College of Sci and Engineering, Chuo Univ, Tokyo, N/A
Abstract
Uplift rate and rainfall intensity are the main factors controlling experimental landform development with rainfall erosion and uplift. However, experimental landforms sometimes show significantly different ways of development even with the same uplift rate and rainfall intensity. This indicates that other factors, such as width of deposition area, and permeability and shear strength of mound-forming material, have important effects.
Experimental landforms increase their elevation linearly with uplift at a little lower rate in the first stage while fluvial erosion overwhelms. After alluvial fans fully develop, the area of deposition becomes the area of transportation. Channel profiles become stable, and the channel bed at the outlet from the rising uplift area stop increasing its elevation. Valley incision in the uplift area is accelerated, and then landslides start to occur frequently. The erosion in the uplift area, which is promoted by the combination of landslides and fluvial transportation, increases enough to offset the rising by uplift, if the uplift rate is in the range of “steady state phase,” which is the usual case.
The width of deposition area determines the duration of alluvial fan development. While alluvial fans develop fan head height increases gradually and this slows down valley incision upstream. With the wider deposition area the average height tends to be higher, because the original flat surface has more time to rise by uplift. After landslides become a major process, landform change itself show no significant difference with different deposition area width except for the average height. As far as the same material (a mixture of fine sand and kaolinite) is used, high compaction yields low permeability/high shear strength, and low compaction high permeability/low shear strength. The combination of low permeability and high shear strength increases overland flow to promote valley incision and makes slopes less vulnerable to failures. High permeability decreases overland flow and low shear strength promotes slope failures. Experimental landforms show various ways of development with complicated interactions among these factors in addition to uplift rate and rainfall intensity.
Geological Society of America Abstracts with Programs. Vol. 48, No. 7