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The Spatial and Temporal Distribution of Freeze-thaw Processes in Mt. Nanhuta (Nanhuta Shan), Central Taiwan
Mt. Nanhuta Nanhuta Shanc;Alpine landforms;Freeze-thaw processes;Ground temperature;Periglacial landforms
|Issue Date: ||2015-04-29T04:08:38Z
|Abstract: ||凍融是一種常見於臺灣高山冰緣環境的作用力，而影響其作用的因子可分爲地勢及天氣（包括氣溫、太陽輻射與地表覆蓋等因子）兩方面，在時間與空間上產生不同型態的作用與地形。本研究採德國柏林自由大學於南湖大山設立氣象測站所蒐集的資料，推估凍融作用的強度、頻率與時間分布，利用氣溫與地溫設計經驗統計式模式，推估凍融作用之空間分布。另外進行野外調查瞭解南湖大山冰緣地形的型態與其分布，藉此瞭解臺灣高山凍融作用的時空特性。由測站之地溫資料顯示出，於地表以下2公分處的凍融作用較其他深度頻繁，其中2 公分深平均凍融次數55次／年；10公分深平均凍融次數8.75次／年；20公分深平均凍融次數1.25次／年，一年之中凍融作用在春季與秋季最頻繁，而平均氣溫最低的冬季因地表長期覆雪（66-71天），地溫變化較小所以凍融作用較少發生。根據經驗統計模式推估的地表溫度與觀測值呈現高度相關(R^2=0.7875)，推估的凍融作用於海拔高度分布，凍融次數從海拔3,000公尺的15次／年至3,742公尺的78次／年，顯示海拔高度的變化影響凍融次數，且兩者的關係呈現對數曲線變化。經由野外調查則在南湖大山區域發現岩屑坡、岩屑堆與草緣小階等冰緣地形，推測南湖大山冰緣環境約出現在海拔3,300公尺以上的亞高山針葉森林帶與高山苔原帶。|
Freeze-thaw is one of the common geomorphologic processes in Taiwan's alpine and periglacial environment. It is affected by topographic and weather factors, such as air temperature, solar radiation and ground vegetation cover, which generate different kinds of processes to create distinct landforms. In this study, we use air and ground temperature data from Mt. Nanhuta measured by researchers from the Geography Department of Free University, Berlin to estimate the intensity, frequency and temporal characteristics of freeze-thaw processes. Furthermore, an empirical-statistical model was used to simulate the spatial characteristics of the magnitude, frequency and periods of freeze-thaw processes in the area. Finally, we also conducted an investigation of periglacial landforms to unveil their relationship with freeze-thaw processes. The results show that the average annual freeze-thaw cycles at 2 cm, 10 cm and 20 cm depths are 55, 8.75 and 1.25 times per year respectively, with the highest frequency occurring at a depth of 2 cm. On a temporal scale, freeze-thaw cycles occur most frequently in spring and autumn, whereas prolonged snow cover (66-71 days) during winter results in lower ground temperature fluctuations, and hence less frequent freeze-thaw cycles. Ground temperatures estimates based on empirical-statistical models show a high correlation with observations (R^2=0.7875). Spatial distribution of freeze-thaw cycles shows that the relationship between elevation and freeze-thaw cycle follows logarithmic regression, rising from 15 cycles per year at 3,000m to 78 cycles per year at 3,742m. Field investigation shows that different kinds of periglacial landforms can be identified in bare land as well as high mountain bamboo bushes above the timberline, including turf-banked lobes terraces, talus accumulation and talus slopes. This discovery provides evidence for freeze-thaw processes in the high mountain areas of Taiwan. The limit line of the periglacial environment is identified at 3,300m by distribution of freeze-thaw process and periglacial landforms.
|Relation: ||地理學報, 59: 1-18|
|Appears in Collections:||[地理學系] 期刊論文|
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