EVOLUTION OF EXPERIMENTAL EROSION LANDFORM WITH UPLIFT

Effects of uplift on the evolution of experimental erosion landform formed by artificial rainfall were examined by generating uplift with the device set under the ground beneath the square mound of a fine sand and clay mixture, on which artificial rainfall was applied. The original height of the mound (90x90cm) was about 15cm above the ground, but it had almost the same dimensions below the ground for the coming uplift. The permeability of mound material was about 0.0003cm/s, and the rainfall of about 38mm/h was applied for 255 hours. The uplift started after 1 hour of rainfall and lasted for 125 hours with the rate of about 1.7mm/h (1-30h), 0.8mm/h (31-62h) and 0.5mm/h (63-126h). Previous experiments without uplift revealed that the average height of experimental miniature landforms decreased exponentially with erosion. H' (0<H'<1) of the surface topography, the parameter expressing the self-affinity of curves and surfaces, decreased first from the value close to that of an inclining plane (1.0) towards 0.5, which is the value of the random Brownian surface. H' then took rather stable values (0.5<H'<1.0) in the later stages of evolution depending on the combination of mound permeability and rainfall intensity. In the experiment with uplift, the average height decreased quickly at first (0-7h), but slightly increased during the hours of high uplift rate (7- 31h), and then gradually decreased. Subtracting the amount of uplift, however, the average height shows a clear exponential decrease. This indicates that the uplift had a minimum effect on the process of erosion. The highest elevation increased with the uplift, while the lowest elevation did not show any trends of change related to the uplift. Ridges, where erosion was minimum without surface flow, became higher with uplift, while main valleys mostly could keep pace with uplift. H' did not have a clear phase of increase after taking a value close to 0.5, which appeared with the abstraction of valleys in the experiment of similar mound permeability and rainfall intensity without uplift. The uplift apparently made the experimental erosion landform keep ragged topography despite the intense erosion. After the uplift ceased, a decrease in the average height accelerated, the highest elevation started to decrease, and H' increased, as in the experiments without uplift.