Last Month’s Mysterious Cape Cod Tsunami

A "Rissaga," or meteotsunami. [Photo by María Amaro Jiménez (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons]

A “Rissaga,” or meteotsunami. [Photo by María Amaro Jiménez (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons]

On June 13, 2013 at 3:27PM, a tsunami of mysterious origins swept through Cape Cod.  “It was the strangest thing I’d ever seen,” said one 60-year-old Falmouth native and restaurant owner.  The water in front of his restaurant seemed to be retreating out of the harbor, “…almost like a riptide,” he said. “Then suddenly surged back in,” a slush which continued for roughly an hour.

Measuring in at only one and a half feet, the June tsunami was merely a distant cousin of Japan’s 2011, 45 foot giant, but it was a tsunami none-the-less.  So what triggered this pint-sized harbor wave? A variety of factors can perpetrate tsunamis: underwater earthquakes caused by tectonic plate motion (as in the case of Japan), submarine landslides, asteroid impacts and even volcanic eruptions.  But there is another tsunami, provoked not by brute force, but by atmospheric pressure (hence “meteo”) At the center of a storm, the pressure is much lower than the surrounding air which can cause the water beneath it to “mound up.”  Coupled with other oceanic and atmospheric processes, that mound can gain tsunami momentum, and when encountering a funnel-like harbor (tsu=harbor, nami=waves) can become amplified.

While the world of science adopted the term “meteotsunami” only in 2006, the phenomenon has been christened by many names in the locals it visits most frequently.  In the Balearic Islands, they are rissaga, in Sicily-marubbio, milghuba in Malta, abiki in Japan’s Nagasaki Bay and in the Baltic Sea-seebar.  The waves have also graced the Yellow Sea, the Adriatic, the Aegean, the English Channel and even the Great Lakes among others.

Though meteotsunamis have remained in the shadows of their havoc-wreaking quake-instigated brethren, they do not always pass as surreptitiously as our Cape Cod sneak. The Balaeric Islands tsunami, circa summer 2006, did tens of millions of Euros worth of damage and packed a punch to 40 boats.  A 10-foot wave killed seven people in a 1954 metotsunami off the coast of Lake Michigan in Chicago.  And in 1979, a 13-foot wall of water hit Nagasaki Bay in Japan.

Is Cape Cod joining the ranks, with Balaeric and Nagasaki, as a meteotsunami destination due to last months wave?  It’s tough to say.  Seismographically speaking, meteotsunamis and quake-caused ones can bare similar signatures.  While the tsunami could be meteo-related, another source, several states southwest, may hold the key.  The underwater Hudson Canyon, at the mouth of the Hudson river between New Jersey and Long Island could also quarter the trigger in the form of a submarine landslide. However, submarine landslides, often spark only local tsunamis with waves that quickly dissipate with distance.  Not the case with our June 13th wave which was measured from buoys as far north as Massachusetts and as far south as North Carolina. Scientists next step is to investigate potential scenes of the crime.  On July 7th NOAA, who mapped the area in 2012, will head back with an ROV to investigate. Presumably, differences in the Canyon’s topography may help give away the perpetrator.  Stay tuned…

Sources

“Weather creates rare Cape Cod tsunami,” capecodonline.com, 6/15/13

“Investigation of Great Undersea Earthquakes and Tsunamis” Lecture by Jian Lin, Woods Hole Oceanographic Institution, 7/3/13

“Meteotsunamis: atmospherically induced destructive ocean waves in the tsunami frequency band” Monserrat et al. 2006

“These Freak Waves Can Attack Anytime Without Warning” bussinessinsider.com

“East Coast Tsunami: What’s the Risk?” news.discovery.com 6/28/13

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