Rock glaciers and related phenomena

Abstract

Rock glaciers are ice-cored lobes or tongues of coarse, angular debris that form below steep rock walls and move slowly across or down valleys. Typically they are associated with glaciated mountain terrain and are transitional forms between glacial and periglacial process regimes. Largely neglected in work on the Karakoram, they are present in great numbers and a wide variety of forms and sizes. They occur in a well-defined elevation band, rarely of more than 1,400 m vertically, varying with slope orientation and across the region. Watershed or interfluve elevations appear as primary constraints. Rock glaciers are absent below the lowest and the highest Karakoram interfluves. They are fairly uncommon in most heavily glacierised parts of the Mustagh Karakoram or Nanga Parbat–Haramosh Massif. The heaviest concentrations are in lower offshoots or sub-ranges of the Karakoram and in surrounding lesser mountains. Where they occur their dimensions, morphology and behaviour reflect relations of seasonal temperatures, snowfall, avalanching, debris sources and delivery. The larger ones tend to be glacier-derived and originate in the upper parts of the rock glacier zone. Some glacier basins like Batura have considerable numbers in their extensive periglacial areas. The genesis of many rock glaciers is hardly separated from the history of glacial advance and retreats. This reinforces the sense that transitional as well as transglacial forms and processes are involved. Rock glaciers are also associated with formerly but not presently glaciated areas, including cirques, glacially sculpted valley walls and floors with abundant glacial deposits. It suggests there are also paraglacial relations. They include numerous and distinctive avalanche- and talus-derived forms, generally concentrated towards the middle and lower parts of the zone, again underscoring their transitional nature. In such cases, an important gradient is that between relatively humid source areas and semiarid, even arid, valley floors into which the lowest lobes spread. Finally, there are a great many inactive or relict rock glacier forms, usually continuous with the zone where active ones occur. This too suggests involvement of the history of deglaciation and Holocene climate change. Regrettably, there are no data to explore these relations or the interior of Karakoram rock glaciers and their mechanics. This chapter can only highlight the scope of this huge but neglected topic and something of what visible morphologies, dimensions and environmental relations can reveal.