Accelerated weathering of a sandstone in the High Atlas mountains of Morocco by an epilithic lichen

Surface weathering features associated with the growth of a species of Aspicilia are described from a sandstone outcrop in the High Atlas Mountains of Morocco. The lichen incises into the rock surface forming circular or crescentic depressions bounded by a micro-scarp which can reach 10 mm in height and which retreats as the lichen grows. The intergrowth and coalescence of simple circles and crescents creates compound forms comprising complexes of multiple scars and scarps. The processes by which the lichen attacks the rock are discussed and estimates are presented of the rate at which the lichen erodes the rock