Coastal morphology; Southwest Great Abaco Island, Bahamas
Geoforum, Vol. 6, pp. 237-246, 1975. Pergamon Press Ltd. Printed in Great Britain Coastal Morphology; Southwest Great Abaco Island, Bahamas* C. N. RAPHAEL, Ypsilantit Summary: An examination of a portion of Great Abaco Island, Bahamas, reveals that the coastal zone may be subdivided into two morphological units: barrier and lagoon complexes, and rock benches with boulder ramparts. The sand barriers, colonized by multistoried vegetation, are stratigraphically thin and are characterized by narrowcoralline beaches and beach rock. The imbricete boulder ramparts adjacent to deeper water, reveal that, on occasion, high wave energy conditions occur. It is apparent that hurricanes and tropical storms are significant in modifying coastal southwest Great Abaco. Introduction km. The Banks are separated by the deep Northwest Providence Channel into two distinct archipelagos; the The Bahama Banks are the most extensive shelf seas in the Little Bahama Bank lies to the north and the Grand tropical Atlantic. Separated from Florida Ily a deep channel, Bahama Bank to the south (Fig. 1). The isalnds occupy the shallow platforms extend over an area of some 150,000 13,200 km* or about 7% of the area, are generally confined 1 I 79 I 77 75 -% % Great Aboco z c 0 26 Eleuthera c5 24 miles C. Nicholas RAPHAEL, Professor of Geography, Eastern Michigan University, Ypsilanti, Mich. 46197, USA. The writer gratefully acknowledges the assistance of Dr. Eugene JAWORSKI in the field. 237 Fig. 1 l Location of the Bahama Banks and the study area. 238 GeoforumlVolume G/Number 31411975 to the margins of the Banks, and resemble very large atolls. The seascape is one of the finest areas of contem- porary limestone deposition in the world and in recent years has attracted considerable interest. Geologists probing for gas and oil, and investigating the nature of carbonate deposition have concentrated their studies on the intertidal and adjacent submarine zones (e.g. MULTER, 1970; SHINN et a/., 1965). Traditionally, the geologic history of the Bahama platform has involved classic rigid earth ideas and conventional concepts of carbonate deposition. One interpretation for its origin suggests that the calcareous platform was deposited on the eroded and dissected North American craton and it therefore overlies a sialic basement (TALWANI. et al., 1959). Others have inferred that the islands form a mega-atoll and could conceivably represent carbonates deposited on the periphery of volcanic islands which have subsided beneath the sea (NEWELL, 1955). A third possibility is that carbonates were deposited on a shallow sea floor. As sedimentation continued, subsidence of the ocean basin to great depths occurred. More recently however, the concepts of sea-floor spreading and plate tectonics have been used to explain the origin of the banks. As postulated by Dietz and others, a small mediter- North America seperated and rotated to the north away from Africa (DIET& eta/. 1970). This rift was then filled with elastic sediments derived from the adjacent continents principally through the process of turbidity currents. With continued separation of the North American and African plates since Late-JurassicKretaceous time, ecological conditions improved for incipient carbonate deposition. Eventually, the Bahama platform was separated from North America and Africa, and deposition and subsidence continued. Coastal geomorphic studies of the Bahama platform are few and are restricted to the cays of the Great Bahama Bank. A their origin. geomorphological reconnaissance by Doran with its large scale maps is confined to the extreme southeastern portion of the archipelago, whereas Lind has limited his work to the landforms of Cat Island (LIND, 1963, DORAN, 1955). Both writers after identifying and mapping exposed marine surfaces considered them as indicators of a higher than present stillstand of the sea in the past 5000 years. Fieldwork undertaken on the southwest coast of Great Abaco (Fig. 2) suggests that here many coastal landforms are the product of hurricanes and tropical storms and hence do not necessarily require higher stillstands for ranean was created during early to mid-Mesozoic time as 2( 7725 l Fig. 2 Location of the investi- gated