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| Map showing West Rib ascent and West Butress descent routes. Map ©1990 Swiss Foundation for Alpine Research, Zurich, Switzerland and University of Alaska Press, Fairbanks, USA. |
Denali is located at the eastern extremity of the Alaska range. This thin, crescent –shaped, 600-mile long, east-west oriented range, lies roughly 200km north of the Gulf of Alaska, on the south-central edge of the state. From west to east, peaks slowly rise in height culminating in the heavily glaciated, snow-covered, granitic peak of Denali, which at 20,320’ is the highest peak in North America. It towers above the surrounding peaks and plains, which at only 800’ to the south and 2,000’ to the north, result in the presence of one of the greatest vertical drops on the planet - a full 18,000’ (over 5 km) - making Denali one of the most impressive mountains to behold. Once about ten years earlier, while trekking in the wilderness of northern Denali National Park, I remember seeing Rockies sized peaks, above them clouds, and yet higher still above the clouds, another cloud that was the summit of Denali.
Geology
Mountain building processes in southern Alaska have been occurring for hundreds of millions of years as the northeast-moving Pacific plate, at times carrying microplates, has subducted beneath the southern edge of the Alaskan craton. During this time, continental accretion has occurred by sedimentation, microplate suturing, and igneous activity. In the mid-Cretaceous, 90 million years ago, the subducting Pacific plate carried along a large volcanic island arc, called the Talkeetna supertarrane, which collided with the Alaskan craton. Over the period from 90 to 60 million years ago, this terrane sutured to the Alaskan craton, pinching up portions of deep seafloor, and compacting and uplifting shallow marine sedimentary rocks of the Susitna Basin located along the southern continental margin. The uplifted cretaceous sedimentary rocks of the Susitna Basin, of a rock type known as agrillite, comprise the bulk of the range. The uplift and associated folding and faulting were mainly centered along the 1,300-mile long east-west trending Denali fault system. The subducting oceanic plate also caused subsequent igneous intrusions such as the 56 million-year-old Denali pluton and the 36 million-year-old Mount Foraker pluton. Erosion has since removed most of the original sedimentary rocks at higher elevations, revealing the granitic intrusive rocks which now comprise most of the higher summits of the range. Uplift and associated earthquake activity continues to this day, although igneous processes have ceased at the eastern edge of the range.
Climbing Routes
Denali has a north and slightly higher south summit, separated by a summit plateau. The majority of climbing routes access the summit from the south, where aircraft can land near the park boundary at basecamp on the Kahiltna glacier. The south-flowing Kahiltna glacier, over 60-km long, and over 5-km wide along most of its length, is the central feature of the south side of the mountain. Straight north up the Kahiltna from the glacier airstrip and basecamp is the West Buttress route - the most frequented route on the mountain. A non-technical ascent, it sees over 80% of the traffic on the mountain and is sometimes crowded with hoards of Americans climbing their nation’s highest peak. The West Buttress route climbs the Kahiltna up to a Kahiltna pass, and then follows the upper Kahiltna glacier which extends eastwards, to finally reach the west buttress of the summit via a steep gully. The upper portion of the relatively low-angled west buttress then leads to the summit via a summit plateau. The classic harder route on the mountain is the Cassin ridge. This also goes up the Kahiltna for some way, but then turns east up the narrow northeast fork of the Kahiltna. This fork is followed to where the glacier ends at a steep col, and the Cassin ridge can be accessed via steep gullies and climbed directly to the summit. The West Rib uses the same approach as the Cassin, up the northeast fork of the Kahiltna, and accesses a west-facing rib via a steep 2,000’ snow/ice gully. The route continues up this aesthetic rib to the summit. Routes on the north end of the mountain are entirely within the national park where aircraft are not allowed to land. They usually involve weeks of overland travel to reach the peak.
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| Map showing West Rib ascent and West Butress descent routes. Map ©1990 Swiss Foundation for Alpine Research, Zurich, Switzerland and University of Alaska Press, Fairbanks, USA. |
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