A model of relief forming by tectonic uplift and valley incision in orogenesis

A model for the change in shape of interfluves by concurrent tectonics and denudation was developed based on the morphometric attributes of landforms. The tributaries flowing down valley side slopes and dissecting low-relief surfaces on the interfluves are one of the most important elements for relief-forming processes. They were named as β-tributaries. The valleyhead altitude ( H ), the junction altitude ( L ) and the valley length ( l ) of the β-tributary were measured. The altitudinal difference ( h=H?L ), which indicates the local relief, and the average slope of tributary (tan θ= h / L ) were calculated. The regression analyses among H , L , l , h and tan θ indicate that the valley length, relief and slope increase with an increase in valleyhead altitude.
Based on the functional relations above, the shape of interfluve is a function of uplift, altitude and erosion. This model is used to illustrate the change in cross-section of interfluves during a period of sustained rock uplift.
Successive changes in shape of interfluve can be divided into two substages: (1) the early substage, characterized by trapezoidal cross-sections with the original low-relief surfaces and residual, shallow stream networks on the ridges; and (2) the later substage, characterized by a triangular cross-section, with the original low-relief surfaces removed and with the interfluves lowered by headward erosion of β-tributaries. In central Japan, the transitional relief from the trapezoidal to the triangular cross-section appears when the ridges of interfluves attain elevations about 1600–2000 m above sea level.