Boulder Beaches 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.

Shoreline deposits and diagenesis resulting from two Late Pleistocene highstands near +5 and +6 metres, Durban, South Africa

In exposures of Pleistocene rocks on the east coast of South Africa, eight sedimentary facies were distinguished on the basis of petrology, grain size, internal structures and field relationships. These are interpreted as deposits of surf zone, breaker zone, swash zone, backbeach, boulder beach and dune environments. Three phases of deposition and diagenesis are recognized. As a result of the stabilising effect of pre-existing coastal facies, the deposits from successive sea level stands are stacked vertically in a narrow coast-normal strip. Early cementation prevented erosion of the deposits during subsequent transgressions. Deposition of subsequent facies took place on an existing coastal dune (Facies 1). A terrace was cut into this dune at a sea level 4.5 to 5 m above present. At this sea level, clastic shoreline sediments were deposited which make up the main sedimentary sequence exposed (Facies 2–7). The steep swash zone, coarse grain size, and comparison with modern conditions in the study area indicate clastic deposition on a high-energy, wave-dominated, microtidal coastline. Vertical stacking of progressively shallower water facies indicates progradation associated with slightly regressive conditions, prior to stranding of the succession above sea level. During a subsequent transgression to 5.5 or 6 m above present sea level, a second terrace was cut across the existing facies, which by then were partly lithified. A boulder beach (Facies 8) deposited on this terrace is indicative of high wave energy and a rocky coastline, formed by existing cemented coastal facies. Comparison with dated deposits from other parts of the South African coast suggest a Late Pleistocene age for Facies 2–8. Deposition was terminated by subsequent regression and continuing low sea levels during the remainder of the Pleistocene. Cementation of the facies took place almost entirely by carbonate precipitation. The presence of isopachous fibrous cements suggests early cementation of Facies 1, 2, 3 and 4 under marine conditions, initially as aragonite which has since inverted to calcite. Facies 5, 6 and 7 are cemented only by equant calcite spar, evidence of cementation in the meteoric phreatic and vadose zones. Lowering of the water table during regression caused the remaining pore space in Facies 1, 2, 3 and 4 to be filled with equant calcite spar. Decementation in a 130 cm wide zone is attributed to water table shifts associated with the later transgression which deposited Facies 8. The vertical stacking of the two depositional sequences may be attributed to rapid cementation of Facies 2, 3, 4, 5, 6 and 7 under humid, subtropical conditions. This lithified sequence then acted as a focus for deposition of coarse-grained shoreline facies (Facies 8) during the subsequent transgression.

Lichenometric Chronology and Archaeological Features on Raised Beaches: Preliminary Results from the Swedish North Bothnian Coastal Region

Growth rates for Rhizocarpon geographicum (L.) D.C. and Rhizocarpon alpicola (Hepp.) Rabh. have been studied at different locales on the Swedish North Bothnian Coast. Shore displacement rates have been used to date maximum thallus diameters of lichens growing on cobble and boulder beaches (wave-washed moraine) at increasing elevations above mean sea level. Linear growth rates have been observed for the period ca. 200 to 1400 BP. These results, in combination with general shore chronology and radiocarbon dating, will be used for determining the ages of coastal archaeological features. Lichenometry may well prove to be an invaluable archaeological and historical tool within the Bothnian and Baltic coastal regions.

