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Abstract: Exceptions to the Rules of Oil-Spill Behavior: Case Studies of Major Oil Spills of the Past Twenty Years

Miles O. Hayes

Studies of major oil spills over the past 20 yr have allowed an evolution of our understanding of how to respond to and remediate the environmental impacts from such spills. There have been a number of spills for which follow-up research has provided major turning points that allowed the development of certain rules of oil-spill behavior. For example, the spill of over 100,000 tons of crude oil by the tanker Urquiola, which impacted a wide range of habitat types on the coast of Spain in May 1976 demonstrated the importance of hydrodynamic energy level in natural cleanup processes. Research on the spill of over 200,000 tons of crude oil along the coast of France by the tanker Amoco Cadiz in March 1978 allowed a better understanding of the long-term effects of spilled il on exposed tidal flats and salt marshes. The oil spilled by the tanker Exxon Valdez in Prince William Sound, Alaska, in March 1989 impacted many miles of gravel beaches, which were treated by a number of methods, including some innovative berm-relocation techniques. As these studies progressed, it became increasingly clear that a thorough understanding of the coastal geomorphology and processes of the spill site was essential for the development of meaningful contingency and response plans.

Research on the impacts of intertidal habitats of the coast of Saudi Arabia during the Gulf War spill of 1991 indicates that some previously held concepts on oil behavior and fate on shorelines must be revised. This is partly due to the unprecedented magnitude of the spill (20 times as much as the Exxon Valdez). One of the best established rules of oil-spill behavior was that the depth of oil penetration on sand beaches and tidal flats increases with increasing sediment grain size. However, no such correlation was found on the Saudi Arabian coast, primarily due to the presence of secondary porosity (e.g., bubble sand. extensive burrows, and gypsum crystals). The oil penetrated to depths of tens of centimeters, even in fine sand,

which has significantly slowed natural removal processes and weathering rates. These sediments remained heavily oiled with incipient asphalt pavements forming two years after the spill.

AAPG Search and Discovery Article #90985©1994-1995 AAPG Distinguished Lecture