Mapping Known and Potential Karst Areas in the Northwest Territories, Canada Derek Ford, PGeo., PhD, FRSC. Emeritus Professor of Geography and Earth Sciences, McMaster University
[email protected] For: Environment and Natural Resources, Government of the Northwest Territories August 2009 (i) Executive Summary The Goal of this Report is to Produce Maps of the Known and Potential Karst Landform Sites in the Northwest Territories (NWT) Karst landforms are those created by the dissolution of comparatively soluble rocks and the routing of the water (from rain or snowmelt) underground via caves rather than at the surface in river channels. The principal karst rocks are salt (so soluble that it is scarcely seen at the surface in the NWT), gypsum and anhydrite (solubility around 2500 mg/l of water), and limestone and dolomite (solubility around 250 -350 mg/l). All of these rock types are common and widespread amongst the sedimentary strata in the NWT. Surface karst landforms include: a) karren, which are spreads of individually small solution pits, shafts, and runnels that, collectively, may cover many hectares (limestone pavements); b) sinkholes of solutional, collapse, or other origin that can be tens to hundreds of metres in diameter and proportionally as deep. Sinkholes are considered the diagnostic karst landform worldwide; c) larger topographically closed depressions that may flood or drain seasonally, poljes if flat-floored, otherwise turloughs; d) extensive dry valleys and gorges, dry because their formative waters have been captured underground. All water sinking underground via karst landforms of all sizes drain quickly in comparison with all other types of groundwater because they are able to flow through solutionally enlarged conduits, termed caves where they are of enterable size.