Drumlins and mega-scale glacial lineations as a continuum of subglacial shear marks: A LiDAR based morphometric study of streamlined surfaces on the bed of a Canadian paleo-ice stream

Sookhan, Shane; Eyles, Nicholas; Bukhari, Syed

doi:10.1016/j.quascirev.2022.107679

Cited by 7 publications

(19 citation statements)

References 87 publications

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“…The resulting map of the bed of GBL shows a relatively simple distribution of elongate MSGL bedforms along its axial trunk surrounded by drumlins around its margins (Figures 4–6). Sookhan et al (2021, 2022) improved on a simple bipartite approach by using an unsupervised machine learning method ( K ‐means clustering) to identify statistically different types of bedforms from the distribution of elongation ratios, within a continuum from drumlins to MSGLs. As related above, the presence of a continuum of streamlined subglacial landforms has been suggested previously (e.g., Aario, 1977; Barchyn et al, 2016; Ely et al, 2016; Eyles et al, 2016; Rose, 1987) and is now confirmed statistically by quantitative study of LiDAR‐derived elongation ratios (Sookhan et al, 2021, 2022).…”

Section: Resultsmentioning

confidence: 99%

“…The input for calculating MAD is a residual DEM calculated by smoothing any undesired roughness elements (e.g., roads, railways) from the original DEM, without smoothing out surface texture, and then subtracting the smoothed DEM from the original (Sookhan et al, 2022; Trevisani & Rocca, 2015). Smoothed DEMs were prepared by using a five‐pass focal statistics filter with a circular neighbourhood of 120 m in radius and were then subtracted from the original DEMs using the Raster Calculator to produce residual DEMs.…”

Section: Methodsmentioning

confidence: 99%

“…Previous work shows that streamlined bedforms cluster together to create distinct statistically validated surfaces characterized by predominant morphotypes. Sookhan et al (2021, 2022) employed a natural neighbour interpolator to analyse the broader spatial patterns of different morphotypes present on the bed of the Seneca‐Cayuga Ice Stream in New York State from an interpolated surface of their elongation ratios. This exercise determined that individual streamlined bedforms can be regarded as elements within genetically related streamlined surfaces of much broader extent with different relief amplitudes and mean elevations.…”

Section: Methodsmentioning

confidence: 99%

“…Whereas much previous work has suggested the existence of a continuum (e.g., Aario, 1977; Ely et al, 2016, and references therein; Eyles et al, 2016; Rose, 1987), Sookhan et al (2021) identified and visualized the specific types of bedforms within a continuum using LiDAR data. The same mapping methodology was tested further and validated by Sookhan et al (2022) who, in addition, recognized that morphotypes are systematically clustered into distinct surface types produced by ice flow across different substrates at changing velocities.…”

Section: Introductionmentioning

confidence: 99%

“…We now apply the same approach used by Sookhan et al (2022) to the bed of a prominent Late Wisconsin ice lobe (GBL) of the Laurentide Ice Sheet (LIS) preserved in Wisconsin, USA, where high‐resolution LiDAR data are available for the entire bed. As we shall show, this analysis confirms the existence of a continuum of bedforms and distinct statistically validated streamlined surfaces, which we relate to the magnitude of subglacial erosion and consequent lowering of the bed.…”

Section: Introductionmentioning

confidence: 99%

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LiDAR‐based semi‐automated mapping of drumlins and mega‐scale glacial lineations of the Green Bay Lobe, Wisconsin, USA: Ice sheet beds as glaciotribological systems

Eyles

Bukhari

Sookhan

et al. 2022

Earth Surf Processes Landf

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A machine learning methodology for processing and visualizing high-resolution LiDAR digital data is used to map drumlins and mega-scale glacial lineations (MSGLs) on the bed of the Late Wisconsin Green Bay Lobe in Wisconsin, USA, which exhibited surge-like behaviour during deglaciation. Previous work has shown that streamlined bedforms are the product of erosional streamlining of pre-existing sediment. Analysis of bedform height and elongation ratio using curvature-based relief separation (CBRS) and K-means clustering of 32,003 bedforms reveals a continuum of six morphotypes ranging from drumlins, through "channeled" more elongated multi-crested drumlins, to MSGLs. Further statistical analysis shows that morphotypes cluster into six types of streamlined surfaces (S1-S6) recording progressive elimination of an antecedent overridden topography to produce a smoother bed. Initial, relatively high-relief drumlinized surfaces (S1, S2) occur around the slowerflowing lateral flanks of the lobe, where a pre-existing hummocky morainal topography was only partially modified by subglacial erosion. More streamlined surfaces (S3, S4) dominated by multi-crested more elongate drumlins of reduced relief amplitude are transitional to flow sets of MSGL-dominated surfaces (S5, S6) indicative of much faster-flowing ice streaming along the lobe's axis. Estimates of basal drag based on roughness calculations for each surface type identify a 61% reduction in frictional retardation from poorly streamlined surfaces S1 and S2 to MSGL-dominated surfaces S5 and S6, with a step-like reduction between drumlins and channeled drumlins (S3, S4) possibly recording the rapid onset of fast flow. Subglacial streamlining is argued to be accomplished by a thin (<1 m) "third layer" of deforming subglacial debris between ice and its bed which functioned as an erodent layer. A thin (<3 m) till cap, formed by aggradation of deforming debris, rests unconformably on heterogeneous core sediments. Streamlined subglacial surfaces are comparable to the "functional" surfaces resulting from erosion by a "third layer" of wear debris in engineering tribological systems, and also by gouge on faults. Pleistocene ice sheets expanded over pre-existing landsystems, pointing to the broader relevance of the methodology and findings reported here.

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