【BBC美丽中国】锦绣华南 16
http://t1.g.hjfile.cn/listen/201205/20120503085106611940.mp3The cave river's course is channelled by the beds of limestone. A weakness in the rock can allow the river to increase its gradient and flow-rate, providing a real challenge for the cave explorers. The downward rush is halted when the water table is reached. Here the slow-flowing river carves tunnels with a more rounded profile.石灰岩河床将洞穴的河道分割成千沟万壑。石灰岩薄弱处被河水冲刷差距的陡坡处水量激增，为洞穴探险带来相当的挑战。水流到达地下水位后便停止下流。这里缓缓流动的河流切割出一条圆形隧道。
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