HONOLULU -- Lumber, boats, and other debris ripped from Japanese coastal towns by tsunamis last year have spread across some 3,000 miles of the North Pacific, where they could wash ashore on remote islands north of Hawaii this winter.
The National Oceanic and Atmospheric Administration estimated the first bits of tsunami debris will make landfall soon at small atolls northwest of the main Hawaiian Islands.
Ruth Yender, the agency's tsunami marine debris coordinator, said Tuesday that agency workers looking for the debris were boarding Coast Guard flights that regularly patrol the archipelago.
NOAA also asked scientists stationed at Midway and other atolls to look for the debris.
Ms. Yender said that so far, no debris confirmed to be from the tsunamis has landed on American shores, including large buoys suspected to be from Japanese oyster farms found in Alaska late last year.
The buoys would have had to travel more rapidly than currents to get to Alaska at that time if they were set loose by the March 11 tsunamis.
Similar buoys have washed ashore in Alaska and the U.S. West Coast before the tsunami, she said.
Nikolai Maximenko, a University of Hawaii researcher and ocean currents expert, said the dispersion of the debris makes it more difficult to track but no less hazardous.
"In many cases it's not density that matters, it's total amount," Mr. Maximenko said. "For example, if there's a current flowing around Midway island, that island would collect debris like a trawl moving across the ocean. It will collect all the debris on its way."
One to 5 percent of the 1 million to 2 million tons of debris still in the ocean may reach Hawaii, Alaska, Oregon, Washington, and British Columbia, Mr. Maximenko said.
That would only be a portion of the 20 million to 25 million tons of debris the tsunamis generated altogether, including what was left on land.
The tsunami left thousands dead and severely crippled Japan's Fukushima Daiichi nuclear power plant.
Almost a year after the disaster, the chief of the Fukushima Daiichi plant said the facility was using makeshift equipment -- some mended with tape -- to keep crucial systems running
"I have to admit that it's still rather fragile," plant chief Takeshi Takahashi said Tuesday. "Even though the plant has achieved what we call 'cold shutdown conditions,' it still causes problems that must be improved."
The government announced in December that three melted reactors at the plant had stabilized and that radiation releases had dropped. Fully decommissioning the plant will take decades, and it must be kept stable until then.
The operators have installed multiple backup power supplies, a cooling system, and equipment to process massive amounts of contaminated water that leaked from the damaged reactors.
But plastic hoses cracked by freezing temperatures have been mended with tape. A set of three pumps sits on the back of a pickup truck. Along with the pumps, the plant has 1,000 tanks to store more than 160,000 tons of contaminated water.
Radiation levels in the Unit 1 reactor have fallen, allowing workers to repair some damage to the reactor building.
No one has died of radiation exposure.