Coastal Features Research Articles

A boulder beach formed by waves from a calving glacier; Eqip Sermia, West Greenland

A large‐scale boulder beach close to a tidal glacier was examined at Eqip Sermia, Disko Bugt, West Greenland, in 1989. Photographs from 1912 and 1929 show an advance of the glacier of more than 1.5 km beyond its present location. Lateral and terminal moraines were formed in the sea, and subaerial parts and their positions can be detected from the old photographs. Today the outermost part of this moraine system has disappeared totally, except for about 1 km of the lateral moraine. The distal 300 m of the still existing moraine apparently has been displaced and transformed into a shape that, in plan view and cross‐section, resembles a barrier spit. The material of the boulder beach consists mainly of coarse clasts with boulders of 1 m to more than 1.5 m in diameter. Distributions of clast sizes and sediment structures on the barrier surface also suggest wave and overwash dynamics as being the responsible agents. Located in the inner part of a fiord system, the fetches are restricted and thus normal waves are very small. Large waves generated by glacier calving, and/or sea‐ice action, are therefore the only processes that can explain the geomorphology and clast distribution of this coastal feature.

A 125 Kyr‐long geological record of seismic source repeatability: the Messina Straits (southern Italy) and the 1908 earthquake (Ms 71/2)

ABSTRACTThe occurrence of characteristic earthquakes along segments of major active belts has been described as early as the beginning of the century. The large 1908, Messina Straits, blind normal faulting earthquake provides an opportunity to investigate the repetition of characteristic earthquakes and the persistency of the main features of the fault zone over a time‐scale in the order of 100 Kyr. We have compared seismological and geodetic descriptions of the 1908 rupture process with long‐term crustal deformation recorded at different stratigraphic levels by marine terraces, marine sedimentary units, and landscape features. The wealth of elevated coastal features in and around a region affected by large normal faulting earthquakes indicates that coseismic strain is superimposed on much faster uplift on a regional scale. We investigated in detail the pattern of deformation of the 125 Kyr‐old, lowest emergent terrace, and found that it mimics the pattern of elevation changes observed following the earthquake. This suggests (1) that the 1908 earthquake is characteristic, (2) that its segment boundaries have been stationary during the past 125 Kyr, and (3) that even the locations of the regions of largest coseismic release do not change through many seismic cycles. Based on a comparison between observed heights of the 125 Kyr terrace and 1908 displacements, we estimated an average repeat time of 1000± yr for a 1908‐type earthquake. We also investigated the height, position, age and state of deformation of older terraces, and found (1) that uplift of the region started about 1 Ma and has since continued rather uniformly at 0.9–1.4 mm yr‐1, (2) that during this time the Straits have narrowed at a rate of 10–20 mm yr‐1, and (3) that all the main geomorphic features of the Messina Straits result from the interaction of fast regional uplift, 1908‐type coseismic subsidence, and global sea‐level fluctuations.

Navigation of coastal AVHRR images

Abstract This paper describes a simple, computationally inexpensive procedure for automatically identifying coastal features in an unnotified, unregistered daytime image. The procedure can be used to identify ground control points for image registration and to provide a local correction for the navigation predicted from the satellite orbit parameters supplied in the T-bus transmission. The correction consists of a horizontal displacement and a rotation, the latter accounting for errors in the roll, pitch and yaw of the satellite platform.

Late Quaternary phreatomagmatic tephra layers and their relation to paleo-sea levels in the area of Aira caldera, southern Kyushu, Japan

Four Late Quaternary phreatomagmatic eruptions occurred during different sea levels and paleoenvironments as determined by study of four tephra units containing fine-grained ash layers, and their relation to coastal features in the Aira caldera volcanic area. These units are: (1) Aira-Ito (22,000 BP), (2) Sakurajima-Satsuma (11,000 BP), (3) Sumiyoshiike (6700–7000 BP) and (4) Yonemaru (6500–6700 BP) formations. These formations contain base surge deposits as well as fine-grained ash fall from phreatomagmatic eruptions. The eruptions occurred under very different conditions of sea level heights and coastal environments. The Aira-Ito eruption occurred during the lowest sea-level stage; the Sakurajima-Satsuma eruption during rapid sea-level rise; and the Sumiyoshiike and Yonemaru eruptions during the final sea-level transgression. The sea-level heights relative to present sea level are 60 m and 20 m below, and 10–15 m above, respectively.

