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A Cyclic Model of Foredune Blowout Evolution for a Leeward Coast: Island Beach, New Jersey

Paul A. Gares and Karl F. Nordstrom
Annals of the Association of American Geographers
Vol. 85, No. 1 (Mar., 1995), pp. 1-20
Stable URL: http://www.jstor.org/stable/2564276
Page Count: 20
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A Cyclic Model of Foredune Blowout Evolution for a Leeward Coast: Island Beach, New Jersey
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Abstract

The formation and development of three foredune blowouts at Island Beach State Park, New Jersey during the period 1981 to 1991 demonstrate the cyclic evolution of these landforms. The evolution is documented with: 1) a long-term study of topographic changes in blowout form documented with systematic surveys carried out at three- to five-year intervals; and 2) a four-week field study involving the collection of wind-speed profiles and wind direction at several locations in two of the blowouts and the measurement of elevation changes resulting from significant wind events. Results show that blowouts on leeward coasts favor onshore sand movement from the beach despite the dominance of offshore winds because vegetation on the landward side of the blowouts traps sand moved onshore and stabilizes the surface against deflation by offshore winds. Feedback between dune morphology, wind flow, and vegetation produces a sequence of landform changes that are conceptualized in a model of foredune blowout development. The model has four distinct stages. In Stage 1, erosional notches are initiated in a foredune by dominant offshore winds that accelerate near the dune crest. In Stage 2, these notches develop into incipient blowouts through deflation in the throat. During Stage 3, the blowout throat deflates to backbeach elevation, and erosion on the lateral walls widens the blowout. In Stage 4, downward deflation ceases and widening slows as the lateral walls develop gentler slopes; this results in a deceleration of air flow in the blowout, sediment deposition, and eventual closure. The progression from blowout formation to closure takes about 20 years.

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