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LOS ANGELES — The National Oceanic and Atmospheric Administration (NOAA) has been doing some serious myth-busting after news reports claimed a massive island of debris from the 2011 Japan tsunami was headed for the West Coast.

There is no floating mass of debris, the agency says.

The disaster swept millions of tons of material out to sea. While some has washed up on the West Coast and Hawaii, what remains afloat is widely scattered across the Pacific.

The source of alarm was a map NOAA posted online without fanfare Sept. 23. The agency has updated the graphic every month or two since developing a debris-tracking computer model shortly after the tsunami.

The latest version shows a blob-shaped zone more than 1,000 miles wide northeast of Hawaii, identifying it as the region with the highest concentration of debris.

Last week, media outlets across the world took notice, warning of a floating island of debris the size of Texas and a “toxic monster” headed for the West Coast.

“This kind of caught fire,” said Keely Belva, a NOAA spokeswoman who spent a full day last week on the phone clearing up misperceptions.

A post on the agency’s marine-debris blog laid out the reality: “Here’s the bottom line: There is no solid mass of debris from Japan heading to the United States.”

The post added that the debris is “spread out so much that you could fly a plane over the Pacific Ocean and not see any debris since it is spread over a huge area, and most of the debris is small, hard-to-see objects.”

NOAA officials said their computer model is not a forecast of where the debris is headed but a “hindcast” that uses winds, ocean currents and weather to show the last area the debris was likely to be.

“It’s kind of a snapshot on that day of where we think the marine debris is,” Belva said. “There’s not an island, but a higher concentration of marine debris versus the rest of the North Pacific.”

Marine debris is one consequence of the magnitude 9.0 earthquake that struck off the coast of Japan on March 11, 2011.

Scientists have been tracking that material’s journey across the Pacific Ocean since, as fuel tanks, volleyballs and fishing vessels have drifted for thousands of miles and appeared on U.S. shores. It’s a massive, tragic experiment — the first time it has been possible to observe so much debris as it dispersed from a single point.

NOAA has collected close to 2,000 sightings of tsunami debris from the West Coast and the Hawaiian Islands, and traced 35 pieces back to the tsunami.