Dust rains in Mallorca (Western Mediterranean): Their occurrence and role in some recent geological processes

Dust rains were observed in Palma de Mallorca (Island of Mallorca, Western Mediterranean) on 253 days in the 22-year period from 1982 to 2003. These and other data from the Western Mediterranean show that dust rains are on the increase. Most occur in the warmest season of the year. Meteorological conditions associated with this phenomenon combine hot advection from the south at low tropospheric levels with southwest winds associated with a depression in the middle troposphere. Dry deposition of dust, often in aggregates 40-300 μm across, is occasionally observed. Analysed samples are silty and mainly composed of quartz and kaolinite. They also contain minor proportions of feldspars and palygorskite, which do not occur as rock-forming minerals in the Balearic Islands. Comparisons of the dusty rainwater samples with soils and recent marine and karstic sediments suggest that dust deposition is an important sedimentary process in the Balearic Islands.