Ervin G. Otvos

Beach ridges - definitions and significance

Abstract Beach ridges, frequent components of Quaternary coastal plains, and other coastal landforms, have been cited as indicators of the positions of ancient seashores and associated sea levels. Numerous authors utilized the term beach ridge for active and relict, usually wave-built supratidal and/or intertidal forms. Wind-built ridges have been only occasionally included in the definition. The term was applied also to submerged, landward-shifting, eventually stranded bars. A consistent redefinition of the term is highly desirable. Beach ridges should include all relict strandplain ridges, whether dominated by wave/swash-built or by eolian lithosomes. All active ridge-like shore features, regardless of dimensions, morphology, and origin are excluded. Because of the resistance of coarse-clastic ridges to wave and wind erosion, swash-built gravel or coarse shell (“storm”) ridges may build several meters above the level of high tide. Swash-built high berms, even on pure sandy beaches, exceed the highest tides during episodes of wind-induced, record water levels. Frequently but not always burying underlying low-relief “berm ridges” of berm lithosomes, sequences of relatively steep multiple foredunes are commonly named beach ridge plains. The narrow, subparallel relict foredunes that form these strandplains presently are designated as eolian beach ridges. Beach ridges, thus, are defined as relict, semiparallel, multiple wave- and wind-built landforms that originated in the inter- and supratidal zones. Until separated from the shoreline by progradation, sandy, pebbly or shell-enriched backshore berm ridges behind an active foreshore should not be considered beach ridges. Strandplain progradation is either continuous or, with the inclusion of subtidal (“cats eye”) ponds, discontinuous. Contrary to claims, transgressive cheniers do not represent “true cheniers” alone; within their overall progradational context, cheniers, a special category of beach ridges bracketed by subtidal–intertidal mudflats, may be transgressive or regressive in character. Landward-driven, transgressive ridges should be designated beach ridges only after they are stabilized on intertidal flats. When recognizable between clearly identifiable intertidal and overlying eolian intervals, the horizontal interface between these lithosomes in beach ridges may help the reconstruction of ancient tide/lake levels. Diagnostic sedimentary textures, structures, and fossils, however, often may be unavailable in the deposits. Along with various types of elevated terraces composed of raised marine deposits and certain coastal landforms of erosional origin that occur worldwide, beach ridges of clearly proven wave-built origin may also serve as indicators of ancient higher-than-present sea levels.

Development and Migration of Barrier Islands, Northern Gulf of Mexico

Historical evidence and drilling results from published sources and U.S. Coast Survey charts 1 indicate that barrier islands form by upward aggradation of submerged shoal areas. Subsequent extensive barrier island migration may completely obscure conditions of formation of the original barrier island. Migration may take place parallel, perpendicular, or at oblique angles to the mainland shoreline and appears to take place much faster when parallel with the shoreline. No evidence indicates barrier island formation from engulfed beach and dune ridges during the early stages of transgression. Many strand plain and chenier ridges form the same wav as barrier ridges.

Hurricane Degradation—Barrier Development Cycles, Northeastern Gulf of Mexico: Landform Evolution and Island Chain History

Abstract Before its western sector was stranded and/or buried ca. 4.0–3.8 ka BP (3.9–3.7 ka 14C), the Mississippi–Alabama chain of regressive barrier islands extended well into present southeastern Louisiana. Westward-directed net littoral drift, ebb-deltas, and microtidal inlet bypassing were instrumental in the formation of elongated, narrow, sandy barrier platform sectors on which these islands, mostly of strandplain topography, have originally emerged. The development of sizable subtidal–intertidal berm basins, ringed by swash and foreshore berm ridges that emerged after storms, then filled by storm-mobilized sand, has aided posthurricane recovery. These processes are linked to discrete stages in aggradational barrier genesis. Increasingly frequent and destructive cyclones reduced island areas to laterally extensive subtidal barrier platform intervals. Enhanced overwash across lengthened platform sectors reduced drift volumes and consequently island progradation. Deepened ship channels facilitated sand loss from littoral drift to offshore seafloor areas. This and the apparent reduction in the longshore sand flux point to natural and human interference with the drift supply. Comparisons of charts, aerial photos, and satellite images provide a quantitative record for the dynamic changes that occurred. Abrupt widening of Petit Bois Pass in 1916 and periodic island diminution and attrition episodes during at least nine hurricanes since had a decisive impact on all the islands. Breaches across low-lying central and eastern (updrift) sectors contributed to long-term island reduction. Starting with Hurricane Betsy (1965), more frequent and destructive tropical cyclones resulted in accelerated island diminution. Damage from wind, salt toxicity, and overwash, combined with shore retreat, seriously impaired the vegetation of several islands in 2005. Because of extensive low and narrow island sectors, Ship and Petit Bois were the most vulnerable. Between 1848–49 and 2005, they suffered 66% and 52% area loss, respectively. Despite recurring but limited post-storm recovery, East Ship now may be approaching extinction. Despite its higher relict beach ridges, secondary dunes, and historically substantial downdrift progradation, even Horn Island has undergone considerable attrition (23%).

