Periglacial vegetation-banked terraces in the Northern Highlands of Scotland: characteristics, activity and formation

Vegetation-banked terraces (VBTs) with bare treads and vegetated risers occur in periglacial environments characterized by strong winds, shallow ground freezing and frequent freeze–thaw cycles. On lee slopes on Scottish mountains they follow the contour, but as exposure to dominant winds increases they dip windward. Comparative analyses of VBTs on mountains with non-frost-susceptible regolith cover and those on mountains with frost-susceptible soils reveal significant differences in dimensions, associated landforms and current activity. The former are generally smaller, lack over-ridden organic material and are associated with aeolian landforms and deposits. They are apparently static features where present activity is limited to needle-ice creep of debris across terrace treads and over risers. The latter are associated with active vegetation-covered solifluction terraces, have over-run organic material and are currently moving en masse downslope through frost creep and possibly gelifluction. We infer that VBTs on non-frost-susceptible regolith cover formed through the accumulation of debris at the upslope margins of wind stripes that formed due to wind erosion during the Little Ice Age. The latter probably represent Holocene vegetation-covered solifluction terraces from which vegetation has been stripped from treads by turf exfoliation (disruption by needle ice, deflation of fines and undermining of soil scarps).