Event Title

Mahony and Tunago, Adjoining but Contrasted Karst Plateaus in the NT, Canada

Streaming Media

Session Type

Technical Sessions: Conservation Science

Start Date

18-8-2020 12:15 PM

Description

West of Great Bear Lake (Lat. 65-66O N; 157 m asl) Canadian Shield rocks are overlain by bedded dolomites (Ordovician) forming a glaciated plateau dipping gently west. A spillway divides it into (i) 'Mahony Dome' (south side, ~1000 km2, ≤460 m asl) and (ii) 'Tunago Dome' (north, ~750 km2, ≤360 m asl). Both drain karstically, chiefly to springs in the spillway. MAT range is -7o to -10oC, precipitation 200-350 mm. Permafrost is widespread to continuous except beneath lakes. Mahony Dome is a plain, with droughty muskeg at the centre (the world's most extensive ‘alvar'?), draining to sinkholes around the perimeter. Larger, glacier-scoured, depressions are/were occupied by karst lakes displaying a progression from (i) perennial lakes, with seasonal overflow; (ii) perennial, no overflow; (iii) seasonally shrinking lakes; (iv) fully drained, with sinkholes: This is likely correlated with the groundwater hydraulic gradients. A small sector of Tunago Dome generally above ~325 m asl is similar, but terrain below it is dissected into tabular blocks (very large clints) with muskeg swamps between them. Deep hydraulic depressions scoured at upstream corners of clints or at narrowings in interclint corridors now function as the local sinkholes. This tabular terrain is the product of sub-glacial floods tearing up a pre-existing shallow karst pavement, a type of 'scablands' noted elsewhere in north-ern Canada, but not at this scale; the technical presence of permafrost does not inhibit modern karstic drainage here, in contrast to the situation in the centre of Mahony Dome.

Comments

This presentation was part of the Technical Sessions on Conservation Science. Presentation topics ranged from cave conservation techniques, environmental education, community engagement, resource protection assessment, and scientific and cultural research from across the globe. Formats vary from traditional PowerPoints to films to story maps and informal interviews.

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Aug 18th, 12:15 PM

Mahony and Tunago, Adjoining but Contrasted Karst Plateaus in the NT, Canada

West of Great Bear Lake (Lat. 65-66O N; 157 m asl) Canadian Shield rocks are overlain by bedded dolomites (Ordovician) forming a glaciated plateau dipping gently west. A spillway divides it into (i) 'Mahony Dome' (south side, ~1000 km2, ≤460 m asl) and (ii) 'Tunago Dome' (north, ~750 km2, ≤360 m asl). Both drain karstically, chiefly to springs in the spillway. MAT range is -7o to -10oC, precipitation 200-350 mm. Permafrost is widespread to continuous except beneath lakes. Mahony Dome is a plain, with droughty muskeg at the centre (the world's most extensive ‘alvar'?), draining to sinkholes around the perimeter. Larger, glacier-scoured, depressions are/were occupied by karst lakes displaying a progression from (i) perennial lakes, with seasonal overflow; (ii) perennial, no overflow; (iii) seasonally shrinking lakes; (iv) fully drained, with sinkholes: This is likely correlated with the groundwater hydraulic gradients. A small sector of Tunago Dome generally above ~325 m asl is similar, but terrain below it is dissected into tabular blocks (very large clints) with muskeg swamps between them. Deep hydraulic depressions scoured at upstream corners of clints or at narrowings in interclint corridors now function as the local sinkholes. This tabular terrain is the product of sub-glacial floods tearing up a pre-existing shallow karst pavement, a type of 'scablands' noted elsewhere in north-ern Canada, but not at this scale; the technical presence of permafrost does not inhibit modern karstic drainage here, in contrast to the situation in the centre of Mahony Dome.