Permafrost Distribution Along the Rocky Mountains in Alberta STUARTA
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Climate and Permafrost 59 Permafrost distribution along the Rocky Mountains in Alberta STUARTA. HARRIS Department of Geography, University of Calgary, Calgary, Alberta, Canada T2N IN4 AND the late R.J.E. BROWN Division of Building Research, National Research Council, Ottawa, Ontario, Canada KIA OR6 Twenty-eight drill holes ranging from 15 to 150 m in depth have been instrumented with strings of thermistors and thermocouples at six study sites between Plateau Mountain and Jasper, south-west Alberta. Measurements are made every four weeks and indicate that the lower limit of continuous permafrost forms a dome-shape with its centre at Bow Summit, at 2575 m. The limit lies around 2130 m at Jasper and 2270 m at Plateau Mountain. This dome appears to be due to increased snowfall around the ice caps and glaciers, and there may be an inverse relationship between the elevation of the glaciation limit and that of the lower limit of continuous permafrost at a given latitude. In areas of low winter snowfall, the zone of discontinuous permafrost usually extends only 25 m in elevation below the lower limit of continuous permafrost but probably increases in altitudinal range as mean winter snowfall increases. Relict permafrost occurs at Plateau Mountain, which is the only site which shows no signs of overriding by Pleistocene glaciers. Even there, present-day heating and cooling waves extend downwards throughout the layers being studied. It is therefore suggested that the "zone of zero amplitude" be renamed the "zone of minimal amplitude" defined as being where the amplitude over a period of two years is less than 0.20°C. Des chapelets de thermistor et de thermocouples ont kt6 install& dans vingt-huit forages d'une pro- fondeur de 15 a 150 m en six emplacements entre le mont Plateau et Jasper dans le sud-ouest de 1'Al- berta. Des mesures effectukes toutes les quatre semaines indiquent que la limite infkrieure du pergdisol continu forme un dame dont le centre est a 2575 m au sommet Bow. Cette limite se trouve a 2130 m a Jasper eta 2270 m au mont Plateau. Le dame semble attribuable a des chutes de neige accrues autour des calottes glaciaires ainsi que des glaciers et il peut exister une relation inverse entre I'altitude de la limite de la zone recouverte par la glace et l'altitude de la limite infkrieure du pergCliso1 continu pour une latitude donnee. Dans les regions ou les precipitations neigeuses sont faibles en hiver, la zone de pergClisol discontinu ne s'enfonce gCnCralement que de 25 m sous la limite inferieure du pergClisol con- tinu, mais son Cpaisseur augmente probablement en fonction de I'tpaisseur moyenne des prkipitations neigeuses en hiver. On trouve du pergelis01 rksiduel au mont Plateau qui est le seul emplacement qui ne semble pas avoir it15 recouvert par les glaciers au PlCistoche. MSme a cet endroit, de nos jours, les ondes de rechauffement et de refroidissement s'etendent vers le bas a I'ensemble des couches 6tudiCes. I1 est par cons6quent suggere que la "zone d'amplitude zero" soit rebaptiske "zone d'amplitude mini- male" et difinie comme etant la zone oh I'amplitude est inferieure a 0,20°C pendant une pkriode de deux ans. Proc. 4th Can. Permafrost Conf. (1982) Introduction strings of thermistors and thermocouples in bore- In 1967, the late Roger J.E. Brown published a holes. It showed that permafrost was continuous in map of the distribution of permafrost in Canada, and the alpine zone above the tree-line at 2286 m, and that included the first attempt at mapping its distribution relict permafrost was also present. The effects of along the Rocky Mountains (Brown 1967). In 1973, snow removal by wind above the tree-line were the authors commenced a programme to provide documented. more-detailed information sponsored by the Division These studies have been continued to the present of Building Research of the National Research Coun- time and altogether twenty-eight boreholes ranging cil and the Department of Geography, University of from 15 to 150 m in depth have been instrumented Calgary. with strings of thermistors and thermocouples at six The first results from Plateau Mountain near study sites between Plateau Mountain and Jasper. Claresholm were summarized in Harris and Brown The sites are checked at monthly intervals! They have (1978), together with the other research work relating permitted the determination of the general elevation to permafrost in the region which had been published of the lower limit of continuous permafrost along a during the previous eleven years. This represented the diagonal line across the mountain ranges through first detailed study of alpine permafrost distribution some three degress of latitude. on a mountain based on regular observations of In addition, there have been a series of other publi- 60 4TH CAN. PERMAFROST CONF. (1982) cations containing specific, relevant information. Method used Crampton (1977 and 1978) discussed the distribution of permafrost in the foothills of north-east British The work was based on six locations chosen for Columbia, while Kershaw and Gill (1979) revisited their position approximating a line along the length and confirmed the presence of palsas at the palsa sites of the mountains in south-western and west-central described by Porsild (1945 and 1951) from about Alberta (Figure 1). 