✍ Scribed by Ian Douglas
No coin nor oath required. For personal study only.
Perhaps it is unreasonable to expect that studies of geomorphic processes in a period of rapid climatic change, where even the composition of the atmosphere is being modified by human activity, will throw much light upon the evolution of landforms. Nevertheless, much of the work on geomorphic processes was begun with the notion of improving understanding of landform evolution. The link between presentday processes and landform evolution is still unclear, even though process studies have made outstanding contributions to soil conservation, hydrology and resource management in all climatic zones.
Concentration on surface processes by most English-speaking geomorphologists has led to a relative neglect of neotectonics and a scant appraisal of the impact of plate tectonics on landforms. Rates of denudation are quoted without reference to rates of uplift, unlike Hjulstrom's pioneering work on the River Fyris, in which he found that the downwearing of the landscape was approximately an order of magnitude less than the rate of tectonic uplift.
The concept of dynamic geomorphology must incorporate tectonics-especially the role of plate tectonics and the abundant evidence of structural change in many areas long considered stable. Recently, writers such as Ollier and Summerfield have drawn our attention to this, particularly in Gondwanaland fragments such as Africa and Australia. However, a whole range of new hypotheses about the role of tectonics in the landforms of eastern North America and western Europe have been explored by the French school led by Alain Godard. To evaluate their inferences about past processes, careful consideration of the products of present-day denudation systems is required, for so much of the evidence relates to accumulations of sediments, deep weathering profiles, paleosols and morphology.
Stimulating evidence for past processes being obtained from boreholes into the down-faulted grabens of structures such as the Irish Sea and Sea of the Hebrides raises interesting questions. Rates of sedimentation do not necessarily reflect rates of erosion. Reservoir and lake sediments have discontinuities caused by scour by currents at the sediment-water interface. Submarine sediments, especially close to land, would be expected to have similar features. A proportion of the eroded sediment will remain on the land surface, while another part will be so finely comminuted or dissolved that it is carried a long distance from the shoreline. Interpretation of cores taken in small basins or close to the bounding faults of major rifts has to cope with this problem of the geomorphic situation of the sedimentation site. The Mochras borehole at the edge of Cardigan Bay on Morfa Harlech, for example, contains coarse sediments which may reflect a regional climatic influence on geomorphic processes or the gravitational movement of material down the adjacent fault scarp. Similar dilemmas may also apply to other sedimentary sequences in the grabens west of Britain. Possibly analysis of processes on contemporary fault scarps in active rift valleys and an associated detailed analysis of scarp foot sediments would help illuminate this problem.
Terrestrial accumulations also provoke new questions about the results of processes. The recognition of widespread silcrete formation in extratropical latitudes raises questions about the formation of such deposits. Several working hypotheses are available but relatively little is known about silica movement and deposition in modern environments. Research into processes needs to be focussed on some of these problems of landform evolution. Both laboratory and field experimentation and observation need to be married to the questions posed by the past. The problem of equifinality still points to the unfulfilled geomorphological promise of earth surface process investigations.
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