Detection and characterization of massive ground ice using Ground Penetrating Radar and seismic shothole records

Daniel E. Odell, I. Rod Smith, Brian J. Moorman

Dans les comptes rendus d’articles de la conférence: GEO2010 Calgary: 63rd Canadian Geotechnical Conference & 6th Canadian Permafrost Conference

Session: M2-E

ABSTRACT: This study utilized Ground Penetrating Radar and seismic shothole drillers' log records to examine the occurrence, distribution and origin of massive ground ice at two locations in Northwest Territories. Through traverses along recent seismic cut-lines, discreet bodies of massive ice were identified in differing sedimentary facies within the Colville Hills, and Little Chicago Œ lower Mackenzie corridor study areas. Ice bodies are between 40-110 m in lateral extent and up to 3.6 m thick. Application of these complimentary methodologies demonstrates their utility to regional ground ice mapping as may be required for future regional infrastructure development activities. RESUME Cette etude utilise la georadar et les donnees des trous de forage sismique pour examiner la presence, la repartition et l'origine de la glace massive du sol a deux endroits dans les Territoires du Nord-Ouest. Par les transects sismiques recent, deux incidences de la glace massive sont identifies dans les facies sedimentaire variables dans les regions d'etudes de les Colville Hills at a Little Chicago-la couloirs-bas Mackenzie. Les masses de glace sont entre 40-110 m d'etendue lateral et jus'qua 3.6 m d'epaisseur. L'application de cettes methods complimentaires demontrents sons efficacite dans la delimitation de la glace de sol dans les deux regions pour la development de l'infrastructure dans la future. 1 INTRODUCTION Massive ground ice, defined as subsurface ice containing gravimetric water content in excess of 250% (Permafrost Subcommittee, 1988), is a prominent feature of periglacial environments. Massive ice is typically considered to be either buried ice or intra-sedimentary ice. Buried ice may include glacier ice, snowbank ice, and river icings (Wolfe et al., 1997). Intra-sedimentary ice is formed in-situ within unconsolidated sediment or bedrock by a variety of processes including segregation and intrusion (Mackay, 1972). Notable forms of intra-sedimentary ice include pingo ice, ice lenses and ice-wedge ice. Occurrences of massive ice in the western Canadian Arctic are well-documented (Rampton and Mackay, 1971; Dallimore and Wolfe, 1988; Mackay and Dallimore, 1992). The understanding of ground ice distribution, extent and origin is important for two main reasons: 1) from a scientific perspective, knowledge regarding the origins of ground ice can offer insights into permafrost geology, landscape evolution and paleoclimate, 2) engineers and geotechnical planners need to know the distribution of ground ice in order to avoid subsidence due to its melting. The melting of excess ice has been identified as one the greatest geotechnical hazards in permafrost environments (Moorman et al., 2003). This latter point is of particular importance to this study as the two areas of interest are regions of active hydrocarbon exploration and potential development. The Colville Hills, in which the Lac des Bois study site is located, contains one of mainland Canada's largest known undeveloped conventional natural gas reserves outside of the Mackenzie Delta (Hannigan et al. 2009). The other study area, the Little Chicago site, lies in the Mackenzie corridor, and could be included in planning of the proposed Mackenzie Valley gas pipeline. Presently, the origin, extent and distribution of massive ground ice for much of the lower Mackenzie corridor and the Colville Hills is unknown. This study uses Ground Penetrating Radar (GPR) and drill records from seismic shotholes to improve the understanding of ground ice distribution and origin within these two regions. 2 STUDY SITES The two study sites for this project are the Little Chicago area in the lower Mackenzie Valley and the Lac des Bois area in the Colville Hills. Both sites are located in the western Canadian Arctic, just south of the southerly limit of continuous permafrost (Heginbottom et al. 1995). The two locations have been categorized as having moderate to low amounts of ground ice (Heginbottom et al. 1995). Norman Wells is the closest weather station to Little Chicago and Lac des Bois (270 and 180 km, respectively) and has a mean annual air temperature of -5.5 °C for the 30 year period ending in 2000 (Environment Canada, 2009). Average annual snowfall for this period was 153 cm. The Little Chicago site (Figure 1) is at 67°6'7'N; 130°15'17'W, and lies on the western bank of the Mackenzie River. Permafrost depths at nearby Fort Good Hope (110 km to the south) range between 33-48 m 128

RÉSUMÉ: on and characterization of massive ground ice using Ground Penetrating

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