sites and the offshore topography (U.S. Naval Oceanographic Office, H.O. Charts 2499 and 5990). GeoforumIVolume G/Number 31411975 239 Physical Setting Tectonically, the Bahama Banks are considered stable; no major displacements have yet been reported. The absence of volcanic activity and submarine trenches would seem to confirm crustal stability. However, as in most active carbonate areas, subsidence is active. A bore hole on Andros revealed that the carbonates have a thickness of at least 5000 m and that these shallow water deposits date from early Cretaceous time (GOODELL & GARMEN, 1969). This and other borings clearly imply downwarping since the upper Mesozoic. Although the dominant geological theme has been shallow water carbonate accumulation and subsidence, other slight changes in elevation have been detected. Doran suggests positive displacements of 8m on Little lnagua (DORAN, 1955). This conclusion is based on the presence of coral in growth position at that level. In southwest Great Abaco a rock bench paralleling the coast varies vertically as much as o.6m. At Rocky Point the bedrock is inundated at normal high tide whereas Fig. 3 A rock surface exposed during low tide near Rocky Point Fig. 4 The bench, terminated by a boulder rampart, dips north- westerly towards Rocky Point where it is at about mean sea level. The wave-cut notch is exposed during low tide. 240 southeastward this level calcarenite surface is above high spring tides (Figs. 3 and 4). Also tension cracks, some of which have been welded, tend to substantiate some slight regional unrest. Local uplifts of similarly stable areas of the Pacific have also been reported by NEWELL and BLOOM (1970). Thus, slight eustatic sea level changes on this coast may be difficult to determine because of slight tectonic modifications. Southwest Great Abaco was selected for this study because of contrasting submarine and subaerial conditions Banks in the vicinity of Sandy Point are shallow; many portions are intertidal exposing elongated sand flats twice per day. The mean depths here are less than 3m and thus a favorable harvesting area for conch fishermen who use 4m poles to harvest these bottom dwellers. From Rocky Point southeastward the coast is adjacent to the Northwest Providence Channel where depths of 10m are rapidly encountered in the rocky offshore area. Swell waves are normally high (0.6-lm) and break directly on the rocky scarp which is less than 1 m in elevation. Due to the character of the submarine bottom, low waves are normally generated and are associated with depositional landforms such as at Sandy Point. Exposed rock coasts adjacent to deeper water such as Rocky Point, are being attacked by higher waves. Great Abaco is frequently struck by tropical storms and hurricanes. Accurate data indicate that between 1871 and 1973 forty-nine tropical cyclones of hurricane intensity passed within 150 km of its southwest coast (CRY, 1965). Within this period of about a century, 6 hurricanes and numerous tropical cyclones passed over southern Great Abaco. Tannehill reports 7 hurricanes within 150 km of Sandy Point between 1804 and 1871 (TANNEHILL, 1956). Although pre-nineteenth century data are sketchy, between 1500 and 1796, 7 storms of at least tropical cyclone intensity have been documented for the Bahamas (MILLAS, 1968). The combined data of Cry and Tannehill and others reveal that between 1804 and the present, 58 hurricanes passed near the study area. More than one-half of these tropical depressions were located between Florida and Great Abaco for at least 24h. Although rainfall is characterized by distinct seasonality (Aw, Koppen), the coastal vegetation is luxuriant and l The upper story includes sea grape (Coccoloba uvifera), coconut palm ~CCJCOS sp.l, palmetto LSabalpalmettol and occasionally Australian pine (Casuarina equisetifolia). Near ground level the thickets are dominated by sea oxeye (Borricbia arborescents), low bushy senna (Cada sp.), the shrub cosmopolitan espancil (Soriana maritima) and dense vines (Smilax sp.). Geoforum/Volume G/Number 3/4/l 975 diverse. Sand barriers, separating shallow lagoons from the sea, are colonized by grasses, especially sea oats (Uniola paniculatal and saltmarsh grass (Distichlis spicata), and prostrate pioneer plants such