The impact of Hurricane Sandy on the shoreface and inner shelf of Fire Island, New York: Large bedform migration but limited erosion. (15th April 2015)

• Record Type: Journal Article
• Authors: Goff, John A.; Flood, Roger D.; Austin, Jr., James A.; Schwab, William C.; Christensen, Beth; Browne, Cassandra M.; Denny, Jane F.; Baldwin, Wayne E.
• Is Part Of: Continental shelf research. Volume 98(2015)
• Page Start: 13
• Page End: 25
• Publication Date: 2015-04-15
• Subjects: Superstorm Sandy -- Sand ridges -- Sorted bedforms -- Shoreface -- Inner shelf -- Ravinement; Continental shelf -- Periodicals; Submarine geology -- Periodicals; 551.41
• DOI: 10.1016/j.csr.2015.03.001
• Languages: English
• ISSNs: 0278-4343

Abstract

Abstract: We investigate the impact of superstorm Sandy on the lower shoreface and inner shelf offshore the barrier island system of Fire Island, NY using before-and-after surveys involving swath bathymetry, backscatter and CHIRP acoustic reflection data. As sea level rises over the long term, the shoreface and inner shelf are eroded as barrier islands migrate landward; large storms like Sandy are thought to be a primary driver of this largely evolutionary process. The "before" data were collected in 2011 by the U.S. Geological Survey as part of a long-term investigation of the Fire Island barrier system. The "after" data were collected in January, 2013, ~two months after the storm. Surprisingly, no widespread erosional event was observed. Rather, the primary impact of Sandy on the shoreface and inner shelf was to force migration of major bedforms (sand ridges and sorted bedforms) 10's of meters WSW alongshore, decreasing in migration distance with increasing water depth. Although greater in rate, this migratory behavior is no different than observations made over the 15-year span prior to the 2011 survey. Stratigraphic observations of buried, offshore-thinning fluvial channels indicate that long-term erosion of older sediments is focused in water depths ranging from the base of the shoreface (~13–16 m) to ~21 m on the inner shelf, which is coincident with the range of depth over which sand ridges and sorted bedforms migrated in response to Sandy. We hypothesize that bedform migration regulates erosion over these water depths and controls the formation of a widely observed transgressive ravinement; focusing erosion of older material occurs at the base of the stoss (upcurrent) flank of the bedforms. Secondary storm impacts include the formation of ephemeral hummocky bedforms and the deposition of a mud event layer. Highlights: The Fire Island shoreface and inner shelf were surveyed after Hurricane Sandy. Major bedforms were significantly moved by the storm. Migrating bedforms modulate the formation of the transgressive ravinement.