One of the primary causes of oil spilling into marine environments in an oil spill is people who are careless or make mistakes, according to the Office of Response and Restoration. Such incidents involve barrages, tankers, refineries, pipelines and storage facilities. Other causes include equipment breakdowns, natural disasters and deliberate acts, such as terrorism, war, vandalism or illegal dumping.
The Exxon Valdez Oil Spill Trustee Council lists several reasons that this tanker ran aground in March 1989. They are all acts of carelessness or human mistakes. While tests showed the captain of the Valdez to have alcohol in his system several hours after the accident, the state of Alaska found him not guilty of operating the vessel under the influence of alcohol.
As oil floats on the ocean, it spreads rapidly across the surface to form an oil slick. Eventually, it spreads to form a very thin layer, known as a sheen, with a rainbow-like appearance. Oil spills are harmful to fish, shellfish, birds and marine animals. The oil affects the ability of fur and feathers to repel water and insulate the animals from the elements. Oil is also toxic to animals that ingest it in attempts to clean themselves.
While the Exxon Valdez spill is no longer among the largest 50 oil spills, it affected 1,300 miles of shoreline. Marine biologists estimate it to have killed 250,000 seabirds, 2,800 sea otters and 22 killer whales, according to the Exxon Valdez Oil Spill Trustee Council.