Journal of Geophysical Research: Earth Surface
© 2014 American Geophysical Union
Impact Factor: 3.44
ISI Journal Citation Reports © Ranking: 2013: 24/173 (Geosciences Multidisciplinary)
Online ISSN: 2169-9011
Associated Title(s): Journal of Geophysical Research
Capsizing icebergs release earthquake-sized energies
A large iceberg can carry a large amount of gravitational potential energy. While all icebergs float with the bulk of their mass submerged beneath the water's surface, some drift around with precarious orientations-they are temporarily stable, but an outside push would send them tumbling over. Large icebergs, like those that split from the Jakobshavn Isbr� glacier in Greenland, can release the energy equivalent to a magnitude 6 or 7 earthquake when they capsize. A 1995 event demonstrated the potential for destruction, as a tsunami spawned from a capsizing iceberg devastated a coastal Greenland community. Measuring how energy is dispersed during capsizing is crucial to understanding the risk associated with these events but is also key to determining their larger role in surface ocean dynamics. Using 27 - 10 cm polyethylene iceberg analogues with varied widths, Burton et al. (2012) measured how energy is released to the surrounding water during capsizing. A camera tracking a floating buoy measured the height of any tsunami waves, and analysis of the iceberg's movement let them determine the kinetic energy involved in the rotation. Corroborating earlier research, the authors found that the size of any tsunami waves will be at most 1% of the iceberg's initial height. Further, they found that 84% of the iceberg's original potential energy would end up as turbulence or heat in the surface ocean waters. While such a large amount of turbulence would be important for surface dynamics in the open ocean, it would be particularly powerful in a semienclosed region like the fjord surrounding the Jakobshavn Isbr� glacier, where dozens of icebergs spawn each summer. In the fjord, trillions of megajoules worth of turbulence redistribute the water, destroying temperature and salinity stratifications.