Late Quaternary alluvial fans, debris cones and talus cones in the Grampian Highlands, Scotland

[摘要] Alluvial fans, debris cones and rockfall talus conesare widespread in upland Britain, but remarkably little isknown about their characteristics, development andsignificance. This research project has three mainobjectives:1. to establish the morphological and surface sedimentarycharacteristics of alluvial fans, debris cones and taluscones in the Grampian Highlands of Scotland;2. to identify the factors that have controlled theirformation and distribution; and3. to determine the timing, nature and rate of fan- andcone-forming processes.On the basis of previous literature, an Orioni modelthat describes a continuum of fan and cone morphological andsurface sedimentary properties was devised. Theapplicability of this model was tested using data for sixvariables (long profile gradient, slope form, downslopechanges in clast size, roundness and form, and a scale ratioof maximum clast size to total fan or cone length) obtainedfor fans and cones in the Grampian Highlands and the LyngenPeninsula in Northern Norway. The results of these testswere then used to produce a modified model appropriate tofans and cones in upland Britain.Using a combination of map, field and aerial photographdata, several environmental and morphometric controls on thedistribution and type of fan and cone development wereinvestigated. The dimensions of different types of fan andcone are shown to be determined by basin morphometry,lithology and glacial history. Discriminant analysisidentified basin gradient, basin width and basin height asthe principal catchment properties that influence thedominant type of fan- or cone-forming process.Stratigraphic and radiocarbon evidence suggests thatmany debris cones are essentially paraglacial landforms thatformed in the earlier part of the Flandrian. Many of thesecones have subsequently been modified in the late Flandrianby fluvial processes, in some cases in response toanthropogenic interference. However, evidence from one sitehas also revealed that substantial debris cone aggradationhas occurred since c 300 BP, implying high rates ofdenudation in the recent past at this site. The volumes ofother debris cones imply that as much as 1-3m of surfacelowering has occurred in gullies upslope since deglaciation.Much lower values of surface lowering are associated withalluvial fan development, suggesting that, locally at least,denudation by fluvial processes has been less significantthan denudation resulting from debris flow.

[发布机构] University:University of St Andrews;Department:Earth & Environmental Sciences and Geography & Sustainable Development (Schools of)