A Mechanism of Formaticn of Fluvial Terraces

Abstract

Two examples of microtopography of fluvial terrace plains are described from the River Shinano, central Japan (Figs. 2 and 3). The topography consists of narrow, shallow depression beneath the backward scarp, and of low swells in front of the depression. They are regarded as abandoned channels and old meander-channel bars, respectively. Another example of the meander-channel bars, just growing into terraces with the similar topography is given (Fig. 4a and 4b).From the observation of these examples, a generalized mechanism of formation of a type of fluvial terraces are reduced (Fig. 5). Wider terraces will be formed from braided river floors which are considered to be aggregates of this kind of channel bars. They belong to non-cyclic erosional terraces which do not necessarily represent discontinuous uplift of the area.