Late Quaternary Deweyville Interval Superfloods

Alluvial terraces characterized by large relict meander scars at levels between the Pleistocene Beaumont terrace and Holocene surfaces along the Sabine River were designated as the Deweyville Terrace by Hugh Bernard in 1950. Two terrace levels have been identified on the Sabine River, traced onto the continental shelf, and correlated with drowned, relict coastal landforms. Meander size and floodplain width indicate flood discharges 5 to 10 times higher than present. Deweyville features occur on other northern Gulf of Mexico and Atlantic coast streams and relict coastal features have been traced on the shelf. The Deweyville interval occurred between 17,000 and 10,000 years B.R

Technical note Coastal geomorphology of Mahe Island, Seychelles

Abstract This note is based on observations and interpretations of aerial photographs. Aerial photocharacters such as tonal differences, texture, shape, size, form, pattern, vegetation and associated features were considered in identifying the geomorphological features: lineaments, terraces, reefs, beaches, beach rock, erosion, turbidity, etc. The island relief is predominantly mountainous with granitic cliffs and rugged peaks. Rocky shores of the island alternate with beach accumulations. Lineaments correspond with the regional trend of the rock exposures. There are three to four levels of terraces, reefs are common along the shores, beaches occur mostly in protected bays and beach rock has been observed at several localities. Based on the disposition of landforms it is surmised that the coastal features are controlled by the regional structures and erosion is more common than the progradation, especially on the west coast.

Exploration and Australian Cartography in East Antarctica

The Antarctic continent is usually described as consisting of two structural units, East (or Greater) Antarctica and West (or Lesser) Antarctica. This paper traces the early exploration and cartography of East Antarctica and describes the techniques used by Australia in mapping the region covered by the Australian Antarctic Territorial claim. Australia has played a major role in mapping the coastal and mountain features in this part of Antarctica. The application of space imagery to Antarctic cartography is examined and future trends identified in the use of digital topographic data for Geographic Information Systems, used for the coordination of Antarctic scientific data for environmental management purposes.

Coastal landform mapping around the Gulf of Khambhat using Landsat TM data

Landsat TM data was utilised for coastal geomorphic mapping around the Gulf of Khambhat. Various landforms like shoreline, estuaries, mudflats, islands, mangroves, relict aluvium, cliffs, dunes, flood plains, paleochannel, paleomeanders, oxbow lake, etc. were delineated. The estuaries were divided into salt-wedge estuary, fully mixed estuary and partially mixed estuary based on amount of freshwater discharge and nature of tidal currents. The mudflats were classified into high tide flats, intertidal slopes and subtidal zones. These classes were further classified based on their composition. It was concluded that TM data has broughtout many new features and improved the classification of coastal landforms. The presence of coastal features like drowned river valleys, paleomudflats, relict alluvium, dunes, paleomeanders, oxbow lake and terraces clearly indicate the sea-level changes of the Quarternary period.

Impact of 1985 Hurricanes on Isles Dernieres, Louisiana: Temporal and Spatial Analysis of Coastal Geomorphic Changes: ABSTRACT

Catastrophic geomorphic changes occurred in the Isles Dernieres barrier island arc as a result of the direct impact of three hurricanes in 1985. The severity of the impact of hurricanes Danny, Elena, and Juan had not been equaled since the landfall of hurricanes Betsy and Camille in the late 1960s. The Isles Dernieres had not been subjected to a direct hurricane landfall since hurricane Bob in 1979. The recent hurricane impacts provided the USGS/LGS Louisiana Cooperative Barrier Island and Land Loss Study the opportunity to examine the process-response characteristics of this low-profile transgressive barrier island arc to multiple hurricane impacts in a single hurricane season. The geomorphic changes along the Isles Dernieres were determined using four sequential airborne videotape surveys acquired in July 1984, July 1985 (pre-storm), August 1985 (post-Danny) and November 1985 (post-Juan) and mapped on 1:24,000 base maps produced from concurrent vertical aerial photography. A coastal geomorphic classification was developed to describe, quantify, and map the alongshore geomorphic, sedimentologic , and vegetative character of this barrier shoreline. The classification consists of three levels of descriptors: (1) primary morphology to define the predominant longshore morphology, (2) modifiers to depict the small-scale longshore features, and (3) variants to locate andmore » quantify important coastal features, not mappable at the scale used.« less

