Beach Ridge Data and Sea Level History from the Americas

Abstract

Many types of information can be obtained from beach ridge plains. Twelve important categories of beach ridge plain data are included here: (1) Position in a 5-D space-time-equilibrium framework, (2) relative age, (3) absolute age, (4) deformation, warping or tilting, (5) vertical position, (6) parallelism, subparallelism and abrupt ends (sand source was offshore), (7) curvature, taper and change in orientation (sand source was generally offshore), (8) eolian decoration or dune strips (historical pauses), (9) spacing between ridges (data about littoral power gradient, wave energy gradient, or transverse transport gradient), (10) height (transverse transport rate and/or wave climate), (11) internal bedding (proportions of wind, swash, overwash and storm surge deposition), and (12) sediment parameters and their areal distribution (data about the offshore sand pool, the variable rate of sand delivery to the beach, and therefore changes in sea level or wave climate). Comparisons along one ridge, from one ridge to another, from one set to another, or from one beach ridge plain to another, may provide useful additional information. Topographic profiles on the plain may produce valuable data (items 3, 4, 5, 10), including information about mean sea level (MSL) changes of one to two meters or more. Cycles of grain size change, along the same profiles, may yield information about MSL changes of a meter or so, or wave climate changes, or both. St. Vincent Island has at least 12 beach ridge sets, containing roughly 180 ridges, spanning about 4,000 or 5,000 years of late Holocene time. Topographic profiling indicates two important MSL rises, and one drop, each exceeding one meter. Grain size studies hint at additional MSL changes, each much less than one meter. The smaller changes are largely clustered in the second half of the beach ridge plain history.