OPEN-FILE REPORT 2009-1250

TILE 1 of 4

Morton, R. A., Rogers, B. E., 2009

Geomorphology and Depositional Subenvironments of Gulf Islands National Seashore, Mississippi

U.S. Geological Survey Open-File Report 2009-1250

Universal Transverse Mercator. 1983 North American Datum-Zone 16 North

This map is not intended for use in navigation.

Project Description

The U.S. Geological Survey (USGS) is studying coastal hazards and coastal change to improve

our understanding of coastal ecosystems and to develop better capabilities of predicting future

coastal change. One approach to understanding the dynamics of coastal systems is to monitor

changes in barrier-island subenvironments through time. This involves examining morphological

and topographic change at temporal scales ranging from millennia to years and spatial scales

ranging from tens of kilometers to meters. Of particular interest are the processes that produce

those changes and the determination of whether or not those processes are likely to persist into the

future. In these analyses of hazards and change, both natural and anthropogenic influences are

considered. Quantifying past magnitudes and rates of coastal change and knowing the principal

factors that govern those changes are critical to predicting what changes are likely to occur under

different scenarios, such as short-term impacts of extreme storms or long-term impacts of sealevel rise. Cat Island, MS was selected for detailed mapping of barrier-island morphology and

topography because the islands offer a diversity of depositional subenvironments and the islands'

areas and positions have changed substantially in historical time. The geomorphologic and

subenvironmental maps emphasize the processes that formed the surficial features and also serve

as a basis for documenting which subenvironments are relatively stable, such as the beach ridge

complex, and those which are highly dynamic, such as the beach and active overwash zones.

Data Description

The barrier-island classification was referenced and mapped using September 2007 highresolution orthorectified aerial photography from the National Agriculture Imagery Program

(NAIP), October 2007 low-altitude color videos of the Mississippi barrier islands acquired from

Great Divide Pictures under contract to the National Park Service, and June 2007 1-meter-pixelresolution Experimental Advanced Airborne Research Lidar (EAARL) collected by National

Aeronautics and Space Administration (NASA) and the USGS. Each geomorphic layer is stored in

standard shapefile format viewable in any GIS software.

Further Reading

Morton, R.A., 2007, Historical changes in the Mississippi-Alabama barrier islands and the roles of

extreme storms, sea level, and human activities: U.S. Geological Survey Open-File Report 2007-

1161, 38 p. (Available online at: http://pubs.usgs.gov/of/2007/1161/.)

Morton, R.A., Guy, K., and Whitko, A., 2007, Morphological impacts of Hurricane Camille

(1969) on barrier islands of Mississippi and western Alabama: U.S. Geological Survey website at:

http://coastal.er.usgs.gov/hurricanes/historical-storms/camille/.

Otvos, E.G., 1979, Barrier island evolution and history of migration, north central Gulf Coast, in

Leatherman, S.P. ed., Barrier islands from the Gulf of St. Lawrence to the Gulf of Mexico: New

York, Academic Press, p. 291-319.

Penfound, W.T., and O’Neill, M.E., 1934, The vegetation of Cat Island, Mississippi: Ecology, v.

15, p. 1-16.

Rucker, J.B., and Snowden, J.O., 1988, Recent morphologic changes at Dog Key Pass,

Mississippi; The formation and disappearance of the Isle of Caprice: Gulf Coast Association of

Geologoical Societies Transactions, v. 38, p. 343-349.

Waller, T.H., and Malbrough, L.P., 1976, Temporal changes in the offshore islands of Mississippi:

Mississippi State University Water Resources Research Institute, 109 p.

Prepared in cooperation with the 

NATIONAL PARK SERVICE (NPS) 

Natural Features

Man Made Features

Geomorphology and Depositional Subenvironments 

of Gulf Islands National Seashore:

Tile 1, Cat Island, Mississippi

Louisiana Florida

Mississippi Alabama

Cat Island Ship Island Horn Island Petit Bois 

Island

Map Area

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Scale 1:11,500

(when printed full size)

Classification Extent

Gulf Islands National Seashore park boundary. Congress authorized adding most of Cat Island to the national seashore, but 

private land remains.

Unclassified water data surrounding a barrier island or small bodies of permanent water within the boundaries of an

island. Island exterior boundary referenced to June 2007 Experimental Advanced Airborne Research Lidar (EAARL)

Water

Material dredged to construct artificial channels and placed along the margins of the channels.

Dredged Material

Sets of long, continuous ridges formed parallel to the ocean shore by sand that is deposited by a combination of wave

run-up and wind. Typically vegetated by trees and salt-tolerant grasses.

Beach Ridge Complex

A mostly unvegetated strip of sand parallel to the shore that extends from the water to the seaward edge of the dunes or

crest of a washover terrace. The seaward part of the beach is regularly inundated by wave run-up during high-water

phases of the tidal cycle.

Beach

Inactive Overwash Zone

An area that was historically overwashed by storm surge, such as during Hurricane Katrina in 2005. These areas are not

flooded frequently by high water and ocean waves, but are still vulnerable to flooding from extreme storms. The former

overwash sand is commonly reworked into low hummocky dunes that can be densely vegetated with salt-tolerant grasses.

Low vegetated wetlands that support plant assemblages tolerant of saltwater. Typically found along the sides of

barrier islands protected from ocean waves or along the margins of tidal creeks. Some marshes on Cat Island

coincide with former beach-ridges or swales.

Marsh

Topographic depressions within a beach ridge complex. May be dry or may intermittently pond freshwater after heavy rain.

Beach Ridge Swale

A narrow, mostly unvegetated strip of sand at the end of a barrier island that extends the island alongshore. Spits

form because of recent deposition by waves and currents.

Spit

An area that is frequently flooded by high water and ocean waves generated by storms. Typically low-lying with

sparse vegetation and composed of sand with patches of shell at the surface.

Active Overwash Zone

Miscellaneous man-made features, including buildings, docking piers, roads, and walkways, and shorelineprotection structures.

Structure

Barren to sparsely vegetated mounds or ridges of wind-blown sand that form hummocky topography landward of the beach.

Active Dune Complex

Mounds or ridges of wind-blown sand that are typically densely vegetated with salt-tolerant grasses. The vegetated dunes

form hummocky topography landward of the beach. The sand in these dunes is protected by the vegetation and is not moving.

Stable Dune Complex

0.5 0.25 0 0.5 1 1.5

Kilometers

0.5 0.25 0 0.5 1 1.5

Miles

2009

By Robert A. Morton1

 and Bryan Rogers2

1

 U.S. Geological Survey, FISC, St. Petersburg, FL

2

 Jacobs Technology, Contracted to USGS, New Orleans, LA

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30°15'0"N 3343000 3346000 3349000

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