利用1979~2009年間航空正射影像及數值地形模型探討草嶺山崩區域之地表變遷
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Date
2014-12-01
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國立臺灣大學理學院地理環境資源學系
Abstract
草嶺山崩在歷史上曾有5次大規模的山崩紀錄，其最早則在1862年因地震引起的山崩，近一次則為1999年集集地震所引發的大規模山崩。集集地震後區域內劇烈且快速的地表作用，提供探究山崩機制、活動構造與地表變遷之相互作用的最佳實例。本研究利用高解析航空正射影像，總共製做及校正自1979至2009年十期高解析度數值地形模型，配合地形斷面、河流剖面圖，針對草嶺地區震後之崩塌區、堆積區以及河道，探討地表變遷。研究中又將時間分為長時間尺度（1979-1989、1989-1999及1999-2009年）共三個十年及短時間尺度（1999-2009年集集地震後）。集集地震引發之草嶺山崩為順向坡滑落；河道流向剖面顯示，清水溪河床在上游呈現下切侵蝕而下游則呈現堆積，因而河川坡度在震後十年間逐年趨緩。山崩區域內崩塌和堆積量體的變化則與年度重大颱風或強降雨事件有關。於航照上觀察地表變遷，堆積區倒交山及春秋斷崖崖坡呈現快速侵蝕造成的崖坡後退，我們藉由選取四個具有最大變化率的代表斷面來計算崖坡後退速率，在2003-2009年間，堆積區的倒交山崖坡平均後退速率為46.1m/year，為坡腳侵蝕造成的崖坡崩塌後退；而春秋斷崖則為33.8m/year，是崖坡前緣的層狀崩塌。
Five gigantic landslides have been recorded in the Tsaoling area since 1862 and the latest landslide was triggered by the 1999 Chi-Chi earthquake. After the earthquake, the changes of the land surface were fast and the rapid surface changes benefit the study of landslide mechanisms, tectonic activities and landform evolution. By using high-resolution aerial orthophotos, ten (10) high-resolution digital terrain models (DTM) from 1979 to 2009 were generated and calibrated. The surface changes in the landslide scar, deposit areas, the river channel were presented. These changes were inspected by three ten-year long-term comparisons (1979-1989, 1989-9999, 1999-2009) and followed by short-term evaluations after Chi-Chi earthquake (1999-2009). The earthquake triggered landslide was a dip-slope failure. The evolution of the river bed profile indicated that incision took place in the upstream section of the Chinshui river and deposition took place in the downstream section. This led to that the river slope became milder in the ten years after the earthquake. In the landslide scar area, the volume of slid mass varied with the extreme climate events, such as typhoons and rainfall in the correspondent period. From landscape observations in aerial photos, the Taochiashan deposit and Chunqiu cliff demonstrated rapid recession from the river. We selected four observation sections at the sites with fastest recession and calculated their recession rates. Between 2003 and 2009, the average recession rate of the Taochiashan slope was 46.1m/year and that of the Chunqiu cliff was 33.8 m/year. The recession mechanisms were the toe erosion and the peeling failure of the cliff front, respectively.
Five gigantic landslides have been recorded in the Tsaoling area since 1862 and the latest landslide was triggered by the 1999 Chi-Chi earthquake. After the earthquake, the changes of the land surface were fast and the rapid surface changes benefit the study of landslide mechanisms, tectonic activities and landform evolution. By using high-resolution aerial orthophotos, ten (10) high-resolution digital terrain models (DTM) from 1979 to 2009 were generated and calibrated. The surface changes in the landslide scar, deposit areas, the river channel were presented. These changes were inspected by three ten-year long-term comparisons (1979-1989, 1989-9999, 1999-2009) and followed by short-term evaluations after Chi-Chi earthquake (1999-2009). The earthquake triggered landslide was a dip-slope failure. The evolution of the river bed profile indicated that incision took place in the upstream section of the Chinshui river and deposition took place in the downstream section. This led to that the river slope became milder in the ten years after the earthquake. In the landslide scar area, the volume of slid mass varied with the extreme climate events, such as typhoons and rainfall in the correspondent period. From landscape observations in aerial photos, the Taochiashan deposit and Chunqiu cliff demonstrated rapid recession from the river. We selected four observation sections at the sites with fastest recession and calculated their recession rates. Between 2003 and 2009, the average recession rate of the Taochiashan slope was 46.1m/year and that of the Chunqiu cliff was 33.8 m/year. The recession mechanisms were the toe erosion and the peeling failure of the cliff front, respectively.