1300 m elevation in the MacMillan Pass (Northwest Boreholes 15 to 30 m deep were drilled at selected Territories). Seppda (1980) has described palsas from locations at each site during the period between 1974 a valley near Atlin, British Columbia, at about and 1980. A hole 150 m deep was drilled at Plateau 1000 m above mean sea level. In all these cases, ice Mountain to attempt to determine the minimum was actually described as being present. thickness of the zone of continuous permafrost Revel (1980) described sorted nets and polygons beneath the centre of the mountain. At first the holes that he "judged to be active" above 1300 m elevation were instrumented with thermocouple strings, but on Morfee Mountain in north-central British Colum- thermistors were used after 1976. The thermocouples bia. Unfortunately he presented no ground tempera- give results accurate to about k 0.2"C while thermis- ture data to support this conclusion. tors give results reproducible to k 0.01 "C. Although Jackson and MacDonald (1980) have remeasured not all the thermistors proved to be calibrated to this the position of readily identifiable blocks of rock on a degree of accuracy, the comparative results from one rock glacier near Tungsten, NWT, at about 1070 to moment of time to another for a given thermistor are 1980 m and have shown that considerable movement reliable. of both the individual blocks and of the front of the Continuous air temperature data as well as meas- ice-cored rock glacier has taken place between 1963 urements of snow depth were collected once a month and 1980. at the key sites so as to obtain base data for inter- Thus several new studies of localized individual preting the possible climatic causes of the permafrost periglacial features have been published since 1978 zones. Measurements of ground temperature have but the drilling and observation programme started at been made at all sites at approximately four-week Plateau Mountain in 1973 remains the only major intervals since the ground temperature cables were regional study of the distribution of alpine perma- placed in position. Notes were also kept of the envi- frost in the region. It is the purpose of this present ronmental conditions at each borehole location. paper to update the results of this programme to March 1981. Results General Permafrost Zonation The present evidence suggests three zones, viz. con- tinuous permafrost, discontinuous permafrost, and sporadic permafrost (Harris 1979). The difference be- tween the last two types is based on an estimate of the abundance of permafrost. Figure 2 shows the general distribution of perma- frost along the mountains and its relationship to the glaciers, to the glaciation limit, and to the tree-line. The lower boundary of continuous permafrost lies between 2180 and 2575 m above mean sea level, but it does not form a simple north-south gradient. Instead it slopes upward from east to west, while a dome appears to be centred on Bow Summit. Except for Plateau Mountain relict permafrost has not been identified, although it may also occur at the crest of Lookout Mountain. 4. Bow Summit Discontinuous permafrost forms a narrow zone up 5. Parker Ridge to 100 m in vertical extent, unless environmental fac- 6. Marmot Basin 490~ tors intervene. Within this zone, permafrost occurs at the most suitable sites, while it is absent under less FIGUREI. Locations of the six main study sites in the Rocky favourable micro-environments, e.g. snow banks. Mountains of south-western Alberta. Sporadic permafrost is represented by occasional ... Climate and Permafrost 61 I"'" 0 Borehole with Permafrost x Ice Cave I + Ice-Cored Moraine I A Active Rock Glacier I I 1 Vertical Extent of Glaciers 0, I 1 0 49. so* sr 52. 53. 54- 5s- Degrees of Latitude FIGURE2. General distribution of permafrost in a north-west-south-east direction along the mountains and its relationship to thegla- ciers, glaciation limit, and tree-line. ice bodies at shallow depths beneath peat, and also by (see Harris and Brown 1978). In the deep borehole, ice caves. It occurs through a zone up to 1500 m in the zone from 60 to 90 m is slightly warmer (0.15"C) vertical extent. Somewhere between Jasper and the than the zones above and below, and the tempera- extreme north of Alberta, the zone of sporadic tures are only just starting to rise again at the base of permafrost shrinks and discontinuous permafrost the hole.