ENVIRONMENTAL CONTROLS OF BLOWING DUST DIRECTION AT LUBBOCK, TEXAS, USA

Blowing dust is a common phenomenon at Lubbock, Texas, on the Southern High Plains. The directional variability of blowing dust estimated wi th the 'sand rose' technique, using wind speed and direction data, sug gest that dust transport occurs from all directions. An empirical meth od of determining directional variability using meteorological data on visibility reductions due to blowing dust, however, indicates that mo st dust comes from the west and south-west. In addition to wind speed and direction, other environmental factors must be considered in expla ining the spatial pattern of dust transport. Soil erodibility is varia ble in the region, with the most extensive area of highly erodible soi ls to the west and south-west of Lubbock. Rangeland dominates land use to the east, while agriculture is extensive to the north, west and so uth. Local farming techniques leave bare soil during the winter and sp ring, when most airborne dust is produced and also when strong winds a re common from the west and south-west. Soil moisture is lowest to the southwest of Lubbock, which leads to a decrease in soil structure and an increase in the potential for wind erosion in that direction. Rela tive humidities affect threshold wind speeds and are lowest during Mar ch and April, when winds are common from the west and south-west. The spatial and seasonal variability and interactions between many factors , both natural and human-controlled, must therefore considered in expl aining the directional variability of aeolian sediment transport at Lu bbock.