Magnitude and Frequency of Blowing Dust on the Southern High Plains of the United States, 1947–1989

Abstract

Abstract The concept of magnitude and frequency in geomorphology maintains that the amount of work done on a landscape (the amount of sediment moved) by geomorphic events is determined by the product of the magnitude of the event and the frequency with which that sized event occurs. For many geomorphic systems, it has been found that events of moderate size produce the most sediment transport. This seems not to be the case for aeolian processes on the Southern High Plains. Using meteorological records on visibility reductions caused by blowing dust–a record of the relative amount of dust transported by the wind–at Lubbock, Texas on the Southern High Plains for the period 1947–1989, we find that small magnitude and high frequency events move the most material; that rare, large magnitude events account for considerable transport as well; and, contrary to findings for many other geomorphic systems, moderate events move relatively little sediment. Magnitude and frequency analysis conventionally assumes an identifiable relationship between force applied and the amount of sediment moved. On the Southern High Plains, the soil's resistance to erosion and the vegetation's modification of wind energy are both highly variable in time and space making it unlikely that the sediment transported by two winds of the same speed will be identical. In cases such as these where the resistance to erosion and the effectiveness of the force vary in space and time, magnitude and frequency relations cannot be easily predicted. Key Words: blowing dustdust stormmagnitude and frequencysoil erosionSouthern High Plains