Residents on the coast of Spain could only watch and wait as a damaged oil tanker called the Prestige floundered, split and then sank into the ocean some150 miles off shore.

Although the Nov. 19 oil spill is smaller than others in years past, the accident has dealt a heavy blow to the local economy and environment. The Spanish government says 4.5 million gallons of oil have leaked from the Prestige, enough to cause considerable damage to the Spanish coastline.

The Sinking of the Prestige

Stormy seas, old age and poor construction are being blamed for the spill. After days of bad weather, the oil tanker encountered strong winds, which ripped a 60 foot hole in its side. The vessel began taking in water through the hole, causing it to break in two and sink into the Atlantic Ocean. It was carrying more than 20 million gallons of oil.

Scientists believe the 15.5 million gallons that remained in the ship after it sank may have solidified due to the cold temperatures of the water below the surface. It is unclear what will happen when the tanker begins to rust and break apart at the bottom of the ocean.

Why it Happened

Aging, single-hulled tankers like the Prestige are vulnerable to oil spills. If the hull is punctured or ripped, no barrier stands between it and the oil to prevent a spill. Many newer tankers have a double-hull design, which protects the oil from spilling if the first hull is broken.

Questions have also been raised as to whether the Prestige was sea-worthy. Built quickly and cheaply in Japan in the 1970s, the tanker had undergone major repairs in 2001 after large cracks were found in the ship's hull.

Consequences

The economy of Spain's Galacia region -- the area most affected by the spill -- is based on fish and other seafood, including beds of shellfish now covered in sludge. The tourism industry could also suffer losses, since people are less likely to visit damaged beaches.

Wildlife have been impacted by the oil too. Oil causes hypothermia by making feathers or fur to stick together, ruining an animal's natural insulation. In Spain, hundreds of birds have already been found trapped in oil, including members of at least one endangered species.

Oil also poisons the animals who ingest it trying to clean themselves or scavenging dead animals; it can cause liver damage and blindness and can impair reproduction.

Cleaning Up

Combating an oil spill at sea requires efforts on both water and land. First, the oil in the water must be contained as much as possible to reduce the amount that hits the shore. Workers surround the oil with long, flexible plastic floats and then attempt to suck up the spill using vacuum-like cleanup vessels.

On land, some of the most successful oil-cleaning techniques are low-tech. Frequently oil is shoveled, scraped, sprayed -- even wiped off individual rocks. The process is slow and laborious, and requires a massive human effort. More than 10,000 people worked to clean up the 1989 Exxon Valdez spill in Alaska's Prince William Sound.

Chemicals can help dissolve the oil, but some have long-term damaging effects on the environment. Another option is the use of bacteria that thrive on the hydrocarbons in the oil, breaking them down into simpler compounds. However, the method is slow, and by no means a "cure" to a spill, science teacher Rebecca Sacra said.

But despite all human efforts to clean up the millions of gallons of sludge that result from oil spills, scientists are beginning to think that the best way to get rid of the oil is to let nature do the work. The continual lashing of waves and wind on the beach did more to clean Prince William Sound than all of the human work involved, scientists working on the clean-up discovered.

Preventing Future Spills

Whether the sinking of the Prestige becomes a chapter or footnote in oil spill history, it may speed up laws designed to prevent these catastrophes.

The Exxon Valdez spill prompted numerous changes to laws governing oil tankers in the United States. For example, oil tankers are more carefully monitored and escorted through sensitive regions like Prince William Sound. Also, all tankers in the area will be required to be double-hulled by 2015.

International organizations hope to phase out the use of single-hulled tankers over the next decade, but about half of the large tankers in operation are single-hulled, marine intelligence organizations estimate.

-- By Emily Birr, Online NewsHour