Longitudinal surface structures (flowstripes) on Antarctic glaciers

Abstract

Abstract. Longitudinal surface structures ("flowstripes") are common on many glaciers but their origin and significance are poorly understood. In this paper we present observations of the development of these longitudinal structures from four different Antarctic glacier systems; the Lambert Glacier/Amery Ice Shelf area, the Taylor and Ferrar Glaciers in the Ross Sea sector, Crane and Jorum Glaciers (ice-shelf tributary glaciers) on the Antarctic Peninsula, and the onset zone of a tributary to the Recovery Glacier Ice Stream in the Filchner Ice Shelf area. Mapping from optical satellite images demonstrates that longitudinal surface structures develop in two main situations: (1) as relatively wide flow stripes within glacier flow units and (2) as relatively narrow flow stripes where there is convergent flow around nunataks or at glacier confluence zones. Our observations indicate that the confluence features are narrower, sharper, and more clearly defined features. They are characterised by linear troughs or depressions on the ice surface and are much more common than the former type. Longitudinal surface structures within glacier flow units have previously been explained as the surface expression of localised bed perturbations but a universal explanation for those forming at glacier confluences is lacking. Here we propose that these features are formed at zones of ice acceleration and extensional flow at glacier confluences. We provide a schematic model for the development of longitudinal surface structures based on extensional flow that can explain their ridge and trough morphology as well as their down-ice persistence.

Glacial geomorphology of the terrestrial margins of the tidewater glacier, Nordenskiöldbreen, Svalbard

“…Therefore, the geomorphology on the southern foreland is a result of interaction between five narrow ice flow units, which facilitated the delivery of supraglacial, englacial and subglacial debris from nunataks and valley sides and its transportation towards the ice margin along longitudinal flow stripes/foliations (cf. Casassa & Brecher, 1993;Ely & Clark, 2016;Glasser & Gudmundsson, 2012;Hambrey, 1975;Roberson & Hubbard, 2010). One further aspect of the southern foreland is the fact that the five southern ice flow units were squeezed by the two larger northern flow units during the advance of Nordenskiöldbreen, resulting in them advancing relatively further and being compressed and contorted over the site of the present foreland, where they are now melting out.…”

Flow-stripes and foliations of the Antarctic ice sheet

“…However, whilst LSSs can be used as useful records of flow direction, their formation is not fully understood. Multiple hypotheses have been proposed for the formation of LSSs (see Glasser & Gudmundsson, 2012, for a review). A leading hypothesis for the formation of flow-stripes sees them as the transmission of basal bumps in the bed to the ice surface, where the rate of basal sliding is high compared to internal deformation (Gudmundsson, Raymond, & Bindschadler, 1998).…”

“…They are generally observed on its outlet glaciers, ice streams and ice shelves ( Figure 1). Collectively, they are referred to as longitudinal surface structures (LSSs; Glasser & Gudmundsson, 2012) and are commonly subdivided into two categories. The term flowstripe (alternatively 'flow-band', 'streakline' or 'flow-line') is usually retained for features which occur on top of fast-flowing ice streams of Antarctica (Figure 1(A)) and that continue onto ice shelves (Figure 1(B)), sustaining themselves for hundreds of kilometres (Crabtree & Doake, 1980;Merry & Whillans, 1993;Swithinbank, Brunt, & Sievers, 1988).…”

The structural glaciology of southwest Antarctic Peninsula Ice Shelves (ca. 2010)

“…Hulbe et al, 2004) are extended features aligned parallel to the principal ice-flow direction and are observed as dark and light couplets caused by shaded surface relief (Figure 2(C)). They are ubiquitous around Antarctica (Glasser & Gudmundsson, 2012) and typically exist in regions of 'active' ice, with their cumulative length governed by the timescale of decay relative to the time taken for ice to travel a certain distance, yet their genesis is unclear. Although some field measurements have been acquired (e.g.…”

“…Campbell et al, 2008;Hulbe et al, 1997;Ng & Conway, 2004), many of the opposing theories of origin have been developed through numerical modelling (e.g. Gudmundsson et al, 1998), remote sensing-based analysis (Campbell et al, 2008;Casassa & Brecher, 1993;Glasser & Gudmundsson, 2012;Raup, Scambos, & Haran, 2005) and transfer of theory developed on valley-glacier structures (e.g. Reynolds & Hambrey, 1988).…”