JUNEAU, Alaska — More than 10 times the usual amount of debris has washed ashore in North America since a magnitude 9.1 earthquake struck seven years ago off the coast of Japan and triggered a tsunami with waves up to 30 feet (9 meters) high, scientists said.

Experts have spent four years monitoring the 2011 tsunami’s aftermath and found that nearly 100,000 items washed ashore from Alaska to Oregon, Alaska’s Energy Desk reported Monday.

Marine ecologist Cathryn Murray said the debris complicated communities’ efforts to reduce shoreline trash.

“There’s not much you can do about it on a local scale. You can’t say to your own community, ‘Let’s stop using plastic bags and then we’ll stop seeing it on the beaches,'” Murray said. “In those cases, it’s not often true because it’s coming from very far away.”

Murray also said she worries that sea creatures from Japan have managed to cross the ocean with the trash.

“Because they had rafted such a long way away and they took a very slow journey across the ocean, a lot of the species ended up in quite good condition,” Murray said. “Some of them were reproductive when they landed. Some of them were growing at sea.”

She said species have always had the ability to raft on natural items, but non-degradable plastics in the ocean have made the phenomenon more likely.

Information from: KTOO-FM, http://www.ktoo.org