Comparison of SLASAR and Landsat MSS Data for Geologic Mapping in Onshore Santa Maria Basin Area, California: ABSTRACT

Comparison of side-looking airborne synthetic aperture radar (SLASAR) data with Landsat Multispectral Scanner (MSS) data for the onshore Santa Maria Basin area in the western Transverse Ranges on the California coast provides two data sets with complementary information for the interpretation of geologic structure and lithology. Near-range SLASAR data, with an east-look direction, bring out north-south-trending coastal features. The low illumination angle accentuates topographic features that reflect structural and geomorphic control. Lithologic differences can be discerned on the basis of image texture (spatial variability), which is controlled by surface roughness. Spatial resolution (pixel size) is 12.5 m. A computer algorithm for analyzing the spatial variability of pixel brightness provides a means for automatically classifying land-cover types in the imagery. Despite poorer spatial resolution (pixel size of 80 m), Landsat MSS data for the area provide valuable spectral information for geologic mapping. The differing responses of rock types and vegetational assemblages in the four channels of the MSS imagery have been analyzed by another computer algorithm to classify land-cover types on the basis of spectral pattern recognition.

Some aspects of geomorphic processes along the Goa coast through remote sensing

This paper deals with the processes operating on the beaches of Goa, interpreted from imagery, followed by ground-truth collection and field checks. Studies on Landsat imagery bring out two distinct coastal geomorphological features, one north and the other south of Vasco-da-Gama. The beaches to the south indicate the prograding shoreline with deposition being the dominant phenomenon. The beaches to the north of Vasco-da-Gama reveal a retrograding shoreline where erosion is dominant.

Coastal Geomorphology of Kerala

Abstract Coastal geomorphological map of Kerala was prepared on a scale of 1 : 500,000 using LANDSAT imagery. Aerial photographs were used wherever necessary, followed by field checking. The coastal features identified include beaches, beach cliffs. stacks. islands, shore platforms, spits, bars, beach ridges, estuaries, lagoons, mudflats, tidal flats and deltaic plains. Of the various lineaments identified over the Kerala region. the fault lineaments parallel to the coast as well as those at right angles to it are found to be neotectonically active and control the configuaration of the shoreline primarily. Of the 560 km shoreline of Kerala, a cumulative 360 km length of shoreline is vulnerable and shows wide fluctuations in its stability. Based on their vulnerability and dynamism, the shoreline is divided into (1) permeable, gently sloping, sandy shoreline (2) semi-permeable, cliffed, sedimentary shoreline and (3) impermeable, crystalline shoreline, arranged in order of intensity of erosion. Apart from the known factors of slope morphometry, lithology and storm-wave generation, the non-parametric factors responsible for coastal erosion include presence or absence of mud banks near-shore and instability of off-shore regions. The Kerala coast is described as a submergent coast, falling under the 'Terrigenous coast of primary morphologic disequilibrium '. Accordingly, the long-term tendency of coastal evolution is to increase the linear extent of erosional coastal segments at the expense of intervening depositional areas and, when the process goes to completion, a coast of equilibrium results.

