A freight car-sized dock that was torn loose by last year’s tsunami in Japan and washed up on an Oregon beach 5,000 miles away has been scraped clean of seaweed, shellfish and other organisms and sterilised with torches to prevent the spread of invasive species.

A nearly-70ft dock torn from a fishing port in northern Japan during the tsunami drifted thousands of miles across the Pacific Ocean and floated ashore on an Oregon beach.