Process Inference from Coastal-Protection Structures to Boulder Beaches

Because boulder beaches and rubble coastal-protection structures have environmental and compositional similarities, beach-boulder movement is examined in the light of engineering studies of protection-structure stability. On a studied boulder beach, sediment transport occurred during 11 storms over a period of 2 years. Wave conditions from these 11 storms are used in two no-damage design formulae in an attempt to mathematically predict boulder movement. The design formulae over-predict the movement threshold of smaller sized beach sediment and under-predict the movement threshold of the larger sediment, however the Hedar formula (developed for low-angle protection structures) yielded the more realistic prediction. Introduction Five boulder beaches located along the central New South Wales, Australia, coast were selected in order to study their sedimentary properties, form, and sediment transport. These beaches were found to differ fundamentally from cobble beaches (Oak, 1984). Each studied beach is aligned obliquely to the approaching waves and is composed of local sediment, the mean particle size being -84) or less (>256 mm). One boulder beach, Kiama, was chosen for the monitoring of boulder movement because of all the studied beaches it is the least accessible and it is not adjacent to a sand beach suitable for recreation. For these reasons there was little chance of human interference with the marked boulders. Kiama Boulder Beach Kiama boulder beach is located approximately 100 km south of Sydney and has a north-northeasterly exposure to the open ocean. This beach behaves as a sediment trap for material liberated from disintegrating cliffs extending approximately 1 km south. These cliffs are composed of Westley Park Sandstone (Branagan and Packham, 1970), the lowest member of the Geringong Volcanics. There are no massive joint patterns or distinct cleavage planes that might influence the shape and size of particles supplied to Kiama beach. A shore platform provides a base and protection from waves for one-third of this boulder beach, while the remainder is underlain by pebbles, cobbles, and boulders; no sand is present. The length of the beach is 150 m and the width averages 23 m, with the minimum being 17 m. Mean foreshore slope ranges between 6° and 12°, a cliff backs only the headland zone, and a berm extends along the whole beach. Mean sediment size is -8.646. Monitoring Boulder Movement On Kiama beach 300 boulders at the intersection points of a grid surveyed from a fixed bedrock position were marked with marine paint and their a, b, and c axes measured so that any sediment movement could be documented. Once a month and after every major storm during a two year period, the beach was examined for evidence of boulder movement. Because the position of each marked boulder was known, the number of those transported could be readily ascertained. When a moved boulder was found, the distance and direction of the movement were measured. When a boulder was removed from its grid-point position, the boulder in its place at the grid point was marked and measured, so at all times a grid of 300 boulders of known size and position was maintained. Coastal-Protection Structures and Boulder Beaches Although little is known about the processes that form and maintain boulder beaches, there has Geografiska Annaler · 68 A (1986) · 1-2 25 This content downloaded from 157.55.39.213 on Sat, 02 Jul 2016 04:19:04 UTC All use subject to http://about.jstor.org/terms

Orientation of cobble and boulder beach clasts

This study of cobble- and boulder-sized clast orientations in pocket beaches indicates that the L-I planes dip seaward at angles steeper than the foreshore slope and that the modal dip direction is generally not perpendicular to the shoreline trend. L-axes are oriented parallel, perpendicular, and at about 45° to the beach trend. Shoreline trends based on orientation data may be estimated incorrectly by as much as 30° because of wave refraction.

