Abstract
AbstractGlacier and ice sheet retreat exposes freshly deglaciated terrain which often contains small‐scale fragile geomorphological features which could provide insight into subglacial or submarginal processes. Subaerial exposure results in potentially rapid landscape modification or even disappearance of the minor‐relief landforms as wind, weather, water and vegetation impact on the newly exposed surface. Ongoing retreat of many ice masses means there is a growing opportunity to obtain high resolution geospatial data from glacier forelands to aid in the understanding of recent subglacial and submarginal processes. Here we used an unmanned aerial vehicle to capture close‐range aerial photography of the foreland of Isfallsglaciären, a small polythermal glacier situated in Swedish Lapland. An orthophoto and a digital elevation model with ~2 cm horizontal resolution were created from this photography using structure from motion software. These geospatial data was used to create a geomorphological map of the foreland, documenting moraines, fans, channels and flutes. The unprecedented resolution of the data enabled us to derive morphological metrics (length, width and relief) of the smallest flutes, which is not possible with other data products normally used for glacial landform metrics mapping. The map and flute metrics compare well with previous studies, highlighting the potential of this technique for rapidly documenting glacier foreland geomorphology at an unprecedented scale and resolution. The vast majority of flutes were found to have an associated stoss‐side boulder, with the remainder having a likely explanation for boulder absence (burial or erosion). Furthermore, the size of this boulder was found to strongly correlate with the width and relief of the lee‐side flute. This is consistent with the lee‐side cavity infill model of flute formation. Whether this model is applicable to all flutes, or multiple mechanisms are required, awaits further study. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.
Highlights
Elucidating the processes which operate at the ice–bed interface is key to understanding how an ice mass moves over its bed (Weertman, 1957; Iverson and Semmens, 1995; Kjær et al, 2006)
The geomorphological map produced from our orthophoto and digital elevation model (DEM) (Figure 5) highlights a range of geomorphological features across the foreland
Our data captured the morphometrics of 88 flutes, compared with the 21 reported by Åmark (1980).The narrowest flute (16 cm) recorded here compares well with the narrowest found by the field based study of Åmark (1980) (20 cm), suggesting that our horizontal resolution is sufficient for defining flute morphology
Summary
Elucidating the processes which operate at the ice–bed interface is key to understanding how an ice mass moves over its bed (Weertman, 1957; Iverson and Semmens, 1995; Kjær et al, 2006). The landforms created by ice sheets, including subglacial bedforms (Clark et al, 2009; Spagnolo et al, 2014), eskers (Storrar et al, 2013) and large moraines (Barr and Clark, 2009), are visible on digital elevation model (DEM) products and satellite imagery, which can have a near global coverage (e.g., the Landsat archive, and ASTER GDEM). Many of the landforms found on glacier forelands (i.e. in recently deglaciated areas) are often too small to be mapped from these sources. Deglaciation exposes forelands to subaerial modification (Mattson and Gardner, 1991; Etzelmüller et al, 2000; Lukas et al, 2005; Irvine-Fynn et al, 2011; Kirkbride and Winkler, 2012) and when the landforms are relatively small, as is the case for flutes, this
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