Twenty years of data on climate–permafrost–active layer variations at the lower limit of alpine permafrost, marmot basin, jasper national park, canada

Abstract

In March 1979, a hole was drilled to a depth of 16.8 m through 1 m of till and loess into the clast‐supported boulders of a fossil Pre‐Late Wisconsin rock glacier just above tree line (2195 m elevation) at the Marmot Basin Ski Area, Jasper National Park (latitude 52∘47′36.5′′N, 118∘06′45.9′′W). Vegetation cover consists of a moist alpine meadow, on a bench which slopes gently to the south on the otherwise steep mountainside. The mean daily temperature for the site has been recorded continuously, and monthly readings have been made of ground temperatures using a thermistor string. Depth of the snow pack has been recorded on each visit, while November to April snowfall data are measured daily at 1985 m elevation. The mean annual air temperature (−2.38∘C) has decreased by about 0.7∘C since 1979, while the average winter snowfall (c. 310 cm) has increased by about 70 cm.A water table occurs at about 12 m depth with a water temperature of about 1.1∘C. Permafrost up to 6.8 m thick was present for almost all the period of study, with the active layer ranging from 2.2 to 4.3 m in depth. Temperatures in the permafrost varied seasonally, ranging down to −2.5∘C. The ground temperatures are constantly changing and are more closely related to thickness and duration of snow cover rather than air temperatures. The geothermal gradient averages 0.45∘ per metre in the upper 10 m, and there is a ‘thermal offset’ of about 4.1∘. Heat conduction is dominant at the surface, being replaced by closed‐cell convection between the blocks. In the early summer, warmer snow melt from the adjacent mountainside increases the thickness of the active layer and sometimes pierces the permafrost so that the warm water descends to the main water table below.