Black Tide

By Kathleen Adams

Battered by rough seas, a breached tanker begins to sink...

The Prestige was built in Japan in 1976 and was scheduled to be phased out in 2005. The tanker was carrying 84,849 tons of heavy fuel oil, bound for Singapore

NOV. 5-12 Tanker sails from Latvia, passing Spanish coast

NOV. 13 Flooding begins; crew evacuated

NOV. 14 Spain won't allow ship to approach coast and forces it out to sea

NOV. 15 Breach opens in vessel, which is towed to calmer waters

NOV. 19 Tanker breaks in two and sinks

HOW THE SHIP SANK

1 When the oil was loaded, two tanks on each side of the ship were left empty for stability. On Nov. 13, the two starboard tanks became flooded. It is unclear how that happened, but some crew members claimed the vessel struck a submerged object

2 Because of the flooding, the ship began listing 25DEG to starboard, increasing the stress on the hull

3 To correct the list, the crew flooded the portside tanks, but the increased load was too much for the hull, which began to crack open in heavy seas

ENDANGERED ECOSYSTEM Currents and winds have carried the slick through coastal fishing grounds and across nearly 200 miles of shoreline. The sludge has coated hundreds of seabirds and closed local fisheries. Now other areas are threatened: shellfish beds and a nature preserve for marine birds, including the near extinct Iberian guillemot

... sending nearly 3 million gallons of oil toward the coast ... The choppy waters of the Atlantic quickly spread the oil, making containment impossible. Preventing further damage and restoring the gunk-coated coast are now Spain's biggest challenges. Here are some cleanup methods:

CONTAINMENT Floating barriers are placed around the oil out at sea or along a shoreline to contain the mess. In rough seas, however, these barriers are useless. Chemical gelling agents could be used to help thicken the slick and make it more manageable

SKIMMING Vessels equipped with skimmers recover the oil from the surface of the water. Onshore, workers with shovels take up the tedious work of scooping up the sludge, along with any oily sand and debris from the beach

SOLVENTS On gravel beaches, where oil sinks and rises with the tide, aggressive microorganisms can be used to help break down the oil and disperse it. Biodegradable chemicals such as water-soluble soap are even more effective. Long term, a combination of enzymes, organisms and nutrients can accelerate the oil's degradation

BURNING On-site burning can be done only in open water, where it would pose little danger to the shoreline. The oil is first corralled with booms and then ignited--though getting oil in water to burn is difficult. A big downside: air pollution

... and trapping still more oil on the ocean floor

TWO MILES DOWN

Oil has never been salvaged at this depth before. Some experts believe that trying to recover the oil would be more dangerous than just leaving it. Since the frigid water will thicken the already highly viscous fuel oil to the consistency of tar, it is unlikely to move anywhere soon. No plans have thus been announced--at least not yet--to try to recover the tanker's 18 million gallons of oil. If the contents leak to the surface, the spill will be twice the size of the 1989 Exxon Valdez disaster

In order to evaluate the wisdom of pumping out the oil, a salvage company will probably send down a remotely operated vehicle (ROV) or small sub equipped with a camera to look at the hull and take a sample of the fuel

If authorities decide to remove the oil, this long-shot option involves using an ROV to drill holes in the hull, heating the oil or injecting a chemical to make it lighter and pumping it the two-mile distance, a very risky and delicate procedure

COULD IT HAVE BEEN PREVENTED?

If the Prestige had been allowed to move into one of Spain's small bays, its leak probably could have been contained. But forced further out into the choppy seas, the tanker sustained more damage. The distance and turbulence greatly widened the oil slick that washed ashore, compounding the environmental loss

ENVIRONMENTAL TIME BOMBS?

Two-thirds of the world's oil tankers have the older single-hull design, but they will be phased out by 2015. Single-hull tankers have been barred from U.S. ports since 2000. In an accident, double-hull tankers offer greater protection to the environment

Tankers in use today Single-hull 5,243 Double-hull 2,077

Sources: American Bureau of Shipping, International Tanker Owners Pollution Federation, SMIT, Agence-France Presse, AP

NOTE: Actual position of ship on sea floor is unknown