2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 162-7
Presentation Time: 3:15 PM


WALLACE, Davin J., Department of Marine Science, University of Southern Mississippi, 1020 Balch Blvd, Stennis Space Center, MS 39529, VAN HENGSTUM, Peter J., Department of Marine Sciences, Texas A&M University at Galveston, 1001 Texas Clipper Road, Galveston, TX 77554 and SMITH, Struan R., Bermuda Aquarium, Museum and Zoo, Flatt's, FL 04, Bermuda, davin.wallace@usm.edu

Do storms have the competency to move boulders? This topic has been a polarizing question in coastal settings around the world. Some researchers have shown boulders emplaced during storms, while others invoke tsunamis as the only appropriate mechanism. Here we present a unique dataset of boulders being transported during relatively minor storms at Spittal Pond, Bermuda. The exposed limestone rock barrier at this site is quickly colonized by a cyanobacterium, Scytonema hofmanni, but this does not occur beneath boulders blocking sunlight. However, when boulders are transported, the fresh, white limestone surface is exposed leaving an outline of the former location. Photographic evidence of large boulders near the site was taken in 2013. During reconnaissance work in 2014, some of the largest boulders were documented to have moved several meters. Numerous smaller boulders were inferred to have moved based on unweathered limestone outlines matching nearby boulders. The only inundation events during this time interval were Hurricanes Fay (category 1) and Gonzalo (category 2) that both made landfall in October 2014. The largest boulders transported were between ~1 and 8 tonnes, and simple numerical modeling suggests that flow velocities would have to exceed ~4 and 6 m/s, respectively. This work suggests that even modest storms have the competency to move boulders.