Ice‐cored drumlins at the surge‐type glacier Brúarjökull, Iceland: a transitional‐state landform

This paper presents data on a glacial landform that, to our knowledge, has not previously been described in the literature: the ice‐cored drumlin. The study area is the forefield of the surge‐type glacier Brúarjökull at the northeastern margin of the Vatnajökull ice cap, East Iceland. Based on sedimentological field investigations and aerial photograph interpretation, a qualitative model for the formation of ice‐cored drumlins is proposed. The drumlin core consists of stagnant glacier ice from a previous advance and bubbly ice formed by snowdrifts, which were incorporated during the most recent advance—the 1963–64 surge. This advance deposited a mantle of basal till and streamlined the ice‐cored moraines. Till deformation and deposition on the drumlin ice‐core is facilitated by a substratum of low‐permeability ice‐cored moraines. In the present climate, the ice‐core is subject to melting and the drumlin landform will degrade. The ongoing melting of the core and re‐sedimentation of the till cover cause the originally streamlined subglacial landform to develop into a patch of hummocky moraine surrounded by a basal till sheet. Thus, ice‐cored drumlins are a transitional‐state landform in the surging glacier landsystem at Brúarjökull rather than a ‘final’ landform.