No abstract

No abstract

No abstract

A study carried out on Carboniferous limestone in the north and west of Ireland supports the idea that rock substrate is removed by the direct mechanical action of lichens. An experiment in which the lichen Collema auriforma was subjected to a number of wetting-drying cycles, showed, using scanning electron microscopy, that contraction of the lichen thallus during the drying phase plucked rock fragments from the substrate surface. This process could contribute to the formation of karstic features including solution basins.

No abstract

Rock shore platforms, present on at least half of the 20 500 km-long coastline of the British Isles, are usually backed by cliffs of varying heights. They form in a range of material types from soft cohesive sediment to sedimentary and metamorphic rocks of varying strengths to very resistant igneous rocks. Lithology influences platform erosion rates: glacial till>London Clay>chalk>schist>limestone>basalt and granite. Chalk platform erosion rates adjacent to engineering structures are significantly higher than elsewhere on the platform. There are no published reports of erosion rates on British platforms developed in igneous rocks such as basalt and granite because they have proved too resistant to record values using a micro-erosion meter. The most intensively studied shore platforms in the British Isles are on Blue Lias limestone in south Wales and Cretaceous chalk in SE England and there is a need for more detailed studies on additional rock types, particularly for understanding key controls on platform morphology and rates of erosion. The issue of whether the shore platforms exposed at present day mean sea-level are inherited from earlier periods remains. The role of platform erosion in helping to drive cliff retreat is understudied and evidence that engineering structures may enhance platform erosion rates comes from only one rock type. Predicted climate change and sea-level rise scenarios combined with more intensive management of coastal systems mean that it is important to improve understanding of platform systems and their link to cliffs. There is much scope, using established and new methods of investigation, to address the issues raised by existing studies of shore platforms of the British Isles.

Microerosion meter (MEM)

A traversing microerosion meter (MEM) was used to measure the rates of surface weathering of limestones in southeastern Australia. There were two groups of MEM sites installed in 1978/9. The aim of the experimental design for the first type, the 13 sites at Cooleman Plain and Yarrangobilly Caves, was to obtain erosion rates for limestones of similar lithology exposed under comparable climate conditions. The sites were positioned to measure erosion over a range of microsolutional forms and with exposure to differing forms of erosion, i.e. subaerial, subsoil and instream. The second set, at Ginninderra close to Canberra, consists of nine limestone slabs of differing lithology, collected from different locations but exposed under identical climatic conditions. The number of individual measurement points at each MEM site varied from 24 to 68.There were major differences in erosion rates between subaerial bedrock and instream sites at Yarrangobilly and Cooleman Plain, but no evidence of differential erosion across the micro-forms. There were differences in the weathering rate for bedrock sites, due to climatic differences, and between the limestone lithologies exposed at Ginninderra. The average rate of erosion for the subaerial bedrock sites at Cooleman Plain and Yarrangobilly over the 13 years was 0.01 3 mm a-' and at Ginninderra 0.006 mm a-' . At some of the sites microflora (lichens and mosses) caused problems for field measurement.The weathering processes that contribute to the surface lowering are discussed in the accompanying paper by Moses et al.