Advances in Cryoplanation Terrace Research: Recent Contributions
Total Page：16
File Type：pdf, Size：1020Kb
Advances in Cryoplanation Terrace Research: Recent Contributions 2021 European Geosciences Union 28 April 2021 Raven J. Mitchell1, Kelsey E. Nyland3, Clayton W. Queen1, Frederick E. Nelson1,2 1Department of Geography, Environment, and Spatial Sciences, Michigan State University, East Lansing, MI, USA 2Department of Earth, Environmental, and Geographical Sciences, Northern Michigan University, Marquette, MI USA 3Department of Geography, George Washington University, Washington, DC USA Introduction 3. Landscape evolution Geomorphometry (continued) Cryoplanation terraces (CTs) are large, staircase-like erosional The unusual deglaciation history of “Frost Ridge” in northwestern Hypsometric analysis was applied over extensive areas of features found in upland periglacial environments British Columbia facilitates estimation of long-term denudation eastern Beringia. Hypsometric curves derived from throughout the circum-Arctic region (Figure 1). They are attributable to nivation processes since the LGM. Snowbanks cryoplanated terrain are convex upward and elevation-relief ubiquitous in unglaciated Beringia. The genesis of CTs has accumulated and persisted in marginal drainage features on the ratios retain high values over local and intermediate scale been a controversial subject for more than a century. ridge’s north-facing ridge flank (Figure 4), creating a series of CTs sampling areas (Figure 7). Glaciated areas have hypsometric This presentation summarizes recent research on these through nivation. Data obtained from an unmanned aerial vehicle signatures distinctly different than those of cryoplanated features conducted in interior and western Alaska and were used to estimate the volumes of eroded material. Estimated terrain, across a spectrum of geographical scale. northwestern British Columbia. The work falls into six erosion rates are comparable to short-term nivation rates reported categories. from Antarctica and mid-latitude alpine periglacial areas. Figure 1. Example of a cryoplanation terrace, with the primary components labeled. Eagle Summit, interior Alaska. 1. Relative Dating Relative weathering indices (fracture counts, Cailleux Figure 4. Large nivation hollow on north-facing flank of Frost Ridge, August Figure 7. Hypsometric curves for glacial and periglacial terrain roundness and flatness, Krumbein sphericity, rebound, and 1976. Note extensive vegetation-free area at base of snow patch. In recent in interior Alaska, derived from a 2 m resolution DEM, using . years this snow patch melts out entirely by early August. sampling areas of differing dimensions. Note greater convexity weathering rind thickness) were measured at a series of in periglacial terrain, at all sampled scales, indicating a sites extending across eastern Beringia. Patterns of these Nyland, K.E. and Nelson, F.E. (2020). Long-term nivation rates, Cathedral Massif, northwestern British Columbia. “signature” of cryoplanated terrain. Canadian Journal of Earth Sciences 57(11): 1305-1311. doi:10.1139/cjes-2019-0176 indices indicate that inner treads were more recently Queen, C.W., Nelson, F.E., Gunn, G., and Nyland, K.E. (2021). A characteristic periglacial landform: Automated exposed than distal locations. A model of time-transgressive recognition and delineation of cryoplanation terraces in eastern Beringia.. Permafrost and Periglacial Processes. 32(1): 35-46.doi:10.1002/ppp.2083 CT development through nivation-driven scarp retreat 4. Process monitoring Queen, C.W. and Nelson (submitted). Characteristic periglacial topography: multi-scale hypsometric analysis addresses the removal of weathered material from terrace of cryoplanated uplands in eastern Beringia . treads down side slopes through piping and gravity-driven Soil thermal and moisture records, particle-size analysis, apparent mass-wasting processes (Figure 2). thermal diffusivity calculations, and sediment-deposition patterns Results from fluvial morphometric analysis (Figure 8) of a were used to examine periglacial processes operating on two sorted-stripe field in northwestern British Columbia verifies active CTs in northwestern British Columbia, Canada (Figure 5). the origins of such networks and their effectiveness for The coarse portions of sorted stripes function as