Ice Segregation as an Origin for Lenses of Non-Glacial Ice in “Ice-Cemented” Rock Glaciers

Abstract

ABSTRACT. In order to flow with the gradients observed (100 to 15 0 ) rock glaciers cannot be simply ice-cemented rock debris, but probably contain masses or lenses of debris-free ice. The nature and origin of the ice in rock glaciers that are in no way connected to ice glaciers has not been adequately explained. Rock glaciers and tal us above them are permeable. Water from snow-melt and rain flows through the lower part of the debris on top of the bedrock floor. In the headward part of a rock glacier, where the total thickness is not great, if this groundwater flow is able to maintain water pressure against the base of an aggrading permafrost, segregation of ice lenses should take place. Ice segregation on a large scale would produce lenses of clear ice of sufficient size to permit the streams or lobes of rock debris to flow with gradients comparable to those of glaciers. It would also account for the substantial loss in volume that takes place when a rock glacier stabilizes and collapses. RESUME. La segregation de la glace a l'origine des lentilles de glace d'origine non glaciaire dans les glaciers rocheux soudis par la glace. Pour qu'ils puissent s'ecouler sur les pentes ou on les observe (100 a 15 0 ), les glaciers rocheux ne peuvent pas etre simplement constitues de debris rocheux soudes par la glace, mais contient probablement des blocs ou des lentilles de glace depourvus de sediments. La nature et l'origine de la glace dans les glaciers rocheux, qui ne sont en aucune maniere relies a des glaciers de glace, n'a pas ete correctement expliquee. Les glaciers rocheux et les tal us qui les surplombent sont permeables. Les eaux de fusion et de pluie coulent a travers la partie inferieure des blocs sur le bedrock. Dans la partie haute d'un glacier rocheux, lorsque l'epaisseur totale n'est pas grande, si l'ecoulement sur le bedrock est suffisant pour maintenir la pression hydrostatique contre la base d'un permafrost en contrepente, il peut y avoir segregation de lentilles de glace. La segregation de la glace sur une grande echelle produirait des lentilles de glace pure suffisamment importantes pour permettre aux courants et aux langues de debris rocheux de s'ecouler sur des pentes comparables a celles des glaciers. Ceci expliquerait aussi la substantielle perte de volume qui intervient lorsqu'un glacier rocheux se stabilise et s'eff"ondre. ZUSAMMENFASSUNG. Eisabsonderung als Ursprung fur Linsen nicht-glazialen Eises in "eiszementierten

High‐latitude rock glaciers: A case study of forms and processes in the Canadian arctic

“…Although a certain amount of sea ice may be incorporated in the rock glacier debris, it would appear that the deformation of the underlying marine silts, which may still be subject to permafrost aggradation, is critical to the production of rock glacier forms. Incomplete permafrost aggradation within the rock glacier mass could produce similar situations to those envisaged by Wayne (1981Wayne ( , 1984 and Giar-din0 (1983), whereby groundwater moving below the rock glacier surface could encourage localized saturation of unfrozen marine silts and still produce ice lenses within the upper rock mass (cf. Haeberli, 1985;Barsch, 1988).…”

Rock glaciers and protalus landforms: Analogous forms and ice sources on Earth and Mars

“…Barsch [1996] has identified a ''rooting zone'' below a glacier system (apparently including moraines) which then becomes suffused with congelation ice and interstitial ice under permafrost conditions. Wayne [1981] and Haeberli [1985] have also Figure 4c. Active glacier with protalus lobe-like feature in front.…”

The effect of topography, latitude, and lithology on rock glacier distribution in the Lemhi Range, central Idaho, USA

“…If an ice core (or, at least, segregated ice) is necessary for rock glacier movement, then there are three possible mechanisms for rock glacier formation. Ice cored rock glaciers may form from burial of preexisting free-ice glaciers (e.g., Potter, 1972;Clark et al, 1994), from burial of successive snowfields by rockslides, or via ice segregation within a rock glacier (e.g, Wayne, 1981). While we agree that rock glaciers can form through burial of free-ice glaciers, the location of the majority of Lemhi Range rock glaciers along well-shaded valley walls (rather than in cirques) leads us to infer that these rock glaciers did not originate through burial of free-ice glaciers.…”