as beach morning glory (lpomeapes-caprae) and sea-purslane (Sesuvium portulacastrum). Landward, where slash- burn or plantation activity has occurred, the vegetation is two-storied. * Distinct vegetation communities similar to those noted on Great Abaco colonize other tropical coasts (SAUER, 1962). Even with the passage of hurricanes the low vegetation adjacent to the coast has a low mortality rate and little difficulty reestablishing itself in spite of heavy seas and washover deposits. This is most evident in the coastal areas where the three fathom contour is displaced seaward such as between Blackwood and George Points, and Sandy and Rocky Points. Here a shallow shelf normally protects the beach to within a few meters of the high water mark. Coastal Types The coasts, which reflect the submarine environment, may be divided into two morphological units: barrier and lagoon complexes, and rock benches with boulder ramparts. The barriers of southwest Abaco are for the most part composed of biogenetic sand and have maximum elevations of 3 m (Fig. 5a). Test pits indicated that sedimentary structures were absent, although buried soil profiles were common. A representative pit on the Sandy Point barrier revealed 25 cm of medium to coarse sand overlying 40 cm of fine organic sand. At a depth of approximately 0.6 m eolianite was encountered which became more consolida- ted with depth. The surficial stands are composed of coral and shell fragments. However, entire conch shells (Strombussp. ) do occur suggesting that waves as well as wind are agents responsible for deposition and modifica- tion of the barriers. Where severe coastal erosion has occurred such as at Sandy Point, exposed eolianite 0.6 m thick outcrops above the level of spring tides. Coastal distribution of eolianite is patchy. However, more prominent exposures occur where coastal erosion of the barrier is evident. Outcrops which dip 7-9 degrees seaward are bored by terrestrial organisms, and commonly contain root fragments and shells, especially Callista eucymata (Dall). Petrographic and hand lens inspection revealed that the eolianite fragments are finer, more rounded, and more tightly packed than beach rock sediments. Cementation of eolianite is possibly caused by the seepage of rain water charged GeoforumlVolume G/Number 3/4/1975 241 a.Sandy Point Fresh Sand b. George Point I 1 0 60 120 270 330 12 c. Hole in the Wall g E6 z 0 1 0 15 30 d. Rocky Point b 15 30 I5 60 75 e. Blackwood Point Boulder Rampart Carbonate Bedrock Fig. 5 l Selected coastal orofiles with calcium carbonate through porous dunes (RUSSELL, 1962). Its development is assisted by occasional wetting of the deposit and is associated with seasonal rainfall. On Great Abaco water tables fluctuate about 0.3 m with the oscillating tides.t Such a fluctuation will also cause periodic wetting of the barrier and probably accounts for t Dr. Daniel TURNER (Eastern Michigan University) has carefully recorded the oscillation of water levels in four open wells in the settlement of Sandy Point. He reports that water level fluctuations in wells, due to the rise and fall of the tide, average around 0.3 m. During a heavy rain in February, 1969, the water levels rose to the surface of the ground causing some flooding of the village. 242 GeoforumlVolume G/Number 3/4/1975 Fig. 6 . Parallel bands of beach rock exposed during low spring tide at Sandy Point. the more indurated eolianite with depth. Thus, the alter- nate wetting and drying may be caused by seasonal precipitation from above or fluctuation of the water table below; quite likely both are significant as they are inter- related. Beach material which has been indurated by calcareous cement is referred to as beach rock. Its occurrence is thought to be controlled by location and temperature of ground water (RUSSELL & McINTIRE, 1965). Beach rock observed on Great Abaco is regionally associated with eolianite and therefore is localized. The outcrops are composed of coarse coral and shell fragments giving the appearance of a cemented shell hash. Beach rock is intertidal ranging from low spring tide to approximately high spring tide (Fig. 6). The individual bands dip 10-l 1 degrees seaward and look cuesta-like. Between the parallel bands, intertidal pools are colonized by coral (Parities sp. ), urchins (Echinoiderms sp. ), rock-boring marine worms and other organisms. The geomorphological significance of beach rock is that it is exposed only on eroding coastlines and the Sandy Point barrier is no exception (RUSSELL, 1962, p.205; RUSSELL & MCINTIRE. 