MORPHOSTRUCTURAL ANALYSIS FOR LINKING STREAMFLOW, LITHOLOGY, AND STRUCTURE - COMPARISON WITH REMOTE-SENSING DATA ON THE CEVENNES (FRENCH MASSIF-CENTRAL)

The morphostructural analysis takes into consideration the regional ir regularities affecting the drainage pattern. The causes of such irregu larities may be lithological, structural or morphological. Following t he establishment of a typology of the irregularities affecting the dra inage pattern, this approach is being applied to the crystalline rocks of the Cevennes (French Massif Central) and the sedimentary rocks of its eastern margin. Numerous, mostly linear structures were detected a nd then compared with information from geological maps and the field. It appears most difficult to find a geological cause for the annular d isturbances which mainly correspond to lithological differences, but n ot to the stratigraphic ones as shown on the geological maps. Linear i rregularities which tend to be shorter than the curved ones, result fr om fracturing in a homogeneous medium. The curved ones more closely co rrespond to the faults shown in the geological maps. On a test site th e main trends of irregularities were compared to those identified in s atellite scenes, mainly Spot stereoscopic imagery, to fractures and fa ults identified on aerial photographs, and to the faults and joints sh own on the geological maps. The direction of the drainage pattern is r epresentative of rejuvenated ancient structures. The irregularities of this pattern, however, as shown on the satellite imagery, allow the d istinction between ancient and recent structural directions.