Introduction and Rationale

Plateaux are topographical features typical of many mountain regions and are perhaps best developed in passive margin settings, that have experienced significant periods of tectonic stability. Such conditions allow the preservation of palaeo-landsurfaces, which may have subsequently been uplifted and/or incised (Goddard, 1989). Good examples of such landscapes are found on the west and east sides of the North Atlantic, for example in Norway, the British Isles, USA, Greenland and in the island archipelago of the Canadian Arctic. Areas of Iceland also contain plateaux (Brown and Ward, 1996), where the plateaux (stapis or tuyas) are often the products of geologically recent subglacial volcanic eruptions (van Bemmelen and Rutten, 1955; Jones 1969). This chapter compiles a diagnostic assemblage of landforms and criteria that can be used to identify or infer the existence of former plateau icefields. Ice masses reconstructed from glacial geology are often used to reconstruct regional palaeo-climate, but evidence of glacierization on plateaux is often subtle and/or missing. It is therefore essential that plateau-style glaciation is recognized and the glaciers are reconstructed with realistic hypsometry (e.g. Furbish and Andrews, 1984; Benn and Lehmkuhl, 2000) as this can have a major impact on equilibrium line altitudes (ELAs) and on the climate thus inferred. A lack of appreciation of valley and associated plateau glaciers has often led to the misinterpretation of the geometry of ice coverage and thus the reconstruction of erroneous palaeo-ELAs.

Plateau and valley landscapes are synonymous with landscapes of selective linear erosion (Sugden, 1968, 1974; Sugden and John, 1976), and it is the juxtaposition of glacier erosion and glacier protection that proved one of the major problems in understanding the geomorphic evolution of these landscapes. The preserved palaeo-landsurfaces containing remnant landforms, sediments and weathering profiles which in some instances are found adjacent to the deeply incised, glacially eroded troughs led to the misinterpretation that these areas had acted as refugia during multiple Pleistocene glaciations. Contrary to this opinion, plateaux have since been viewed as the loci of glacier initiation and expansion during cooling events and as a haven for glaciers during warming in interglacials and interstadials, depending upon the latitude and altitude of the plateau and the global climate characteristics at the time. In most instances it is the valleys that contain the bulk of the geological information (e.g. deltas, shorelines, moraines.) used in reconstructing the geometry of former glacier cover. The thermal and dynamic properties of the plateau ice in such landscapes dictate the geomorphic signature that is produced. In some instances this signature may be very subtle or non-existent.

The plateau icefield landsystem model presented in this chapter is based upon contemporary examples from Ellesmere Island in arctic Canada, Troms and Finnmark regions in North Norway, and Iceland. These systems provide geomorphological evidence from both cold-based and warm-based plateau icefields and associated valley glaciers. Potential errors in ELA calculation associated with the misinterpretation of glaciation style will be highlighted using examples of plateau icefields dating to the Little Ice Age (LIA) and Younger Dryas, in North Norway.

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