Holocene development and geomorphic processes at Omnsbreen, southern Norway: Evidence for glacier–permafrost interactions

Abstract

Omnsbreen is a small (<0.5 km2) and degrading glacier situated at the regional lower limit of present-day permafrost distribution and glaciation. At present, the existence of Omnsbreen is mainly dependent on wind-borne snow redistributed by the prevailing westerly winter-wind, and lies in an area of marginal permafrost occurrence. During the ‘Little Ice Age’ (LIA) both the glacier and the distribution of permafrost in the area reached their maximum late-Holocene areal extents. The first occurrence of Omnsbreen is recorded in sediment cores retrieved from a proglacial lake and dated at ad 1425, and marks the onset of the local LIA. Reconstruction of the maximum LIA extent by means of geomorphic indicators revealed a size of 7.1 km2, a volume of more than 0.25 km3 and a maximum glacier thickness of 110 m. Since the LIA Omnsbreen has been reduced by more than 90% in area. Omnsbreen retreated rapidly from its LIA maximum, which we suggest was determined by the shape of the glacier, filling up the valley, and hence being unable to accumulate wind-borne snow. Prominent glacier marginal landforms are absent along the maximum LIA extent of Omnsbreen. We propose that the lack of glacier marginal landforms in this case is indicative of a cold glacier margin, and that the landscape evolution in maritime and marginal permafrost regions is characterised as being closely connected with glacial activity.