1965, p.20, 23). The beaches are narrow and with high tide and moderately strong onshore winds the low barrier is undercut. According to local informants at Sandy Point, 25 m of shoreline has been lost since 1965. This is substantiated by the erosion of roads leading to the beaches and dead Casuarina trunks which litter the shore. Stratigraphically the barrier-lagoon complexes are thin. Sections in several auger holes and pits indicate that the barrier is about 3 m thick south of Sandy Point and overlies a carbonate bedrock (Fig. 5a). The lagoon margins are fringed with red mangrove (Rhizophora mangle) which attain heights up to about 6 m. Landward of the red mangrove to approximately high tide, the lagoon shore is colonized by black mangrove (Avicennia nitida) 5-6 m high. The open waters of the lagoon, with the exception of localized sand, are free from sediment. Drowned sinks or blue holes and subaerial sinkholes suggest that the hard carbonate beneath the lagoon and barrier is pre-Recent in age. Considering the dense vegetation canopy fringing the lagoon, peat deposits are relatively thin and pinch out at the mean high tide level. The peat forms a dense reddish organic mat with occasional living Rhizophora roots. Cores, 1 m long, revealed 0.6 m of alternating peat and shelly sand above the bedrock. The barrier and lagoon occupied by low mangrove (R. mangle) is veneered with 40 cm of dense peat. Beneath the peat the flat carbonate surface was again encountered. One other estuarine environment visited northeast of Sandy Point was cored to a depth of 1 m before the hard carbonate surface was encountered. The auger holes and cores indicate that the carbonate surface located at approximately low tide is the base upon GeoforumlVolume G/Number 3/4/1975 243 Fig. 7 l An imbricate boulder rampart between Blackwood and Rocky Points. The bench exhibits a whitish-gray zone and is not inundated during high tide. which the barrier and shallow lagoons are resting. The elevation, widespread occurrence, and lateral seaward extent of the carbonate surface suggest that the modern patch reefs are growing on this surface. The barrier and the relatively thin peat deposits overlying carbonate rock suggest these coastal features are probably Recent in age. On southwest Abaco, a rock bench extends from Rocky Point to the vicinity of Blackwood Point and has an average elevation of 0.6 m above mean sea level (Fig. 5d). At Hole in the Wall another bench surface is encountered at an elevation of 10 m (Fig. 5~). Inland, both benchesare terminated by a spectacular boulder rampart composed of limestone blocks up to 1.5 m across (Fig. 7)*. The bench in the vicinity of Rocky Point averages 30 m in width and displays color zonations noted on other benches in the Bahamas and Florida (MULTER. 1970). An intertidal yellow zone is characterized by rock pinnacles and intensive weathering; a black zone inundated by spring tides illustrates some effects of intertidal erosion; and a smooth grayish-white zone covered during storms extends to the base of the boulder rampart. The only unconsolidated materials are the large boulders. Smaller gravels are welded onto the flat surface particularly on the intermediate black zone. A prominent feature are tension cracks which have been filled by such fragments and cemented. Planation and solution weathering have left these tension cracks 12-15 cm above the bench surface. The erosion occurring on tropical limestone coasts is complex and involves chemical, biological, and mechanical processes. The general consensus is that solution weather- * In the literature it is also referred to as a storm ridge, boulder ridge, or typhoon rampart. ing in some form is responsible for notch development (NEWELL, 1964). Notches in the bench observed near Rocky Point are sporadically distributed and are best developed in sheltered embayments. At Hole in the Wall, a well- defined, continuous notch and visor parallels the lee of that narrow calcareous peninsula suggesting that chemical