Process Inference from Coastal-Protection Structures to Boulder Beaches

Process Inference from Coastal-Protection Structures to Boulder Beaches

THE DENSTONE EXPEDITION TO INACCESSIBLE ISLAND

Inaccessible Island, the second largest in the Tristan da Cunha group, is a volcanic remnant which, owing to its steep cliffs on all sides, remained unmapped and largely unexplored until 1982, when the Denstone Expedition to Inaccessible Island, a party of 16 in all, carried out the first shore-based survey and scientific exploration there. The main party was put ashore from a South African ship and established a base on the only part of the Island from where there is access to the interior. This paper gives a brief description of Inaccessible Island, a summary of the work undertaken in the major disciplines of biology and geology, and includes the resulting map. INACCESSIBLE ISLAND is situated 40 km south west of Tristan da Cunha in the South Atlantic Ocean and is British territory, under the Protectorate of St Helena. It is roughly rhomboidal in shape, approximately 4x5 km in area, of volcanic origin and characterized by steep cliffs on all sides, with narrow beaches. Prior to the Denstone Expedition, there had been only six previous scientific visits, all of short duration and limited, in all but two cases, by failure to gain access to the interior of the Island. Thus, no previous shore-based map of Inaccessible Island existed and both biological and geological collections were limited. No detailed study had been attempted of any endemic species, or of the Island's geomorphology from ashore. The object of the Denstone Expedition was to make good these deficiencies. This was successfully achieved between October 1982 and February 1983 by a team of past and present pupils of Denstone College, Staffordshire,with three Tristan Island guides. Figure 1 is the resulting initial map. Topography The Island is surrounded by near-vertical sea cliffs of between 155 m at East Point and 490 m in the south west. The western part ofthe Island contains the highest ground from where a number of ridges run south-eastwards, forming the major catchment area of three drainage basins emptying immediately south of Joe's Hill. The extreme north-west part of the Island is drained to the north by two streams with outlets over the cliffs at North Point. This area is separated from the north-central and north-eastern parts of the Island by the prominent Long Ridge running north-south. To the east of the ridge lies the third drainage basin containing a stream which flows over the cliffs at the western end of Waterfall Beach. The eastern side of the Island is dominated by Round Hill, a breached parasitic cone. Inland of East Point is a low, flat plateau with no drainage system. The Island is subject to severe weathering and erosion as evidenced by numerous and often large landslides along the cliffs. Blenden Hall is part of a large low-lying area at sea level which would appear to constitute landslide material, possibly instigated during the formation of a large parasitic cone just to the north of the area. On its surface is Skua Bog. Pebble and boulder beaches occur intermittently around the Island, totalling approximately two-thirds of the coastal perimeter, and a well developed storm beach occurs at West Point.

The Denstone Expedition to Inaccessible Island

Inaccessible Island, the second largest in the Tristan da Cunha group, is a volcanic remnant which, owing to its steep cliffs on all sides, remained unmapped and largely unexplored until 1982, when the Denstone Expedition to Inaccessible Island, a party of 16 in all, carried out the first shore-based survey and scientific exploration there. The main party was put ashore from a South African ship and established a base on the only part of the Island from where there is access to the interior. This paper gives a brief description of Inaccessible Island, a summary of the work undertaken in the major disciplines of biology and geology, and includes the resulting map. INACCESSIBLE ISLAND is situated 40 km south west of Tristan da Cunha in the South Atlantic Ocean and is British territory, under the Protectorate of St Helena. It is roughly rhomboidal in shape, approximately 4x5 km in area, of volcanic origin and characterized by steep cliffs on all sides, with narrow beaches. Prior to the Denstone Expedition, there had been only six previous scientific visits, all of short duration and limited, in all but two cases, by failure to gain access to the interior of the Island. Thus, no previous shore-based map of Inaccessible Island existed and both biological and geological collections were limited. No detailed study had been attempted of any endemic species, or of the Island's geomorphology from ashore. The object of the Denstone Expedition was to make good these deficiencies. This was successfully achieved between October 1982 and February 1983 by a team of past and present pupils of Denstone College, Staffordshire,with three Tristan Island guides. Figure 1 is the resulting initial map. Topography The Island is surrounded by near-vertical sea cliffs of between 155 m at East Point and 490 m in the south west. The western part ofthe Island contains the highest ground from where a number of ridges run south-eastwards, forming the major catchment area of three drainage basins emptying immediately south of Joe's Hill. The extreme north-west part of the Island is drained to the north by two streams with outlets over the cliffs at North Point. This area is separated from the north-central and north-eastern parts of the Island by the prominent Long Ridge running north-south. To the east of the ridge lies the third drainage basin containing a stream which flows over the cliffs at the western end of Waterfall Beach. The eastern side of the Island is dominated by Round Hill, a breached parasitic cone. Inland of East Point is a low, flat plateau with no drainage system. The Island is subject to severe weathering and erosion as evidenced by numerous and often large landslides along the cliffs. Blenden Hall is part of a large low-lying area at sea level which would appear to constitute landslide material, possibly instigated during the formation of a large parasitic cone just to the north of the area. On its surface is Skua Bog. Pebble and boulder beaches occur intermittently around the Island, totalling approximately two-thirds of the coastal perimeter, and a well developed storm beach occurs at West Point.

