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TitleThe origins of s-forms: form similarity, process analogy, and links to high-energy, subglacial meltwater flows
AuthorShaw, J; Gilbert, R G; Sharpe, D RORCID logo; Lesemann, J -E; Young, R R
SourceEarth-Science Reviews vol. 200, 102994, 2019 p. 1-23,
Alt SeriesNatural Resources Canada, Contribution Series 20190641
Mediapaper; on-line; digital
File formatpdf; html
Subjectssurficial geology/geomorphology; sedimentology; geophysics; Nature and Environment; Science and Technology; sedimentary structures; depositional environment; hydrologic environment; glaciation; ice sheets; glaciers; glacial features; glacial landforms; erosional features; scouring; landforms; escarpments; basins; paleocurrents; flow trajectories; models; flow structures; fluid dynamics; remote sensing; satellite imagery; photogrammetric surveys; airphoto interpretation; photography; subglacial meltwater corridors
Illustrations3-D images; block diagrams; photographs; satellite images; aerial photographs; 3-D diagrams; schematic representations; geoscientific sketch maps; digital elevation models; profiles; models
ProgramGroundwater Geoscience National Aquifer Evaluation & Accounting
Released2019 11 09; 2020 03 04
AbstractThis paper first presents the history of ideas on s-form formation, with an emphasis on meltwater models. The main approach is based on form similarity between modern erosional marks and subglacial s-forms. Form similarity is then extended to process similarity, which promotes understanding of s-forms. Three classes of erosional marks are identified: obstacle scours, basin-shaped erosional marks and landforms related to escarpment flow. Identification is based on form, with recognition of elements, though it mainly depends on recognition of the whole form in much the same way as we recognize family members or familiar flowers. Flow conditions related to the various flow features are determined by flow visualization and computational fluid dynamics. Some s-forms are produced in flume models, though most are natural features observed in the field. Examples from beneath past ice-sheets are seen in the field and illustrated by air and ground photographs, satellite images and DEM (digital elevation model). The results of this work show remarkable similarity between modern erosional marks and ancient, subglacial s-forms. Consequently established processes are attributed to ancient forms. In turn, s-forms may be used abductively to interpret subglacial, hydrological conditions. The lack of waning stage bedforms scoured into primary forms, suggests that erosional marks form under abruptly terminating, catastrophic flow.
Summary(Plain Language Summary, not published)
This paper presents the history of ideas on sculpted glacial erosion forms (s-forms). S-forms occur in tandem with classic glacial erosion forms such as striations and plucked forms. However, s-forms were created by high-velocity, turbulent meltwater flow beneath the former glaciers across North America.
Flow conditions related to the various erosional features are determined by flow visualization and computer fluid dynamic tests. Sculpted forms can be produced in stream-flow models, though most are natural features observed in the field, for example on wind-eroded snow. The wide distribution of s-forms across glaciated terrain requires re-thinking of glacial landform models, related rapid sea level rise and changing climates due to very large glacial meltwater floods.

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