Publication Date:
2022-05-25
Description:
© The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution.. The definitive version was published in Continental Shelf Research 98 (2015): 13-25, doi:10.1016/j.csr.2015.03.001.
Description:
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.
Description:
This work was funded primarily by a rapid response grant from the Jackson
School of Geosciences, The University of Texas/Austin
Keywords:
Superstorm Sandy
;
Sand ridges
;
Sorted bedforms
;
Shoreface
;
Inner shelf
;
Ravinement
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
Permalink
