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Coarse-Clast Ridge Complexes of the Caribbean: A Preliminary Basis for Distinguishing Tsunami and Storm-Wave Origins

¹ U.S. Geological Survey, 600 Fourth Street South, St. Petersburg, Florida 33701, U.S.A.; present address: U.S. Geological Survey, 10100 Burnet Road, Austin, Texas 78758 U.S.A.; rmorton{at}usgs.gov
² U.S. Geological Survey, 400 Natural Bridges Drive, Santa Cruz, California 95060, U.S.A.
³ U.S. Geological Survey, 400 Natural Bridges Drive, Santa Cruz, California 95060, U.S.A.
⁴ U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, U.S.A.

Coastal gravel-ridge complexes deposited on islands in the Caribbean Sea are recorders of past extreme-wave events that could be associated with either tsunamis or hurricanes. The ridge complexes of Bonaire, Jamaica, Puerto Rico (Isla de Mona), and Guadeloupe consist of polymodal clasts ranging in size from sand to coarse boulders that are derived from the adjacent coral reefs or subjacent rock platforms. Ridge-complex morphologies and crest elevations are largely controlled by availability of sediments, clast sizes, and heights of wave runup. The ridge complexes are internally organized, display textural sorting and a broad range of ages including historical events. Some display seaward-dipping beds and ridge-and-swale topography, and some terminate in fans or steep avalanche slopes. Together, the morphologic, sedimentologic, lithostratigraphic, and chronostratigraphic evidence indicates that shore-parallel ridge complexes composed of gravel and sand that are tens of meters wide and several meters thick are primarily storm-constructed features that have accumulated for a few centuries or millennia as a result of multiple high-frequency intense-wave events. They are not entirely the result of one or a few tsunamis as recently reported. Tsunami deposition may account for some of the lateral ridge-complex accretion or boulder fields and isolated blocks that are associated with the ridge complexes.