海岸山脈東翼河階發育因子之探討特論地層配置的影響

Environmental Factors of Fluvial Terraces in the Eastern Coastal Range, with Special Reference to the Spatial Arrangement of Rock Formations

孫稜翔(Leng-Hsiang Sun) ； 沈淑敏(Su-Min Shen)

《地理學報》 78期 (2015/09) Pp. 1-19

https://doi.org/10.6161/jgs.2015.78.01

摘要

臺灣海岸山脈河階、海階地形發育良好，過去多認為是全新世的高抬升率所致。孫稜翔、沈淑敏（2013）判釋出海岸山脈東翼二百餘條小溪流，其中半數有河階發育，並且指出流域面積及軟岩（沉積岩）出露面積都和河階總面積高相關。海岸山脈東翼環境的另一特色是地層的配置狀況：整體而言，出露在各流域上游段的主要是抗蝕力高的火成岩（都巒山層），而出露在中下游段的主要是抗蝕力較低的沉積岩（八里灣層、利吉層）。本研究擬進一步統計分析，本區兩種主要地層的空間配置，是否有利於本區這些小流域的河階發展。結果顯示，在不同流域面積尺度時，地層配置的角色不盡相同。當流域面積小於數十公頃時，各流域河階面積均小且零星，但以出露地層均為軟岩的流域，河階面積相對較大；當流域面積達數十至兩三百公頃時，屬於上游岩石強度高於下游這種地層配置的流域，其河階總面積隨著流域面積增加的趨勢，較其他地層分布類型者更為顯著。這可能是因為，在海岸山脈東翼發育的溪流，隨著流域面積擴大而逐漸包含上下游兩種抗蝕力截然不同的地層岩性時，來自上游高岩石強度、粗顆粒的底床載於中下游軟岩河道中所產生的磨蝕、覆蓋或埋積效應將更顯著，進一步促進谷床拓寬及後續河階的生成。

關鍵字

河階 ； 岩石強度 ； 地層配置 ； 海岸山脈

並列摘要

The widespread fluvial and marine terraces found on the eastern flank of the Coastal Range are believed to be mainly due to the high uplift rate. Sung and Shen (2013) identified fluvial terraces within up to half of the small basins in this area, and concluded that the size of the drainage basin and the outcropping soft rock are strongly related to the total terrace area. Based on the statistical analysis, this study further discusses the role of the spatial arrangement of rock formation on the very well-developed terraces in the eastern Coastal Range. Analytical results show that this environmental factor is only effective when the drainage basin area is up to tens to hundreds of hectares. In the study area, along with the development of the drainage basin, it is very likely to incorporate volcanic-origin formation in the upper stream and supply the more resistant and coarser bedload, probably in the form of debris flows, when a drainage basin is older and large enough. The downstream movement of these resistant and coarse materials should increase the width of the channels, leading to the development of the fluvial terraces.

並列關鍵字

fluvial terrace ； rock strength ； rock type arrangement ； Coastal Range

參考文獻

孫稜翔、沈淑敏(2013)。臺灣海岸山脈東翼小流域之河階分布與類型的探討。中國地理學會會刊。50，37-56。

經濟部中央地質調查所 [Central Geological Survey, MOEA] 2010。臺灣活動斷層分布圖 [Tai wan huo dong duan ceng fen bu tu; Active Fault Map of Taiwan]。http://fault.moeacgs.gov.tw/TaiwanFaults/PageContent.aspx?type=C&id=5 (擷取日期：2011.08.11)

Boison, P. J.,Patton, P. C.(1985).Sediment storage and terrace formation in Coyote Gulch basin, South-central Utah.Geology.13(1),31-4.

Bull, W. B.(1979).Threshold of critical power in streams.Geological Society of America Bulletin.90(5),453-64.

Bull, W. B.(1991).Geomorphic responses to climatic change.New York:Oxford University Press.