The Many Landscapes of South Nahanni National Park

South Nahanni National Park comprises the S. Nahanni and Ram River basins, c. 38,000 km2 in area and extending from the continental divide (Yukon boundary) eastwards to the margins of the Mackenzie River plains. Elevations range from 2500 masl (polar desert ecozone) to 200 masl (boreal forest). Continuous permafrost conditions begin c. 600 masl. The geomorphic landscapes are exceptionally rich and diverse, including (1) rugged Cordilleran glacial landforms (cirques, arêtes, horn peaks, etc.) in resistant batholithic rocks of Cretaceous age in the west; (2) broader glacial troughs and V-form fluvial tributaries in weak, structurally deformed Lower Paleozoic sedimentary strata in the centre; (3) deep antecedent river canyons, stripped anticlines and synclines in stronger Upper Paleozoic limestones and dolostones in the east, with (4) an inter-basin belt of karst landforms and caves, the most accentuated reported in any sub-arctic or arctic region; (5) thick deposits of sand, silt and clay in proglacial lakes created by Laurentide continental ice blocking the river outlets to the Mackenzie plains: the deposits are terraced or dissected and, in the last 25 years, beginning to display widespread slumping that is due to the thawing of ground ice.