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Coastal Change Processes

Fire Island,New York Study Site

Geologic Framework

maps showing acoustic backscatter and bathymetry collected with interferomentric sonar
Maps showing (A) acoustic backscatter and (B) bathymetry collected with the inteferomentric sonar.  High backscatter is displayed by light tones and low backscatter is displayed as dark tones within the backscatter image.  Regional bathymetric contours are in meters.  West of Watch Hill, the modern sand deposit is organized into a series of shoreface-attached ridges oriented at oblique angles to the shoreline. 
map showing holocene sediment thickness
Map showing Holocene (modern) sediment thickness in meters overlain on bathymetry. Regional bathymetric contours are in meters. Note the shoreface-attached sand ridges west of Watch Hill.
map showing thickness of a
Map showing the thickness of a relatively young Pleistocene outwash lobe in meters mapped using chirp seismic-reflection profiles collected in 2011, overlain on acoustic backscatter imagery. Regional bathymetric contours are in meters.
Comparison of acoustic backscatter collected in 1996 to backscatter collected in 2011.  Dashed lines depict features on 1996 backscatter and are transposed onto the 2011 backscatter to show change.  A) Acoustic backscatter depicting a series of ~50-cm-high bedforms that have migrated ~75 m to the west. B) Acoustic backscatter depicting a ~1-m-high scarp on seaward flank of low backscatter shoreface-attached ridge. Backscatter comparison shows the feature has migrated ~100 m to the north.  C) Map showing acoustic backscatter mosaic and the location of A and B.  Change detected in comparison of acoustic backscatter collected in 1996 and 2011 is also displayed; red arrows indicate bedform migration direction and yellow arrows indicate migration of seaward flank of low backscatter shoreface-attached ridges and, in places, the toe of the beach platform. 

In 2011, we mapped the inner-continental shelf and lower shoreface offshore of Fire Island using Chirp high-resolution subbottom and interferometric sonar technology.  These data have been processed and interpreted to examine sediment distribution patterns, shelf physiography, antecedent stratigraphy and the interaction of this geospatial/sedimentologic framework with coastal change.

Preliminary findings from this mapping activity were published in FY2013 showing that the Holocene evolution and decadal- to century-timescale behavior of Fire Island is linked directly to the geologic framework of the inner-continental shelf.  The eastern segment of the island is migrating landward, while the central and western segments are relatively stable or accreting.  This behavior is likely related to the presence of a relatively larger, mobile Holocene sediment supply on the inner-continental shelf offshore of the central and western segments of the island which are organized into a series of shorface-attached sand ridges.  This larger sediment supply was created by erosion of a Pleistocene outwash lobe off central Fire Island by oceanographic processes associated with ongoing marine transgression.  Final interpretation of these geophysical data is scheduled for early fy2014 and will include maps of the regional coastal plain unconformity, the Holocene marine transgressive surface, and the modern sediment thickness and distribution. Comparison of these mapping products with marine geophysical data collected in the late ‘90s shows that the modern sand deposit is mobile and that ravinement processes are continuing to modify the inner shelf and lower shoreface (http://woodshole.er.usgs.gov/project-pages/newyork/).

Related Publications

Schwab, W.C., Baldwin, W.E., and Denny, J.F., 2016, Assessing the impact of Hurricanes Irene and Sandy on the morphology and modern sediment thickness on the inner continental shelf offshore of Fire Island, New York: U.S. Geological Survey Open-File Report 2015–1238, 15 p., http://dx.doi.org/10.3133/ofr20151238.

Schwab, W.C., Baldwin, W.E., and Denny, J.F., 2014, Maps showing the change in modern sediment thickness on the Inner Continental Shelf Offshore of Fire Island, New York, between 1996–97 and 2011: U.S. Geological Survey Open-File Report 2014–1238, http://dx.doi.org/10.3133/ofr20141238.

Schwab, W.C., Denny, J.F., and Baldwin, W.E., 2014, Maps showing bathymetry and modern sediment thickness on the inner continental shelf offshore of Fire Island, New York, pre-Hurricane Sandy: U.S. Geological Survey Open-File Report 2014–1203, http://dx.doi.org/10.3133/ofr20141203.

Schwab, W.C., Baldwin, W.E., Denny, J.F., Hapke, C.J., Gayes, P.T., List, J.H., and Warner, J.C., (2014). Modification of the Quaternary Stratigraphic Framework of the Inner-Continental Shelf Offshore of Fire Island by Holocene Marine Transgression: Marine Geology, v. 355, 346-360 p. http://www.sciencedirect.com/science/article/pii/S0025322714001960.

Schwab, W.C., Thieler, E.R., Allen, J.R., Foster, D.S., Swift, B.A., Denny, J.F., 2000a, Influence of Inner-Continental Shelf Geologic Framework on the Evolution and Behavior of the Barrier-Island System between Fire Island Inlet and Shinnecock Inlet, Long Island, New York. Journal of Coastal Research 16, 408-422.

Hapke, C.J., Lentz, E.E., Gayes, P.T., McCoy, C.A., Hehre, R., Schwab, W.C., Williams, S.J., 2010, A review of sediment budget imbalances along Fire Island, New York: Can nearshore change explain the deficit?. Journal of Coastal Research 26(3), 510-522.

Lentz, E.E., Hapke, C.J., Stockdon, H.F., Hehre, R.E., 2013. Improving understanding of near-term barrier island evolution through multi-decadal assessment of morphologic change. Marine Geology 337, 125-139.

Schwab, W.C., Baldwin, W.E., Hapke, C.J., Lentz, E.E., Gayes, P.T., Denny, J.F., List, J.H., and Warner, J.C., 2013, Geologic evidence for onshore sediment transport from the inner-continental shelf: Fire Island, New York. Journal of Coastal Research 29(3), 536-544.


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