臺灣造山帶崩積物不同時間尺度下之保存與搬運

Preservation and transportation of landslide deposits under multiple timescales in the Taiwan orogenic belt

陳展懋(Chan-Mao Chen)

指導教授 ： 徐澔德

國立臺灣大學/理學院/地質科學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201902456

摘要

對於活躍造山帶的地形、構造、沉積物系統與碳循環,崩積物的搬運與保存趨勢具有一定的重要性,然而現今對其仍未了解透徹,故本研究藉由觀察臺灣崩積物在十年與千年時間尺度下的搬運與保存,來增進此方面之認識。
在十年時間尺度方面,本研究利用遙測影像判識、野外調查與數值地形比對,研究 1999 年集集地震所引發的兩處大型崩塌地—九份二山與草嶺之崩積物演化,並發現現今九份二山崩積物仍約保存 95%,但草嶺崩積物僅約保存 42%,此現象說明崩積物的保存與河流水力強弱緊密相關。
在千年時間尺度方面,本研究在荖濃溪流域中調查大型土石流扇階系統的內部堆積物形貌,重建其堆積前後的地形,計算出這些崩積物的搬運與保存,並發現經過數千年的地表作用後,扇階普遍保存不及原有的 30%,其中年代小於 4000年的扇階保存較好(15%-30%),年代大於 4000 年的扇階保存較差(2.5%-15%)。
綜合本研究與前人研究結果,崩積物的保存狀況似乎有時空上的變化性。總體而言,遠離河流系統的崩積物可於山脈內保存一段相對長的時間,而崩入河流系統的崩積物則被快速搬離山脈。未來若有更多此方面之研究,將可為其他活躍造山帶相關研究提供一定的制約。

關鍵字

崩積物 ； 沉積物搬運 ； 集集地震 ； 荖濃溪 ； 臺灣

並列摘要

The transportation and preservation of landslide deposits are important for topography, tectonics, sediment routing system, and the carbon cycle of active orogenic belts. However, the evolution of landslide deposits has not been fully understood. To address out this issue, we study decadal and millennial timescale transportation and preservation of landslide deposits in the Taiwan orogenic belt.
In decadal timescale, we study the Jiufengershan landslide and the Tsaoling landslide, which are the two largest landslides triggered by the 1999 Chi-Chi earthquake, with analyzation of satellite images and digital elevation models, and field investigation. We found that the Jiufengershan’s landslide deposits have preserved about 95% of the total volume but the Tsaoling’s landslide deposits have preserved about 42% of the total volume in 2019. These observations demonstrate a close relationship between the storage of landslide deposits and fluvial processes.
In millennial timescale, we reconstructed the topography before and after the deposition of the large debris-flow fan terrace systems in the Laonong River catchment to quantify their preservation and transportation with field data. We found that in general less than 30% of the total volume have been preserved since they deposited. Among them, the fan systems younger than 4000 years are better preserved (15%-30%) and the fan systems older than 4000 years are worse preserved (2.5%-15%).
Based on the results from different timescales and previous studies, it seems that the evolution of Taiwan landslide deposits varies in time and space. The landslide deposits far from the river system can be preserved for a relatively long time period, whereas the landslide deposits within the river system may be rapidly transported. Therefore, more results in the future provide more constraints for other active orogenic belts in the world.

並列關鍵字

landslide deposits ； sediment transportation ； Chi-Chi earthquake ； Laonong River ； Taiwan

參考文獻

English

Avouac, J. P. (2015). Mountain Building: From earthquakes to geological deformation. Treatise on Geophysics, 6, 381–432.

Benda, L. (1990). The influence of debris flows on channels and valley floors in the Oregon Coast Range, USA. Earth Surface Processes and Landforms, 15, 457–466.

Bishop, M. P., Shroder, J. F., Jr, & Colby, J. D. (2003). Remote sensing and geomorphometry for studying relief production in high mountains. Geomorphology, 55, 345–361.

Burbank, D. W., Leland, J., Fielding, E., Anderson, R. S., Brozovic, N., Reid, M. R., & Duncan, C. (1996). Bedrock incision, rock uplift and threshold hillslopes in the northwestern Himalayas. Nature, 379, 505–510.