A Polygenetic Landform At Stiga, Orafajokull, Southern Iceland

摘要

Recent research has identified problems inherent in the identification and description of landforms. Morphologically similar small-scale glacial and periglacial landforms can be misinterpreted, thus hindering environmental reconstruction. This study reveals that a landform resembling a moraine at Stigarjokull, southern Iceland, is the product of both glacial deposition and mass movement. The landform has two distinct morphological and sedimentological components: a basal, lithologically diverse component, and an upper, lithologically homogenous component. Clast lithological analysis, particle shape and particle size measurements demonstrate that the basal component of the landform consists of sediment whose characteristics match nearby moraines. In contrast, the source of the upper component is a narrow outcrop of rock above the valley floor. Evidence suggests that frost-shattered material was transported across a perennial snow patch to a small moraine, leading to growth of the 'moraine'. This combination of processes is unlikely to be unique, but the geological peculiarities of the field site permitted their identification. It is possible that many similar 'moraines' could be enlarged by subaerial feeding, leading to false reconstruction of glacier form and/or associated rates of erosion and sedimentation. Such polygenetic landform genesis therefore has implications for environmental reconstruction.