than it was: By the time a tsunami wave travels a few tens of thousands of kilometers across an ocean basin, the shape of the basin, obstructions, and the effects of bouncing off of continental margins complicate the wave considerably. So, this was not just a matter of estimating the speed of the wave and then checking the ice sheets for damage. Also, a tsunami wave travelling across the ocean isn't exactly visible from a satellite, so ground based and rather diffuse data (from numerous measurement points) needed to be examined and analysed.

This is interesting because it had been suggested many years ago that ocean waves of various types, including tsunamis, could be a factor in weakening structures of ice extending from continental glaciers thus causing calving. Five years ago, one team of researchers suggested that a major storm in the North Pacific caused energy transmitted across the ocean surface to precipitate a very large calving event near Cape Adare, Antarctica in 2005. In that case, scientists concluded that the sea swell was a minor factor in that particular breakup, but it was also noted that a tsunami four years earlier had shifted the ice and contributed to its being ready to calve.

In other words, it's complicated. It isn't the case that a big wave or bunch of waves from an earthquake or a storm knocks off glacial ice that was just sitting there minding its own business. Rather, the ice is busy shifting and moving seaward and a number of different factors are in play, with ocean swells and other factors contributing to the position and moviement of the ice, and then one day the ocean-born energy provides an important part of the equation where X + Y + Z = "holy crap, the glacier just fell off."

This study presents the first observational evidence linking a tsunami to ice-shelf calving. Specifically, the impact of the tsunami and its train of following dispersed waves on the SIS, in combination with the ice-shelf and seaice conditions, provided the fracture mechanism needed to trigger the first calving event from the ice shelf in 46 years. This observation adds to the mounting evidence that environmental and tectonic conditions in the far field, including the Northern Hemisphere, can have an important role in defining Antarctic ice-shelf stability.

Oh, and there's a video:

Brunt, Kelly M., Okal, Emile A., & MacAyeal, Douglas (2011). Antarctic ice-shelf calving triggered by the Honshu (Japan) earthquake and tsunami, March 2011
Journal of Geology, 57 (205), 785-788


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The video reinforces the complex nature of the process, the calving event seems to proceed along a preexisting fault line across the length of the shelf. The tsunami somehow deposits enough energy to not only recrack along the line but also get the new icebergs moving enough to prevent refreezing. Neat that satellites can give us such a birds-eye view of large scale events.

Hi Greg- I'm first author on this paper. Great writeup! You even got gist of our quote right, without hearing it first-hand:
"holy crap, the glacier just fell off."

No matter how much the modeling or math suggested this was possible, we were all very surprised to see a Manhattan-sized Antarctic iceberg as a result of a northern hemisphere earthquake and tsunami. We thought it was wicked cool! Glad to hear that you were interested as well!

Thanks! .... And, we now expect another glacial event within the next few days to be reported. A glacier in Europe dumped a chunk of ice near a tourist boat a couple of days ago, so that makes two events, and since things 'happen' (are reported to happen) in threes, anyone standing near a glacier right now should check over their shoulder!

Wonder if there was a corresponding sea-level rise...

By Randomfactor (not verified) on 11 Aug 2011 #permalink

No, Randomfactor, the real question is whether a calving of this magnitude caused another tsunami, like in Titanic II?!?

Sorry, still a little traumatized by that movie, even though I knew it couldn't be any good going in.

Just one question - i don't know the particulars about water depths and sea bed topology in the region, but how is a tsunami able to emerge in the deep sea?

USB, I'm not sure what you are getting at exactly, but are you referring to the idea that the ice shelf is off the edge of the continental shelf?

Yes, this is such a large piece of ice, that I persume that much of it was loacated far out from shore

I am pretty sure that the ice sheets affected run over the continental shelf which varies in that region to modest in size to huge (the bay next to the ice sheet in question is all shallow). Of course, the height of the wave may not be what matters, here, but rather, the total energy and its resonance. (I'm guessing at that.)