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Lookup NU author(s): Professor Andrew RussellORCiD
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Active aeolian sandsheets cover an area of 270 km2 in the Askja region of NE Iceland. The sandsheet is divided into (i) a deflationary upwind part that is characterised by deflation lags, ventifacted boulder fields and restricted aeolian sand patches in the lee of obstacles, (ii) an accumulating central part that is characterised by continuous aeolian sand cover up to 10 m thick, where three scales of aeolian ripples are evident along with larger scale forms including longitudinal zibars, and (iii) a downwind part that is currently subject to aeolian bypass with only localised accumulation occurring in topographic hollows between basaltic lava fields. Trains of aeolian granule megaripples are a characteristic landform of the downwind part of the sandsheet. These sinuous-crested, oblique bedforms attain heights of 0.35 m and downwind spacings of 6 m. They are composed principally of low-density, pebble-grade pumice clasts and other reworked volcaniclastic detritus derived from the nearby Askja volcanic centre. The distribution of landforms across the sandsheet reflects a regional aeolian sediment budget that is controlled by dynamic interactions between glacial, ice-margin fluvial, aeolian and volcaniclastic processes under the influence of a distinctive climatic regime. Sediment supply at the upwind sandsheet margin, adjacent to the Dyngjujökull glacier, increases during summer periods when rates of glacial ablation are at a maximum. Longer term controls on sediment supply rate are determined by episodes of glacier surging and retreat, and by periodic eruptions of volcaniclastic debris from the Askja volcanic centre. The availability of sediment for aeolian transport is controlled by the level of the groundwater table, the depth and continuity of the permafrost layer in the proglacial area, the degree of development of armoured pebble lags and freezing of the sandsheet surface during winter months. The transport capacity of the wind varies on a seasonal basis with mean wind velocities and wind gustiness reaching a maximum during winter periods. Both winter and summer mean wind velocities have been steadily increasing since formal records began in 1969. The suite of aeolian landforms developed within the Askja region, as defined by sediment texture and composition, and bedform scale, morphology and spatial distribution, reflects a special set of controlling circumstances, which mean that the Askja Sandsheet deposits differ significantly from those described from elsewhere.
Author(s): Mountney NP, Russell AJ
Publication type: Article
Publication status: Published
Journal: Sedimentary Geology
ISSN (print): 0037-0738
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