Breaking of storm waves on sand and reef zone in the Lesser Antilles Arc
0
Citation
0
Reference
20
Related Paper
Abstract:
The most part of the exposed coastal zone of the Lesser Antilles Arc are composed by sand and coral reef. The high frequencies of passage of cyclones near these islands and anticyclone’s swell subject them to waves of large amplitude. These waves are 4 to 5 times lager to the normal conditions. The weak slopes observed on these zones are particularly sensitive to this type of waves and cause the process of surfing. The mode of dissipation of these waves influenced the run-up and the floods on the coast. The surf zones are situated in 5 in 20 meters of the line of coast. A displacement of sea water towards the coast line is provoked by the breaking of the waves. These quantities of water are held by the particularly bathymetry of these islands and provoke a raised of the sea level. The propagation of the waves are allowed by the sea elevation in the surf zoneKeywords:
Swell
Surf zone
Anticyclone
Fringing reef
Storm Surge
Cite
Shoal
Seabed
BENGAL
Deposition
Cite
Citations (30)
ABSTRACT Large tidal current ridges (tidal sand banks) in the southwestern Yellow Sea are located offshore of northern Jiangsu Province, China. These ridges radiate to a depth of 20-30 m. The dimensions of the ridge system are about 200 km long and 90 km wide. Their morphology indicates the strong influence of tidal currents. The ridges are composed of well-sorted fine sands (size range is 2-4 ). The grain size distributions of the sands show that the sands are transported and deposited by tidal currents. The ridge system formed on the abandoned Yellow River and ancient Yangtze River deltas has an abundant sand supply from the former deltas. Of particular importance is the existence of two tidal wave systems in the Yellow Sea: the rotary ti al wave system in the southern Yellow Sea and the Pacific progressive tidal wave system propagated into the southern ridge area of the southwestern Yellow Sea. Under the interaction of the two tidal wave systems, the huge tidal current system in the southwestern Yellow Sea has formed.
Tidal current
Cite
Citations (51)
Abstract The coast of southeastern Australia has a high-energy embayed and cliffed coast that receives only minor amounts of modem sediment from streams. This setting, coupled with an apparently stable sea level for the past 6000 years, results in a thin erosional veneer of Holocenc sediment overlying truncated Pleistocene and older deposits on the shelf. In several locations, however, large sand bodies have accreted on the lower shoreface and these sand bodies are unlike those described from other shelves in the world. They arc 10 to 30 m thick, several kilometres wide, tens of kilometres long, and result in a convex shoreface profile. Radiocarbon dates indicate that most of the sand bodies were deposited in the past 6000 years after the sea level reached its present position. From the study of the texture and composition of long-core samples, it appears that the sand was derived from adjacent beaches and cliffs, and seismic-reflection profiles indicate progradation of sand bodies has occurred across the steep (2° to 5°) seaward flank into water depths of 60 to 80 m. Three major factors appear to control formation of these sand bodies: an initially steep inner-shelf profile; local high-energy conditions; and a long time period of a stable sea level. Based on sediment texture, seaward dipping reflectors, and surface channels, we infer that sediment is transported seaward from the upper shoreface to the sand bodies by storm-induced downwelling. In areas of strong regional flows, such as off Cape Byron, where the East Australian current impinges on the coast, these flows play a major role in modifying the shape and textural character of the sand bodies.
