THE ORIGIN OF UPHILL-FACING SCARPLETS DISTRIBUTED ON THE HIGH MOUNTAIN SLOPES OF JAPAN

Abstract

Uphill-facing scarplets are often distributed on the high mountain slopes of Japan. They have been called “double ridges”, or “linear depression”, the origin of which has been disputed among geomorphologists. In this paper the author investigated their topographical characteristics such as mode of occuerrence, height, distribution and cross sections of rides on which they appear. He also refers to their origin applying a two-dimensional finite-element calculation of the self gravitational stress to a model mountain, on the slopes of which the scarplets are often distributed. The results can be summarized as follows. 1. The scarplets are mostly recognized in high mountain areas with high relief caused by the rapid uplift during the Quarternary (Fig. 2). 2. Most of them appear on the mountain slopes higher than 2, 000m a. s. l., but some are recognized on the slopes lower than 1, 000m a. s. l. in case of the slopes with high relief (figs. 3, 5 and 6). 3. They are mainly formed on ridges deeply dissected by V-shaped valleys (e. g. the Kurobe) (Fig. 7), cross sections of which consist of two parts; very steep lower slopes formd by deepening and gentle upper slopes or flat surfaces around ridges. Therefore, the sections generally show convex outlines as a whole (Figs. 8 and 9). Scarplets are usually located just above breaks between steep and gentle slopes. 4. Brittle fractures caused by the self load of mountain will be expected to occur around ridges of mountain (Figs. 11 and 12) by the analysis applying the finite-element method. Therefore, uphill-facing scarplets may be originated from the subsidence of ridges caused by local faulting.