SEATTLE (Reuters) - Debris from Japan's 2011 tsunami will continue to litter the North American coastline over the next three years, with everything from refrigerators to lumber and sports balls still floating offshore in the Pacific, an expert said on Tuesday.
About one million tonnes of debris were still lingering in the Pacific Ocean four years after a magnitude 9.0 earthquake, the most powerful ever recorded in Japan, set off a series of massive tsunami waves that devastated a wide swathe of Honshu's Pacific coastline and killed nearly 20,000 people.
It also damaged the Fukushima Daiichi nuclear plant, leading to a series of explosions and meltdowns in the world's worst nuclear disaster since Chernobyl 25 years earlier.
The Oregon Sea Grant, a programme at Oregon State University funded by the National Oceanic and Atmospheric Administration (NOAA), has been working with researchers at Japan's Tottori University to monitor tsunami debris.
An estimated five million tonnes of wreckage - everything from cars to building materials, boats and docks - washed into the Pacific, and about 70 per cent sank quickly to the ocean floor, experts in the United States and Japan said.
But items with buoyancy eventually caught the Pacific Ocean's currents and have since lodged as close as 40 km off the North American coast, covering an area from California to Alaska, said Sam Chan, an aquatic invasive species expert at Oregon Sea Grant.
"When it comes into our Pacific shores in North America it (the debris) tends to stay offshore for months and sometimes a year," he said. It's not until we actually end up with local storm events or changes in the season that debris comes ashore."
Over the past year, warmer temperatures and a lack of major storms have kept most of the refuse from washing up on land, but wave patterns and other oceanic conditions were likely to send more items headed to West Coast beaches this summer, he said.
Last summer, 26 Japanese boats floated ashore in Oregon, Washington state and Canada's British Columbia, Chan said.
In 2012, a massive 20m-long dock ripped from its moorings in Japan floated up on a beach north of Newport, Oregon, southwest of Portland.
The Japanese team has sent out about 70 battery-operated tracking devices that float at different heights to simulate different kinds of debris in order to understand where in the Pacific the refuse has clustered.