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Japan tsunami debris helps UH researchers learn about ocean winds, currents

Japan’s March 11, 2011, earthquake and resulting tsunami were unmitigated disasters with far-reaching impacts that continue to be felt by people around the world.

However, they also presented a unique opportunity for University of Hawaii researchers to learn how wind and ocean currents interact in the Pacific Ocean to push debris from place to place.

Now, researchers say their window to learn from the disaster might be closing.

But not before they learned valuable lessons that can be used to produce computer projections of where something floating in the ocean might end up months or even years later. In fact, the researchers said they were able to use their computer modeling software to narrow down possible search areas for the Malaysian Airlines jet that went missing March 8.

“The strongest contribution, the most important thing we learned from the tsunami, is the effect of the wind on debris,” said scientific computer programmer Jan Hafner, who has worked with principal investigator Nikolai Maximenko at the International Pacific Research Center to model and document the movement of marine debris created by Japan’s tsunami as it has made its way across and around the Pacific Ocean.

“Initially, when we started, we did not have a clear understanding of what is the effect of the wind on some objects,” Hafner said. “This event gave us a much clearer idea of what the effect is on marine debris.”

Smaller, or more buoyant, items tend to sit high in the water, leaving much of their surface area to catch breezes, which often blow in different directions than the prevailing currents. As a result, they can end up in very different movement patterns than larger items that sit low in the water and mainly affected by currents, he explained. Knowing this allows scientists to make far more accurate computer models to project where certain items can go when allowed to float in the ocean.

Earlier this year, when Mexican fisherman Jose Salvador Alvarenga claimed to have survived 13 months lost at sea, drifting from Mexico westward across the Pacific in a small, disabled fishing vessel, Maximenko and Hafner were able to show he was very likely telling the truth. Using their computer modeling software, the researchers showed the path of a boat adrift would have followed a relatively narrow path during the 13-month period, eventually leading to an area spanning not more than 2 degrees latitude, or 120 miles, of where the man was found on Ebon Atoll, according to a February UH press release.

“That is one application of our product,” Hafner said. “We cannot make predictions yet, but we can make projections … showing a range of possible locations. … Using ocean surface currents and wind, we can apply those two factors on anything that floats in the ocean.”

Shortly after the tsunami in Japan, Maximenko and Hafner released a computer model showing how they thought the tsunami debris would react as it made its way across the Pacific. That model has largely remained true, Hafner said.

“Initially, we said the first places to see tsunami debris would be the West Coast of the U.S. Generally, most of the lighter type of debris was deposited on the shores there. The intermediate debris, which is half submerged, was balancing between the force of the wind and currents. In the winter, when the wind is stronger, it was being blown onto land on the West Coast. In summer, when the wind was weaker, it was following more the currents, ending up in the Pacific Garbage Patch,” he said. “The completely submerged types of debris also followed the currents and tended to accumulate in the North Patcific Garbage Patch between Hawaii and California.”

The debris that made it into the garbage patch did not necessarily stay there, however.

Often, pieces swirling about in the gyre will break off and head westward, making landfall in Hawaii or continuing on to Southeast Asia. On Hawaii Island, most of that debris ended up on windward facing shores — mainly in areas commonly known to be magnets for marine debris, including Kamilo Beach, which earned a reputation for debris and is often the focal point of community clean-up projects.

A page on the IPRC website lists all confirmed tsunami debris sightings, including 10 items found on Hawaii Island since 2012. Hafner explained there likely has been far more items that made landfall here, but the list is limited mainly by how many people reported their findings. Among them: a small freezer door bearing kanji characters, found on Kamilo Beach in February of this year; a large boat fragment weighing about 325 pounds, also found on Kamilo Beach; a large tree trunk found in Hilo Bay in January; and a large, 12-foot-tall, 20-foot-diameter metal object found in October 2012 on the shore below Naalehu.

The researchers used a variety of methods to confirm whether spotted items were actually from the tsunami, including part numbers, writing, and even identifying the species of wood used to build the items.

“On the Big Island, the first items we started seeing were made of wood, construction lumber. We have confidence it was from Japan because of the species of the tree, the tsuji, a type of Japanese cedar using in home construction in Japan and grown in Southeast Asia. It’s only found in a few places,” Hafner said.

Tracking the debris has helped perfect the team’s software, but now, Hafner said, the usefulness of tracking the items could be coming to an end.

“It’s becoming difficult to tell with time because the marine debris deteriorates,” he said. “We’re approaching that time that we won’t be able to tell if its just general debris or tsunami debris, unless we can find a specific registration number, like on boats, or license plates.”

For more information, visit http://iprc.soest.hawaii.edu/news/marine_and_tsunami_debris/debris_news.php.

Email Colin M. Stewart at cstewart@hawaiitribune-herald.com.

 

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