Boulder beds in the glaciogenic Permo‐Carboniferous Dwyka Formation in South Africa

ABSTRACTSingle‐layer and massive boulder beds, which include boulder pavements, are sporadically distributed in the glaciogenic Permo‐Carboniferous Dwyka Formation. These matrix‐supported beds consist of moderately to poorly sorted, rounded boulders, cobbles and pebbles with a clast composition similar to those in the underlying or overlying diamictite. Alternatively, the clasts are composed of monolithic basement rock‐types. The clasts show a long‐axis orientation which, in the case of the boulder pavements, is parallel to the striae on the pavements.The various types of boulder beds have a similar mode of deposition and their subglacial origin is evidenced by the clast orientation, clasts with stoss and lee sides, stacking of clasts, and the development of a cleavage in the matrix due to horizontal stresses exerted by the boulders in the subglacial sediment. Subglacial streams, kame mounds, subaqeously winnowed till, or boulder beaches supplied the coarse debris which was entrained in the basal ice by plastic flow and regelation. Selective lodgement of the transported boulders occurred down‐glacier when the basal thermal conditions changed from cold‐freezing to warm‐melting. The formation of the different types of boulder beds is thought to depend primarily on the concentration of coarse debris in the basal ice.

The Boulder Beach: A Fundamentally Distinct Sedimentary Assemblage

Abstract Five boulder beaches located along the coast of New South Wales, Australia, were examined in order to determine if beaches composed of boulders differ in basic sedimentological structure and behavior from beaches composed of cobbles or pebbles. Each beach is aligned obliquely to the approaching waves and is composed of locally derived sediment. Investigation of beach-particle size, morphology, and roundness, along with foreshore slope, reveals consistent up-beach particle fining, positive size skewness, absence of shape zoning, absence of sphericity grading, and low foreshore slope. These characteristics of the five studied boulder beaches contrast markedly with the known characteristics of beaches composed of finer sediment, which suggests that boulders appear to form fundamentally distinct coastal sedimentary assemblages.

Shape Evolution and Fabric in a Boulder Beach, Monument Cove, Maine

ABSTRACT Unequal spacing of nearly vertical joints and sheeting in hornblende granite at Monument Cove, Maine, forms large tabular blocks which accumulate as talus on the backbeach. The blocks are subsequently rounded by wave action to form a pocket boulder and cobble beach. Measurements of the talus blocks and boulders indicate that the initial structurally controlled, bladed and elongate habits are manifested in the boulders; however, as abrasion progresses, more compact (spherical) and more platy (discoidal) boulders evolve. The data suggest that the greatest change is toward compactness and that the ultimate clast shape at Monument Cove would be spherical. The orientations of the L-I planes and the L-axes of the rounded clases were also measured. The L-I planes are well oriented, dipping m inly offshore. The L-axes orientations form three main clusters, one subparallel to the shoreline, one down the dip of the beach, and one oblique to the shoreline. The latter two clusters lie within the modal dip of the L-I planes.

Coastlines of the Eastern Arctic

A computer approach was developed and used to analyse the characteristics of coastlines present in the eastern Arctic. Results of this analysis indicate that: 1) almost 75% of all coastlines include a beach; 2) backshores are mostly steep and made up of bedrock; 3) beaches are made up mostly of coarse sediments; 4) the most abundant types of coastal zones consist of steep rocky backshores without beach, and steep rocky backshores with colluvium and continuous boulder beaches; 5) the average slope of backshores and the size of the dominant beach sediment decrease towards the north; 6) fetch has little influence on coastal characteristics; and 7) coastal characteristics are determined primarily by the physiography of the adjacent land and by the nature of backshores.Key words: eastern Arctic, coastlines, geomorphology

