Search

Evidence for former fast glacier flow (ice streaming) in the southwest Laurentide Ice Sheet is identified on the basis of regional glacial geomorphology and sedimentology, highlighting the depositional processes associated with the margin of a terrestrial terminating ice stream. Preliminary mapping from a digital elevation model of Alberta identifies corridors of smoothed topography and corridor-parallel streamlined landforms (megaflutes to mega-lineations) that display high levels of spatial coherency. Ridges that lie transverse to the dominant streamlining patterns are interpreted as: (a) series of minor recessional push moraines; (b) thrust block moraines or composite ridges/hill–hole pairs constructed during readvances/surges; and (c) overridden moraines (cupola hills), apparently of thrust origin. Together these landforms demarcate the beds and margins of former fast ice flow trunks or ice streams that terminated as lobate forms. Localised cross-cutting and/or misalignment of flow sets indicates temporal separation and the overprinting of ice streams/lobes. The fast-flow tracks are separated by areas of interlobate or inter-stream terrain in which moraines have been constructed at the margins of neighbouring (competing) ice streams/outlet glaciers; this inter-stream terrain was covered by more sluggish, non-streaming ice during full glacial conditions. Thin tills at the centres of the fast-flow corridors, in many places unconformably overlying stratified sediments, suggest that widespread till deformation may have been subordinate to basal sliding in driving fast ice flow but the general thickening of tills towards the lobate terminal margins of ice streams/outlet glaciers is consistent with subglacial deformation theory. In this area of relatively low relief we speculate that fast glacier flow or streaming was highly dynamic and transitory, sometimes with fast-flowing trunks topographically fixed in their onset zones and with the terminus migrating laterally. The occurrence of minor push moraines and flutings and associated landforms, because of their similarity to modern active temperate glacial landsystems, are interpreted as indicative of ice lobe marginal oscillations, possibly in response to seasonal climatic forcing, in locations where meltwater was more effectively drained from the glacier bed. Further north, the occurrence of surging glacier landsystems suggests that persistent fast glacier flow gave way to more transitory surging, possibly in response to the decreasing size of ice reservoir areas in dispersal centres and also locally facilitated by ice-bed decoupling and drawdown initiated by the development of ice-dammed lakes. Copyright © 2008 John Wiley & Sons, Ltd.

In spite of a widespread distribution, the way in which plateau icefields affect the glaciation and deglaciation of adjacent terrains is not particularly well-known. This paper aims to identify how the deglaciation of the fjord and plateau terrain of north Norway has influenced the glacial geomorphology and relative sea-level history of both local and adjacent areas and so serve as a model for interpreting similar areas along the continental margins of northwest Europe and elsewhere. The identification of moraines and their relationships with the Main shoreline of northern Norway allows the margins of the Oksfjordjokelen, Svartfjelljokelen and Langfjordjokelen plateau icefields to be identified in the adjacent terrains. In locations where ice margins are uncertain, it is also possible to reconstruct ice limits by means of glacier models appropriately constrained by known local conditions and dates. Earlier glacier margins, characterised in north Norway by ice shelves floating in the local inlets of major fjords, also can be related to known regional shorelines. The distribution of high shoreline fragments, augmented by radiocarbon dates, helps show the extent to which inter-island channels and outermost parts of fjords can become deglaciated relatively early in comparison with published maps of regional deglaciation. Plateau-icefield-centred glaciation became important sometime after 14 000 14C yr BP and was characterised by glacier readvances up to, and in some locations beyond, earlier moraines and raised marine features. Although overlooked until recently, the identification of the influence of plateau icefields on local glaciation, and their interaction with local and regional marine limits, is of great importance in accurate palaeoenvironmental reconstruction. Copyright © 2002 John Wiley & Sons, Ltd.

Landform assemblages and associated stratigraphy, sedimentology and structure are used in the reconstruction of palaeo-ice-sheet dynamics in Alberta, western Canada. Interpretations are based upon the modern analogues from four outlet glaciers at the margins of Vatnajokull and Myrdalsjokull, Iceland. In the area between Lloydminster and Lac la Biche, central Alberta, an extensive landform assemblage of megaflutings, crevasse-squeeze ridges and thrust-block-moraine arcs document the former surging of part of the margin of the Laurentide Ice Sheet during later stages of recession. This landform assemblage, including numerous exposures of glacitectonised bedrock and Quaternary sediments, is comparable to the landsystem of the surging glaciers Eyjabakkajokull and Bruarjokull in Iceland. Near High River southern Alberta, the former existence of an ice lobe characterised by active recession is recorded by closely spaced, low-amplitude recessional push moraines that drape tunnel valleys. These are comparable in form and pattern to annual push moraines and fluted till surfaces produced by Breidamerkurjokull and Sandfellsjokull, Iceland, and also include rimmed depressions produced by the escape of artesian water during ice-marginal pushing. This study provides interpretations of the regional glacial geomorphology of Alberta based upon comparisons of form and stratigraphy with modern glacial analogues, and provides an alternative to recent models which invoke large floods of subglacial meltwater to explain many of these same features. Implications for ice dynamics and regional till stratigraphies are discussed. Copyright © 1999 John Wiley & Sons, Ltd.