Formation of submarginal and proglacial end moraines: implications of ice‐flow mechanism during the 1963–64 surge of Brúarjökull, Iceland

Abstract

The morphology, sedimentology and architecture of an end moraine formed by a ∼9 km surge of Brúarjökull in 1963–64 are described and related to ice‐marginal conditions at surge termination. Field observations and accurate mapping using digital elevation models and high‐resolution aerial photographs recorded at surge termination and after the surge show that commonly the surge end moraine was positioned underneath the glacier snout by the termination of the surge. Ground‐penetrating radar profiles and sedimentological data reveal 4–5 m thick deformed sediments consisting of a top layer of till overlying gravel and fine‐grained sediments, and structural geological investigations show that the end moraine is dominated by thrust sheets. A sequential model explaining the formation of submarginal end moraines is proposed. The hydraulic conductivity of the bed had a major influence on the subglacial drainage efficiency and associated porewater pressure at the end of the surge, thereby affecting the rates of subglacial deformation. High porewater pressure in the till decreased its shear strength and raised its strain rate, while low porewater pressure in the underlying gravel had the opposite effect, such that the gravel deformed more slowly than the till. The principal velocity component was therefore located within the till, allowing the glacier to override the gravel thrust sheets that constitute the end moraine. The model suggests that the processes responsible for the formation of submarginal end moraines are different from those operating during the formation of proglacial end moraines.

A polyphase glacitectonic model for ice-marginal retreat and terminal moraine development: the Middle Pleistocene British Ice Sheet, northern Norfolk, UK

“…Thrusting within zone SZ-Tr1 also affected the Briton's Lane Formation, providing further evidence for glacitectonism having coincided with the deposition of at least the stratigraphically older parts of this extensive outwash succession. The high-angle and geometry of the faulting in this zone are consistent with deformation having occurred in a proglacial to ice-marginal setting (Hart et al, 1990;Van der Wateren, 1995;Benediktsson et al, 2009). Krüger (1993) and Evans and Twigg (2002) have suggested that relatively large thrust-moraines composed of high-angle faulted blocks provide a record of ice-marginal still-stand.…”

“…Examination of the internal structure of terminal moraines has historically been achieved using direct observations of structure and sedimentology (Van der Wateren, 1995;Phillips et al, 2002;Benediktsson et al, 2009) and non-invasive geophysical methods such as GPR (Bakker, 2004;Kuriger et al, 2005). In this study, we employ a range of different field and remote techniques.…”

“…At a smaller scale, they can provide specific information regarding the mechanics of ice-marginal events, submarginal conditions and the ice-bed interaction. Several recent studies have suggested that terminal moraines may record evidence of surging glacier flow (Matthews et al, 1995;Krüger, 1996;Boulton et al, 1999;Bennett, 2001; Evans and Hiemstra, 2005;Benediktsson et al, 2009Benediktsson et al, , 2010, or alternatively, substrate conditions leading to the termination of fast flow conditions (Christoffersen and Tulaczyk, 2003). Consequently, terminal moraines can provide valuable insights into the dynamics and nature of the ice-marginal landsystem, and potentially the internal and external controls that influenced glacier/ice sheet behaviour (Bennett, 2001;Benn and Evans, 2010).…”

The pattern and style of deglaciation at the Late Wisconsinan Laurentide and Cordilleran ice sheet limits in northeastern British Columbia

“…6A, 6B, log G) suggest advancing Laurentide ice deformed partly frozen outwash (cf. Kleman and Borgström 1994;Bennett et al 1998;Boulton et al 1999;Bednarski 2008;Evans et al 2008;Benediktsson et al 2009). Ice-thrust moraine ridges formed on the down-ice side of preglacial or buried valleys were subsequently overridden and streamlined by southwest-to west-flowing ice (Fig.…”

Depositional environment of the glacigenic deposits from the Holy Cross Mountains (Poland) – interpretation based on macro- and microstructure analyses

“…Stud ies of ice-mar ginal mo raine ridges of mod ern gla ciers in dicate that they are formed from de formed bed rock and ice-contact de pos its as a re sult of dump ing, squeez ing, push ing and glaciotectonic de for ma tion pro cesses (e.g., Ev ans and Hiemstra, 2005;Benediktsson et al, 2009;Rob erts et al, 2009;Krüger et al, 2010;Benn and Ev ans, 2010). The com plex of glacigenic de pos its near M¹chocice has no fea tures of such mo raines.…”