The morphology of altiplanation in interior Alaska

ABSTRACT

Altiplanation (cryoplanation) terraces are conspicuous and widespread elements of upland landscapes in Alaska’s interior. They occur in staircase-like series, primarily along divides in ridge-crest positions, and as summit platforms. Flanks (side slopes) consist of a steep upper section composed of coarse clastic debris and amorphous solifluction forms, grading through a break in slope (the ‘solischrund’) to a gentler lower section (cryopediment) dominated by well-defined solifluction lobes and low-order hillslope hydrological networks. An individual terrace unit consists of a steep scarp (riser) and a subjacent gently inclined tread (platform). A sequential group or series of adjacent terrace units, descending from a summit platform along ridge crests, are referred to collectively as an altiplanorium. Altiplanation terraces are a prominent feature of the altitudinal zonal arrangement of landscape phenomena in interior Alaska, and are confined to the upland periglacial zone between 915 and 1675 m.a.s.l. They are positioned below the contemporary snowline. Three study areas are given detailed verbal, cartographic, and photographic description. These areas (Mount Fairplay, High Valley/Denali Mountain, and Goodpaster Uplands) could serve as type localities for altiplanation landform assemblages. An appendix identifies the locations of many other areas in the Alaskan interior containing well-developed altiplanation landforms, and demonstrates the widespread geographic distribution of these landforms.

KEYWORDS:

• Alaska
• altiplanation
• climatic geomorphology
• cryosphere
• cryoplanation
• permafrost
• periglacial
• zonation

Acknowledgments¹⁹

I should like to express my gratitude to the U.S. Army’s Cold Regions Research and Engineering Laboratory, in particular to Dr. R.W. Gerdel, chief of the Environmental Research Branch, for giving me full freedom in research procedures and excellent support in scientific and logistical matters. I feel indebted to the military and scientific personnel of the U.S. Army Arctic Test Center at Fort Wainwright and Fort Greely, especially to Colonel Applewhite, for organizing two helicopter flights, and to Drs. Kolb and Rasche for an illuminating discussion on topics of common interest. The personnel at the USA CRREL Alaska Field Station are to be commended for a very efficient handling of personal matters during my stays in Fairbanks. The help I received from Richard K. Haugen with respect to field work organization and through exchange of ideas, and from Matt Lynch in his capacity as field assistant are gratefully acknowledged. Finally, I would like to thank bush pilot Marc Stella, whose knowledgeable navigation during six flights aided greatly in extending the regional coverage well beyond expected limits.

Editor’s acknowledgments

FEN is grateful to Dr. David P. Lusch (MSU) for discussions about Dieter Brunnschweiler and the manuscript. Mr. Heath Sandall (Heath Sandall Photography, Fairbanks, Alaska) re-created Brunnschweiler’s photographs on the ground and in the air in Alaska and carefully checked their positions in the manuscript. Three anonymous reviewers provided numerous suggestions for improvements to the initial submission Thanks to Henry Brunnschweiler (Haslett (Michigan) High School) for Figure 1, and for relating details about his father’s personal life. Dr. Kelsey Nyland made improvements to the quality of the Frontispiece and to all figures involving line work. Ms. Raven Mitchell (MSU) researched biographical and bibliographic details about Dieter and his graduate students. Raven Mitchell and Mr. Vasily Tolmanov (MSU) processed photographs. Dr. Jerry Brown (Falmouth, MA) provided information about former CRREL personnel. My largest debt is to Dieter Brunnschweiler for his outstanding mentoring and for his inspirational zest for life and lifelong learning.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

There are no numerical data associated with this paper, other than the geographic coordinates appearing in Appendices I and II.

Notes

1 The Brunnschweiler report did not include an abstract. This abstract was prepared by report editor F.E. Nelson.

2 The word ‘altizonation’ is subsequently used in lieu of altitudinal zonation, and ‘latizonation’ for latitudinal zonation.

3 Editor’s note: Brunnschweiler is undoubtedly referring here to local geographical scales. At the regional scale cryoplanation landforms show close correspondence with the elevation trend of the climatic (glacial) snowline (Nelson & Nyland, 2017).

