Effects of Uplift on the Development of Experimental Erosion Landforms Rising from a Flat Surface

Artificial rainfall of about 40mm/hour was applied on a square (60x60cm) sand mound rising from a flat surface. A mixture of fine sand and kaolinite compacted in a square cuboid stainless container was pushed out above the ground level by a stepping motor and worm gears set beneath the bottom plate. The surface topography in the area of 110x110cm including the surrounding area was periodically measured by a laser point gage. Three Runs (582 hours each) with the uplift rates about 1.2mm/hour (270 hours), 0.5mm/hour (582 hours), and 5.0mm/hour (62 hours) are reported here.

The erosion started with a series of shallow and fine grooves on mound edges, and the clear valley incision by head-ward erosion was not observed. Wide and flat bottomed valleys and mountain-like topography with steep side slopes developed with uplift. Maximum height increased as much as uplift first and then stayed around a certain height while the uplift continued. Average height of the uplifted area increased at a rate lower than uplift, but the rate of increase declined with time and seemed to reach a relatively stable height corresponding to the uplift rate towards the end of uplift. After the uplift the height decreased exponentially. Minimum height slowly increased with the uplift reflecting the development of alluvial fans around the mound, but became relatively stable when alluvial fans reached to the edge of experimental platform. The value representing the standard deviation of height in the 10x10cm area increased rapidly with uplift and erosion, but soon became oscillating around a certain value corresponding to the uplift rate, while the uplift continued and the average height was increasing. This indicates a certain type of equilibrium between local relief and uplift. The stable average height, another type of equilibrium, occurred long time after alluvial fans reached to the edge.