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

Abstract

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.

What and where are periglacial landscapes?

“…Such terraces consist of gently sloping treads and steep risers cut into bedrock and tend to form benchlike staircases that dominate certain hillslopes. 18,180 The terraces are particularly well developed in unglaciated highlands of Beringia and show similar regional trends in elevation to cirques from the last major glaciation. 181 Some field evidence suggests that cryoplanation terraces develop through locally intensified weathering and mass wasting associated with late-lying snow patches (nivation).…”

“…Third, there is growing evidence that frost action can contribute towards a characteristic periglacial landscape formed by erosion of cryoplanation terraces in uplands. Such terraces consist of gently sloping treads and steep risers cut into bedrock and tend to form bench‐like staircases that dominate certain hillslopes 18,180 . The terraces are particularly well developed in unglaciated highlands of Beringia and show similar regional trends in elevation to cirques from the last major glaciation 181 .…”

“…In turn, this may permit their evaluation at different spatial scales (i.e., “scale linkage” 183 ) and establishing the degrees to which periglacial landscapes morphologically resemble or differ from nonperiglacial landscapes. Recent advances in recognition and delineation of cryoplanation terraces in eastern Beringia through semi‐automated digital terrain analysis are providing promising opportunities for objective mapping and interpretation of upland periglacial landscapes 180 …”

“…Recent advances in recognition and delineation of cryoplanation terraces in eastern Beringia through semi-automated digital terrain analysis are providing promising opportunities for objective mapping and interpretation of upland periglacial landscapes. 180 Finally, the designation of characteristic landscapes may sometimes be difficult to apply when climatic and environmental change leads to substantial slowing or cessation of morphological evolution while periglacial conditions and processes persist, but at lower intensity than previously. For example, the uplands of Beringia have probably experienced periglacial conditions continuously during much or possibly all of the Pleistocene, with the result that some periglacial landforms such as cryoplanation terraces and cryopediments experienced different levels of activity at different times (e.g., greater activity during full-glacial stages versus limited activity during interglacial stages).…”

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

“…Elevation of the lower terrace tread is 1,150 m a.s.l. Reger 8 reported that the area of cryoplanation terrace treads in interior and western Alaska ranges from 3,000 to 819,000 m 2 (also see 9,10 ) [Colour figure can be viewed at wileyonlinelibrary.com]…”