Evidence of glacial activity at Mt Allen, southern Stewart Island, New Zealand

Abstract

Arcuate ridges of poorly consolidated conglomerate located on the eastern face of Mt Allen, southern Stewart Island, represent moraines deposited during the Otiran Glaciation. The size of the ridges, their distance from the steep eastern face of Mt Allen, the presence of a sandy matrix and some subrounded pebbles and boulders indicates that they are not protalus ramparts or slump deposits.The altitudes of the moraines and an associated cirque indicate an equilibrium line altitude ("snow line") between 580 and 620 m at Mt Allen during the Otiran Glaciation. This relatively low altitude is compatible with other Otiran equilibrium line altitudes determined in the central and southern parts of the Southern Alps that predict an Otiran equilibrium line altitude between 300 and 550 m at Mt Allen, assuming comparable amounts of precipitation during Pleistocene and modern times. The presence of Otiran moraines at Mt Allen implies that remains of earlier moraines associated with more extensive earlier phases of glaciation are also likely to be present on the higher hills of Stewart Island.

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.…”