Shore platforms on the South Coast of New South Wales

Bird, Eric; Dent, O. F.

doi:10.1080/00049186608702463

Cited by 53 publications

(34 citation statements)

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“…The results show that a high degree of jointing within the bedrock is associated with a lowering of the platform surface by over a metre, from MHWS to MLWS levels. Where joint surfaces are open waves can be very efficient in removing blocks (Kanyaya and Trenhaile, in press), with wave quarrying occurring along these planes (Bird and Dent, 1966), and on highly jointed platforms, such as in Wellington, NZ (Kennedy and Beban, 2005), block plucking appears to be a significant process in platform evolution. On Shag Point, however, joints are most commonly closed, filled with iron precipitation, and surfaces appear to erode through enhanced downwearing along these planes, caused by weathering and subsequent wave excavation.…”

Section: Discussionmentioning

confidence: 99%

Lithological control on the elevation of shore platforms in a microtidal setting

Kennedy

Dickson

2006

Earth Surf Processes Landf

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The shore platforms on Shag Point, southern New Zealand, are quasi‐horizontal surfaces and are developed between supratidal and low water spring levels. A range of morphologies occur, with more exposed platforms having a distinct low‐tide cliff, in contrast to low‐tide surfaces where the seaward edge is buried beneath rubble and macro‐algal growth. The platforms range in width from 20 to 80 m and are eroded into Late Cretaceous/Early Tertiary fine marine sandstones and mudstones. Shore platforms have formed in two principal lithological units: a homogeneous unit that is characterized by few discontinuities, and a fractured unit with joints spaced about 0·5 m apart. Rock hardness is low in both units (L‐type Schmidt hammer rebound values of 31 ± 4), and there is little systematic variation in values between the two units in which platforms have developed. Case‐hardened concretions within the sandstone are significantly harder than surrounding rock and cause local relief of metre scale as the spherical diagenetic features are eroded from the bedrock. They do not, however, appear to affect broad‐scale platform geometry. Joints within the bedrock are a primary control on platform elevation. Platforms formed in jointed rock occur at the lower portion of the intertidal zone, in contrast to platforms formed in unjointed bedrock, in which horizontal surfaces occur at or above mean high water spring tide level. Rock structure, therefore, appears to be the primary determinant factor of platform geometry at Shag Point. Copyright © 2006 John Wiley & Sons, Ltd.

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Section: Discussionmentioning

confidence: 99%

Lithological control on the elevation of shore platforms in a microtidal setting

Kennedy

Dickson

2006

Earth Surf Processes Landf

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“…Such terms include: shore platform (Dana 1849;Bartrum 1935Bartrum , 1938Jutson 1939;Wentworth 1938Wentworth , 1939Wentworth , 1940Hills 1949;Edwards 1951;Cotton 1963;Mil 1962;Bird and Dent 1966;McLean and Davidson 1968;Healy 1968a, Hills 1971Trenhaile 1971Trenhaile , 1972Trenhaile , 1974aTrenhaile , 1974bTrenhaile , 1978Trenhaile , 1980Trenhaile , 1983aTrenhaile , 1983bAbrahams and Oak 1975;Takahashi 1975Takahashi , 1977Robinson 1977aSunamura 1978aSunamura , 1983Sunamura , 1990Sunamura , 1991Sunamura , 1992Layzell1980, 1981;Hansom 1983;Trenhaile and Bryne 1986;Tsujimoto 1987;Lawrie 1993;Griggs and Trenhaile 1994), rock bench (Bell and Clarke 1909), high water rock platform and Old Hat Type platform (Bartrum 1916), abrasion platform (Johnson 1919;Cinque et al 1995), shore bench …”

