Micro-landform Units Composing a Valley-head Area and their Geomorphic Significance

Abstract

A valley-head area, where a stream is elongating towards watershed, is composed of the following five micro-landform units: Crest slope, Side slope, Head hollow, Head floor, and Channelway; which is followed with Bottomland (Fig. 1). The conclusion is drawn from the study on landscapes of some hill-lands in eastern Japan (Fig. 2) and may be applicable to the whole hilislopes with adequate soil and vegetation cover in humid temperate zone.Hydrological conditions and present geomorphic processes prevailing in each micro-landform unit are listed in Tab. 2. The conditions and processes are inducible from characteristic surface features and soil morphology of each unit. The induction is supported with knowledge in slope hydrology, especially with facts and theories concerning throughflow (Fig. 3).These processes are considered to be not generative but modificatory agent to a valley-head. Somewhat catastrophic processes such as large landslide (with about 103m3 of debris), which is also provoked with throughflow, may be concerned with outbreak of a new valley-head. It is suggested with morphological and stratigraphic evidences in some micro-landform units.The extent and proportion of each unit in a valley-head area may reflect the total morphogenetic condition of the area. Especially interzonal comparison of the distance between the headmost divide and the point of Channelway initiation (modified 10 of Horton) must be significant from a climato-geomorphological viewpoint.