ERDKUNDE BandXVIHeft2 FERD. DOMMLERS VER LAG/BONN Juli 1962 CASCADE ALP SLOPES AND GIPFELFLUREN AS CLIMA-GEOMORPHIC PHENOMENA Will F. Thompson With 8 Figures and one Map. des Kas Zusammenfassung: Alphange und Gipfelfluren Dawson did, in terms of a single level of ac kaden-Gebirges, USA, als klima-geomorphologische Pha cordance. that it extends far to the nomene. They reported south in that I. C. Bailey Willis, Die Erklarung der Obereinstimmung der Gipfelhohen range; Russell, im nordlichen Kaskaden-Gebirge, wie sie erstmals von G. O. Smith, and F. C. Calkins, all of the U. S. G. M. Dawson (1896) vorgeschlagen und durch Reginald Geological Survey, described it as a peneplain in Daly (1912) gestiitzt wurde, wird mit einer gewissen Mo studies between 1900 and 1906. difikation die Fastebenen in die published bestatigt; hypothetischen In 1912 Reginald Daly the sem Gebirge wurden jedoch als nicht bestehend gezeigt. challenged pene Abtragung durch Massenbewegung, die iiber der Baum plain explanation and supported Dawson's prior im grenze wesentlich kraftiger ist als darunter, hat ganzen theory, yet he may never have noticed Dawson's in von Alaska bis Kaskaden-Gebirge, den Kustenketten His work was done within the northern Kalifornien und im von Idaho gipfelflur. Felsengebirge ?Alphange" of the where a few (Daly's Ubereinstimmungsniveau) gebildet. Diese werden fringes high Cascades, only als Anzeichen eines maritimen klimatischen Einflusses in peaks approximating 2,500 meters can be seen at Hohen Die ihrer alpinen angesehen. Analyse Entwicklung once. Dawson's theory, as stated, drew his atten griindet sich auf die Beschreibung der alpinen Klima tion of the well defined accordance at timberline des Gebietes, die auch als Basis Geomorphologie geeignete in that area. He fiir klimatische und naturraumliche Vergleiche mit ande (about 1,800 meters) presumably ren Gebirgsregionen dienen kann. dismissed the 8,000 foot elevation given by der wahrend Inter Schwankungen Baumgrenze quartarer Dawson as an error. To explain the accordance glazialzeiten scheinen Alphangbildungen in verschiedenen he Dawson cited a difference in verursacht zu haben. Sie haben described, great grofieren Hohenlagen rates of and erosion above and below alpine Gipfel in diesen Hohenlagen gekopft und damit weathering zahlreiche Riicken mit bedeutender Erstreckung in der timberline, observable throughout the region. Es daB gleichen Hohenlage gebildet. wird angenommen, However, his description of the accordance he eine gut ausgepragte Gipfelflache (Dawson's Gipfelflur), saw in the Cascades from across the Fraser low die sich in 8000 FuB Hohe durch das nordliche ungefahr land makes it clear that the elevation was Kaskaden-Gebirge erstreckt, einer interglazialen Hohen given um un correct was lage der Baumgrenze entspricht, in der das Klima and that he looking at the high gip warmer war. gefahr 7? F als das gegenwartige Nur wenige felflur of that range, about 700 meters above tim Gipfel nicht vulkanischen Ursprungs erheben sich wesentlich berline. From that Daly's meter dariiber. Die bedeutenden im Kaskaden distance, 1,800 weniger Gipfel accordance was obscured haze. Gebirge von Washington und Oregon, und in Idaho, wur probably by den einheitlich iiber weite Flachen an der Baumgrenze durch The true explanation of Dawson's gipfelflur die Alphange von Daly's Obereinstimmungsniveau ge seems to be a variant of his Keine der in niederen Hohen fairly simple original kopft. Lage Baumgrenze one but the issue has been confused for scheint genug angedauert zu haben, als dafi sie heute long lange reasons noch sichtbare morphologische Auswirkungen im Kaskaden various other discussed in this paper. Gebirge hinterlassen hatte. Neither alpine peneplains or Dawson and Daly's observations have ever been completely accepted Introduction as solutions of the problem of alpine accordances, either in this or in the In a report published in 1896, the pioneer Ca country Alps, though had advocates nadian geologist G. M. Dawson noted that a alpine peneplains long many among remarkable number of summits rise to altitudes geologists working in the Rockies. The problem has been discussed in recent de of about 8,000 feet (actually about 2,500 meters), only occasionally cades. It is revived here because of the usefulness both where he was working on the east flank of of such features in the southern British Columbia Coast Range and clima-geomorphic defining climatic inmountains. in the nearby northern Cascades (see location regions map). Nevertheless, very few non-volcanic peaks Our concern with alpine clima-geomorphology within the area of his observations rise much is even wider than that, however. Whether one's higher, and those only to about 2,800 meters. In interest in mountains is esthetic, scientific, eco the Alps such an accordance of alpine summits is nomic, conservational, or military, it iswell to un