Frost action features as a consequence of fire devegetation in a montane Mediterranean environment

As a consequence of forest fire devegetation in a Mediterranean zone (over 625 m a.s.l.) changes in geomorphological processes have been produced. Environmental changes, and in particular the ground climate, enhance the occurrence of frost-thaw structures previously absent in the zone with the usual forest cover. During the survey period (winter 1986–1987) four months after the fire, the main frost action features observed were ice cementation, pipkrake and high laminar porosity and gaps around the stones. Extrusions of fine material not related to faunal activity and probably associated with frost-thaw processes were also observed. In neighbouring areas with equal altitude and exposure but with forest cover, (outside the fire limit) no frost action features appeared, except in the small pathways where the local microclimate conditions were similar to the burned areas because of the absence of vegetation. Thus, the environmental modifications derived from fire devegetation induce more severe soil temperature conditions and give rise to periglacial type processes, normally absent in this zone. Analysis of polished blocks from hardened undisturbed soil samples aided the interpretation of the extrusions.