Barrier platforms: northern Gulf of Mexico

Abstract Barrier platforms, integral components of barrier island complexes, provide essential information for establishing development stages of islands with various genetic backgrounds. Detailed studies of core samples from rotary and vibracore drillholes and related investigations of four Holocene island—lagoon complexes on the northern Gulf of Mexico coast are summarized. Comparisons of vertically and horizontally inter-related foraminiferal biotopes and sediment parameters provided the major diagnostic tools for the reconstruction of platform and island evolution by establishing marsh, lagoonal, open marine, shoreface, inter- and supratidal depositional facies of different salinity gradients. Based on characteristics of the platform surfaces and, when available, of underlying shoreface-shoal sediment sequences, three main platform types have been identified: (1) aggradational-progradation platforms (Mississippi and Apalachicola island chains); (2) composite platforms (Dauphin and Santa Rosa Islands); and (3) transgressive platforms (Chandeleur and Derniere Islands).

Holocene Gulf Levels: Recognition Issues and an Updated Sea-Level Curve

Abstract Several new concepts have challenged the traditional view of northern Gulf coast sea-level history in recent years. Claims for higher than present mid and late Holocene sea-levels implied substantial sea-level oscillations. Such high-stands, known globally in low latitudes, have never been credibly documented on the Gulf or on unglaciated Atlantic coasts. Lacking direct indications, numerous lines of indirect proof have been suggested. Proxy evidence was based on items as the reinterpreted geological record of NW Florida lakes, estuaries, and depositional conditions of Texas coast landforms. Pleistocene barrier sectors, barrier islands, relict foredune ridges, washover fans/flood-tidal deltas, and other sedimentary units and their morphology were claimed as highstand indicators. Unrealistically old or young radiocarbon and luminescence dates, the result of diagenetic changes and other contamination have resulted in questionable conclusions. A large body of sediment, stratigraphic and geomorphic data collected during two decades, including more recently obtained Holocene sea-level dates indicated the absence of mid and late Holocene marine high-stand stages on the Gulf. Late Holocene variations in coastal sediment supply, on the other had, are apparent from shore progradation-recession episodes on the SW Alabama and adjacent NW Florida coast. One, recently revived school of thought proposes a step-like pattern of sea-level rise. Such prolonged stillstands that alternated with abrupt, large-amplitude sea-level rise episodes more recently were based on the genetic interpretation of broadly dated backstepping parasequences, emplaced in incised Pleistocene shelf valleys. Three loosely constrained multimillennial stillstands of 1.2–3.4 ka duration were inferred, each associated with a given Gulf paleoshoreline. These and postulated intervals of abrupt high-amplitude (1.5–6.0 m) sea-level rise conflict with the actual mid to late Holocene coastal development and sea-level history. The absence of backstepping parasequences in the incised Mobile Valley suggests that changes in sedimentation and erosion rates in such settings had greater impact on sequence development than sea-level changes had. Newly acquired information helped the formulation of a new regional sealevel curve that replaces two critical intervals in the old Nelson-Bray record. It conforms with more recently established sea-level histories in tectonically stable west Atlantic-Gulf areas, primarily Bermuda, the Bahamas, and Florida.

Assumed Holocene Highstands, Gulf of Mexico: Basic Issues of Sedimentary and Landform Criteria: Discussion

Record high mid and late Holocene relative sea levels, significantly above the current sea level have been widely documented in certain areas of the Australo-Pacific region, Brazil (Lessa et. al. 2000), and parts of Africa and India that were not characterized by tectonic uplift and/or glacio-isostatic rebound. Such elevated sea levels are yet to be reliably identified on our Gulf and Atlantic shores. Radically departing from traditional Gulf of Mexico sea-level curves, Morton et al. (2000) now suggest recurring highstands throughout the entire second half of the Holocene Epoch. Their findings echo earlier ideas in the same vein (see Otvos 1995, 1997, 1999). However, a detailed analysis of several lines of evidence presented by Morton et al. raises serious doubts about these conclusions. Morton et al. accept the position of beach-ridge summits as indicative of higher-than-present elevations. Thus, seaward-declining beach ridge summits on Bolivar Peninsula, Galveston Island, and other coastal areas of Texas in their view reflect late Holocene sea levels that fell from their highest elevations. Although beach ridges are of wave-constructed (berm ridge), foredune, or composite origins (Otvos 2000), Morton et al. fail to distinguish adequately among these categories by sediment and landform analysis. The problem is that under favorable circumstances, wave-built berm ridges may be accurate markers of ancient sea levels or lake levels. Foredunes, on the other hand, aggrade to varying supratidal elevations, rising several meters above the associated high-tide level. For this reason, summit elevations of relict foredunes can not provide precise data on corresponding sea level (Otvos 1995). ### Foredune Ridges Foredune ridges often overlie, mask, and bury wave-built berm ridges (Beal and Shepard 1956). Because sand is usually readily available for wind transport on most Gulf shores, the upper interval in most beach ridges tends to be of eolian origin. Except when wave-built …