Progradation
Cite
Citations (0)
Abstract. A coral-rubble ridge fringes part of the north shore of Anegada, a low-lying island in the northern Caribbean. Both historical reports and the geological record underline its vulnerability to tsunami and hurricanes. In this study we document the sedimentary characteristics of a coral-rubble ridge, which extends discontinuously along 1.5–1.8 km of chiefly north-facing shores at Soldier Wash. The ridge is less distinctive and appears only in patches along the west-facing shoreline at Windless Bight, where the wave regime is calmer. It is located ca. 8 m from the fair-weather shore, has a maximum width of 15 m and a maximum thickness of 0.8 m. The lower seaward-facing slope of the ridge is relatively flat, probably due to successive reworking, whereas the upper seaward slope is steep and partly displays avalanching faces. The landward flank is gently sloping and terminates abruptly. The ridge is mainly composed of well-rounded, encrusted and bored coral rubble (average diameter of 16 cm) that has been reworked in the shallow marine environment prior to transport. Only a few pieces of angular beach rock and karstified Pleistocene limestone are incorporated. The components build a clast-supported framework. No sand is present in the interstices. Imbrication of flat clasts indicates a deposition during landward bed load transport. The ridge morphology, composition and related hydrodynamic conditions during its emplacement are typical for coral-rubble ridges deposited by hurricane-induced storm surges. In comparison, nearby evidence for tsunami inundation is very different because the tsunami-transported coral boulders on Anegada are much bigger (2 m) than the biggest components in the ridge, they are deposited much farther inland (up to 1.5 km), and the corals seem to have been freshly broken out of the reef by the tsunami. The age of the ridge is difficult to estimate. The dark grey surface of the ridge is caused by bioweathering by endolithic organisms that takes tens of years and may give a very rough estimate of the minimum age of the ridge. Storms and related surges that built the ridge were likely stronger than 2010 hurricane Earl, which attained category 4 north of the island. Earl was able to slightly rework the lower seaward part of the ridge, but transported only few and smaller pieces of coral rubble and sand onshore. Therefore, the coral-rubble ridge found at the north shore of Anegada may imply that the island is vulnerable to hurricane-induced surges of greater impact (in relation to storm path and intensity) compared with the any of the recently documented storms which were only able to rework the ridge.
Rubble
Headland
Overwash
Cite
Citations (18)
Cite
Citations (34)
Abstract Storm surges generated by tropical cyclones have been considered a primary process for building coarse‐sand beach ridges along the north‐eastern Queensland coast, Australia. This interpretation has led to the development of palaeotempestology based on the beach ridges. To better identify the sedimentary processes responsible for these ridges, a high‐resolution chronostratigraphic analysis of a series of ridges was carried out at Cowley Beach, Queensland, a meso‐tidal beach system with a >3 m tide range. Optically stimulated luminescence ages indicate that 10 ridges accreted seaward over the last 2500 to 2700 years. The ridge crests sit +3·5 to 5·1 m above Australian Height Datum ( ca mean sea‐level). A ground‐penetrating radar profile shows two distinct radar facies, both of which are dissected by truncation surfaces. Hummocky structures in the upper facies indicate that the nucleus of the beach ridge forms as a berm at +2·5 m Australian Height Datum, equivalent to the fair‐weather swash limit during high tide. The lower facies comprises a sequence of seaward‐dipping reflections. Beach progradation thus occurs via fair‐weather‐wave accretion of sand, with erosion by storm waves resulting in a sporadic sedimentary record. The ridge deposits above the fair‐weather swash limit are primarily composed of coarse and medium sands with pumice gravels and are largely emplaced during surge events. Inundation of the ridges is more likely to occur in relation to a cyclone passing during high tide. The ridges may also include an aeolian component as cyclonic winds can transport beach sand inland, especially during low tide, and some layers above +2·5 m Australian Height Datum are finer than aeolian ripples found on the backshore. Coarse‐sand ridges at Cowley Beach are thus products of fair‐weather swash and cyclone inundation modulated by tides. Knowledge of this composite depositional process can better inform the development of robust palaeoenvironmental reconstructions from the ridges.
