Periglacial cirque analogs: Elevation trends of cryoplanation terraces in eastern Beringia

Permafrost & Periglacial

2019

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Six hundred sixty‐one rock glaciers in the northern Absaroka and Beartooth Ranges of south‐central Montana were digitized and evaluated using geographic information systems technology and an array of topographic and environmental parameters. Beartooth rock glaciers are larger, occur at higher elevations, receive more precipitation, and are subject to lower temperatures than northern Absaroka rock glaciers. Elevation is strongly correlated with rock glacier activity. Comparative analysis of these adjacent mountain ranges indicates that Beartooth geomorphic landscapes are shifting from predominantly glacial to periglacial regimes, and that the northern Absarokas have largely completed this transition. Because glaciers are declining in response to climate warming, rock glaciers could soon become the most important source of ice in the region.

Section: Discussionsupporting

confidence: 61%

Rock glaciers of the Beartooth and northern Absaroka ranges, Montana, USA

Seligman

Klene

Permafrost & Periglacial

2019

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“…This interpretation is consistent with the nivation‐based hypothesis for CT formation, driven by climate through the mass balance of highly localized snowpacks, although structure can play a role in the initial location of late‐lying snowpacks (e.g. Demek, ; Reger and Péwé, ; Nelson, , ; Nelson and Nyland, ).…”

Section: Discussionmentioning

confidence: 99%

“…The data on relative ages across CT tread surfaces presented here support inferences drawn from subcontinental‐scale spatial analyses of CTs in Alaska. Statistically significant preferred poleward orientations of terrace scarps, and elevational trends closely tracking those of glacial cirques, are suggestive of strong climatic controls, analogous to those understood to act on glacial landforms (Nelson, , ; Nelson and Nyland, ). This study detected statistically significant differences in relative weathering indices (fracture counts, Cailleux roundness, Cailleux flatness, Krumbein sphericity, rock rebound, and weathering rind thickness) across CT treads at three widely separated sites with different lithologies and bedding structures.…”

Section: Discussionmentioning

confidence: 99%

“…Many writers invoke a continuation of nivation-driven scarp retreat in the formation of CTs (Figure 1) (e.g. Demek, 1969;Reger and Péwé, 1976;Nelson and Nyland, 2017).…”

Section: Introductionmentioning

confidence: 99%

“…(A) Side slope of terrace series near Eagle Summit and (B) oblique aerial view of a terrace tread and side slope on the Seward Peninsula (afterNelson and Nyland, 2017). [Colour figure can be viewed at wileyonlinelibrary.com] Sub-meter topographic profile of terrace cross-sections.…”

mentioning

confidence: 99%

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Time‐transgressive cryoplanation terrace development through nivation‐driven scarp retreat

Nyland

Earth Surf Processes Landf

2020

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Cryoplanation terraces are elevated bedrock features resembling giant staircases, with alternating steep scarps and shallow sloping treads. These landscape‐scale features have long been associated with periglacial environments, but the processes involved in their formation remain vaguely specified and contentious. The two leading hypotheses for the formation of cryoplanation terraces are centered on: (1) geologic structure; and (2) nivation‐driven scarp retreat. The nivation‐formation hypothesis invokes scarp retreat under erosion processes associated with late‐lying snowbanks. To test whether cryoplanation terraces develop through scarp retreat, six relative weathering indices (fracture counts, Cailleux roundness, Cailleux flatness, Krumbein sphericity, rebound, and weathering rind thickness) were measured across well‐developed terraces in unglaciated eastern Beringia (central and western Alaska) at Mt Fairplay, Eagle Summit, and Skookum Pass. Statistically significant differences in relative weathering indices detected through chi‐square and multiple‐comparison procedures indicate that material is less weathered closer to scarps, i.e. that these areas were more recently exposed than those distant from the scarp. Based on these findings, a refined model of time‐transgressive cryoplanation terrace development through nivation‐driven scarp retreat is proposed. This new qualitative model addresses the removal of weathered material from terrace treads down side slopes through piping and gravity‐driven mass‐wasting processes. © 2019 John Wiley & Sons, Ltd.

A characteristic periglacial landform: Automated recognition and delineation of cryoplanation terraces in eastern Beringia

Queen

Permafrost & Periglacial

Gunn

et al. 2020

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Automated recognition and delineation of specific landforms and their constituent elements ranks among the most active areas of contemporary geomorphological research. This study contributes to that literature by applying semi‐ and fully automated recognition procedures to upland periglacial geomorphic landscapes. The Cryoplanation Terrace semi‐Automated Recognition (CTAR) algorithm utilizes basic terrain parameters to identify locations of cryoplanation terraces (CTs) from the high‐resolution ArcticDEM. Using a multistep process, candidate areas are identified based on morphometric characteristics. CTAR uses terrain derivatives to search ridges, hills, and mountains for flat areas bounded by abrupt breaks in slope. Because CTs are found exclusively in upland periglacial environments, some locations require that low‐lying areas be filtered out. To assess accuracy, CTAR was tested at five local study sites distributed across eastern Beringia, each containing multiple CTs delimited manually in a previous study. CTAR performed well, with an overall accuracy of 90%. A strong linear relationship exists between the size of CTAR‐delimited terraces and those identified in a previous study through air‐photo interpretation. In addition to identifying nearly all of the CTs in the five study areas, a fully automated version of the algorithm (GEE‐CTAR), implemented in Google Earth Engine, identified nearly 8,000 previously unmapped potential CTs in the Seward Peninsula region of western Alaska. The ability to identify CTs from digital elevation models provides a useful tool for recognizing and delineating upland periglacial topography. Objective recognition of large erosional landform elements created by periglacial processes is a critical step in developing the field of periglacial geomorphometry.