Recent Morphologic Changes at Dog Keys Pass, Mississippi: Formation and Disappearance of Isle of Caprice

James B. Rucker, Jesse O. Snowden

Approximately 70 years ago the Isle of Caprice, originally known as Dog Island, emerged on the northern margin of an interchannel shoal in Dog Keys Pass, located between Horn and Ship Islands, 18 km southeast of Biloxi, Mississippi. Because the island was emergent for less than 15 years, it would probably have gone largely unnoticed were it not for its colorful history as a popular gambling and sunbathing resort during the Prohibition era.

The Isle of Caprice was not a true barrier island like neighboring Horn and Ship Islands, but rather an emergent shoal that developed from the coalescence of several small ephemeral sand keys known locally as the Dog Keys. Early bathymetric charts show that between 1854 and 1917 Horn Island migrated 3,600 m westward into Dog Keys Pass. This island migration restricted the current flow through the pass. The current velocity increased, causing a secondary channel to the west to be eroded. The formation of a secondary channel left an interchannel shoal between the original Dog Keys Pass and the new channel, Little Dog Keys Pass. Sand eroded during the development of the secondary channel was redeposited on the interchannel shoal and supplied the sediment needed to build and nourish the I le of Caprice.

The island formed and grew rapidly between 1917 and 1924, reaching a length of nearly 3,000 m and a width of 400 m by 1924. Low dunes developed on the island, which were reportedly thinly vegetated with Uniola paniculata (sea oats). The sediment supply needed to nourish the Isle of Caprice diminished as the secondary channel reached equilibrium. The island then began to erode gradually in response to the normal effects of winds, waves, and tides. By 1931, the island was reduced to a duneless sand bar; a year later it was completely awash.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.