4 Editor’s note: Subsequent literature (e.g., Demek, 1969; Reger, 1975; Nelson, 1989) uses the term tread rather than Brunnschweiler’s platform, except occasionally in the case of ‘summit platforms’. It seems preferable to use ‘tread’ if for no other reason than to continue the staircase analogy. The terms can, however, be used interchangeably, as is the case with ‘scarp’ and ‘riser’.

5 Editor’s note: This appears to be a reference to a genetic discussion (‘A Theory of Altiplanation’) that was planned, but apparently not written.

6 Editor’s note: Subsequent work has shown that some cryoplanation terraces have developed in such positions. Reger (1975) referred to these as ‘hillside cryoplanation terraces’. However, they constitute a very small proportion (1%) of the 686 cryoplanation terraces delimited by Reger.

7 In analogy to Bergschrund, which separates the fixed and the moving portions of glaciers. The Solischrund is the line along which the relatively stable steep free rock face or scree slope changes into the gentle slope of the unstable solifluction fan. Even though Schrund translates into cleft, the absence of such in our case does not detract too much: the importance of the change in the processes on either side of the line is nicely preserved in the simile. If another name has been suggested for this phenomenon the author is not aware of it.

8 Editor’s note: More recent U.S. Geological Survey topographic quadrangles covering the three field study areas discussed in this report are vast improvements compared with the versions Brunnschweiler was working with. Many of the terraces discussed by Brunnschweiler are readily apparent on the newer maps. See web links in captions to Figures 5, 11, and 15.

9 Editor’s note: See Wahrhaftig (1965).

10 The point marked ‘X’ on Figure 7(a) is shown in telephoto form in Figure 7(b). Note how insignificant the conspicuous scarp in Figure 7(b) appears on Figure 7(a). More often than not, scarps become escarpments – if one has to climb them!

11 Editor’s note: More likely the frost table.

12 Editor’s note: DHB is clearly making reference here to water tracks, features that were not named until well over a quarter century after his fieldwork was completed (e.g., McNamara et al., 1999). It is also clear that these drainageways are operating on both cryoplanation terrace treads (Mitchell, 2020; Mitchell et al., 2019, 2021) and on cryopediments downslope from the solischrund.

13 Hamelin and Clibbon (1962) suggest the excellent term gelifluction (or periglacial solifluction) coulee, which includes both process and form.

14 September 14, or shortly after the end of the usually wettest two months of the year, July and August.

15 Editor’s note: At the time Brunnschweiler’s report was prepared the mountain now known as ‘Denali’ (the highest peak in North America) was referred to as ‘Mt. McKinley’. In retrospect, it is an unfortunate irony that Brunnschweiler chose this name for this site, apparently because of its close proximity to the Denali Highway. I have chosen to replace ‘Denali Mountain’ with ‘High Valley/Denali Mountain’ throughout the remainder of the text. Information about the name change from Mt. McKinley to Denali is available at https://www.nps.gov/dena/learn/historyculture/denali-origins.htm.

Reger (1975, pp. 6 and 254–257) referred to the Boulder Mountain and High Valley/Denali Mountain study sites as ‘Phalarope Lake’ and ‘Whistler Ridge’, respectively. The latter appears as ‘Whistle Ridge’ on recent USGS maps.

16 I don’t think that the mere occurrence of lichen – nor of ptarmigan nests – is proof of the inactive status of patterned ground.

17 It was interesting to note the awareness of the permanently frozen ground by members of a road construction crew working on the highway at the base of the mountain. They were somewhat puzzled at our denied request to bulldoze the mountain top to help us find out about the depth of the ground ice!

18 The recently published map, ‘Surficial Geology of Alaska’ (Karlstrom, 1964) was not available until the last week of fieldwork. It will provide a long-needed basis to study the relationship between altiplanation and glacial features.

19 From original report to USA CRREL.

Additional information

Funding

Professor Brunnschweiler’s 1964 field campaign in Alaska was supported by the U.S. Army’s Cold Regions Research and Engineering Laboratory, Hanover, NH, CRREL Project 4.3 (‘Physical Geography of Alaska’).