- 期刊
- OpenAccess
The Topographic Landscapes of Volcanic Necks in the Coastal Range and Lutao, Eastern Taiwan
臺灣東部海岸山脈與綠島火山頸地質地形景觀
摘要
Hot magma was transmitted through a conduit system or fractures to the ground surface in a volcanic eruption. These volcanic conduits are mostly formed through the consolidation of the magma. Generally speaking, there are quite resistant to weathering processes, and can be preserved through long periods of time. In the Coastal Range and the offshore islet Lutao of Taiwan well-developed volcanic necks, typified by the occurrence of columnar joints, are found in Tafengfeng, Tuweihsi (Chungan) in the Coastal Range and Lantzuhu, Yotzuhu, Haishenping and Kungkuantsun in Lutao. The columnar joints found in Lutao andesites or in the basalts of the Coastal Range are either horizontal or clino to pleated-skirt formed manifesting geological structure specific to volcanic conduits present in the volcanic necks. The shapes of the columnar jointing in the volcanic necks depend on the diameter of the passage conduit, the thickness of the emitted lava, the composition of the magma, and the topographic features of the strata underlying the site of eruption. The occurrence of volcanic necks in the coastal Range and in Lutao is highly diversified and these volcanic necks are worthy of permanent preservation simply for tourism and educational purposes. We report 3 typical examples of volcanic conduits occurred in the Coastal Range and Lutao. (1) Haishenping, Lutao: a typical volcanic crater with clino columnar jointing. (2) Tuweihsi, Coastal Range: a volcanic dike with horizontal to clino-columnar jointing in basaltic the cliff wall of lava breccias. The pillow lavas and hyaloclastite flows indicate possible submarine eruption. Both of (1) and (2) may be formed in the trunk of the volcanic neck, Tuweihsi's position maybe lower than that of Haisenping's. (3) Tafonfon, the Coastal Range: the exposed volcanic neck in basaltic rock at Tafonfon is small, but the pleated-skirt configuration is perfect with a well exposed volcanic conduit in the upper portion looking like a corolla or crown. We suggest that it may be used as the Logo for the Coastal Range Volcanic Scenic Area. This outcrop illustrates well the mechanism to form columnar jointing in a volcanic conduit.
並列摘要
臺灣東部火山區（東部海岸山脈、蘭嶼與綠島）爲呂宋火山島弧北延的部分，由安山岩質島弧岩漿凝結而成的中新世至上新世火山岩與含火山岩質的海相沈積岩所組成。火山爆發時岩漿經由裂隙孔道傳輸至地表。這些火山通道常由岩漿凝固而成，質堅硬抗風化，故可留存甚久，海岸山脈大峯峯、都威及綠島海參坪、油子湖、蘭子湖、溫泉村與公館村等地有典型火山頸構造之柱狀節理型態之地形地貌。此等有塔狀柱狀節理或平躺式近乎水平之柱狀節理，爲典型火山通道所形成的火山頸之地質構造特徵；火山頸構造之柱狀節理型態取決於岩漿通道之口徑、溢出熔岩流厚度、岩漿組成成分與原始地貌等因素。東部火山區火山頸五花八門，爲鄉土科學教育之極佳素材，深具地質科學教育意義並值得長期保存。東海岸大峯峯百褶裙式火山頸構造雖小但十分完整，可媲美美國懷俄明州魔鬼塔。建議內政部、地方政府、東海岸風景區管理處等主管單位加緊地景保育工作輔導保護成為一觀光景點，籌劃為東海岸火山地景徽章及旅遊地標。未來希望能結合東部特殊火山地質地形景觀、秀姑巒溪風光、石梯坪壺穴、小野柳倒轉濁流岩沉積構造與大坡花東縱谷活動斷層，成立臺灣東部地質國家公園。更進一步搭配蘭嶼等南島原住民文化與卑南文化遺址爭取列入聯合國科教文組織世界文化與自然遺產名錄。