Abstract
We combine the use of the unique Glacsweb in situ embedded sensors, surface velocity measurements (from dGPS and remote sensing), and UAV and field photographic surveys, to understand the subglacial processes responsible for the formation of a series of subglacial bedforms composed of both till and bedrock. There is till deformation throughout the year, with spatial and temporal variations. We estimate the ice velocity associated with the formation of a range of subglacial bedforms (9.2–31 m a−1) and the erosion rate on the bedrock flutes (2.13 mm a−1). We show that there is simultaneous deposition and erosion (either at the base of till or directly by ice) which generates flutes, large flutes and drumlins (rather than just depositional processes required by the instability theory). The flutes form behind obstacles associated with mobile till. Where a stationary obstacle is below a threshold height (which at this site is 1.56 m), either till tails will form behind the obstacle or a large flute will develop. Where a stationary obstacle is above a threshold height, then drumlins may form. Using these results as an analogue for larger bedforms, we discuss the bedform continuum in relation to elongation ratio, height, glacier velocity and bed mobility. These bedforms form associated with an overall net erosional regime, and once bedforms are produced, they may become fixed due to the presence of stationary obstacles, and so the resultant bedforms result from the most recent, as well as legacy, processes as they evolve over time.
Highlights
The formation of subglacial bedforms is a fundamental process of the subglacial environment (Menzies 1979; Boulton 1987; Hart 1997; Stokes et al 2011)
This research extends the previous large scale study by Hart (1997) into the examination of smaller bedforms. From these it is proposed that simultaneous deposition and erosion produces the full range of bedforms from flutes to drumlins
It is stressed that all these form due to a negative sediment flux
Summary
The formation of subglacial bedforms is a fundamental process of the subglacial environment (Menzies 1979; Boulton 1987; Hart 1997; Stokes et al 2011). Investigations of the subglacial environment are logistically difficult, but recent technological developments have allowed data collection from this zone. This includes using geophysics to detect and measure the growth of drumlins (Smith & Murray 2009) and MSGLs (King et al 2009) beneath the Antarctic ice sheet. Other developments in recent years include the studies of drumlins emerging from the glacier margin This includes examples from Vestari-Hagafellsjökull (Hart 1995a) and Mulajökull (Johnson et al 2010; Jónsson et al 2014; Benediktsson et al 2016; McCracken et al 2016; Iverson et al 2017 and others in this special volume)
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