Mid-Permian Shelf Margin Erosion Surfaces, Western Escarpment, Guadalupe Mountains, Texas: ABSTRACT

Three basin-sloping erosion surfaces, interpreted as submarine seismic sequence boundaries, are spectacularly exposed along the Guadalupe Mountains' western escarpment. Each surface has about 300 m of basin margin relief over 2 to 3 km and displays 30 to 80 m of local channeling and/or listric-shaped relief. The upper (post-Grayburg) and lower (post-Victorio Peak) surfaces truncate predominantly flat-bedded, shoaling-upward bank (or low-angle ramp) dolomite strata. The middle surface (post-Cutoff) locally cuts through the deep marine drape of 300 m relief of the 75-m thick Cutoff formation. The post-Grayburg surface is listric-shaped and truncates about 140 m of Grayburg in a basinward distance of 1.5 km. This post-Grayburg erosion surface marks a major change in Permian carbonate sedimentation from earlier bank strata to the steep foreslopes of 400 + relief of the Goat Seep-Capitan reef complex. Erosional retreat of the Grayburg and Victorio Peak bank margin may have been 100 m to 1 km or more. Evidence of submarine erosion includes deep marine facies directly overlying the erosion surfaces, the regional improbability of hundreds of meters of sea level lowering, and the lack of recognition of subaerial or coastal features. The erosion processes remain uncertain. Retrograde slumping is favored for the listric-shapedmore » post-Grayburg surface. Bottom-hugging density currents were likely important for the lower two surfaces and perhaps for all three surfaces. Bare and eroded slopes are increasingly being recognized in modern submarine environments. They are likely more abundant and important in the geologic record than has been recognized to date.« less

Space and time variability of the surface color field in the northern Adriatic Sea

A time series of coastal zone color scanner images for the years 1979 and 1980 was used to observe the spatial and temporal variability of bio‐optical processes and circulation patterns of the northern Adriatic Sea on monthly, seasonal, and interannual scales. The chlorophyll‐like pigment concentrations derived from satellite data exhibited a high correlation with sea truth measurements performed during seven surveys in the summer of both years. Comparison of the mean pigment fields indicates a general increase in concentration values and larger scales of coastal features from 1979 to 1980. This variability may be linked to the different patterns of nutrient influx due to coastal runoff in the 2 years. The distribution of surface features is consistent with the general cyclonic circulation pattern. The pigment heterogeneity appears to be governed by fluctuations of freshwater discharge, while the dominant wind fields do not appear to have important direct effects. The Po River presents a plume spreading predominantly in a southeastern direction, with scales positively correlated with its outflow. The spatial scales of the western coastal layer, in contrast, are negatively correlated with this outflow and the plume scales. Both results are consistent with, and may be rationalized by, recent theoretical and experimental results involving a dynamical balance between nonlinear advection and bottom friction, with alternate predominance of one of the two effects.

Coastal tidal jets and tidal fringe development around the Isles of Scilly

Tidal jets are a ubiquitous feature of the coastal environment and result from strong tidal streaming off coastal features such as promontories. Around the Isles of Scilly there exist two tidal jets which tend to propagate in a clockwise sense around the island group. Currents in excess of 90 cm s −1 appear necessary for their production and the jets are characterized with a Reynolds number of about 30. It is shown that the jets indicate the direction of the maximum stream and the residual circulation around the islands. With an offshore component to the residual flow, tidal fringes may develop from the jets and such fringes were observed on the northern side of the islands.

Influence of surface slicks on the distribution and onshore movements of small fish

The surface slicks of internal waves were sampled in continental shelf waters off the east coast of Northland, New Zealand, from 1982–1985. Densities of small fish and zooplankton from surface waters were higher in slicks than in the rippled water adjacent to them. Presettlement fish, of species found as adults nearshore, were abundant in ichthyoplankton samples and visual counts from slicks. These fish ranged from fish with primordial fins to those with adult fin-ray counts. Some small reef fish aggregated around drift algae. Drift algae were also abundant in slicks. Slicks moved at 0.5 to 1.25 km h-1 in the direction of shore. Hence, a consequence of aggregation in slicks is that presettlement fish may be transported onshore. When slicks were absent, drift algae were found in scattered patches at different distances from shore. In the presence of slicks algae were aligned in them. Internal waves, therefore, may have the ability to turn scattered distributions into regular patterns. Because the surface slicks that internal waves produce are common coastal features, we should modify our perspective of how small fish and zooplankton are distributed in local water masses. Furthermore, the occurrence of internal waves should influence the way in which surface waters are sampled. We suggest that fish settlement patterns need to be investigated concurrently with measurements of physical mechanisms which may promote aggregation, and onshore movements of small fish (e.g. internal waves). These waves may contribute to the variability in settlement rates of small fish.

