Sir, The Formation of Ogives

The review by Mr. W. V. LewisReference Lewis ¹ on the status of present-day knowledge on the formation of ogives, and suggestions for the direction that future research should take, is a most stimulating contribution to this important problem.

Mr. Lewis concludes by “posing the greatest puzzle of all—are these ogives the upturned ends of the parcels of annual layers which spill over the lip of the ice fall?” From observations in southeast IcelandReference King and Ives ² , conducted by Dr. C. A. M. King and the writer, it appears that the answer to this question is “no”! Ogives on the south-east side of Morsárjökull were seen to form despite the fact that this glacier has been severed from its accumulation area since the 1930’s and that the mode of supply is now entirely by avalanching ice. During this process all traces of the original stratification must be completely destroyed. Mr. M. M. Miller has described to the writer a similar glacier in Patagonia where ogives form beneath avalanches. Neither is it likely that such large-scale features as the stratification of the névé could descend through a broken ice fall without disruption.

Too much emphasis must not be placed upon the apparent annual formation of ogives, which has admittedly been proven on several glaciers. The spacing of the ogives does not always correspond to the annual movement of the relative section of the glacier. On Svínafellsjökull five ogives were seen to form in the space of one year’s movement, albeit every fifth, or annual, ogive was more pronounced than the intervening ones. On Falljökull, however, the spacing, and presumably the time of formation, of the ogives was found to be irregular, and it appears that between six and twelve ogives form during the course of one year.

To explain these characteristics differential movement within the ice fall, or avalanche cones, including possible surges of flow and release of accumulated pressure along zones of thrusting, must be considered, together with the association of pressure ridges at the base of the ice fall with the formation of the ogives. In this connection Professor S. Thorarinsson has aptly commented on the formation of “ogives“in lava streamsReference Thorarinsson ³ where the question of an annual rhythm cannot be considered.

The paper by Dr. J. W. GlenReference Glen ⁴ appears to substantiate the relation between the formation of ogives and the mechanism of movement within the ice fall, and surely any theory must take into account the formation of ogives under the different conditions mentioned above.