May 9, 1985 - Considerable quantities of new data have become available recently regarding the nature and distribution of permafrost along the eastern ... Subdivision of the alpine permafrost into stable, metastable and ...... New Jersey.
ARCTIC VOL. 39, NO. 1 (MARCH 1986) P. 29-38
Permafrost Distribution, Zonation and Stability along the Eastern Ranges of the Cordillera of North America STUART A. HARRIS' (Received 12 February 1985; accepted in revisedform 9 May 1985)
ABSTRACT. Considerable quantities of new data have become available recently regarding the nature and distribution of permafrost along the eastern an elevation view of permafrost in the ranges north of the 35"N parallel. south,Inthere the is a zone of ranges of the Cordillera. These are used to produce sporadic permafrost up to 1000 m in vertical extent overlain by continuous permafrost. The zone of discontinuous (3040% permafrost of the surface with permafrost) is only about 70 m in verticalextent. North of 54"N this changes, with discontinuous permafrost encroachingon the sporadic permafrost zone. The apparent permafrost boundaries differ from those of Brown (1967), Pkwk (1983a) and Cheng Guodong (1983). Their work was based on considerably lessdata, and it is clear that the terrain factors of mean winter depth,snow local moisture and ground water conditions, the distribution of the different air masses and cold air drainage have considerable effect locally, causing undulations and abrupt changes in the lower limit of the permafrost boundaries to about 56"N. Farthernorth, the climatic factors become dominant. The lower boundariesare different for a given latitude in North America and China. Subdivision of the alpine permafrost intostable, metastable and unstable classes is useful in indicating the instability of alpine permafrost (Cheng Guodong, 1983) and shows that mostof the permafrost found in mainland Canada and Alaskais unstable or metastable. Key words: permafrost distribution, permafrost thermal stability, eastern Cordillera of North America, alpine permafrost, permafrost zonation &SUME. De nouvelles dOMkeS en quantitks considkrables sont depuis peu disponibles portant sur la nature et le distribution du pergklisol le long des chaines estde la Cordilltre. Elles serventB produire une vue d'klkvation du pergklisol dans les chaines au nord du paralltle 35"N. Plus au sud se trouve une zonede pergklisol sporadiqued'une longueur verticale allant jusqu'B 1000 m, recouverte d'un pergklisol continu. La zone de pergklisol discontinu (30 B 80%de la surface avec pergklisol)fait neque quelque70 menlongueur verticale. Au nord du 54"N, cependant, le pergklisol discontinu empitte sur la zone de pergklisol sporadique. Les limites apparentes du pergklisol difftrent de celles de Brown (1967), de Pkwk (1983a) et de Cheng Guodong(1983). Leur travailfut fond6 sur des donnkes beaucoup plus restreintes et il est clair que lesfacteurs du terrain,c'est-&dire la profondeur moyennede neige hivernale, I'humiditk locale, les conditions d'eau terrestre, la distribution des masses d'air et le drainage d'air froid, ont un effet local considkrable entrainant des variations et des changements brusques dans la limite infkrieure des limites du pergklisol aux environs du 56"N. Plus aunord, les facteurs climatiques dominent. Les limites infkrieures diferent B toute latitude dkterminkeen Amkrique du Nordet en Chine. I1 est utile de subdiviser le pergklisol alpin en classes stable, mktastableet instable puisque ceci permet d'indiquer l'instabilitk du pergklisol alpin (Cheng Guodong, 1983) et dkmontre que la plupart du pergklisolsur la partie continentale du Canadaet de 1'Alaska est instable ou mktastable. Mots clks: distribution du pergklisol, stabilitk thermale du pergklisol, cordill&re est de 1'Amkrique du Nord, pergklisol alpin, zonage du pergklisol Traduit pour lejournal par Maurice Guibord.