NOAA satellite and air-borne sensing of a small-scale, coastal tidal jet

Koombana Bay, on the south-west coast of Australia, contains a tidal jet that emanates from Leschenault Inlet via a man-made channel 150 m wide. The tides are of mixed diurnal-semidiurnal character. The strongest jets are induced by the diurnal tide and flow at night in summer and during daytime in winter. The duration of the discharge is about 9 h, after which the maximum length of the jet is a few kilometres. Extensive field studies together with numerical and analytical modelling have recently been completed on the jet. These allowed predictions of optimum times for viewing the jet via an air-borne thermal scanner aboard the CSIRO Fokker F27 aircraft, and a NOAA7 satellite image. The air-borne image mapped the late-summer jet, which consisted of night-cooled water from the shallow Inlet. Because the satellite pass occurs in late afternoon, the seasonality of the tide limits visibility of the jet in the imagery to late winter. The NOAA7 image shows a jet composed of warm water that has been heated during the day inside the Inlet. These observations confirm the sea data and model results and are believed to be the first use of NOAA imagery to resolve a coastal oceanographic feature of this scale.

琉球列島南部における完新世の海岸地形および海水準

1. Marine terraces, marine notches, beachrock, in situ coral reef and emerged shellbeds are used as indicators of Holocene sea-levels in Kohama, Kuro and Hateruma Islands, the South Ryukyus. A sea-level slightly higher than the present one, about 1 m AMSL is found from ca. 3, 300 to 800yBP in Kohama and Hateruma Islands and about 1.5m AMSL at about 4, 200yBP in Kuro Island (Table 2). It is, however, difficult to distinguish local differences in these three islands, owing to the limited number of observations and some uncertainty in the value of some coastal features as indicators of former sea-level. Late Holocene emergence is very small. 2. Shorelines which records the culmination of Postglacial (Jomon) transgression at about 6, 000yBP have been found along many parts of the Japanese coastline. Such evidences of shorelines, however, have not been observed in these three islands. The buried notch in Kuro Island, covered by beachrock at ca. 4, 200yBP, may correspond to this early transgression. 3. The relative sea-level drop causing the emergence of marine features in several Ryukyu islands is a recent phenomenon. Slight emergence dated at ca. 800 to 600yBP occurs not only on Hateruma Island, but also on Yoron Island (DELIBRIAS and PIRAzz0LI, 1983), on central Okinawa Island (KAWANA and PIRAZZOLI, 1983) and on Tarama Island (PIRAZZOLI et al., 1984). 4. Deposits found on the southeast coast of Hateruma Island, can be interpreted as the result of a tsunami, which accompanied the great earthquake of 1771.

Review of evidence for late Tertiary shorelines occurring on South Atlantic coasts

