Date of Award

Summer 1988

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean/Earth/Atmos Sciences

Program/Concentration

Oceanography

Committee Director

George F. Oertel

Committee Member

John C. Ludwick

Committee Member

Donald J. P. Swift

Committee Member

Stephen J. Culver

Committee Member

Stephen P. Leatherman

Abstract

Analysis of historical shoreline position, cross-island profile change, and stratigraphic data provided a shoreline response model for low-profile barrier island systems. Historical shoreline data illustrates continuous, shore-parallel retreat between 1852 and 1957, at which time the island narrowed to a width of approximately 200 m. Between 1957 and 1981, ephemeral inlet breaching along southern Metompkin Island disrupted longshore sediment transport, increased the rate of shoreline recession, and resulted in differential rates of retreat associated with an abrupt break in backbarrier morphology. By 1981, a 400 m offset had formed at a position midway along Metompkin Island, suggesting that ephemeral inlet processes were the primary mechanisms for accelerated migration rates along the southern island shoreline segment. More recently, a two-year island profiling study (11/83 to 11/85) showed significant deficits of sand along northern Metompkin Island and small additions along the southern island segment. Washover was the primary sand source to landward profile segments during recession, supporting the concept of barrier rollover.

Sediment deposits of the barrier island system include thick sequences of fine-grained, bioturbated backbarrier material that are capped by 0.6- to 2-m thick marsh deposits along northern Metompkin Island and by finely laminated sand to bioturbated silty sand units, associated with inlet sedimentation in Metompkin Bay. Configurations of the pre-Holocene surface affected the distribution of coastal lithosomes. Lagoonal mud thickens to the east and south towards a prominent antecedent valley associated with Folly Creek.

A model describing the late Holocene depositional history of the Metompkin Island system starts with a period of relative shoreline stability when fine-grained deposition was dominant throughout the back-barrier system. Between 1859 and 1887, formation of the Fishing Point spit complex significantly reduced the magnitude of longshore transport to the beach along Metompkin Island. Consequently, the rate of shoreline recession increased and the island narrowed. When island width decreased to approximately 200 m, inlet breaching was frequent along bay-backed southern Metompkin Island, increasing the rate of shoreline retreat. The primary mechanism by which the northern marsh-backed shoreline segment migrated landward was washover.

DOI

10.25777/qh0t-n783

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