Cuspate Spits Research Articles

Growth of cuspate spits

ABSTRACT Bouchette, F., Manna, M., Montalvo, P., Nutz, A., Schuster, M.,Ghienne, J.-F., 2014. Growth of cuspate spits. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70 pp. 047–052, ISSN 0749-0208. The present work concerns cuspate spits: slightly symmetrical geomorphic features growing along the shoreline in shallow waters. We develop a new formulation for the dynamics of cuspate spits. Our approach relies on classical paradigms such as a conservation law to the shoreface scale and an explicit formula for alongshore sediment transport. We derive a non-linear diffusion equation and a fully explicit solution for the growth of cuspate spits. From this general expression, we found interesting applications to quantify shoreline dynamics in the presence of cuspate spits. In particular, we point out a simple method for the datation of a cuspate spit given a limited number of input parameters. Furt...

Number One Reef: An overstepped segmented lagoon complex on the KwaZulu-Natal continental shelf

This study of the bathymetry of the mid-shelf of the Durban Bight, KwaZulu-Natal revealed a series of previously undocumented seafloor features. These features were mapped using a high-resolution multibeam bathymetric echosounder and a detailed map of the seafloor topography was produced. We recognised several features that closely resemble features of contemporary segmented lagoon and lake systems: semicircular seafloor depressions, arcuate ridges, cuspate spits and prograding submerged barriers. Based on the striking similarity in morphology to Kosi Bay - a segmented lagoon system from the sandy northern KwaZulu-Natal coastal plain - a similar evolutionary model is proposed. This model is of an incised valley formed following a sea level lowering to the Last Glacial Maximum at about 18 000 BP. Thereafter, continued transgressive infilling occurred to a point where an extensive lagoon and back-barrier system was established. At this point, sea levels remained static, causing the net segmentation of the system and the slow closure of the tidal basins or circular depressions. This type of seafloor topography is rarely preserved and is the result of fortuitous cementation after deposition and the later removal of sediment that would ordinarily bury such features.

Feedback between ridge and swale bathymetry and barrier island storm response and transgression

The shoreface of Santa Rosa Island in northwest Florida is characterized by a ridge and swale bathymetry that forces an alongshore variation in beach and dune morphology. The alongshore variation in dune morphology in turn controls the modern island response to and recovery from tropical storms and hurricanes, and is therefore, an important control on island transgression with relative sea-level rise. Field sampling and remote sensing are used in the present study to describe the geologic framework of Santa Rosa Island, and to elucidate on the origins of the shore-attached ridge and swale bathymetry. Vibracores and seismic and GPR surveys were completed along 42 cross-shore transects and 3 shore-parallel transects to examine the structure of the 21 ridge and swale structures found along Santa Rosa Island. The shore-parallel seismic surveys reveal strong near-horizontal reflectors through the ridges at depths consistent with thick back-barrier muds extracted from vibracores taken across and along the ridges. Near-horizontal reflectors are identified in ground-penetrating radar (GPR) surveys between the ridges and cuspate spits along the back-barrier shoreline, but are not present in the narrow sections of the island landward of the swales. Continuation of the seismic surveys in the back-barrier also reveals near-horizontal reflectors at the cuspate spits that are characterized by seagrass beds, salt marsh and maritime forest. Consistent with the GPR survey, there is an absence of horizontal reflectors between cuspate spits where the washover deposits extend to the back-barrier shoreline. It is argued that the ridge and swale bathymetry is a transgressive surface and the remnants of cuspate spits that are present along the back-barrier shoreline. In this respect, the cuspate spits had to first develop along the back-barrier shoreline and eventually evolve into the mud-cored ridges as the island transgressed with relative sea-level rise. Once the ridge and swale bathymetry emerged on the Gulf of Mexico shoreface it was able to reinforce the alongshore variation in dune height and storm response. It is further argued that the cuspate spits are reinforced by the shoreface ridges through alongshore transport of sediment from adjacent washover fans although the ridge orientation suggests that the spits have migrated westward by ~750m. In this respect, the alongshore variation in beach and dune morphology on this island is the expression of this large-scale feedback and suggests a top-down model in which meso-scale processes and landforms depend on the geologic context.

