Report upon a Survey of Karst Landforms around Norman Wells, Northwest Territories for the NWT Protected Areas Strategy Department of Environment and Natural Resources Government of the Northwest Territories

Karst geomorphology is the study of natural landforms and caves created by the dissolution of comparatively soluble rocks. Karst hydrogeology studies the flow of ground waters through the karst rocks, via the systems of caves and micro-caves (mouse-sized) created by solution along paths through fractures in the rocks. At the surface the principal types of karst landforms represented in the region around Norman Wells are: (i) at small scale, karren – solutional pits, runnels and micro-shafts developed on bare rock surfaces or under shallow soil cover. Individuals are rarely greater than a metre or two in size but they usually occur in clusters or wider spreads that may cover many ha or even square km. (ii) at intermediate scale, sinkholes – ranging from a few metres to hundreds of metres in diameter and up to 100 metres or more in depth. There are two principal origins – first by surface runoff water dissolving a funnel-shaped depression downwards that delivers flow to the underground cave systems – second, by collapse of a cave upwards to the surface. Both types are well represented in the Norman Wells region. (iii) at large scale, dry valleys and gorges where dissolution has captured original surface streams and diverted them underground with the result that surface channels are abandoned either permanently or at all times except high flood periods when there may be overflow. Turloughs and poljes are large, topographically closed depressions drained underground by sinkholes within them, that are subject to periodic flooding when the underlying caves become swamped with water. Both may accumulate alluvium that forms central flat floors around the sink points. Turloughs are rarely greater than 2-3 km in length. Poljes may be larger, in part because the flood waters are able to dissolve benches into the hills of soluble rock enclosing the depression. Most types of rock are essentially insoluble in the very mildly acidic waters that occur naturally on the surface of the Earth. As a consequence, karst landforms and