EFFECT OF ROCK FRAGMENTS ON EOLIAN DEPOSITION OF ATMOSPHERIC DUST

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 pebbl es, on the deposition of dust between and underneath the pebbles, and on total dust deposition (pebbles + interpebble space) was measured se parately. Deposition on the pebbles increased with pebble size, pebble flattening and wind speed. Deposition between and underneath the pebb les increased with increasing wind speed and with decreasing pebble fl attening, but there was no consistent relationship with pebble size. T otal dust deposition was not influenced by pebble size, pebble flatten ing and cover density, but it increased linearly with wind speed. It w as 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 s eems to play a primary role in the spatial distribution of dust deposi tion within a rock fragment field, as it determines the location and s ize of the low-sedimentation areas that are connected to the air flow separation bubbles. It should be noted that all data in this study ref er to dust deposition (not accumulation), since only wind velocities b elow the dust deflation threshold were used.