Section: Thesis Aimsmentioning

confidence: 99%

Development of shore platforms on Kaikoura Peninsula, South Island, New Zealand

2000

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Shore platforms on the Kaikoura Peninsula have been examined to determine the roles of marine and subaerial weathering processes in platform evolution. Erosion was measured to assess rates of development and processes of erosion. Lowering rates on platforms are presented from two years of monitoring using a traversing micro-erosion meter. Cliff retreats were calculated using aerial photographic interpretation. Marine processes were investigated by using deep water wave data, by measuring waves on shore platforms and by analysing measured tidal data. Weathering processes were investigated using tidal data, climate data, the Schmidt Hammer test, and a laboratory experiment on wetting and drying.Lowering rates over two years ranged from 0.07 to 19.80mm, and annual rates ranged from 0.154 to 9.194mm/yr. Rates of erosion varied with lithology and the type of platform.Erosion on Type A mudstone platforms was 1.98mm/yr; on Type B mudstone platforms erosion was 0.733mm/yr; and on limestone platforms it was 0.88mm/yr. The grand mean lowering rate for all shore platforms was 1. 13mm/yr . These rates fall in the middle of the range of published rates from previous studies at Kaikoura and at locations around the world. For the fITst time, erosion data from a traversing micro-erosion meter were presented as volumes of material eroded.The total volume of rock eroded from study sites having, each with an area of 45.4cm 2 , ranged from 1.20 to 92.50cm 3 • A significant finding was that rock surfaces swell up as indicated by a rise in surface level rather than lowering from erosion. The maximum measured swelling was 8.90mm. At some measurement sites as much as 90 per cent of measurements showed swelling over a period of 98 days. Values for erosion and swelling were higher during summer months.Both erosion and swelling were shown to be statistically related to season, suggesting that weathering is the group of processes causing both erosion and swelling. Summer provides better conditions for wetting and drying, which is thought to be the most important weathering process on shore platforms. Horizontal retreat rates were calculated over 52 years for cliffs, beaches and lagoon deposits backing shore platforms at Kaikoura, these ranged from 0.05 to 0.91mJyr.Investigation of marine processes showed that the deep water wave environment off the Kaikoura Peninsula is very energetic, but the amount of wave energy delivered to platforms is very low. A comparison of deep water wave energy flux with wave energy flux at the landward cliff of platforms, showed that there was a reduction by as much as five orders of magnitude. An analysis of the role of breaking waves revealed that these were ineffective as an erosional agent ii because the depth of water offshore causes breaking well before waves arrive on platform surfaces. Shear stresses and dynamic forces under waves were calculated from waves measured on shore platforms. TIus showed that these forces never exceeded the compressive strength the platform rocks at Kaikoura. It was co...

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“…Several processes have been identified in the literature as being responsible for shore platform generation, such as wave erosion, abrasion, chemical weathering and biological weathering (Bartrum, 1916;Johnson, 1919;Wentworth, 1938;Bird and Dent, 1966;Trenhaile, 1987Trenhaile, , 2000Stephenson and Kirk, 2000a,b;Trenhaile, 2001a,b;Stephenson and Kirk, 2001;Trenhaile, 2002a,b;Andrade et al, 2002;Twidale et al, 2005), but it is not clear which of these processes assume the greatest importance. This difficulty is probably due to the observation that shore platforms develop in very diverse geomorphologic, geologic, oceanographic, climatic and biologic contexts, and therefore the first-order factors responsible for shore platforms probably vary according to the macroenvironment in which they form.…”

Section: Intertidal Zone Shore Platform: Factors Controlling Platformmentioning

confidence: 99%

“…Studies of shore platforms have generally focused on the relevance of weathering and wave energy on sculpting these features (Bartrum, 1916;Johnson, 1919;Wentworth, 1938;Bird and Dent, 1966;Trenhaile, 1987;Sunamura, 1996;Trenhaile, 2000;Kirk, 2000a,b, 2001;Trenhaile, 2001aTrenhaile, , 2002aAndrade et al, 2002;Trenhaile, 2005;Kanyaya and Trenhaile, 2005;Twidale et al, 2005). This is a topic not completely clarified because the relevant morphogenetic processes vary depending on (for example) lithology, oceanic environment and shore morphology.…”

Section: Introductionmentioning

confidence: 99%

Morphological features and processes in the central Algarve rocky coast (South Portugal)

et al. 2006

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Morphological features along the Algarve rocky coast, South Portugal, are identified and described, with an emphasis on shore platforms and notches. The contributions of processes, such as wave attack, chemical weathering and bioerosion, to sculpting the shore platforms are discussed. The preferential localization of shore platforms on sites exposed to waves, and the lack of significant chemical weathering, point to wave erosion as the first-order factor in platform formation, whilst bioerosion/bioprotection, lithology and geological structure determine platform morphological variations. In addition, platforms above the present intertidal zone appear to have a polygenetic evolution, being inherited from former sea-level highstands and currently undergoing chemical weathering. The occurrence of notch features is independent of the degree of exposure to waves, but they mostly occur where the substratum is sand. Hydrostatic pressure appears to be an important factor in the formation of marine caves in the more sheltered sites..

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Shore platforms on the South Coast of New South Wales

Cited by 53 publications

References 2 publications

Lithological control on the elevation of shore platforms in a microtidal setting

Lithological control on the elevation of shore platforms in a microtidal setting

Development of shore platforms on Kaikoura Peninsula, South Island, New Zealand

Morphological features and processes in the central Algarve rocky coast (South Portugal)

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