Abstract
Understanding the evolution of the ice-bed interface is fundamentally important for gaining insight into the dynamics of ice masses and how subglacial landforms are created. However, the formation of the suite of landforms generated at this boundary — subglacial bedforms — is a contentious issue that is yet to be fully resolved. Bedforms formed in aeolian, fluvial, and marine environments either belong to separate morphological populations or are thought to represent a continuum of forms generated by the same governing processes. For subglacial bedforms, a size and shape continuum has been hypothesised, yet it has not been fully tested. Here we analyse the largest data set of subglacial bedform size and shape measurements ever collated (96,900 bedforms). Our results show that flutes form a distinct population of narrow bedforms. However, no clear distinction was found between drumlins and megascale glacial lineations (MSGLs), which form a continuum of subglacial lineations. A continuum of subglacial ribs also exists, with no clear size or shape distinctions indicating separate populations. Furthermore, an underreported class of bedform with no clear orientation to ice flow (quasi-circular bedforms) overlaps with the ribbed and lineation continua and typically occurs in spatial transition zones between the two, potentially merging these three bedform types into a larger continuum.
Highlights
The interface between moving water, air, or ice and unconsolidated sediment is often populated by undulating landforms, collectively referred to as bedforms (e.g., Allen, 1968; Wilson, 1973; Aario, 1977; Rose and Letzer, 1977)
The size and shape of all 96,900 subglacial bedforms in our data set is displayed in Fig
Flutes could only be mapped from aerial photography (Tables 1 and 2), rather than digital terrain models or satellite images, but we do not interpret their separation to be a consequence of higher resolution imagery being used for mapping
Summary
The interface between moving water, air, or ice and unconsolidated sediment is often populated by undulating landforms, collectively referred to as bedforms (e.g., Allen, 1968; Wilson, 1973; Aario, 1977; Rose and Letzer, 1977). Elucidating the genesis of subglacial bedforms is an important goal in geomorphology and for understanding ice dynamics. In addition to their composition, the morphological properties of bedforms provide constraints for hypotheses and models of their formation (e.g., Jackson, 1975; Clark et al., 2009; Worman et al, 2013). For example, discrete populations of bedforms are found, increasing in size from ripples to dunes draas (Wilson, 1973; Lancaster, 1988). Bedforms can belong to populations within which there are no clear size distinctions, forming size and shape continua [e.g., aeolian ripples (Ellwood et al, 1975), aeolian dunes Bedforms can belong to populations within which there are no clear size distinctions, forming size and shape continua [e.g., aeolian ripples (Ellwood et al, 1975), aeolian dunes (Lancaster, 2013, p. 159), and subaqueous dunes (Ashley, 1990)]
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