Loess Distribution from a Source

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AbstractLoess thickness and particle size changes along six Peoria loess traverses in Illinois and southwestern Indiana were investigated by fitting the data to various mathematical models by computer. An exponential model, a logarithmic model, a power function, and an additive exponential model developed in this study were tested. The decrease in mean particle size, which is due to changes in the coarse silt content, both windward and leeward from the source is explained best by the additive exponential model. Mean particle size changes much more rapidly near the source than afar.Leeward of the source, two changes in the rate of loess thinning occurred. The change closest to the bluff is related to particle size differences with distance from the source. The second change is attributed to greater loess deposition in a wider zone near the source by winds from different directions. Windward of the source, no change in the rate of loess thinning due to particle size differences was observed.Based upon the particle size and thickness data presented, the decrease in loess thickness from its source is explained best by an additive exponential model. Leeward of the source where two changes in the rate of loess thinning occur, three exponential terms are needed to accurately characterize loess thickness. The decrease in loess thickness with distance from the source which is due to the more rapid decrease in particle size near the source is defined by the first exponential term. The decrease in loess thickness associated with deposition by winds of different directions is described by the second exponential term. The third exponential term depicts the regional loess thinning due to a decrease in the number of loess particles with distance from the source. Windward of the source only two exponential terms are needed to accurately describe loess thickness because no change in the rate of loess thinning due to particle size differences was observed.