Large rock slope failures in the Highlands of Scotland: Characterisation, causes and spatial distribution

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• 作者：David Jarman
• 关键词：Rock slope failures ; Slope deformations ; Scottish Highlands ; Landslide typologies ; RSF clusters ; Glacial breaches ; Preglacial watersheds
• 刊名：Engineering Geology
• 出版年：2006
• 出版时间：28 February 2006
• 年：2006
• 卷：83
• 期：1-3
• 页码：161-182
• 全文大小：1943 K

文摘

A comprehensive database of larger Rock Slope Failures (RSFs) has been compiled and characterised for a whole mountain range, possibly for the first time apart from Iceland. Most RSFs in the Scottish Highlands occurred soon after deglaciation. A threshold size of 0.25 km² focuses on RSFs which contribute significantly to gross erosion in the glacial–paraglacial cycle, and on the spatial concentration of this poorly recognised process. Database verification indicates that at least 90 % of the total extant population in the Highlands is covered. Standard mass movement typologies are broadly applicable, but require some refinement to characterise RSFs in a passive-margin glaciated mountain range comprised mainly of ancient metasediments. Most larger RSFs here are complex and difficult to categorise. A continuum from ‘cataclasmic’ failures (including rock avalanches) through arrested translational slides to almost in situ slope deformations is identified. The prevailing modes of large RSF are arrested (short-travel) translational sliding and gravitational sagging. Cataclasmic failure is rare, and sub-cataclasmic outcomes are more evident. A significant class of deformations exhibits compressional rather than extensional features, and may be responding to localised glacio-isostatic rebound stresses. The large RSF population is widely but very unevenly distributed across the main mountain areas: 65 % are in seven main clusters, with the rest non-randomly scattered. Previous glaciological, lithological, and seismotectonic explanations are insufficient to explain this spatial pattern, and overlook the basic engineering geology prerequisites for failure. Massifs of similar relief and lithology can display intense or sparse RSF incidence. Geomorphological appraisal suggests an association with recently active glacial breaches of main and secondary watersheds, with RSF being scarce or absent in valleys inherited from Tertiary uplift, and in mountain groups away from the main watersheds. Valleys which adapted early to ice discharge are seen as ‘stress-hardened’, with their slopes unlikely to reach critical thresholds for failure after subsequent reoccupations by ice. Concentrated erosion in the last glaciations is most likely to be found close to where breaches are actively forming or enlarging. Such erosion in the slope foot and valley floor may have daylighted failure planes or generated rebound stresses augmenting those from other endemic sources sufficiently to provoke widespread paraglacial RSF. Slope stress models for deglaciated valleys and comparative studies in other glaciated mountain ranges are required to test this concept, and may assist in geohazard assessments.