underground transporting water and suspended sediment across CT channels (pipes) for sediment transportation across CT treads by surfaces. flowing water. Late-lying snowbank environments are highly dynamic during warm weather, with large amounts of sediment Figure 2. Block diagram transported over short periods showing idealized features from typical cryoplanation terraces in eastern Beringia. Figure 8. A) Flow pathways identified through manual digitizing efforts. Figure 5. Locations of field equipment used to analyze soil depositional (B) Flow pathways identified through flow modeling methodology. Both patterns and the ground thermal regime. Soil troughs at coarse stripe termini results indicate an interconnected system of the coarse components of (left and right photos) and mast with monitoring equipment supporting an extensive field of sorted stripes. ground temperature and moisture sensors (center photo). Nyland, K.E., and Nelson, F.E. (2020). Time-transgressive cryoplanation terrace development Mitchell, R.J., Nelson, F.E., and Nyland, K.E. (2021). Preliminary observations of nivation processes, Cathedral Massif, Mitchell, R.J. (2020). The Contribution of Fluvial Processes to the Formation of through nivation-driven scarp retreat. Earth Surface Processes and Landforms 45(3): 526- northwestern British Columbia, Canada. Physical Geography (in press). doi:10.1080/02723646.2021.1893142 Cryoplanation Terraces. M.S. thesis, Michigan State University. 534. 2. Absolute dating 5. Geomorphometry 6. Climatic dependence Several 10Be and 36Cl Terrestrial Cosmogenic Nuclide ages Semi- and fully automated recognition algorithms (CTAR) were CT elevation rises from Bering Sea islands to the Alaska- reveal that terrace scarps in the Alaskan Yukon-Tanana applied to high-resolution DEMs to identify the locations of CTs Canada border (Figure 9) at rates nearly identical to those of Upland were last actively eroding during the last glacial (Figure 6). CTAR achieved an overall accuracy of 90 percent at Wisconsinan cirques, indicating close genetic links between maximum (LGM). CT treads exhibit time-transgressive several sites in interior Alaska. A strong linear relation exists the two classes of feature. Cryoplanation terraces can be development. Boulder exposure ages and distances between the size of CTAR-delimited terraces and those identified in considered the periglacial equivalent of glacial cirques. between sampled boulder locations were used to a previous study. estimate rates of scarp retreat (Figure 3). The numerical Figure 9. (a) Locations of exposure ages demonstrate that CTs are diachronous five transects of CT and surfaces actively eroding during multiple cold intervals. snowline elevation. (b-f) CT and snowline elevation along five transects, labeled T1 through T5. Open symbols represent median CT elevation, vertical lines indicate range of CT elevation values. Filled circles are snowline elevation. Solid and dashed lines are regression equations for CTs and snowlines, respectively. Figure 3. (A) Cryoplanation terrace series near Eagle Summit, Alaska. (B) photo from outer edge of a terrace tread in series pictured above looking toward higher scarp, and (C) oblique Nelson, F.E. and Nyland, K.E. (2017). Periglacial cirque analogs: regional trends of cryoplanation terrace view of terrace tread (approx. 150 m) with current and previous elevation in eastern Beringia. Geomorphology 293: 305-317. Figure 6. Comparison of CTAR method compared with mapping conducted scarp-tread junctions (dashed lines). Acknowledgments previously at Eagle Summit, AK by R.D. Reger. Red lines represent approximate Funding for this project was provided by the Michigan State University (MSU) Nyland, K.E., Nelson, F.E. and Figueiredo, P.M. (2020). Cosmogenic 10Be and 36Cl geochronology of locations of previously delimited terraces; black areas are CTs identified by Department of Geography, Environment, and Spatial Sciences, the MSU College of cryoplanation terraces in the Alaskan Yukon-Tanana Upland. Quaternary Research 97: 157-166. doi: CTAR. Note the close spatial correspondence between observed and computed Social Science, the United States Permafrost Association, and the U.S. National 10.1017/qua.2020.25. terrace locations. Science Foundation. Access to the ArcticDEM was provided by Polar Geospatial Center., University of Minnesota.