The origins of s-forms: Form similarity, process analogy, and links to high-energy, subglacial meltwater flows

• Published in: Earth-science reviews 2020-01, Vol.200, p.102994, Article 102994
• Main Authors: Shaw, J., Gilbert, R.G., Sharpe, D.R., Lesemann, J.-E., Young, R.R.
• Format: Article
• Language: English
• Subjects: Furrows; Megaflood; Meltwater sheet flow; s-forms; Subglacial; Transverse troughs
• ISSN: 0012-8252; 1872-6828
• DOI: 10.1016/j.earscirev.2019.102994

This 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.