and biological agents may indeed be more significant than. mechanical activity. The level at which active notches occur also varies. Fairbridge states that the maximum undercut below the visor occurs at mean sea level whereas Russell believes notches are cut between sea level and an elevation of 1.5 m or more, with visors to about 3 m higher (RUSSELL, 1963; FAIRBRIDGE, 1947). In the investigated areas the notch floor is just below spring tide, and the visor is partly inundated during high tide (Fig. 4). The conspicuous absence of well-developed notches in many localities and the presence of tension cracks indicate that the visors collapse rapidly. Immediately seaward, in 5-6 m of water, several large tabular boulders were observed suggesting that this is the case. Landward of the cliff face, a rampart approximately 2.5 m high is normally encountered (Fig. 5d). Although occasion- ally composed of sand or a mixture of sand and blocks, the principal constituents are blocks of varying size. The larger blocks are tabular and exhibit an imbricate structure leaning inland. The average length along the long axis is aboutl.2 m, however blocks with lengths of 2.5-4 m are frequently encountered. Boulders composing the higher elevations of the barrier generally are more spherical and have diameters of about 0.6 m. The barriers composed of blocks have contrasting vegetative covers (Fig. 8). Generally the boulders are covered with a dense coppice of woody vegetation, especially sea grape (C. uvifera). Others are 244 Geoforum/Volume G/Number 3/4/1975 Fig. 8 The leeward side of a boulder rampart which has washed over and exhibits a tongue- like morphology. To the right and left .of center the ramparts have been vegetated. Fig. 9 A gravel ridge at Blackwood Point consisting of coral fragments. The coral is derived from patch reefs 3 km offshore. virtually devoid of vegetation and the blocks are loose and not compacted. Morphologically, the boulder ramparts resemble washover fans commonly noted on sand barriers which have been breached by storm waves. One such washover was lobate in shape with the tongue of the ram- part extending 60 m back onto a sand ridge. The rampart was so fresh that no pitting, staining, or any other type of weathering was evident. Isolated blocks from this and the other ramparts were noted 70 m leeward of the barrier crest. Occasionally large coral heads are incorporated in the ramparts indicating that patch reefs as well as the cliff face is a source area for the ramparts. A barrier profiled at Blackwood Point has characteristics of the Sandy Point area as well as the Rocky Point area (Fig. 5e). The offshore zone slopes seaward and is colonized by living coral approximately 1-2 km out to sea. A low sand barrier separates a shallow mangrove lagoon from the platform. Mangrove (R. mangle) isattempting to gain a foothold on the rocky offshore zone as evidenced by a few scattered prop roots. Sporadic peat deposits occur suggesting that the mangrove may have been more extensive in the past. However, occasional high energy waves discourage extensive development. Between the high tide strandline and the established sand barrier a GeoforumlVoturne G/Number 3/4/l 975 rubble ridge composed of coral averaging 25 cm in diameter and unharvested conch (Strombussp. ) shells has been deposited (Fig. 9). Sea Level, Tropical Storms, and the Coast With the retreat of Pleistocene glaciers at higher latitudes meltwaters returned to the ocean basins and sea levels rose. The eustatic rise, which began about 20,000 years ago, continued until 4000 years ago when a standstill was reached (BLOOM, 1970, REDFIELD, 1967, COLEMAN & SMITH 1964). Therefore the present level of the sea is at its highest since the last interglacial. Some writers, however, suggest that in the past 4000 years sea level eustatically deviated 2-3 m from the present level (FAIRBRIDGE, 1961, BLOCH, 1965). Lind concluded that many Holocene coastal landforms on Cat Island, including boulder ramparts and sand barriers are a response to late- Recent higher than present stand of the sea (LIND, 1969). A seaward decrease in spacing and width of accretionary ridges in the southeast Bahamas has been cited as probable evidence of a eustatic sea level drop by Doran (WRAN, 1955, p.32). The only