EFFECTS OF UPLIFT RATE AND ITS CHANGE ON THE DEVELOPMENT OF EXPERIMENTAL EROSION LANDFORMS RISING FROM A FLAT SURFACE

The development of experimental landform with rainfall and uplift shows the time sequence of landform development in a small scale of experiment. This time, the latest run, in which the uplift rate changed, is reported together with the results of previous runs with constant uplift.

A mixture of fine sand and kaolinite compacted in a square-prism-shaped stainless container (60x60x30 cm) was pushed out above the ground level by a stepping motor and worm gears set beneath the bottom plate. Artificial rainfall of 40mm/h was applied on this square sand mound rising from a flat surface. The surface topography in the area of 110x110cm was periodically measured by a laser point gage. Previous runs (Runs 18-21; 646-1350 hours) are the runs with constant uplift of 0.22-5.1mm/h. In Run 22 (1222 hours), the rate of uplift was 5.1mm/h for the first 30 hours and then reduced to 0.22 mm/h for 680 hours.

In the runs of constant uplift, average height of the uplifted area increased at rates lower than uplift, but this increase declined with the increase in relief and erosion rate. Average height became stable at the level corresponding to uplift rate, except for Run 20. Relief increased to about 120mm as maximum height increased with uplift, before slope failures lowered remaining hills, while the uplift continued. Relief increased again with uplift and then lowered again by slope failures. This process repeated while the uplift of constant rate continued. In Run 20, the uplift rate was too high and its duration was too short to reach this stage. The hills slowly became thinner through this repeating process, and this indicates the attainment of dynamic equilibrium. Ultimately, the process would be dominated by fluvial erosion and a more stable surface of low relief would develop.

In Run 22, relief first increased with the rapid uplift (5.1mm/h) and decreased after the uplift rate reduced to 0.22mm/h. Relief then stayed around 100mm while the uplift continued. Average height shows a similar change, but it gradually decreased while the relief remained roughly constant. The rapid uplift generated the mountain-like topography with steep slopes, and slope failures overwhelmed the uplift after the uplift rate reduced. Relief decreased and fluvial erosion became dominant. This may explain the gradual decrease of average height with rather constant relief.