Could it Happen to Us? Bowman recalled March 11's tsunami as the worst natural and human disaster he could remember. Additionally, it was the fourth largest earthquake in the world since 1900 and the largest in Japan's history. Forty percent of Japan's coastline had seawalls built to protect the island nation but a ten-meter wave surged through towns and cities, completely sweeping many of them away. As of March 25, more than 10,000 dead and 17,000 missing were reported. Bowman showed a computer animation of a solitary wave traveling at 500 miles per hour in the deep ocean and explained that these tsunami waves may be as much as 250 miles or more apart in space, occurring 20 minutes to two hours later in time. People on board a ship on the ocean could not distinguish the difference between a tsunami wave and other wave motion because the ship would only move vertically about a meter as the wave passed below it. Therefore the safest place to be during a tsunami would be on the ocean. The tsunami only becomes dangerous near shore where it increases in height and breaks. A regular surf wave also curls over itself and breaks, but except during violent storms, does not come onto shore. Another factor contributing to the complex nature of a tsunami is the hundreds or thousands of extinct volcanoes projecting up from the ocean floor, causing the tsunami to bend (wave refraction). Refraction also bends the oncoming wave near shore and causes it to come straight at the beach. The March 11 tsunami reached Hawaii after eight hours, came ashore on the West Coast of the United States after nine-and-a-half hours and had traveled throughout the Pacific in 22 hours. The 2004 tsunami that devastated Indonesia took 230,000 lives partly because the earthquake's epicenter was so close to shore and partly because that area of the world lacked an adequate warning system unlike the more sophisticated one in the Pacific Ocean located in Hawaii. He noted the preponderance of earthquake-generated tsunamis in the Pacific Ocean compared with relatively few in the Indian and Atlantic Oceans. Bowman called up a National Oceanic and Atmospheric Administration animation depicting the operation of DART (Deep-ocean Assessment and Reporting of Tsunamis) buoys strategically placed throughout the Pacific Ocean to aid in real-time tsunami monitoring. DART buoys float tethered in the deep ocean and record seismic information by a nearby bottom-mounted tsunami meter situated on the ocean floor. When struck by an earthquake, the tsunami-meter transmits the signal using sonar to the DART buoy above, which in turn transmits a radio beacon call via satellite to tsunami warning centers in Honolulu and other locations. Is the metro New York area at risk as a tsunami hazard zone? "Yes and no," depending on how long we look into the future," said Bowman. Looking back on the past 60 years or so, Bowman cited two powerful storms that caused a storm surge to flood portions of New York City - one in November of 1950 that left LaGuardia Airport flooded and a nor'easter in December 1992 that left the FDR Drive under water and seawater flooded the Hoboken train station and the PATH train systems and also inundated and shut down the New York City subway system for several days. Bowman said that we could learn a lot from the Dutch, whose major cities of Amsterdam and Rotterdam are six feet below sea level and whose hydraulic engineers are looking to protect the country against a monster storm that could occur every 10,000 years. "Building codes need to be updated in New York City." Present codes are designed for 1-in-100-year storms. This should be upgraded to 1-in-250 or 1-in-500-year storms. How do you evacuate two to three-million people if one train station floods with sea water and all of the power goes off?" Bowman also revisited a study conducted by English geologists of unstable volcanic islands collapsing in the Canary Islands and how that would create a giant tsunami racing 500 miles an hour across the Atlantic and reaching our East Coast in nine hours. "It's not likely to happen in our lifetimes, but it could.

• published: 11 May 2011
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