investigated coastal area clearly suggesting higher stillstands of the sea is at Hole in the Wall (Fig. 5~). Rather than uplift or Recent eustatic change, this bench probably represents a pre-Recent level. The investigated areas of Great Abaco suggest that the accretionary landforms are products of present environ- mental conditions. When the eye of Hurricane Betsy passed 65 km south of Sandy Point in 1965 the settlement, which stands 2-3 m above sea level, was inundated with 1 m of water according to local informants. Thus, it is obvious that the low barrier can be overtopped. Although not topographically well developed, washover fans do occur on the Sandy Point barrier. As noted, this barrier has shells incorporated in it testifying to the fact that high wave energies do occasionally occur. Washover deposits are thin and are generally distributed over a short horizontal distance (Fig. 5a). Test pits and auger holes reveal that the maximum accumulation occurs on the crest of the ridge adjacent to the sea. A comparison with post-hurricane profiles on Mauritius generally reveals similar deposition (McINTIRE & WALKER, 1964). In fact, beach-ridge development in Tabasco, Mexico, is attributed to storm activity (PSUTY, 1967). The surface morphology of the barriers is related to overtopping by storm waves. Variation in height between the two beach ridges south of Sandy Point and contrasting sediment size at Blackwood Point are possibly due to storm and do not necessarily indicate sea level changes (Fig. 5a, b). On the average, the width of washover deposits is about 10 m. However, 245 stringers of fresh sand have penetrated 3-12 m inland and on occasion reached the lagoon. The interfingering peat and sand deposits on the lee of a barrier such as at Sandy Point probably indicate occasional periods of intensive storm activity followed by calm conditions and normal mangrove development. The amount of sedimentation associated with hurricanes is not always predictable. A comparison of two hurricanes of comparable size and intensity passing over the Florida-Bahama area illustrated that supratidal sedimenta- tion can not be associated with every hurricane (PERKINS & ENOS, 1968). The washover fan examined at Sandy Point may have accumulated during one tropical storm and may not necessarily represent a deposit increasing in thickness with every storm. Similarly the thick upper peat on the fringe of the lagoon suggests that washover sands seldom reach the lagoon. Because no sand was introduced into the lagoon fringe, does not mean no storms occurred during the accumulation of the dense peat. Although the shallow platforms at Blackwood Point are normally indicative of low energy coastal environment, the very coarse sediment of the low barrier clearly reveals that on occasion storms are capable of breaking up the reef offshore, traversing the platform, and depositing the rubble l-1.5 m above the high tide line and onto the backslope of the barrier. These storm-accumulated gravels, except for their uncemented nature, are similar to those noted on Pacific atolls where they have been deposited by tropical storms (cuRR~Yeta/. 1970; NEWELL & BLOOM, 1970, PP. 1874-1877; MARAGOS etal., 1973). Boulder ramparts also favor a storm hypothesis. The boulders are stacked and display an imbricate structure indicating that they were shoved rather than tumbled onto the platform. They are dispersed randomly over the entire bench and therefore not entirely concentrated at the barrier front. If Recent sea levels were significantly higher, it would seem likely that a pre-modern shoreline would have survived and consisted of reworked or wave-washed sedi- ments. No evidence of pebbles or small cobbles similar to the size fraction noted at Blackwood Point were observed. Tabular boulders noted at the base of the boulder rampart at different coastal localities exhibited varying degrees of weathering suggesting that they were deposited at different times. Perhaps the most striking evidence are boulder ramparts which have the configuration of washover fans. The possibility of moving such large boulders can only be associated with storm conditions. Although there may have been eustatic sea level changes in the past few thousand years, many of the landforms of southwest Great