Coastal Barriers: Fresh Look at Origins, Nomenclature and Classification Issues

Document Type

Article

Publication Date

4-15-2020

Department

Coastal Sciences, Gulf Coast Research Laboratory

School

Ocean Science and Engineering

Abstract

Based on numerous publications and field work on the northern Gulf of Mexico coast, U.S. and other coastal areas, the present objective is to meet the need for an improved system of the definition and classification of barriers and their components. This topic includes morphological and functional interrelationships between beach ridges, barriers, and similar landforms. The term “beach ridge” was applied to a plethora of sub- and supratidal ridge types. In contrast, the presently proposed definition restricts the term to relict berm and foredune ridges, composed of sand or gravel and stabilized after isolation from shore zone of active processes. Barriers sustain paralic hydrology, sediment, biotic and nutrient condition in the coastal realm. In combination with adjacent lagoons and river deltas, these landforms represent physical barriers that lessen marine and related influences in brackish paralic-coastal environments. Benefiting from historic evolution of concepts and nomenclature, the task also involves the correction of misattributions rooted in early publications. Island, spit, and mainland barriers thus maintain lower salinities, reduce wave erosion, protect nutrient-rich paralic deposits and mitigate storm-induced inundation. “Fetch-limited lagoonal barrier islands” are considered valid barriers only in lagoons where they face inlet-transmitted full-marine conditions. “Mainland barriers” of several subcategories often are important sediment archives of past sea levels, hydroclimate, climate and tectonic-isostatic changes. They consist mostly of ridgeplains, at the start firmly attached or later migrated and welded to the mainland shore. In addition to local hydrodynamic and topographic influences, formation conditions may reflect overall paleogeographic conditions, including fluvial impact. In progradational (regressive) island settings, barriers islands of strandplains that laterally may alternate with narrow spit-like sectors. They include only single, marine, respectively, lagoon-side shore ridges, with secondary dune fields sandwiched between them. Field observations and drillcore studies of microfossil- and sediment-based depositional facies suggest that most barrier islands originated by the often underestimated shoal-aggradation mode. Two additional genetic models are recognizable; a fourth remains hypothetical. Remotely-sensed images indicate that post-hurricane regeneration of the largest deltaic barrier chain in the Gulf of Mexico stalled in recent years. Late Pleistocene barriers significantly influenced present coastal landforms in two extensive regions. Dramatic changes in past decades indicate that sea-level rise and stormier future hydroclimate may likely accelerate the degradation of deltaic and non-deltaic barrier islands.

Publication Title

Geomorphology

Volume

355

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