Morphological characteristics, formation and glaciological significance of Rogen moraine in northern Scotland

Abstract

Rogen moraine are enigmatic landforms whose exact origin is still debated. We use NEXTMap digital surface models and aerial photographs to map the distribution of previously unreported fields of Rogen moraine in the vicinity of Loch Shin, northernScotland. Existing models of formation are tested against detailed morphological Rogen moraine characteristics obtained from the remote sensing data and field observations. Detailed morphometric analyses combined with their geographical setting lead us to postulate a likely mechanism of formation. Rogen moraine appear to have formed in areas where there were strong basal ice-flow velocity gradients. Thrusting by compression, or fracturing by extension of preexisting partially frozen sediment probably occurred in these areas, resulting in Rogen moraine formation. A general down-ice increase in ridge crest spacing suggests that the latter process may have been dominant, and is consistent with the location of Rogen moraine in the lee of topographic obstructions, in areas that experienced overall extensional ice flow. We also suggest that at least one field of Rogen moraine formed where lateral basal ice-flow velocity gradients were strongest -possibly in a subglacial shear margin setting.Given their location, the landforms may be consistent with formation during headward scavenging of the Moray Firth palaeo-ice stream into a shrinking core of cold-based ice.

Landform signature of the Laurentide and Cordilleran ice sheets across Alberta during the last glaciation

“…However, as new data become available, particularly greater LiDAR coverage, some of this information may require further revision or rejection, as well as evolve beyond portraying glacial landforms as simple line features, and instead outline individual landforms as polygons parameterized by length, width, and height (cf. Smith et al 2006;Finlayson and Bradwell 2008;Spagnolo et al 2011Spagnolo et al , 2012. The intent of this work is that the GIS are periodically updated to include revisions and newly published information.…”

“…In contrast, ice-thrust ridges document short-lived, relatively rapid advances of lobate snouts associated with non-steady flow conditions resulting from fluctuating basal thermal regimes and (or) increases in submarginal pore-water pressure (Croot 1988;Evans et al 2008Evans et al , 2014. Overridden moraine ridges, which include ribbed moraine, are considered to evolve in areas with strong basal ice-flow velocity gradients, such as towards an inward-migrating core of subglacial thawing (Finlayson and Bradwell 2008;Kleman et al 2010), which may coincide with the locations of ice stream onset zones (Dyke et al 1992;Bradwell et al 2008). Eskers and tunnel valleys document melting, mass loss, and the extent of subglacial drainage systems evolving within inwardly transgressive zones close to the ice margin during deglaciation.…”

Subglacial bedforms of the last British Ice Sheet

“…Ribbed moraine has rarely been observed in Britain in contrast to discoveries in neighbouring Ireland and beneath other palaeo-ice sheets (Smith, 2003;Dunlop and Clark, 2006;Finlayson and Bradwell, 2008). However, new mapping has revealed a total of 1,868 ribbed moraine ridges grouped into 19 separate patches or fields.…”

A Younger Dryas plateau icefield in the Monadhliath, Scotland, and implications for regional palaeoclimate

“…Lukas (2006) reviewed a comprehensive body of literature dating back to the 1970s that supports this approach, and, to date, this formalised approach has been utilised as a first-order approximation to infer a Younger Dryas age in two independent areas (e.g. Lukas, 2005Lukas, , 2006Finlayson and Bradwell, 2008) and has been used to guide later numerical dating programmes to test the hypotheses put forward by Lukas (2006). In both cases, numerical dating has confirmed the hypotheses of a Younger Dryas age of lake sediments accumulated just outside the Younger Dryas limits and key boulders on the outermost moraines concerned Finlayson et al, 2011).…”