MICROPIPING PROCESSES AND BIANCANA EVOLUTION IN SOUTHEAST TUSCANY, ITALY

Biancane badlands consisting of small domes dissected by rills and mic ropipes, with rough disordered microrelief, can be found along the Ape nnines in Italy. The dominant processes forming biancane differ from t hose of badlands formed on smectite-rich mudrocks, as micropipes assoc iated with pseudokarstic enlargement of pores and cracks predominate a nd form the main routes for evacuation of eroded material. Biancana ev olution is controlled by water infiltration into intact bedrock, produ cing an erodible weathering 'rind' which is more porous than intact ro ck. This rind is easily removed by rill or micropipe flow, and erosion is therefore 'weathering-controlled', depending on rind production by infiltrating water. Infiltration is initially slow and stepped, due t o slow water movement through very small capillary pores in intact roc k alternating with rapid filling of macropores and cracks. This occurs due to rapid matrix pore enlargement by dispersion and/or dissolution . The infiltration pattern is accurately reproduced by a model built o n progressive development of weathering layers by moisture penetration . Model results are consistent with weathering rind depths and erosion observed in the field, and show that a pipe network can be generated on newly exposed rock by the rainfall of one year. Propagation of the pipe network diverts a progressively larger proportion of runoff into micropipes, expanding weathering rind production within the biancana a s well as on the surface. Internal weathering and flow progressively d ominate with few unweathered corestones, and the biancana gradually co llapses into a penultimate 'souffle-like' form. (C) 1997 Elsevier Scie nce B.V.