Tsunami snapped off pieces of Antarctic ice shelf


The Tohoku Earthquake on March 11 unleashed massive amounts of geophysical energy.

“The tsunami and earthquake released the equivalent of 320 gigatons of TNT,” according to the U.S. Geodesic Survey, “or approximately 600 million times the energy of the Hiroshima bomb.”

Dr. Richard R. Gross of NASA’s Jet Propulsion Laboratory calculated that this huge release of energy shortened the length of a day by 1.8 millionth of a second and affected the tilt of the earth.

“Portions of North Japan moved as much as 2.7 meters closer to North America.” says Dr. Gross. “The earthquake was so strong that it shifted the earth on its axis between 10 to 25 centimeters and the redistribution of the earth’s land mass affected the rotation of the earth.”

Waves from the tsunami are now also known to have hit the Antarctic with enough intensity to break off or “calve” several mega-icebergs, each the size of Manhattan. While the Tsunami that hit Japan was 18 meters in height in some places, the waves that reached Antarctica were only 30 cm tall, but they still managed to break off an ice shelf over 80 meters thick that has been stable since the first satellite pictures of it were taken in the 1960s.

“It’s the same principal as soldiers walking across a bridge,” said Dr Douglas MacAyeal, one of three researchers that brought the link between the Tohoku earthquake and the icebergs to light. “They have to break step so as not to run the risk of collapsing it by vibrations. It’s the same principle here. Vibrations on the ocean surface caused by the tsunami…vibrated the surface of the ice at the right resonance frequency, and it just broke.”

The link between earthquakes, tsunamis, and the calving of icebergs from the ice shelf has long been suspected. Darwin, when cruising off the coast of Chile, speculated that the large number of icebergs he sighted may have been related to a recent earthquake. Several more recent studies have advanced similar ideas.

However, Kelly Brunt, a NASA scientist and the project’s team leader, says, “This event marks the first direct observation of such a connection between tsunamis and icebergs.”

One question remains. In 2004, when the Sumatra tsunami occurred, no icebergs broke off the Antarctic ice shelf. Scientists point out that in the space of just seven years, there has been a marked decline in Antarctic drift ice, which acted as a kind of buffer between the ice shelf and the open ocean. “Ice shelves are not as isolated as they seem,” says Dr. MacAyeal.

Perhaps both the Arctic and Antarctic are now showing the effects of global warming more quickly and to a greater extent than we have imagined. Be it polar bears drowning because they can’t swim the distances between increasingly isolated ice floes in the Arctic or the effect of a tsunami off the coast of Japan being felt a full world away on the Antarctic ice shelf, deep and worrisome changes are happening to the geophysical fabric of our planet.


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