On the genesis of granite pits on top of the Shigujian Peak of the Dayangshan Mountain in Jinyun County, Zhejiang Province |
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| Authors: | ZHU Cheng CUI Zhijiu LI Zhongxuan GAO Jie WANG Lixin WU Xianglin ZHENG Chaogui SHEN Qingfan ZHENG Xianzhang |
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| Institution: | 1. School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210093, China|
2. School of Environment, Peking University, Beijing 100871, China|
3. Zhejiang Institute of Geological Investigation, Xiaoshan 311203, Zhejiang, China|
4. Department of Geography, Chuzhou College, Chuzhou 239012, Anhui, China|
5. The People’s Government of Jinyun County, Jinyun 321400, Zhejiang, China|
6. Meteorological Bureau of Jinyun County, Jinyun 321400, Zhejiang, China |
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| Abstract: | On top of Shigujian Peak (1477 m a.s.l.) of the Dayangshan Mountain in Jinyun County, Zhejiang Province, large amounts of granite pits with diameters ranging from several dozens of centimeters to around one meter and depth from 10 cm to 45 cm are found on rock surface. These pits mainly appear on the NE and SE sides, and their drainage mouths are in the same direction. The identification results through micropolariscope and X-ray fluorescence spectrometer reveal that bedrock of pits is from middle to fine-grained moyite being apt to be weathered and modified. In Dayangshan region the annual mean temperature is 9.2℃ and annual precipitation is over 1700 mm. On the one hand, there always experiences a period of periglacial action with temperature oscillating near 0℃ for 4 months, i.e., from December to March next year. As a consequence, the freezing-thawing cycles may be remarkable to disintegrate the bedrock. On the other hand, the windward slope of Shigujian Peak meets typhoon of over force 10 on the Beaufort scale in summer, therefore, the blowing makes suspending sands or pebbles grind in swirling form. Based on field investigation and periglacial geomorphic theory, the pits on top of Shigujian Peak are attributed to freezing- thawing of periglacial action. Meanwhile, storm and strong wind accelerate the process. Observation shows that both the actions are still undergoing and variant directions of wind are the main cause for making different shapes of the pits. Because the top of Shigujian is 1500 m lower than the present snow line, some scholars considered that “glacial pothole” formed in the Quaternary is hard to work, even though in the Last Glacial Maximum (LGM). |
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| Keywords: | the Shigujian Peak in Dayangshan Mountain genesis of granite pits wind-water erosion freezing-thawing weathering |
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