Glacier Fluctuations and Rock Glaciers in Tröllaskagi, Northern Iceland, with Special Reference to 1946–1986

Rock glaciers are variously thought to be of glacial or non-glacial origin. Those in Tröllaskagi, northern Iceland include features that appear to have evolved from debris-covered glaciers and co-exist with glaciers in this marginally-glacierized area. Monitoring of one such rock glacier, in Nautadalur, since 1977 and with aerial photographs since 1946, allows an assessment of its activity and comparison with nearby rock glaciers and glaciers. Aerial photograph analysis reveals that this and other rock glaciers in Tröllaskagi have exhibited little movement or morphological change since 1946. By contrast, neighbouring glaciers have fluctuated significantly over the same period, with some having experienced a net retreat of over 300m. The fluctuations of a valley glacier, Gljúfurárjökull, have been directly linked to temperature changes. A corresponding temperature-induced retreat or glacier core disintegration is not seen on the rock glaciers, either as a contemporaneous or lagged response over this timescale. The stability of rock glaciers is apparently due to the insulation of the relict glacier ice core by the debris cover. Rock glaciers of glacial origin in northern Iceland do not respond to temperature fluctuations in the manner of debris-free glaciers but may well show effects of precipitation increases by changes in then-flow patterns, albeit over longer time scales. Rock glaciers should be used in paleoenviron-mental reconstructions only with care.