CGRG Bibliography of Canadian Geomorphology
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Author : Dredge, L.A.; Kerr, D.E.; and Wolfe, S.A.
Date : 1998
Title : Ground ice and frost action in surficial materials, Slave Geological Province, northwestern Canadian Shield.
Publication : Permafrost, Seventh International Conference, June 23-27, Yellowknife, Canada. Edited by: A.G. Lewkowicz and M. Allard. Université Laval, Centre d'études nordiques, Collection Nordicana.
Issue : 57:
Page(s) :
Abstract
Ground ice is prevalent in surface materials in areas of current mining activity and proposed infrastructure development in the western Canadian Arctic mainland. Surficial geology mapping and detailed site investigations have shown that some relationships can be drawn between regionally mappable material types and certain ground ice conditions. The amount and type of ground ice, and resultant behavioural characteristics of materials, depend on rock types underlying and outcropping in the area, and the nature of unconsolidated surface deposits. The cryo-geotechnical properties of glacial and postglacial deposits depend on the provenance of materials, depositional conditions, and postglacial climatic history. While ice contents in rock are generally low, significant frost heaving of bedrock is pervasive in extensive areas of Archean schist and along linear belts of Proterozoic argillite, where rocks are weaker and fractures are more abundant than in other rock types. Scattered rock burst features, resulting from excessive water pressure during freeze-back, are present where igneous rocks lie at the surface. Glacial till is the most prevalent surface material, and most till veneers and blankets have low ground ice contents. Large solifluction lobes have developed on till blankets, but thermokarst features are absent. Till derived from granitic and gneissic sources is less frost-susceptible than siltier till derived from pelitic metasediments and dolomite. Well-defined belts of hummocky till have distinctive surface relief characterized by small kettle lakes or depressions, rim-ridges, and shallow thaw flowslides, which can be attributed to massive ice, possibly remnant glacial ice. Although most eskers appear to be well-drained near the surface and have low ice contents, massive ice in excess of 5 m thick can occur in eskers, and is responsible for regional occurrences of thermokarst, slope movement and collapse features in some features. Broad-crested eskers in the south, near Jolly Lake, are silty and contain both ice crystals and segregated ice laminations; these materials make poor aggregate sources. Up to 10 m of massive ground ice, possibly of glacial origin, have been documented in one ice-contact outwash deposit; sediments of similar genesis in other places that exhibit kettle lakes and circular thaw lakes may have similar ground ice conditions. Outwash deltas and postglacial sandy raised marine deposits contain polygons that are in the order of 10 m diameter, with troughs about 0.5 m deep. Active ice wedges underlie the troughs, although ice contents are low in polygon centres. Larger polygons, up to 100 m diameter with troughs 2 m deep, appear to be relict features, although small active ice wedges are inset within them. Silty marine deposits inland from Coronation Gulf form surface deposits or underlie thin, sandy, marine sediments. They range from the coast up to an elevation of 170 m near Coppermine (Kugluktuk) in the west, to 210 m at Tree River in the east. These sediments are saline, and contain segregated ice in the upper few metres of permafrost. Retrogressive thaw slumps are common features along river banks and active layer detachment slides occur on moderate slopes where coarse littoral sand overlies frozen silty clay marine sediments having a wide range of ice contents. Slope stability problems are due to excessive ice. Particular ground ice conditions give rise to distinctive surface features such as ice-wedge polygons, solifluction lobes, retrogressive thaw slumps, thermokarst, and active layer detachments. Many features can be regionally mapped using air photographs, while others are too small, and require detailed ground observations. An understanding of glacial history, maps of surface materials, together with observations on small-scale surface features serve as a preliminary guide in assessing potential for ground ice and active periglacial processes prior to detailed geotechnical investigations wherever mining activities or infrastructure development are planned.
Bibliography of Canadian Geomorphology