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USCG Summary

Prudhoe Bay crude oil has an API gravity of 27.0, and a pour point of 0 degrees
C.  The bulk of the oil spilled from the Exxon Valdez was released within 6
hours of the ship's grounding.  The general trend of the oil was south and west
from the point of origin.  For the first few days after the spill, most of the
oil was in a large concentrated patch near Bligh Island.  On March 26, a storm,
which generated winds of over 70 mph in Prince William Sound, weathered much of
the oil, changing it into mousse and tarballs, and distributed it over a large
area.  By March 30, the oil extended 90 miles from the spill site.  Ultimately,
oil would extend more than 500 miles from Bligh reef, oiling shorelines in
Prince William Sound, the Kenai peninsula, the Alaskan peninsula and Kodiak
island.  Oil impacts in the Prince William Sound region were the most severe.
In addition to the storm of March 26, the spill occurred at a time of year when
the spring tidal fluctuations were nearly 18 feet.  This tended to deposit the
oil onto shorelines above the normal zone of wave action.  
  
The diversity in shoreline types in the affected areas led to varied oiling
conditions.  In some cases, oil was present on sheer rock faces making access
and cleanup difficult, or rocky beaches with grain size anywhere from coarse
sand to boulders, where the oil could percolate to a sub-surface level.  The
spill affected both sheltered and exposed (to high wave/weather action)
shorelines.  Once oil landed on a shoreline it could be floated off at the next
high tide, carried to and deposited in a different location, making the tracking
of oil migration and shoreline impact very difficult.  This migration ended by
mid-summer 1989, and the remaining cleanup dealt with oiled shorelines, rather
than oil in the water.

Cleanup operations continued during the summer months of 1990 and 1991.  By
1990, surface oil, where it existed, had become significantly weathered. 
Sub-surface oil, on the other hand, was in many cases much less weathered and
still in a liquid state.  The liquid sub-surface oil could give off a sheen when
disturbed.  Cleanup in 1991 concentrated on the remaining reduced quantities of
surface and sub-surface oil.