GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 103-10
Presentation Time: 10:45 AM


MYLROIE, John E., Department of Geosciences, Mississippi State University, Mississippi State, MS 39762,

One of the issues regarding global climate change is the hypothesis that warmer global temperatures will increase hurricane activity, either in numbers, intensity, or both. If correct, then past warmer intervals such as the last interglacial (MIS 5e) should have left such evidence in the geologic record. Recently it has been proposed, with titillating titles and media fanfare, that deposits in The Bahamas record such superstorms. Fenestrae in eolian calcarenites at elevations up to 43 m are interpreted to be washover features from superstorms, and large coastal boulders and chevron ridges are also stated to be a product of superstorms. The problem with these interpretations is that alternate explanations exist, and critical associated evidence is not present.

In the case of the fenestrae, their existence on three Bahamian islands is interpreted as wash-over features. To wash over a dune 43 m high means that all landscapes at lower elevations would also be washed over, and materials associated with a major tempestite should be present, but do not exist. Each fenestrae layer in these dunes is argued to be a separate storm event, yet the dunes at all elevations show no evidence of scour. The existing interpretation of the fenestrae as a rainfall slurry remains an interpretation that allows multiple events and requires no tempestite presence.

On Eleuthera Island, the chevron ridges contain climbing wind ripples and are eolian. There are no tempestites present. The boulders rest on pedestals, indicating they have acted as karrentisch. To emplace them would require extreme energies, but other interpretations such a fossil tower karst and boulders rolling down slope remain viable. The footprint of the boulder area is extremely small, within a few kilometers on the northeast shore of Eleuthera, and such a small footprint is more than an order of magnitude smaller than that for Sandy or Katrina, recent large storms. The hypothesized super storm is proposed to have left behind fine-grained sand as chevron ridges, and large boulders, but no particles in between those size extremes exist, an unexplained outcome.

  • Superstorms17Aug16.pdf (5.4 MB)