The photos are uncannily similar: Bridges destroyed in Biloxi Back Bay, bridges destroyed in Namegata, Japan; rail containers scattered through Gulfport, rail containers scattered in Sendai, northern Japan.
Even a satellite image of a huge whirlpool created by the catastrophic Japan tsunami bears an eerie resemblance to a satellite photo of the swirl of Hurricane Katrina in South Mississippi in August 2005.
“I’ve been struck by the similarity, also, in the images I’ve seen, as have colleagues I’ve chatted with,” said oceanographer Stephen Baig, retired director of storm surge research with the National Hurricane Center. He studied and viewed the aftermath of both hurricanes Camille and Katrina.
Solomon Yim, director of the Hinsdale Wave Research Laboratory at Oregon State University and one of the world’s foremost tsunami experts, also saw and studied Katrina’s aftermath. He also has been struck by the similarities in damage seen in Japan.
“I saw the cargo containers washed in (by Katrina), and I’ve seen the cargo containers (in Japan) carried in,” Yim said. “The debris swept in, damaging other buildings. The entire casinos hit other buildings. We see similar things after the tsunami, as well as all the wooden frame buildings being destroyed.”
Scientifically, a tsunami and a hurricane storm surge differ in some ways. But their end result, destruction, is similar both visually and scientifically, tied to the most basic physical laws and classical mechanics.
“The first thing to point out is Newton’s laws, particularly that force equals mass times acceleration,” Baig said. “Regardless of how the water is moved, if the same force is obtained, then the same effects are going to be observed.”
Tsunamis are powered by underwater disturbances -- earthquakes, volcanic explosions, landslides -- and generally occur in the Pacific Ocean, about 80 percent.
They typically produce three to seven large waves that hit within 15 minutes to half an hour apart, Yim said.
They can be very hard to detect when offshore.
“The bump they cause out in the ocean is tiny, sometimes less than an inch,” said Helmut Portmann, director of the National Weather Service’s National Data Buoy Center at Stennis Space Center. “The amount of warning you get with a tsunami depends on where they are created and where they are located. In Japan, the problem was it was created close. The same thing happened off Chile.”
Imagine, then, Katrina’s tidal surge arriving with only hours of warning, not several days as is usually the case with hurricanes.
“A tsunami can occur within minutes or hours, and move at a speed of 500 mph, like the speed of an airplane,” Yim said. “That’s why, when estimating how long it would take it to get from Japan to San Francisco, you can do so by estimating the flight time. It can move all the way across the ocean and arrive within 10 hours.
“But a storm surge can take 24 hours, 48 hours to form -- the speed of the eye of the hurricane is the speed of the surge,” Yim said.
A hurricane’s storm surge is powered by low pressure and wind. Less a wave than “rising water,” Baig said, its most destructive forces are from smaller wind-driven waves atop the surge.
“Wind waves on top are what batter and shatter things in a storm surge,” Baig said. “The rising water brings the ocean into places where it wasn’t expected to be, and those shorthand waves are doing the structural damage more so than the rising water.”
Yim said: “With Katrina, you had two actions -- the inundation from the surge, then the storm waves hitting the structures many, many times. Wind generated waves of a period of every 6 to 16 seconds usually accompany a storm surge. Imagine in an hour having hundreds of waves hitting the same structure.
“Tsunamis usually are solitary waves that are independent of each other, given that each wave is 15 to 30 minutes apart.”
Baig said: “A tsunami is a wave, a huge wave, deep-ocean wave that doesn’t do much until it comes in and begins to feel the bottom, interact with the seabed and build amplitude,” Baig said. “That’s why you don’t really see waves breaking out in the middle of the ocean.”
But the destruction either leaves behind can be very similar. Scientists researching results from pre-modern era coastal disasters sometimes argue whether tsunamis or storm surges were the cause.
As with Katrina’s storm surge vs. its wind, Japan’s tsunami appears to have caused far more damage than its preceding earthquake. Early estimates are that the tsunami caused 90 percent of the damage.
To read the complete article, visit www.sunherald.com.