福建福安白云山河床侵蚀微地貌特征及成因浅析

On the Characteristics and Genesis of the Channel Erosion Microtopography in Baiyun Mountain of Fu'an City

福安白云山蟾溪、龙亭溪、长洋溪为花岗岩峡谷溪流,河谷中发育有数量众多、规模巨大、形态各异的石穴、凹槽,成为遐迩闻名的"地学奇观"。调查表明,白云山河床基岩及岸壁上所发育的石穴、凹槽,是更新世以来河床受不同水动力条件影响及大气降水长期侵蚀形成的各类壶穴、垂直冲蚀弧形凹槽等,是发育在晶洞碱长花岗岩中的河床侵蚀微地貌。流水及漩涡流侵蚀,砂、卵石随漩涡流磨蚀是形成壶穴的主要外动力。河床岸壁上垂直冲蚀弧形凹槽主要由大气降水侵蚀而成。白云山地区河床壶穴数量众多、类型齐全,系统地展示了不同水动力条件流水侵蚀作用、壶穴发展及基岩河床演化过程,是宝贵的地质遗迹。

The Zhang Stream, Longting Stream and Changyang Stream in Baiyun Mountain of Fu＇ an City belong to the type of the granitic canyon rivulet. There occurs a multitude of giant and difform rock hollows and stone cisterns in the river valley, which becomes a distinguished marvellous spectacle of the geoscience. The rock hollows and stone cisterns found in the riverbed bedrock and quaywall of the Daiyun Mountain are the channel erosion microtopography developed in the miarolitic alkali syenitic granite in which the all classes of potholes and stone hollows take shape since Pleistocene because of the prolonged erosion of the different hydrodynamical conditions and atmospheric precipitation. The major external power of forming the potholes is the erosion of running water and whirlpool flow and the abration of pebbles and whirlpool. The vertical and arc-shape eroded stone hollows on the quaywall of the riverbed are formed by the erosion of atmospheric precipitation. The riverbed potholes in the Baiyunshan area, with a large scalar quantity and complete types, show on the fluvial erosion of different hydrodynamical conditions, the pothole development and the evolutionary process of the bedrock riverbed, which are a precious geologic relic.