Geoarchaeological study of the Phoenician cemetery of Tyre‐Al Bass (Lebanon) and geomorphological evolution of a tombolo

AbstractThe geoarchaeological record of the Phoenician necropolis of Al Bass (Lebanon) provides information concerning the geomorphological evolution of a late Holocene tombolo. Physical and chemical analysis of sediments indicates that the cemetery (9th century B.C.) was located near a littoral lagoon, between the dunes of a cuspate spit pointing toward the island of Tyre. From the sea apex of this spit, the moles mentioned in historical chronicles were constructed. Once mainland and island were connected, at the northern coast (where the port of Sidon was located), a sediment trap was formed, which quickly filled with silt. Afterwards, an extensive field of sand dunes buried all the archaeological remains from Phoenician to Roman times. © 2008 Wiley Periodicals, Inc.

Beach Erosion of Futtsu-Misaki Cuspate Spit Separating Tokyo Bay and Uraga Channel

Beach changes around Futtsu-misaki cuspate spit located at the mouth of Tokyo Bay and protruding west are investigated through the comparison of aerial photographs. It is found that shoreline has been eroded in recent years mainly due to lack of sand supply from the southern coast caused by the obstruction of continuous littoral transport by Shitazu fishery harbor. At the tip of the spit the seawall was destroyed and a concave shoreline was formed due to erosion as the shoreline became stable under the condition of two fixed control points at Dai-ichikaiho island and the tip of the seawall. Sand eroded from the tip of the spit was found to be carried to the north coast of the spit by wave action.

Holocene depositional history of a microtidal cuspate foreland cape: Cape Lookout, North Carolina

The Holocene stratigraphy of Cape Lookout, North Carolina, and the connecting barrier limb (Core Banks) displays sharply contrasting depositional histories. Beneath the Core Banks barrier chain a transgressive sequence of overwash storm deposits rests on back-barrier silty sands and salt marsh peats, evidence of the island's erosive landward migration. However, core holes drilled at Cape Lookout reveal a regressive vertical stacking of sediments that marks a major Holocene facies change. Here, fine-grained, burrowed shoreface deposits are overlain by coarse-grained, horizontally bedded, barrier-washover sands. Cape Lookout has evolved during the late Holocene as a prograding cuspate spit type of headland. This accretion is a result of the combined effects of oceanic washover deposition with sand accumulated from a dominant southerly longshore transport. During the past 4000 years the rate of sea-level rise slowed markedly in the area resulting in a decreased rate of landward migration for Core Banks. As the island became relatively stable with respect to sea-level rise, large volumes of sand were being transported along-shore to Cape Lookout and offshore to its subaqueous shoals. The slower landward retreat of the island probably allowed for a rapid southerly extension of Core Banks along with a buildup of the Cape Lookout shoals. The sedimentation and growth of Cape Lookout over the past 4000 years probably reflects a similar history of development for other capes and shoals along the southeastern coast of the United States. The large-scale cuspate morphology present today may therefore be a relatively recent phenomenon.

GREAT SOUTHWARD MIGRATION OF SAND SPITS ALONG THE WEST COAST OF FORMOSA

The chart “Hoko Suido (1/150000) ” was published by Naval Hydrographic Office of Japan for the first time in 1904 and showed the development of three great sand spits along the coast of Formosa. In 1932, a descriptive remark was added on the chart that these sand spits appear to be migrating southward. After the World War Second, Hydrographic Office of Taiwan surveyed around the same area and published the new chart “Hoko Kodo”. From the comparison of two charts mentioned above, it was able to observe clearly that these sand spits had migrated greatly to southwestward or southward direction during the past 60 years. North spit is a cuspate spit. Middle spit is about 20km in length and extends southwe-stward from the coast. It's termination has a recurve (hook) trending southward. Two older recurves on the landward side of the spit mark former terminations of a spit stretched inter-mittently. South spit is a barrier spit which extends about 30km in the SSW direction. Each barrier are about 3 or 6km long. Salt marshes develop on the sheltered landward sides of the middle and south spits. Seaward side slopes of each spits are steep, and flat terraces develop at the depth of -7.5 to 15m on. the seaward slopes of spits. Sandy shoals exist off recurves of spits beyond the depression. All sand spits were eroded remarkably on the seaward (northwestward) side and were deposited on landward (southward or southeastward) side. The seaward side slope of the north spit retreated landward about 2km over a distance of about 7km during the past 60 years. It retreated about 4.5km over a distance of about 15km on the middle spit and 1 km over a distance of 20km on the south spit during the same period. The rate of recession is about 75m/year on the middle spit. Each spit extended its length southwestward or southward about 11km at north spit, about 6km at middle spit and about 5km at south spit. And the terminations of these new spits reached to the position of shoals which situated off the distal ends of former spits. That is to say, a spit may grow by the process that a shoal off the distal end of spit grows by material supply fed by abrasion of seaward side slope of spit, then it connects with the termination of the former spit. We observed a embryo of new shoal happened off the distal end of north new spit in 1969. As a result of abrasion of seaward side slopes, flat planes developed at the foots of new spits. These flat planes are at the depth of -7.5 to 15m. The formation of new abrasion planes demonstrated that the base of vigorous abrasion related to the present sea level exists at a depth of -7.5 to -15m. North cuspate spit stretched southwest ward and a depression was formed between the coast and the spit. Orientaion of middle spit was changed from N 39°E to N 49°E. New middle spit entered to Hoko Channel deeper than the former stage by southward migration, so that the direction of prevailing wave with relatively long fetches which determines the shape of spit altered from northwest to north. It seems that middle spit increased the angle against the general direction of the coast in order to adjust its orientation to make right angle with the direction of prevailing wave from north. South spit did not change its orientation because the angle was similar to right angle against the prevailing wave from Hatto Channel.

