Characteristic periglacial topography: Multi‐scale hypsometric analysis of cryoplanated uplands in eastern Beringia

Abstract

General geomorphometry is concerned with the geometric form of the continuous land surface and can be useful for identifying topographic "signatures." Hypsometry has found numerous applications in several subfields of geomorphology, but has not been used extensively in published periglacial work. Hypsometric analysis was applied in this study to several unglaciated and glaciated locales in Alaska's Yukon-Tanana Upland and Indian River Upland physiographic sections, extensive areas of eastern Beringia in which cryoplanation landforms are ubiquitous. Never-glaciated terrain in this region has a hypsometric signature distinctly different from that of glaciated areas within sample areas ranging in size from 0.25 to 100 km 2 . Cryoplanated terrain exhibits a distinctive convex-upward hypsometric signature, a reflection of a greater proportion of the reference solid (land mass) remaining intact than in typical mature fluvial or glaciated terrain. Because the elevational position of cryoplanation terraces is slightly below and parallel with snowline position it is, in effect, climatically determined from above, and localized planar surfaces develop near that level. Comparison with terrain in the southwestern USA demonstrates that substantial differences also exist between the hypsometry of upland periglacial terrain in eastern Beringia and that of inselbergs and pediments in warm-desert geomorphic landscapes, casting doubt on a suggestion that cryoplanation terraces and cryopediments in high-latitude mountains could be inherited from past intervals of subtropical desert conditions We conclude that characteristic periglacial erosional topography exists in unglaciated areas of Beringia and can be detected and described quantitatively through objective methods.

Little tools, big job: The periglacial conveyor system in cryoplanated uplands

“…The field is dominated by a network of sorted stripes extending from the scarp–tread junction to the toe of the CT tread. Nelson 16,44,64 and Queen 10 provided descriptions of this large (5 ha) patterned ground field. The width of sorted‐stripe units ranges from 1.7 to 5.4 m and averages 2.75 m. The pattern diameter (2.75 m) to depth of sorting (0.8 m) ratio is 3.44, within the range reported by Uxa et al 65 Additional site information is summarized in Table 1.…”

“…Abundant evidence for geomorphic activity was apparent in the mid‐1970s, but the processes slowed down by the 2010s in response to warmer summers and drastically reduced the residence time of the snowpatch at the Splinter Peak–Frost Ridge junction. The primary indications of past periglacial activity atop the ridge are ossified solifluction lobes (fine stripes) and subdued coarse stripes, through which the preferential flow of water was documented in the 1970s 10,16 …”

“…Queen 10 applied the concept of periglacial form communities 46 to cryoplanated landscapes, demonstrating that repeating assemblages of minor periglacial features such as patterned ground are the elemental building blocks of larger units that are recognizable and operational at the landscape scale, that is, CTs. Patterned ground, solifluction lobes, and late‐lying snowpatches favor development of characteristic CT profiles and the shallow mantle of rubble that typifies CT treads (Ballantyne, p. 220 2 ).…”

“…12 2 | WHERE ARE THE RAMPARTS? 2.1 | A possible "missing piece" in the nivation hypothesis Some workers have alluded to the transportation and removal of weathering products over lateral terrace margins (e.g., Thorn and Hall, 9 Queen, 10 Nyland, 11 Brunnschweiler and Nelson, 14 Demek, 15 Nelson, 16 Taylor 17 ), but limited quantitative data exist to substantiate this proposition. Competing opinions within the literature assert that the presence of patterned ground is indicative of geomorphic quiescence (e.g., Karte, p. 81 18 ; Thorn and Hall, p. 545 9 ), whereas others [19][20][21] emphasize the dynamic hydrologic and geomorphic controls exerted by patterned ground features, although not in the context of their presence on cryoplanation landforms.…”

“…Material transported over the distal edge of a tread is recycled to the subjacent CT scarp-tread junction, downslope of which another conveyor transport system operates. If transported over tread margins and onto side slopes, material is rapidly removed from the ridge entirely, through piping in amorphous rubble,45 and is incorporated into nonsorted patterned ground (water tracks) or solifluction lobes on cryopediment surfaces downslope 14,102. The lower parts of CT side slopes (cryopediments) in interior and western Alaska are festooned with water tracks and solifluction lobes more comprehensively than on the south-facing flank of Frost Ridge, where Neoglacial moraines dominate.…”