EFFECTS OF UPLIFT ON THE DEVELOPMEMT OF EXPERIMENTAL EROSION LANDFORM

Experimental erosion landform developing on the square mound of a fine sand and clay mixture (ca. 90x90x15cm) by artificial rainfall (ca. 38 mm/h) was uplifted with a rate of about 0.5mm/h for 216 hours, after the peneplain-like landform developed with 255 hours of rainfall. The average height of experimental landform increased at a reduced rate during the uplift, while it decreased exponentially before and after the uplift. The erosion apparently could not keep up the average height against the uplift of this rate. Both the minimum and the maximum heights also increased with the uplift, but the rate of increase was higher for the maximum height; and therefore, overall relief slightly increased. H', the parameter expressing the self-affinity of surfaces, first increased and then decreased during the uplift. In the previous experiment with the same material and rainfall intensity, in which uplift started at the beginning of erosion on a flat-topped square mound, H' first decreased rapidly towards 0.5 and then gradually increased. This change in H' is not different from the experiment without uplift, although Zi, which is the standard deviation of heights in a 10x10cm square, increased significantly with the uplift. The development of valley system by rapid incision into the flat-topped mound and parallel retreat of valley walls probably created surface topography different in relief magnitude but similar in relief characteristics even with the uplift. The erosion landform of low relief with alluvial fans surrounding the mound at the beginning of uplift in this experiment was apparently more stable and no rapid valley incision occurred, although the decrease in H' from about 0.9 to 0.7 with the slight increase in Zi indicates that the elaboration of valley system occurred again to a certain degree. After the uplift ceased, artificial rainfall continued for 320 hours. Landform changes became even slower in this period, but the gradual decrease in the average height indicates the tendency of lateral planation. H' staying at the value around 0.5-0.6 suggests that this slow planation proceeded with slope decline.