SIR,
Investigations of wave ogive systems on glaciers have led to a wide variety of postulated mechanisms of formation for these surprisingly uniform phenomena. A widely accepted mechanism is the seasonal-ablation–plastic-deformation hypothesis of Reference NyeNye (1958). An annual process is untenable for some slow moving polar glaciers. Reference HughesHughes (1971, in press) proposed an alternative ablation hypothesis; a differential-ablation–longitudinal-compression model that operates on north-flowing polar glaciers to account for ogives on some Antarctic alpine glaciers. Holdsworth (unpublished) rejected ablation as a causative factor and postulated a Reference BiotBiot (1960) type stress-induced buckling instability as a wave initiator.
My own studies have thrown some doubt on the validity of the Nye model and have shown that probably as many south-facing as north-facing ogive systems exist in the extreme southern latitudes for which Hughes’ model was proposed. Ogive systems figured in the literature have an overwhelming preponderance of facings toward the equator with a very weak secondary mode in the opposite direction. This apparent geographical control is somewhat disquieting to the writer, who favours the stress initiation model of Holdsworth.
The excellent photographs of Reference Post and LaChapellePost and LaChapelle (1971) are of value to this writer’s cause. Their illustrations of pairs of ogive systems originating from separate ice falls with different orientations (their figures 68 to 70) suggest that there is no simple geographic control. The illustrations also show interference between coalescing ogive systems, strongly suggesting a stress-dependent mechanism of formation and supporting the principle of Holdsworth’s model of stress initiation.
The author issues a plea for information that members might possess regarding the orientations of ogive systems at sites of initiation, and particularly regarding the occurrence of multiple interfering ogive trains.
9 May 1972