Glaciation of mt allen, stewart island (rakiura): the southern margin of lgm glaciation in new zealand

Abstract

Brook, M.S., 2009: Glaciation of Mt Allen, Stewart Island (Rakiura): the southern margin of LGM glaciation in New Zealand. Geogr. Ann., 91 A (2): 71-81.ABSTRACT. The origin of two ridges on the eastern slopes of Mt Allen, southern Stewart Island, has remained equivocal, with differences of opinion over the exact process-mechanisms of formation. A variety of approaches was used to test a number of possible hypotheses about the origin of the ridges. These include topographic and spatial positioning, geomorphology, sedimentology and palaeoclimatological extrapolations to reconstruct two small former cirque glaciers with equilibrium line altitudes (ELAs) of c. 600 m. It would appear the two ridges reflect a glacial origin, the glaciers interpreted as forming during the Last Glacial Maximum (LGM) in New Zealand. Whilst glaciation during this time (18-19 ka) was extensive in the Southern Alps, the restricted nature of glaciation on Mt Allen suggests the low altitude restricted glaciation to niche sites on the lee side of upland areas.

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

“…, ; Shakesby ; Mills ) since it was envisaged that only such material could move across the snowbed surface, comprising firn and ice, by way of the simple supranival gravity fall process. Ramparts are thus frequently noted with angular‐shaped clasts, which are then typically attributed to the supranival transport of frost‐shattered debris (Shakesby and Matthews ; Brook ); although ‘frost’ weathering processes do not necessarily produce angular‐shape debris (see Hall et al . ).…”

“…Washburn 1979;Colhoun 1981;White 1981;Lindner and Marks 1985;Oxford 1985;Harris 1986;Tinkler and Pengelly 1994;Shakesby et al 1995Shakesby et al , 1999Shakesby 2004;Mills 2006) since it was envisaged that only such material could move across the snowbed surface, comprising firn and ice, by way of the simple supranival gravity fall process. Ramparts are thus frequently noted with angular-shaped clasts, which are then typically attributed to the supranival transport of frostshattered debris (Shakesby and Matthews 1993;Brook 2009); although 'frost' weathering processes do not necessarily produce angular-shape debris (see Hall et al 2002). The constituent material of pronival ramparts is not constrained to angular material with some studies of active features reporting appreciable quantities of fines (e.g.…”

“…The use of this criterion is thus questionable. Introduction of the absence/presence of fines (<2 mm) in the set of diagnostic criteria is based on comparison of constituent material of moraines and pronival ramparts by Brook ().…”

Response to Reviewer 2

“…8 of Golledge and Levy, 2011). Here we instead follow the approach of Bueler and Brown (2009) and superpose velocity solutions from the SIA with those from the shallow-shelf approximation (SSA). The latter essentially represents the sliding component of glacier flow by explicitly incorporating the effects of longitudinal stresses.…”

A Relict Pronival (Protalus) Rampart in the Tararua Range, North Island, New Zealand

“…Small solifluction lobes and terraces have been observed on the central volcanic peaks of the North Island by McArthur (), the only study to report active periglacial activity on the North Island. Allibone and Wilson () and Brook () did report the presence of an unconsolidated ridge on Stewart Island, but concluded it was of glacial origin on the basis of rounded clasts within a silty matrix rather than being a relict pronival rampart. Thus, given the abundance of cold ‐climate landforms in New Zealand, it is somewhat surprising that pronival ramparts (active or relict) have never been reported from either the North or South Islands.…”