a called "peak plain" (gipfelflur). Later students derstand how their landscape is organized and the of the phenomenon in the Cascades thought, as significance of its elements. Various climate-re 82 Erdkunde Band XVI LOCATION MAP: THE NORTHERN CASCADE MOUNTAINS NUMBERS REFER TO PHOTOGRAPHS ACCOMPANYING THIS ARTICLE lated landscape elements, such as the alp slopes rest of the northern Cascades. No significant and accordant summits discussed here, play con summit upland exists near or above the 2,500 sistent roles as summit follows summit and gorge meter level anywhere in the range. One gorge en follows gorge across a mountain region. Regional ters the quadrangle at an altitude of about 300 unity in climatically homogeneous mountains is meters only 4 kilometers from a 2,400 meter sum thus like that created by repetition of complex mit. Five other valleys enter below the 800 meter pattern-units in a very boldly-printed fabric. Be level. Most of the big valley-head cirques have cause regional climatic homogeneity can never be floors at about 1,000 meters, though the floor of complete, however, climate-induced consistency the McMillan Creek cirque, between the two of landscape elements is always imperfect and is Picket Range serrate crests, is at about 850 meters. less in broad regions than in their sub-regions. Several large cirques near Mt. Redoubt have Nevertheless, it is very real and worthy of atten floors above 1,200 meters. tion. Within the small sector of the range covered by theMt. Challenger quadrangle, fourteen summits Dawson's Gipfelflur carry spot heights between 2,270 and 2,575 me One of the best places to see Dawson's gipfel ters; the map shows about fifty unsurveyed peaks flur is in and around the Picket Range (Figs 1 and minor pinnacles in that range of altitude also. a one and 4), part of the northern Cascades covered Only peak in the quadrangle rises higher, by the fifteenminute Mount Challenger quad to 2,730 meters. On it the map shows one minor are rangle (see location map). The Pickets pinnacle rising to about 2,680 meters. The gipfel most like of the high Cascades in having local flur thus forms a very distinct, though not abso more relief of than a kilometer and a half through lute, ceiling on summit heights in the Picket Range. out. Total relief in the quadrangle is about 2,400 The same is true of non-volcanic peaks throughout meters. The Pickets are deeply and completely the northern Cascades, very many of which ap are dissected by steep-walled glacial gorges, as the proximate 2,500 meters but only a thin scattering as Will F. Thompson: Cascade Alp slopes and gipfelfluren clima-geomorphic phenomena 83 on of which exceed 2,700 meters and those only by to different rates of weathering and erosion about a hundred meters at most. The Mount Terror timbered subalpine and open alpine slopes allows massif in the Picket Range is a 3 kilometer serrate us to assume development of his gipfelflur late in mass ridge, all summits of which are between 2,300 and the history of the range after the mountain 2,485 meters high. The 5 kilometer Challenger had become completely dissected. Long survival not Fury ridge is closely similar and has five surveyed of precariously sharp alpine ridges thus need peaks 2,450 to 2,530 meters high. The precarious be assumed. However, Dawson's 8,000 foot gip sharpness of those two serrate crests, and the felflur is 2,000 feet (actually about 100 meters) presence nearby of a number of accordant or above the present timberline and its once much moderately sub-accordant peaks now isolated more continuously accordant ridges are now being from them by convergence of erosion on flanking dismembered. Thus it seems a relic of times past valley walls, suggests strongly that they are rem and in that sense not related tomodern timberline. nants of much more extensive even-crested ridges The known variability of Pleistocene timberline to which have been dismembered by erosion to form levels has long been the leading objection the present topography. Dawson's explanation of alpine accordance. Study of the Cascades allow us to answer that ob In view of the considerable relief and complete may at the same time thatwe Dawson's dissection of the high Cascades, and the great jection explain number and sharpness of those of its peaks which gipfelflur. comprise Dawson's gipfelflur, that accordance Accordance can hardly be considered a peneplain or other Daly's ancient surface. On the crest of uplifted graded Brink has pointed out (1959) that the present the central Wind River Range inWyoming, which climatic timberline in the southern British Co because it stands on a has somewhat high plateau lumbia Coast Range lies somewhat above the less local relief than the there is a Cascades, lowerlying meadows of the accordance Daly felsenmeer-mantled sum strongly rolling graded studied and that it has recently been rising.