André Ozer

Lichenometric application to historical and subrecent dynamics and sediment transport of a Corsican stream (Figarella River—France)

Abstract Lichenometry has been applied to blocks, canyon walls and terrace deposits. A growth curve, specific to Corsica, was made based on information obtained from tombstones, old monuments from the Genoese occupation of Corsica and Roman megaliths. This allowed us to create a curve going as far back as 2000 years. The curve is similar to those developed in Mediterranean environments (Cevennes and Eastern Pyrenees), but is very different from those developed in Alpine and Arctic regions. Lichens present on boulders of the bedload allow the time at which the boulders were laid down to be determined. The lichenometric study of the Figarella shows firstly that there is high stream competence. Blocks approximately 100xa0cm wide are moved during the 5-year flood. Recent important flood events were identified in 1973 and 1869. These correspond well with historical sources. Other older and much more important floods were also identified. This analysis has allowed us to extend the specific streampower curves proposed by Costa (Geol. Soc. Am. Bull. 94 (1983) 986) and Williams (Geogr. Ann. 65A (1983) 227) to blocks of more than 2xa0m wide. Lichens present on the canyon walls and on terrace sides in the plain allowed the last main incision phase to be dated to the Little Ice Age. Aerial photograph analysis has shown that the present braided system in the lower course of the river is no longer active.

Relationship between the Evolution of the Shoreline and the Posidonia oceanica Meadow Limit in a Sardinian Coastal Zone

RESUME Cet article concerne letude de processus cotiers dans le Golfe dOristano (Sardaigne occidentale, Italie) ou dimportants changements environnementaux ont ete observes. Cette recherche, utilisant comme principal outil la teledetection, vise a evaluer levolution du littoral au cours du temps, sur la periode allant de 1977 a 2000, et a examiner sil existe une relation entre la tendanc evolutive du trait de cote et celle de la limite superieure de lherbier a Posidonia oceanica (L.) Delile, principal ecosysteme en place. Les resultats obtenus montrent dune part que certaines portions cotieres, concentrees sur la partie sableuse du littoral, ont subi des variations significatives et quil existe dautre part une correlation entre levolution de la limite superieure de lherbier et la position de la cote lui faisant face. Principalement dorigines naturelles, cette tendanc evolutive doit egalement etre reliee a limpact anthropique sur lherbier de posidonies. Ce dernier exerce une influence capital...