Beach ridge
Swash
Progradation
Berm
Cite
Citations (48)
In order to understand more fully the principles of transportation in shallow parts of all marine systems, a series of studies by diving geologists at the University of Southern California are aimed at providing new data on the mechanisms of sediment movement from the surf zone to depths of approximately 100 ft. It is evident from the first results of this program that much of the theoretical information on wave transport based on wave-tank observations must be modified. Measurements have been made of rates of sand movement using dyed sand (Vernon, 1965), magnitude of wave-generated surges over the bottom in shallow depths (Vernon et al., 1966), changes in energy in the surf zone (Ingle, 1966; Schiffman, 1965), regional changes in beach characteristics (Gorsline, 1966), movement and quantity of suspended sediment over the shelf (Rodolfo, 1964; Wildharber, 1966), and movement of fine sediment in canyons (Gorsline, in progress). These various measurements show that the wave transport of sediments is active to depths of 60-80 ft off California during an average year and that the flow of sand along the coast probably is matched in magnitude by the flow of fine suspended material. It is also demonstrated that sand moves around headlands below surf depth an is then moved back into the surf system by onshore wave action. Much of the sand entering submarine canyon heads probably is moved in below surf depth by this same ripple-transport mechanism. All of these systems are strongly controlled by bottom or coastal physiography. In addition to the commonly considered physiographic barriers to sedimentation, End_Page 2175------------------------------ numerous contemporary examples of water barriers also exist that have effects at all scales on the distribution and character of marine sediments. Because these are also the precursors of most source and reservoir rocks, an understanding of their effects is of basic importance to petroleum geologists. On a relatively small scale, circulation patterns in Florida Bay, at the southern tip of the Florida peninsula, are slow tidally controlled gyres which create a flow that probably prohibits sediment transport into the central portions of the individual lakes of this broad shallow embayment. Thus the sediment accumulation occurs around the periphery of the individual segments and these lines of sedimentation in turn appear to coincide with the locus of points of small or zero tidal amplitude. Current transport of these materials also takes place and thus they ultimately come to rest in the deep water of the Florida Straits. In large coastal bays on the Pacific coast, water circulation also plays a strong part in the distribution of sediment types. Sebastian Viscaino Bay is an open, broad, north-facing embayment that also forms the southern extremity of the continental borderland off California and Baja California. Within this huge embayment the California Current turns back on itself and forms a large gyre. The patterns of texture, bioclastics, and organic content are strongly controlled by this circulation pattern and, in fact, parallel the contours of flow. Work by K. S. Rodolfo at U.S.C. shows that the shift in the monsoon and the period of strong river flow combine in the Andaman Sea to restrict Irrawaddy sedimentation to the confines of the sea even though no physiographic barrier is present to hinder flow to the adjacent Bay of Bengal. Thus, the sedimentation in the two areas is from two different sources producing lenses of sedimentation of geosynclinal scale side by side from different sources. The development of the entire Andaman margin is effectively controlled by these circumstances. Off the southern Atlantic coast of the United States, the Gulf Stream forms an effective boundary to the detrital terrigenous sediments of the upper shelf and the bioclastic sediments of the outer shelf and Blake Plateau. The combination of broad shelf and strong regional current also influences the form of the coast and apparently also prevents the active formation of submarine canyons. End_of_Article - Last_Page 2176------------
Cite
Citations (0)
Paleo-wave conditions during the Shimosueyoshi Transgression (130, 000-100, 000 years B.P.) are estimated from oscillatory ripples preserved in prodelta, shoreface and tidal flat deposits of the Paleo-Tokyo Bay. Possible combinations of wave conditions and water depths that could have generated the observed ripples are determined by ripple spacing and grain size of ripple forming sediments using the method of Komar (1974) and others, which are based mainly on Airy wave theory. In addition, paleo-depths are calculated independently by the following two methods using stratigraphic thickness from the ripples to the above foreshore deposits and the height of longshore bars containing some of the ripples in shoreface deposits. Therefore, combinations of wave height and wave period under the water depth, which was estimated by the above method, can be determined.Waves with a height of lower than 2.3 m and a period of 2-8 s are obtained from the ripples in prodelta deposits. Such waves represen “storm waves” of the present Tokyo Bay. This wave condition may have been formed by relatively small waves of post-storm stage, because the ripples occur in the upper part of storm-generated sheet sand and are covered by a clay layer deposited from suspended matter in flood fluvial water into the Paleo-Tokyo Bay. Waves with lower than 2.5 m in height and 1.5 to more than 10 s in period are reconstructed from the ripples in shoreface deposits. These waves can generally represent “storm waves” of the Tokyo Bay and “fairweather waves” of the Kashima beach facing the Pacific Ocean. Waves of smaller 1 m high and less than 5.5 seconds are reconstructed from the ripples in tidal flat deposits. These small waves are approximately equal to “fairweather waves” of the Tokyo Bay. No ripples representing more big waves, such as winter waves and typhoon-generated storm waves on the present Pacific coast, are preserved in the Paleo-Tokyo Bay sediments. This may be caused by the shallow seawater-depth, less than 10 m, of the Paleo-Tokyo Bay where big wave motion during storm event may have changed most of the bottom sediments to flat bed rather than ripples.
Ripple marks
Cite
Citations (6)