Effect of rock fragments on eolian deposition of atmospheric dust

Abstract

The effect of rock fragments and rock fragment cover on the deposition of airborne dust was examined in a wind tunnel. Four parameters were studied: pebble size, pebble flattening, cover density and wind speed. The effect of these parameters on the deposition of dust on the pebbles, on the deposition of dust bewween and underneath the pebbles, and on total dust deposition (pebbles + interpebble space) was measured separately. Deposition on the pebbles increased with pebble size, pebble flattening and wind speed. Deposition between and underneath the pebbles increased with increasing wind speed and with decreasing pebble flattening, but there was no consistent relationship with pebble size. Total dust deposition was not influenced by pebble size, pebble flattening and cover density, but it increased linearly with wind speed. It was also demonstrated that the larger and the flatter the pebbles, and the higher cover density, the more the dust will tend to settle on the pebbles rather than between or underneath them. Air flow separation seems to play a primary role in the spatial distribution of dust deposition within a rock fragment field, as it determines the location and size of the low-sedimentation areas that are connected to the air flow separation bubbles. It should be noted that all data in this study refer to dust deposition (not accumulation), since only wind velocities below the dust deflation threshold were used.