Aeolian contributions to the development of hillslopes and scree sediments in Grænagil, Torfajökull, Iceland

Abstract

Scree cones and slopes are common sedimentary landforms created by rock fall and rock particle fall in mountainous environments. These formative processes are attributed to various weathering and particle detachment mechanisms. However, the aeolian contributions to the weathering of rock faces and formation of scree sediments are poorly understood and often underestimated. A case study in the southern highlands of Iceland provided a geological setting in a subarctic environment where the contribution of various erosion and deposition mechanisms to the development of scree deposits could be studied. Here, moderately-cohesive subglacial volcanic eruption products are continuously undercut by local streams, creating exposed and steep-sided canyon walls where scree cones and slopes are formed by dominant influences of freeze–thaw cycles and the wind on rock particle fall. The stratigraphy and the morphometry of these sedimentary landforms indicate that wet formative processes can contribute but are not as dominant. Avalanching of accumulated material occurs in dry conditions and creates distinct stratified sediments. The aeolian contribution to the scree development was studied by determining the physical requirements of particle detachment using wind tunnel simulations. Simulated threshold wind speeds of the removal of fines show that these wind and gust conditions are common in these areas in Iceland. A detailed particle analysis of the sediment from an isolated scree cone and the contributing rock face showed that sediments were depleted in the silt fractions. Field observations confirmed the influence of deflation where fine material is removed by the wind from exposed sediments whereas larger particles are excavated by the deflation of the surrounding matrix on the overlying rock face. The outcomes highlight the role that aeolian processes can fulfil in subarctic environments. As similar glassy materials are also found on other planets, the studied processes can for example offer insights in hillslope processes at the surface of planet Mars.