Recognition of (late) Tertiary shorelines on continental coasts is becoming increasingly common. It is argued that the elevations of such features are central to their approximate dating and the demonstration of contemporaneity with similar features elsewhere. South Atlantic coasts have not had a long history of investigation, yet there exist many diffuse observations, in both time and space, which are here drawn together into a preliminary synthesis and the case for widespread occurrences of late Tertiary shorelines in the region reviewed. This allows comparison with other areas from which Tertiary shorelines are known, the Atlantic seaboards of the Southeastern United States and Northwest Europe, for example. The coasts of oceanic islands are probably the best places to examine the legacy of late Cenozoic sea-level changes. It is suggested that, since many of the cliffed shores of these islands appear to be the result of a rapid emergence, coastal features predating this event might be preserved on the cliff-tops. Possible late Tertiary shorelines from South Atlantic islands are described, as are those which have been positively dated to this period, in the Eastern Canary Islands, for instance. Sedimentary and morphological indicators of Tertiary high sea-levels are described from Antarctic coasts. South American and African Atlantic continental margins. Evidence from the latter two areas is most suspect, owing to their generally more complex Quaternary tectonic histories. A summary of the evidence for Tertiary shorelines on South Atlantic coasts is tabulated. Methods which have been or could be used to date late Tertiary shorelines are described. Minimum age can be deduced from that of deposits resting on an erosional surface, maximum age from that of the youngest formation across which a surface is cut. More precise age can be estimated where a marine surface is sandwiched between datable non-marine formations or where periods of tectonic activity (responsible for differential surface deformation) can be dated. Elevations of surfaces can be used to estimate ages. Problems in both recognising and dating Tertiary shorelines are discussed. Recognition of their origin is made more difficult by their degraded state and, if they occur within a Quaternary erosional sequence, their antiquity may not be realised. It is suggested that fluctuations in the Antarctic ice sheet during the late Tertiary induced substantial glacio-eustatic changes of sea-level which may have been most marked in adjacent areas. This is considered to be the mechanism through which late Tertiary shorelines in the area were formed yet, considering the paucity of the morphological and sedimentary data, these should not be used as the basis for a eustatic chronology.

Quaternary stratigraphic evolution of the southern Delmarva Peninsula coastal zone, Cape Charles, Virginia

The Quaternary evolution of the coastal zone along the southern Delmarva Peninsula of Virginia was investigated by means of a high-resolution seismic survey and supplemental shallow core borings. The seismic stratigraphic framework of the area is composed of three depositional sequences separated by two prominent unconformities. In ascending order, the three seismic sequences represent a late Tertiary substrate, Pleistocene deposits of post-Illinoian(?) age, and Holocene deposits. Stratigraphic analysis indicates that the evolutionary development of the area was controlled mainly by glacio-eustatism and paleotopographic features. The late Tertiary substrate was dissected by southeasterly flowing streams of the ancestral Susquehanna fluvial system, resulting in a highly furrowed surface consisting of valleys and interfluves that exhibit as much as 46 m of local relief. The erosional surface probably represents a mature multicyclic landscape of pre-Sangamonian(?) age. The unconformably overlying Pleistocene deposits attain a maximum thickness of 41 m. Pleistocene sedimentation was closely controlled by the paleotopography, with relatively thicker deposits accumulating within ancestral valleys. In contrast, thinner deposits accumulated over the ancestral interfluves, which did not become active sites of sedimentation until after the topographic relief had been substantially subdued by valley infilling. Pleistocene deposits are characterized by complex fades relationships, multiple generations of fluvial channeling, and the presence of a variety of coastal geomorphic features. Fluvial channel zones largely overlie the thalwegs of major southeasterly trending ancestral valleys, indicating a paleotopographic control of Pleistocene drainage routes. The youngest Pleistocene geomorphic feature, which constitutes a distinctive sand lithosome, is a coastal barrier ridge that appears to have developed during a Sangamonian interglacial or mid-Wisconsinan interstadial high stand of sea level. During the late Wisconsin regression, Pleistocene deposits were eroded, resulting in the development of a relatively low-gradient subdued landscape compared to the highly furrowed pre-Sangamonian landscape. Holocene deposits unconformably overlie the Pleistocene sequence and attain a maximum thickness of 19 m. Sedimentation during the Holocene transgression was primarily influenced by late Wisconsinan paleotopography, with relatively thicker deposits accumulating within paleochannels and along the modern shoreface. Holocene deposits also exhibit complex facies relationships, extensive channeling, and coastal geomorphic features. The Holocene sediments consist of two distinct lithosomes that are representative of modern barrier-island and lagoon–marginal-lagoon subenvironments. Microfossil assemblages indicate paleosalinities ranging from upper estuarine to marginal marine–inlet conditions. Vertical environmental transitions during the late Holocene transgression reflect a progressive restriction of the southern Delmarva coastal area by barrier-island development, with subsequent lagoonal infilling. The modern barrier islands are retrograding, and lagoonal infilling has progressed to varying degrees, having been influenced by both back-barrier sedimentation rates and pre-Holocene topography.