The Geomorphic Characteristics of Debris Flows in the Ninety-Nine Peaks Area, Nantou
Resource
地理學報, 38, 001-016
Journal
地理學報
Journal Issue
38
Pages
001-016
Date Issued
2004-12
Date
2004-12
Author(s)
Lu, K.K.
Hsu, M.L.
Abstract
Conglomerate formations are broadly distributed in the populated western foothills of Taiwan. Since conglomerates are subject to debris flows, many disasters have taken place in areas covered by this type of geologic formations. This study aims to deduce the geomorphic thresholds for debris flows from data derived from field investigation and aerial photograph analysis of the Dry Creek and the Tien-wei-keng Creek watershed in the ninety-Nine Peaks area in Nantou. The debris flows took place in the study area were classified into two categories according to their size and location. One is the slope-type debris flows, the other is the valley-type debris flows. The geomorphic characteristics of the former were compared with those of the other two most commonly een slope movements, i.e. debris slides and debris avalanches, while valleys with debris flow deposition in their valley mouths are compared with those without. This study shows that the slope-type debris flows always took place on converged convex slopes. They usually had a bowl-shaped appearance, with a constriction of 4 to 6 meters wide below the sliding area. The main axis length, the depth of the slide and the size of both the sliding area and its watershed of slope-typed debris flows are all significantly greater than those of the other two types of slope movements. It is discovered that when the contributing area of a landslide exceeds 1,000 square meters and is larger than 2 to 6 times of the sliding area, debris flows are very likely to take place. The watershed size and the total area of landslides contained within the watershed where valley-type debris flows took place are significantly larger than those without such phenomena. Valley-type debris flows tend to occur in watersheds that are larger than 15,000 square meters with 20% of its area occupied by landslides.
Subjects
九九峰
礫石層區
土石流
地形特徵
地形閾值
The ninety-nine peaks
Conglomerate formation
Debris flow
Geomorphic characteristics
Threshold
Type
journal article
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