Effect of rock fragment embedding on the aeolian deposition of dust on stone-covered surfaces

Many stone-covered surfaces on Earth are subject to aeolian deposition of atmospheric dust. This study investigates how the deposition of dust is affected when rock fragments become gradually more embedded in the ground or, inversely, become more concentrated on the surface. Experiments were executed in an aeolian dust wind tunnel with eight different types of pebbles. The following parameters were measured: dust deposition on the pebbles, dust deposition between and underneath pebbles, total dust deposition (pebbles + inter-pebble space), and the fraction, of total deposition, of dust caught by the pebbles alone. The absolute amount of dust deposition and the dust deposition density (dust deposition per unit surface) were studied for each parameter. The effects exerted by pebble size, pebble flattening, pebble elongation and wind speed were also investigated. Dust patterns on and around pebbles were also studied via flow visualization. The absolute amount of dust settling on pebbles decreases the more that the pebbles become embedded. Dust deposition density on pebbles, on the other hand, increases with embedding. The more pebbles become embedded in the soil, the more efficient the process of dust deposition on pebbles becomes. Dust deposition between and underneath pebbles increases with pebble embedding. Dust deposition density between and underneath pebbles is maximum at 50 per cent embedding, showing that in this area dust deposition is most efficient when pebbles are halfway embedded. Total deposition slightly decreases the more pebbles become embedded, but total dust deposition density increases with embedding. Aerodynamic flow separation and diverging and converging airflow play an important role in the process of dust deposition on stone-covered surfaces. The more pebbles protrude above the soil, the more they act as an obstacle and the more they disturb the air and dust flow creating scouring zones, flow separation bubbles and shelter areas for the dust. All these effects diminish as pebbles become more embedded in the soil. However, perturbations in dust patterns remain visible until pebbles have disappeared entirely. Copyright © 2005 John Wiley & Sons, Ltd.