Injection Features in Mid-Altitude Mediterranean Soils

During the 1986/87 winter in a Mediterranean area at 625 m altitude (in the Montserrat Mountains, Catalunya, Spain), injection features have been recorded on Cambisols. Soil freezing occurred in areas burned down by a 1986 summer fire but did not affect vegetated areas. Injected material from the subsurface horizon, yellow-red in colour, became apparent in contrast to the black, burnt organic matter of the soil surface. Besides injections, other frost action features were observed: pipkrakes, frost heaving and gaps around stones. Field work and macromorphological analysis of polished blocks enabled the understanding of extrusions as being due to freeze-thawing cycles. Micromorphological analysis contributes new data and confirms this interpretation. Micromorphological features related to the injection phenomena include: a) parallel-striated b-fabric in protruding B-horizon material, not related to faunal passages, b) high porosity in soil masses lying adjacent to injected material and c) sand grain alignment. Other micromorphological features related to the freeze-thaw process are horizontal planar pores. Injections as frost features are consequently not exclussive to Alpine or Arctic soils, but in this case, they are associated to a local microclimate change due to fire devegetation.