Beach and nearshore morphology and sedimentation in Fiordland, New Zealand: a comparison between fiords and glacial lakes

Abstract The morphology of 56 beaches from the Fiordland coast is described. Four groups of beaches are recognised: open coast sand beaches, fiord margin sand/gravel beaches, fiord margin boulder beaches, and bay head deltas. Fiord margin beaches and deltas have a shelf profile; on the fiord margin beaches this shelf is narrow and steep and is formed by local wind waves, and on the bay head deltas the shelf is wide and flat and the morphology is controlled by the rate of sediment supply. The ocean fiord beaches have a deep-water shelf. On sheltered beaches sediments fine across the shelf, with a transition from sand to mud at the shelf break. The sediment distribution and morphology of the inner fiord beaches is similar to that on nearby glacial lakes and is a model of progradational shelf formation on the continental margins.

Food and foraging behaviour of the Snares fernbird

Abstract The Snares fernbird (Bowdleria punctata caudata Buller, 1894) is an opportunistic insectivore, its prey ranging greatly in size and type. Birds forage over a wide variety of sites, including forest, tussock, boulder beaches, cliffs, penguin colonies, and floating kelp. Foraging methods vary with the prey sought, and at times birds adopt specific “search images” when hunting certain insects. Details of foods brought to nestlings are given. Four postures used by fernbirds when foraging actively are described.

The morphology and development of the northeast Yorkshire shore platform

Four types of shore platform are recognised in northeast Yorkshire: 1. Class 1 — the platform is a sub-horizontal plane which has erosion rates of the order of 0.01–0.20 cm year −1 though these are exceeded near the cliff foot. Erosion rates increase with altitude but the platform develops by landward extension of the plane. 2. Class 2 — the platform has a ramp, a slope greater than 2.5°, at the cliff foot and a plane seaward of this. The ramp is covered by a beach of debris that can be moved by waves. Erosion rates are of the order of 0.10–3.00 cm year −1, the grain size and thickness of the beach and its altitude being important determinants of these. The plane encroaches on the base of the ramp which moves landward as the cliff foot is eroded. Development of the ramp increases the height of the cliff foot which rises at an angle of up to 2° as it retreats. The high erosion rates lead to this being the widest type of platform. 3. Class 3 — the platform is a ramp throughout its width. It may be overlain by large boulder beaches which protect it from wave action and allow almost negligible erosion rates. This is the narrowest type of platform. Changes in the size or nature of the debris on these three types of platform may lead to changes in their morphological class. 4. Class 4 — the platform is affected by geological factors and so the ramp and plane cannot be easily recognised.

Distribution and changes in shell form of Thais SPP. (Gastropoda) near Bamfield, B.C.

The distribution and shell form of the three species of Thais present have been investigated along the southeast shore of Barkley Sound (Vancouver Island) along a gradient of decreasing exposure to waves, from Pachena Point (open Pacific) to Grappler Inlet (extreme shelter). The 20 stations comprised rocky promontories and adjacent boulder beaches, the latter giving some local shelter. Thais emarginata (Deshayes), which has the lowest shell weight per unit of shell capacity, was found to range (mainly in the upper littoral) from full exposure to waves to considerable shelter. It corresponds most nearly in range of wave-exposure to the North Atlantic Nucella (= Thais) lapillus (L.) and the New Zealand Lepsiella Iredale, but is probably more tolerant of wave-exposure and less of shelter than these. Its shell was found to be lighter per unit of capacity. T. canaliculata (Duclos) was normally confined to low levels on the shore and to wave-exposed situations; it is somewhat better armoured. T. lamellosa (Gmelin) was found to occupy low levels from moderate to extreme shelter. It is very heavily armoured, no doubt in relation to the greater risk of predation inherent in its habitat. In laboratory tests it was found to be much more resistant than T. emarginata to crabs. Measurements of 477 Thais emarginata, divided between 9 stations, showed that the shell form changed from short and broad on the open coast to tall and narrow on sheltered promontories and on boulder beaches. With increasing shelter the whorl ratio ( R) and apical angle decreased and spiral angle (as defined by D'Arcy Thompson) increased. The ratio of increase of the tubular cavity of the shell per turn of the spiral (proportional to R 2) may reflect the growth rate of the animal.