“Pseudokarst” and “pseudokarst terrains”: Problems of terminology

For decades, the term “pseudokarst” has been used for a diversity of landforms, evolved in various types of commonly insoluble, as well as chemically soluble rocks, sediments, and soils. There is a need to restrict the usage of the term. Morphology, genetic conditions, and the hydrological function were used as criteria in the evaluation of the problem. It is proposed that only processes and forms involving predominantly piping and thermokarst be termed pseudokarstic. Collapse depressions in non-soluble sediment karst-cover, where piping, did not play an important role, are karst-related features. No justification exists for keeping “volcano-karst” as a viable geomorphological term. Nonkarstic honeycombed and (or) pitted terrains (with lava rock, caves, eolian blowouts, ice-surface depressions, and so on) are neither karstic nor pseudokarstic. Field work has shown that the “gravel-and-sand plain pseudokarst terrains” along the Mississippi-Alabama-Florida Panhandle Coast in fact represent Citronelle Formation surfaces dotted by relict eolian and covered karst-related depressions.

Observation of beach cusp and beach ridge formation on the Long Island Sound

ABSTRACT Observations at Westbrook, Connecticut, suggest that the following conditions are necessary for the formation and preservation beyond one tide period of sandy and pebbly beach cusps and of pebble ridges, developing perpendicular to the shoreline: Adequate amount of available and transportable source material. Sufficient breaker energy for the accumulation of prospective cusp and ridge material. Maintaining of balance between the swash energy and the source material for a certain amount of time to allow the construction of the cusps and preventing their erosion. In the case of fine sandy cusps the still-stand of the sealevel for 30-45 minutes is held to be necessary for this purpose. Subsequent lowering of the sealevel without breaker energy increase. Pebbly-coarse sandy cusps are forming in a much shorter time than fine sandy cusps of the same dimensions do. Pebble ridges, perpendicular and oblique to the beach trend develop if the beach contains an abundant amount of coarse material below the high tide level and the swash energy is in balance with the material during the receding tide. Oblique ridges form during strong longshore drift. Fine sand cusps were found to have been built by the combination of erosion and accumulation.

Beach Aggradation Following Hurricane Landfall: Impact Comparisons from Two Contrasting Hurricanes, Northern Gulf of Mexico

Abstract While the effects of major hurricanes have been intensively studied, less is known about the impact of the weaker but more frequent tropical cyclones, such as Hurricane Georges (1998). This hurricane, Category 2 at landfall, was non-typical in its effects. While high waves offshore and slow forward speed just before landfall resulted in island degradation, identical to that of Category 5 Hurricane Camille in 1969, the impact on the mainland was quite different. Only approximately 15% of the sand volume eroded by Camille in 1969 was removed from the Harrison Countys mainland beach this time. Backshore areas of East Belle Fontaine Beach have prograded by 3–7 m. 20–90 cm vertical aggradation took place at several locations on its 10–45 m wide backshore. The short duration of hurricane-strength winds over the mainland and the availability of compensating sand supplies from adjacent sediment sources in the waning phase of the storm explain the limited extent of mainland shore erosion. Retreating shore bluffs and backfill from demolished bulkheads replaced eroded beach sand. Sand derived from artificial dunes on the backshore and from sand-rich nearshore areas have also mitigated effects of wave erosion.

Island evolution and “stepwise retreat”: Late Holocene transgressive barriers, Mississippi delta coast — Limitations of a model

Abstract Several vital components of a new three-stage barrier shore development model on delta coasts require further scrutiny to be acceptable even with modifications. Solid evidence for a proposed continuous evolutionary sequence, involving genetic relationship between islands associated with erosional headlands and firmly established island arcs, as well as between these detached arcs and inner shelf shoals has not yet been demonstrated convincingly in the few examples that were presented. The range of probable roles of erosional or prograding headlands, active or inactive subdeltas, subtidal shoals and barrier spits in barrier island formation, variable rates of island evolution and decomposition in different settings, and genetic alternatives of shelf shoal formation introduce many more possible variables than could be harnessed into the rather restrictive three-stage model. The highly changeable south Chandeleur islands are unsuitable analogs for a model of barrier and primary surf-overstep during relative sea-level rise. Alternating erosion-accretion cycles during recorded history of the islands, as a whole, cast doubt on the likelihood of their future total elimination. Even in absence of the barrier chain, wave dampening across shallow Chandeleur Sound would be expected to prevent a primary surf zone from forming along the mainland shore.