Effects of lithology, time and exposure on the stabilization of loess matled slopes. A comparative study

Abstract

The stabilization of side-slopes in the small valleys of two major loess regions, the American Midwest and E Transdanubia in Hungary, were studied based upon the field measurements of 224 relatively stabilized slope profiles; for comparison, 97 profiles were also measured in non-loessic areas near the American loess region. Data from the field measurements were then subjected to frequency distribution analyses according to various groupings and the mean values were compared in terms of slope declivity and angularity.

The effect of lithology on slope development is demonstrated by the finding that the valley side-slopes in loess are steeper by 6° and more angular by about 7° than those in non-loess. Also, the valleys in loess tend to be more symmetrical than those in non-loess. A comparison of the upper and lower sections of the valleys that were subjected to a double-cycle of erosion into the same sediment within the same region, i.e., into loess in the American Midwest, indicate the effect of time. The lower, which are also younger, sections of these valleys are steeper by 10° and more angular by 9° than their upper ones; thus the model of reclining slope retreat seems to be confirmed here. A moderate effect of exposure on slope development is indicated by the slightly steeper and more angular (by 1° – 2°) slopes exposed to the N-NE-E versus those exposed to the S-SW-W.

Because of the complex and interrelated dynamic processes involved in slope evolution there are probably many factors which are responsible for the stabilization of the valley side-slopes of the study areas; some explanations are offered in this paper. It was also found that differences in lithology, time and exposure influence primarily the youngest, which are also the relatively least stable, components of the slope.