台灣大規模岩石崩坍的初探

大規模岩石崩坍(Rock avalanche)常見於年輕造山帶(如喜馬拉雅山、紐西蘭阿爾卑斯山、洛磯山脈)，為一種由滑落、崩移的岩屑彼此碰撞、研磨所形成的顆粒流(granular flow)。此種崩坍具有規模大、速度快(100-250 km/h)、移動距離長(>1 km)的特性，因此能造成巨大災害。岩石崩坍常由地震和(或)暴雨引發，但如2006菲律賓萊特島的例子，卻與大地震無關，且暴雨停止後五天才發生。根據文獻回顧，岩石崩坍最小臨界崩坍體積為1*106 m3，來源區最小坡度約25度、高差至少150公尺，且所有岩石崩坍都發生在逆向坡。台灣雖然構造運動活躍，也多暴雨、地震，但卻很少有岩石崩坍的報導。我們檢視了既有的遙測影像(Google Earth)與照片，發現只有極少數山崩疑似為岩石崩坍(如一位於阿里山區者，及2010梅姬颱風造成蘇花公路坍方、遊覽車墜海的事件)。我們尋遍野外露頭，也甚少發現岩石崩坍的地層紀錄(多見土石流堆積)，唯二的例外見於：高雄壽山海崖及花東海岸的各沖積扇階地(其來源區各為石灰岩與火山岩)。這些岩石崩坍的剖面具有以下特徵:(1)主要岩粒具稜角(angular)，常呈碎裂狀(crushed)；(2)顆粒支持，富含基質，且基質成分與所圍繞的岩粒一致；(3)無層理、雜亂無章，或具有高角度傾斜層理；層理的形成是由於成分與粒度的不同，厚度從數公分至數公尺。推測台灣少有岩石崩坍的原因可能反映其岩質相對的軟弱與破碎(即發生山崩的門檻很低)，加上頻繁的暴雨與地震，小規模崩移成為常態。其次，台灣山區溪谷大多狹窄、曲折，即使發生岩石崩坍，也無移動(runout)空間，卻可能在進入河道後轉變成土石流。然而，在特定地區卻可能仍有岩石崩坍的發生，特別是臨海(或平原)、具堅硬(或塊狀)岩石的山嶺。

關鍵字

顆粒流；山崩；岩石崩坍

並列摘要

Rock avalanche is a kind of rapid (average >100 km/h) granule flow caused by crushing and pulverization of rockmaterials during catastrophic rock slide. Literature researches show that rock avalanches typically occur on steep, high-relief slopes underlain by hard rocks, and have volumes >10,000,000 m3. Rock avalanches also are characterized by long runoutdistances, which are 5 to 10 times the total fall heights. Some cases can run up the opposing valley wall. Rock avalanches generally occurred in active mountains (e.g., New Zealand) and were triggered by earthquakes or rainfall (snowmelt), but with exceptions. There were few rock avalanches in historical time in Taiwan.This could reflect: (1) intrinsic instability of hillslopes due to weak rock, frequent earthquakes/heavy rains, which resulted in landslides of high frequency/low magnitude; (2) limited runout space along deeply incised river-valley systems, which increased the likelihood of rock-slope failures to transform to debris flows.However, there are ancient rock-avalanche records, found at Shou-shan coast (SW Taiwan) and Shin-she, Chang-pin, Tu-lan along Hua-tung coast (E Taiwan), which is likely to have undergone coseismic uplift. These places, with steep slopes, underlain by hard rock, and free for materials to run, are most prone to rock avalanches in the future.

並列關鍵字

granular flow ； rock avalanche

參考文獻

劉哲欣、吳亭燁、陳聯光、林聖琪、林又青、陳樹群、周憲德 (2011)，台灣地區重大岩體滑動案例之土方量分析，中華水土保持學報，第42卷，第2期，150-159 頁。

Benn, D. I., & Owen, L. A. (2002). Himalayan glacial sedimentary environments: a framework for reconstructing and dating the former extent of glaciers in high mountains.Quaternary International, 97, 3-25.

Brideau, M. A., Yan, M., & Stead, D. (2009). The role of tectonic damage and brittle rock fracture in the development of large rock slope failures.Geomorphology, 103(1), 30-49.

Catane, S. G., Cabria, H. B., Tomarong Jr, C. P., Saturay Jr, R. M., Zarco, M. A. H., & Pioquinto, W. C. (2007). Catastrophic rockslide-debris avalanche at St. Bernard, southern Leyte, Philippines. Landslides, 4(1), 85-90.

Capart, H., Hsu, J. P., Lai, S. Y., & Hsieh, M. L. (2010). Formation and decay of a tributary‐dammed lake, Laonong River, Taiwan. Water Resources Research, 46(11).

國際替代計量

台灣大規模岩石崩坍的初探

未授權

主題瀏覽