Fisher). The results of the latter are publishedas part of a study ofpermafrostdistributionanditspredictionintheWestern It has been realizedfor several decades that permafrostexists at Yukon Temtory (Harris, 1983). various locations along the North American Cordillera, but its Some of the available published data from south of the 49th actual distribution isstill poorly known. Thisis partly due to the parallel have been summarized in PtwC (1983a). Additional data immense size of the area (over 6OOO km long and upto 1200 km are availableinthe form of studies of thedistributionand wide) and partly due to the limited number of adequate field characteristics of caves in Montana(Campbell, 1978) and Wyoobservations. Thispaperanalyzesthe available data for the ming (Hill et al., 1976), while similar data are available for ice eastern ranges of the Cordillera (Fig. 1) from the Beaufort Seato caves in southwest Alberta, southeast Yukon, and southwest northern New Mexico (some 38" of latitude). Northwest Temtories(Thompson, 1976; Harris, 1979). By collating this information and plotting it on diagrams showing the maximum heights of the mountains at different latitudes, a METHODS USED reasonable idea of the zonation and distribution of permafrost in Since 1973,the author has made a continuing study of groundthe eastern Cordillera can be obtained(Fig. 1). This can then be temperatures at various locations in the eastern ranges of the compared with the previous predictions of Brown (1967), PCwt Cordillera in southwest and west-central Alberta in cooperation (1983a) and Cheng Guodong (1983), all of whom augmented the with the late R.J.E. Brown and, more recently, G.H. Johnston, available limited field observations by fitting mathematical of the Building Research Division of the National Research curves to the data. It is clear that thedata for the lowest limitof Council of Canada. The methods and preliminary results have permafrost plot at a much lower elevation for a given latitude been described by Harris and Brown(1978, 1982). Since 1981, than the data quoted by Cheng Guodong (1983). further work along the Alaska Highway west of Fort Nelsonhas The informationongroundtemperatures at thelevel of been carried out under contract withJ.A. Heginbottom, Terrain minimumamplitudethroughmountainrangesalong the Sciences Division, Geological Survey of Canada. A study was Dempster Highway is plotted against altitude (Figs. 4 and 5) in also made of the available borehole and thermistor cable data order to check on the consistency of the changes in ground obtained by Foothills Pipelines, Yukon Ltd., along their protemperature withaltitude. The available data on ground temperposed Dempster lateral route (courtesy of S . Elwood and D. ature at the level of minimum amplitude are used to produce a INTRODUCTION
'Dept. of Geography, University of Calgary, 2500 University Dr. N.W., Calgary, Alberta, Canada T2N 1N4 @The Arctic Institute of North America
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S . A . HARRIS
map of the thermal stability of permafrost in North America (Figs. 6 and 7), using a simplification of the classification of ChengGuodong (1983). Finally, anewmapofpermafrost distribution (Fig. 8) has been drawn using the new results. TOPOGRAPHY ALONG THE EASTERN RANGES OF THE CORDILLERA
If the eastern ranges of the Cordillera were viewedfrom the east from space, it would be seen that they become progressively higher southward from the Richardson ranges in the north to latitude 34”N, and then tend to become lower (Fig. 1). A similar slope is seen in the maximum level of the high plains
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being used. The variety of maps, mapping units and definitions is illustrated in Heginbottom(1984), Kudryavtsev et al. (1978, 1980), Kreig (1985) and Washburn (1979) and in the references contained therein. This phenomenon isdue to differences in the scope of the maps, the types, qualities and quantities of information available and theobjectives of the classification. Most classifications used on mapsof permafrost distribution inNorthAmericaandinChinahavebeen qualitative (see Brown, 1967,1978;Cheng Guodong, 1983,pers. comm. 1985; Harris, 1979;HarrisandBrown, 1978,1982). Themaindetailed quantitative classifications are used in the U.S.S.R., where up to six subdivisions may beused, based primarily on the percent-
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LATITUDE [ d e g r e e s ) FIG.I .
Evidence for and distribution of permafrost in the eastern rangesof the Cordillera northof 35”N. The sources and data are listed in the Appendix.
adjacent to the mountains. This is the result of the Tertiary drainage pattern, which featured a drainage divide at latitude 40-44”N (Lemke et al., 1965). The Yellowstone and Missouri rivers usedto flow north and east to Hudson Bay. They became divertedduringthe latter part of theQuaternary by glacial deposits laid down by the Laurentide glaciers just south of the 49th parallel. This resulted in capture of this drainage by the Mississippi River along proglacial drainagechannels. This northerly slope of both the mountains and the adjacent high plains is importantto the understanding ofthe distribution of permafrost since this slope to the north parallels the permafrost boundaries and causes the persistence of patches of continuous permafrost at high altitudes through 35” latitude of the mountains. Thus the problem of mapping the distribution of permafrost and its lower limit is one of plotting the available information on the highest peaks of each mountain range andof attempting to delimit the lower limits. CLASSIFICATION INTO PERMAFROST ZONES
Beforediscussingthe detailed distribution of permafrost along the eastern Cordillera, it is necessary to define the terms
age of the earth’s surface (including lakes and seafloor) underlain by permafrost (State Committee . . . , 1960, in Brown, 1963:viii; Kudryavtsev et al., 1978). This greater detail is the result of intensive studies in permafrostareas undergoing development, but this detailed classification cannot be applied in NorthAmerica at present due to the limitedavailability of information. Proving that there is a zone with less than 5% of the surface underlain by permafrost requires ground temperahm data from more than20 boreholes in the mappingunit. For the same reason, it would bedifficult to reliably map continuous permafrost if it weredefinedas land 100%underlain by permafrost. Fortunately the Russians (Kudryavtsevet al., 1978, 1980)use a broad subdivision into “continuous permafrost’’ (>80% underlain by permafrost), a category with 30-80% of the ground underlainbypermafrostand “sporadic permafrost” (