Walrus ethology. II. Herd structure and activity budgets of summering males

Male walruses, Odobenus rosmarus (L.), summering (outside the breeding season) at an Alaskan hauling ground, use all available kinds of beach habitat: cobble and boulder beaches, rock benches, and large boulders. Formation and dissolution of large herds on land can occur rapidly. Walruses are very gregarious and positively thigmotactic. In cool weather about 98% of walruses on land lie in passive body contact with other walruses. Dominant walruses (large, with long unbroken tusks) are most successful in entering herds on land, and in keeping positions in them. This results in overrepresentation of subordinates in the periphery of herds. Agonistic interactions occupy 5–10% of the time of walruses in large herds on land, and cause local disturbances that lead to agonistic involvement of up to 20 animals. Fewer kinds of social activity occur on land than in water. On land and in shallow water, small walruses are generally more active than large ones. Extensive body contact while they are hauled out is chiefly an adaptation for heat conservation and may also facilitate molting. The extreme gregariousness of walruses may have evolved because individuals joining large herds have a greater probability of achieving extensive body contact than have those joining small herds.

Ecology of the black shore skink,Leiolopisma suteri(Lacertilia: Scincidae), in boulder beach habitats

The ecology of the nocturnal black shore skink, Leiolopisma suteri, was studied on a boulder beach at Cable Bay, Motutapu Island, for 19 months. Distributions over a stable beach (Motutapu Island) and an exposed beach (Cuvier Island) were compared, and the effects of storms on the Cable Bay population were noted. Density, aggression, thermal preference, feeding, and fat reserve fluctuations were also studied. The L. suteri population at Cable Bay has, in favourable areas, one of the highest densities (13/m2) recorded for a lizard species. Spatial distribution of this population varies between the different age classes: adults congregate in the most stable areas, whereas hatchlings are commonest in the least stable areas. Storms cause changes in the beach structure and in the spatial limits of the population.

Reproduction and growth of the black shore skink,Leiolopisma suteri(Lacertilia: Scincidae), in north‐eastern New Zealand

Reproduction and growth of a boulder beach population of the nocturnal skink Leiolopisma suteri on Motutapu Island were studied for 19 months. Epididymes contain sperm from April to November, and copulation probably occurs in October or November (spring). Ovulation occurs in late October or early November, and three or four (mean, 3.7) eggs are laid in late December. Incubation takes 3 months. Total development time from ovulation to hatching is 5 months, one of the longest development periods recorded for Scincidae. Growth to sexual maturity is slow, most females depositing their first clutch 33 months after hatching; males mature at 29 months.

Distribution and abundance of New Zealand fur seals on the snares islands, New Zealand

Abstract The distribution and abundance of the New Zealand fur seal, Arctocephalus forsteri (Lesson), on the Snares Islands, New Zealand, were investigated during November and December 1970. Excluding pups, 1,021 seals were counted on the main island in late November, giving an amended total of 1,156 when correction factors for time of day were applied. The greatest number of seals was ashore between 1200 h and 1500 h daily. Fur seals were widely but discontinuously distributed along the coast of the main island. Rookeries were present only on the boulder beaches of the west and south‐west coasts and the South‐West Promontory. Non‐breeding seals aggregated on rocky headlands, points and spurs mainly on the east coast. Breeding bulls defended territories containing, on average, three females. The first pup was seen on 30 November 1970, and pupping continued throughout December. On 30 December, when pupping appeared to have finished, 234 pups were counted on the island.