EFFECTS OF SLOW UPLIFT ON THE DEVELOPMENT OF EXPERIMENTAL EROSION LANDFORM --- DOES THE DYNAMIC EQUILIBRIUM APPEAR? ---

Miniature erosion landform developed by artificial rainfall on the square mound of a mixture of fine sand and kaolinite (ca.90x90x12cm) was slowly uplifted after a low-relief surface developed. Two runs of this type with different uplift rates and one run without uplift, each of which lasted for 1759 hours, are reported here. Erosion started with the rapid development of valley system. The average height decreased exponentially without uplift, and a very flat surface developed towards the end of experiment. The development of alluvial fans around the mound worked to keep the local base level high, and their dissection, which slightly accelerated the surface lowering, occurred with the integration of drainage basins into a dominant one. The slow uplift (ca. 0.1mm/3hours) worked to reinforce this alluvial fan development. Subtracting the amount of uplift, the average height shows an exponential decrease just as in the case without uplift. After the alluvial fan dissection started and one dominant drainage basin developed, the erosion was accelerated more due probably to the faster incision on the alluvial fan which had developed larger and higher. The overall relief increased with the uplift, but the elimination of small irregularities compensated it. The uplift apparently did not affect the way of erosion significantly, and slight excess of erosion over the uplift appeared as slow decrease in the average height. The alluvial fan development was reinforced more and prolonged longer by the uplift of higher rate (ca. 0.2mm/3hours). The average height stayed at nearly the same level as a result. This seems to indicate that the dynamic equilibrium (or flux steady state) is achieved. However, as indicated by the experiment with lower uplift rate, this quasi-equilibrium may result from a mere coincidence of balance between uplift and erosion. Even under this quasi-equilibrium condition the overall relief increased with the elimination of small irregularities.