Some observations on the formation of an active pronival rampart at Grunehogna Peaks, Western Dronning Maud Land, Antarctica

Abstract

Downslope extension of pronival (protalus) ramparts has been proposed to occur at the foot of thickening snowbeds or firn fields. A suggested morphological characteristic of such landforms is that the distal slope is formed at repose (34-38°) by the accumulation of cohesionless cascading debris. However, data on rampart morphology and debris accumulation, in terms of locality of deposition, of an actively-forming pronival rampart at Grunehogna Peaks, Western Dronning Maud Land, Antarctica demonstrates that, although rockfall debris accumulation indicates downslope (outward) rampart extension, this landform does not possess a distal slope at repose. In addition, observations from the austral summers of 2006/7 and 2008/9 suggest that the firn field size is stable. The aim of this paper is to demonstrate that the morphological characteristics and environmental conditions under which pronival ramparts develop according to the model of downslope extension may be more varied than originally thought. Moreover, this paper questions the use of the morphology of fossil features to infer rampart formation and highlights that caution should be used when using pronival ramparts in palaeo-environmental reconstructions.

Diagnostic criteria for pronival ramparts: site, morphological and sedimentological characteristics

“…Hedding et al . () indicate that the morphological characteristics and environmental conditions under which ramparts develop may be more varied than conceived in current models, particularly when rampart age or stage of development, underlying slope angle, the different mechanisms of supranival (and subnival) debris transport and the possibility of ‘form‐convergence’ for discrete debris accumulations (Whalley ) are taken into account. Given the uncertainty around some of the diagnostic criteria and the confusion over the origins and nomenclature of pronival ramparts (Shakesby and Matthews ) the diagnostics presented here are based on actively accumulating features and adopt multiple‐working hypotheses when investigating the origins of landforms (Table ; Shakesby ; Curry et al .…”

“…Hedding et al . (, ) report backwall heights of 52 m and 120 m, respectively, which could enable investigations of backwall retreat and the growth rates of ramparts. Few of other such site data are available.…”

“…Hedding et al . () adapted the criteria of Hedding et al . () by removing ‘Erratics’ from the set of diagnostics since not all moraines contain erratics.…”

“…Hedding et al . () dropped the criterion ‘Crenulate or lobate plan form of outer margins’ tabulated by Hedding et al . () but it is reintroduced here as a valid criterion for the identification of protalus rock glaciers (White ; Wilson ).…”

Pronival rampart formation in relation to snow-avalanche activity and Schmidt-hammer exposure-age dating (SHD): Three case studies from southern Norway

“…As our SHD results clearly demonstrate the possibility of dating when pronival ramparts were last active, this may enable further testing of models of pronival rampart development (cf. Ballantyne and Kirkbride, 1986;Ballantyne and Benn, 1994;Hall and Meiklejohn, 1997;Hedding et al, 2007,Hedding et al, 2010. However, such modelling should take account of the delivery of sedimentary material to the rampart by snow avalanching as well as rockfall.…”