臺灣第四紀高山冰川後退模式

「冰川地形發育的時空範圍」和「冰期劃分及雪線高度」是目前研究臺灣高山地區第四紀冰川地形問題的焦點。因此，本研究根據前人在雪山、南湖大山、秀姑坪與嘉明湖地區的調查成果，討論冰川地形的發育順序，歸納冰川退縮模式，以判釋相關冰川地形定年成果所代表的意義，釐清冰期劃分和雪線高度判釋的問題。第一類是「偏轉後退型」，發育於偏北向之背陽坡，冰斗位於縱剖線呈連續凹、凸坡的狹長谷地最高處，推測是東、西向或偏北向的冰斗，消融過程中受局部熱力差異影響，長時間持續侵蝕冰斗後壁並往高處退縮，斗口方向漸轉爲北，修飾冰川發育最盛期的冰斗地形，形成”r”字形與反”r”字形的冰斗偏轉退縮地形。如秀姑坪與南湖大山的西向大型冰斗（較雪山一號圈谷更典型），退縮時於南向坡形成短而陡的小冰斗，北向坡則發育狹長而坡度較緩、年代較輕的小冰斗。第二類是「直接消融型」，位於偏南之向陽坡，常只發育單一冰斗，推測是受接近直射的太陽輻射影響，冰川直接、快速向高度最低的冰斗底部退縮、消融，故未發育明顯的持續偏轉侵蝕、後退地形。如嘉明湖的冰斗冰川持續退縮至冰斗底部而消失，大濁水南溪的冰川則發育典型的冰斗、U形槽谷和端冰磧，不過相關定年均較老且未發育偏轉後退地形。

關鍵字

冰河地形；冰川後退模式；第四紀

並列摘要

Recently, the study of Taiwan's Quaternary mountain glaciations has focused on ”spatial-temporal distribution of glacial landforms” and ”glacial stage divisions and equilibrium line altitudes (ELAs)”. Based on investigations into Quaternary glaciations in the Sheshan, Nanhuta Shan, Showguping and Chiaming Lake areas, this study aims to probe into the development sequence of glacial landforms, and induce glacial retreat models, which can help to interpret the meanings of glacio-chronological estimates and clarify the problems of glacial stage divisions and ELAs. Two feasible models for Quaternary glacier retreat in Taiwan's mountain areas are presented here. One model is ”retreat and turn”, in which cirques usually stand on the northern slope against the sunlight and at the highest point of the trough valleys, which appears with convex-concave long-profiles. It is interpreted that the glaciers retreat back slowly to the headwall, eroding it and creating new cirques. Because of the effect of the sunlight heating differential, the cirques of western, eastern or nearly north-trending directions will eventually change their directions to the north, and create an r-shaped or reverse r-shaped glacier retreat route. Cirques in Showguping and Nanhuta Shan areas are the instances. The other is the model of ”rapid meltdown”. Cirques in this model usually appear on the southern slope and each glacier only develops one cirque only. We interpret that the glaciers move back and the quick meltdown reaches the bottom of the cirque, under the sun's direct heat. Therefore, the features of continuing retreat and turn are absent in this scenario. Cirques in Chiaming Lake and the Datsuoswei Nan Chi in the Nanhuta Shan areas exemplify this model.