THE MORPHOLOGY AND ORIGIN OF NABKHAS, REGION OF MOPTI, MALI, WEST-AFRICA

Nabkhas near Mopti in Mali, West Africa have formed as a result of con tinued cultivation coupled with grazing during periods of severe droug ht. Dune development at three investigated sites was initiated after t he onset of drought conditions. The dunes have formed on deltaic soils which were previously cultivated. Although most of the dunes are at l east partially vegetated, the interdune surfaces are generally devoid of vegetation, highly compacted and continually disturbed by animals. The dunes are elongate and average 0.57 m high, 3.45 m wide and 5.45 m long. They are strongly aligned ESE-WNW with stoss (windward) sides o riented towards the ESE. Dune sediments are sandier and better sorted than the parent deltaic soils but contain a high proportion of silt an d clay thought to be transported onto the dunes as sand-sized aggregat es. The nabkhas have developed as a consequence of climatic and anthro pogenic stresses on the arid ecosystem and are linked to desertificati on within the region. Ongoing disturbance from grazing and cultivation will cause further vegetation reduction and surface destabilization a nd may result in more widespread dune development.