Abaco appear to be closely related to tropical storm activity. Sands in the Sandy and George 246 Geoforum/Volume G/Number 31411975 Point lagoons are either confined to the lee of the barrier or are absent. The gently seaward slope of the bench and widespread occurrence of the offshore bedrock strongly suggest that this feature is a nip-coastal form. The lack of broad accretionary topography and the presence of thin washoever fans, narrow beaches, and beach rock at the investigated sites reveal that coastal erosion is now occurring. Tropical storms and hurricanes are not normal events, however, they are a significant phenomena contri- buting to the coastal morphology of southwest Great Abaco. References BLOCH, M.R. (1965): A hypothesis for the change of ocean levels depending on the albedo of the polar ice caps. Paleogeography, Paleoclimatology, Paleoecology, Vol. I, BLOOM, A.L. (1970): Paludal stratigraphv of Truk, Ponape and Kussaie, Eastern Caroline Islands. gaol. Sot Am. Bull. 81. 1895-l 904. COLEMAN J.M. and W.G. SMITH (1964): Late recent rise of sea level, geol. Sot. Am. Bull. 75, 833.840. CRY, G.W. (1965): Tropical cyclones of the North Atlantic Ocean, Weather Bureau Technical Papers, No. 55, l-48. CURRAY, J.R., F.P. SHEPARD and H.H. VEEH (1970): Late quaternary sea-level studies in Micronesia: Carmarsel Expedition,geo/. sot. Am. BUN, 81, 1865-1880. DIET?!, R., J. HOLDEN and W. SPROLL (19701: Geotectonic Evolution and Subsidence of Bahama Platform. Gael. Sot. Am. Bull. 81, 1915-1926. DORAN E. Jr. (1955): Land Forms of the Southeast Bahamas. p. l-37. Publication No. 5509, The University of Texas. FAIRBRIDGE, R.W. (1947): The geology and geomorphologv of Point Peron, Western Australia, .I. Proc. R. SOC. West. Aust. 34, 35-72. FAIRBRIDGE, R.W. (1961): Eustatic changes in sea level, Physics and Chemistry of the Earth, Vol. 4. GOODELL, H.G. and R.K. GARMEN (1969): Carbonate geochemistry of Superior Deep Test Well, Andros Island, Bahamas, Am. Ass. Petrol Geologists Bull. 53, 513-536. LIND, A.O. (1969): Coastal Landforms of Cat Island, Bahamas, p. 149-I 50. Research Paper 122, The Universitv of Chicago. MARAGOS, J.E., G.B. BAINS and P.J. BEVERIDGE (1973): Tropical Cyclone Bebe Creates a new land formation on Funafuti Atoll, Science, 181, 1161-I 164. MclNTIRE. W.G. and H.J. WALKER (1964): Tropical cyclones and coastal morphology in Mauritius. Ann. Ass. Am. Geogr. 54, 582-596. Ml LLAS. J.C. (1968): Hurricanes of the Caribbean and Adjacent Regions, 7492-7800. Academy of the Arts and Sciences of the Americas, Miami, Florida. MULTER, H.G. (1970): Field Guide to Some Carbonate Rock Environments, P. 19-21. Madison, N.J. NEWELL, N.D. (1955): Bahamian platforms, in: A. POLDEVAART, ed., Crust of the Earth, pp. 303-315. Geological Society of America, Special Paper No. 62. NEWELL, N.D. (1964): Recent terraces of tropical limestone shores, Z. Geomorph. 8,87-l 06. NEWELL, N.D. and A.L. BLOOM (1970): The reef flat and two-meter Eustatic terrace of some Pacific atolls, Bull. Gee/. Sot. Am. 81, 1881-1893. PERKINS, R.D. and P. ENOS (19681: Hurricane Betsy in the Florida-Bahama Area-geologic effects and comparison with Hurricane Donna. J. Gee/. 76, 71 O-71 7. PSUTY, N.P. (1967): The Geomorphology of Beach Ridges in Tabasco, Mexico. P. I-51. Louisiana State University Press, Coastal Studies Series, No. 18. REDFIELD, A.C. (1967): Postglacial change in sea level in the western North Atlantic Ocean. Science, 157, 687-692. RUSSELL, R.J. (1962): Origin of beach rock. Z. Geomorph. 6, l-16. RUSSELL, R.J. and W.G. MclNTlRE (1965): Southern hemisphere beach rock. Geogrl. Rev. 55, 17.45. SAUER, J.D. 11962): Effects of recent tropical cyclones on the coastal vegetation of Mauritius. J. Ecol. 50,275.290. SHINN. E.A., R.N. GINSBURG and R.M. LLOYD 11965): Recent supratidal dolomite from Andros Island, Bahamas. Dolomitization and Limestone Diagenesis, Special Publication NO. 73. 112-123. Society of Economic Paleontologists and Mineralogists. TALWANI. M., J. WORZELL and M. EWING (1959): Gravitv anomalies and structure of the Bahamas. Second Caribbean Geological Congress Transitions, pp. 156-I 60. TANNEHILL, I.R. (1956): Hurricanes, Their Nature and History. Princeton University Press. RUSSELL, R.J. (1963): Recent recession of tropical cliffv coasts. Science, 139,9-l 5.