Cyclic Cuspate Sand Spits and Sediment Transport Efficiency [with Discussion and Rejoinder

Contrasts in the occurrence of cyclic cuspate spits are found (1) between a smooth sandy oceanic barrier shoreline and spit-decorated shorelines of the associated narrow barrier lagoon, and (2) in spit development varying from none on a straight sandy shoreline to progressively prominent development with increasing convexity along an adjoining sandy headland. Critical factors in this selectivity seem to be wave fetch and shoreline curvature; both factors present contrasts in the efficiency of longshore sediment drift of coarse particles. Examples of wave fetch include southeastern Alabama and the coasts of St. Lawrence Island, Alaska; examples of shoreline curvature are believed to include both the large salient of the Cape Hatteras-Cape Fear-North Island sandy cuspate foreland and the small sandy foreland of Cape Sable, southwestern peninsular Florida. These contrasts seem to have escaped previous notice. The conditions are not found on all barrier-lagoon or sandy headland shorelines.

RECENT SEDIMENTARY HISTORY OF ST. JOSEPH BAY, FLORIDA1

SUMMARYThe history of St. Joseph Bay, on the west coast of Florida, begins with the last rise in sea level about 5,000 years ago. The formation of an extensive cuspate spit has formed a basin which is now in the process of being filled by detrital sands delivered via longshore drift from the eastern Apalachicola River. Prior to or during early stages of spit development, a wedge of fine material was deposited over the old terrace surface from an old distributary of the Apalachicola. Present sedimentation has as yet failed to obscure portions of this older surface within the lagoon.Clean quartz sand and biological carbonates comprise the bulk of the present sediment contribution. The typical East Gulf “kyanite‐staurolite” heavy mineral suite is present, as is the kaolinite‐montmorillonite‐illite clay mineral suite common to this coast.Sediments in this area have an average organic content of about 1.4%. A high organic carbon/organic nitrogen average of 15.4 has resulted from the accumulation of highly carbonaceo us plant debris under the restrictive environment of the lagoon.

On the Genesis of Cuspate Spits along Lagoon Shores

In Fisher's article (1955) unusual beach projections (cuspate spits) in the lagoons of St. Lawrence Island, Alaska, were described. The question of their formation remained unsettled and led to further discussion by Price and Wilson (1956). The present author reports the data obtained while the problem was studied by the scientists of the U.S.S.R. There exist similar projections in the numerous lagoons of the northeastern part of the U.S.S.R., as well as in a number of other narrow gulfs. Their formation reflects peculiarities of shores of elongated water bodies in which the resultant wave regime is oriented at an acute angle toward the shore. Cuspate spits are formed by shore-drifting processes and do not result from seiches, as suggested by Price and Wilson.

Cuspate Spits of St. Lawrence Island, Alaska

Field and laboratory studies of large triangular projections in the lagoons of St. Lawrence Island in the Bering Sea indicate that these deposits were built by longshore drift of beach sand and were modified by currents in the lagoons. The term "cuspate spit" is suggested to designate such features. Possible origins include (1) deposition by opposing eddy currents, (2) deposition within wave shadows, (3) longshore drift, building a series of recurved points on a spit with later modification by waves, (4) repeated breaching of the lagoon barrier beach, with deposition of sediment washed through the opening, and (5) development by currents deflected or modified by sediment masses washed over the barrier beach during storms. Lagoon constrictions may be important in localizing the formation of these deposits.