甘肃文县天池地质成因及环境效应分析
摘要：碳酸盐岩地区永久型堰塞湖地质成因鲜有研究，在少雨区域这类堰塞湖的环境效应也缺乏系统分析，其地质成因机制具有理论与现实意义，但目前其成因机理并不十分清楚。通过野外详细调查和C14测年，对文县天池的形成原因和环境效应进行较深入研究，得出如下结论：天池是（6 450±73）年前，强震触发下天池沟右、左岸同时发生相向高位高速远程滑坡堵塞天池沟形成的，滑坡堆积体的“反粒序堆积结构特征”使堰塞坝物质粒径结构具有“下部小上部大”和“中间小两边大”的特征，致使天池能够长期稳定存在，成为天然的水库，形成独特的小气候，进而塑造丰富、多样和异质的景观类型。天池的长期存在，加快了堰塞坝下游的侵蚀下切速率，使湖区内的下切受到控制，对湖区上游的沟谷下切速率影响较小。地貌上形成鲜明的对比。
关键词：文县天池；滑坡；成因分析；环境效应
中图分类号：P642.5；P694文献标志码：A文章编号：16721683（2018）03009408
Analysis of the formation mechanism and environmental effects of
Tianchi Lake in Wenxian，Gansu Province
LI Jia，WANG Yunsheng，CHEN Ming，LIANG Ruifeng
（State Key Laboratory of Geohazard Prevention and Geoenvironment Protection，
Chengdu University of Technology，Chengdu 610059，China）
Abstract：The geological formation mechanism of permanent barrier lakes in carbonate areas is rarely studied.Systematic analysis is also lacking on the environmental effects of such barrier lakes in arid areas.Their geological formation mechanism has theoretical and practical significance，but the mechanism is not very clear yet.Using detailed field surveys and C14 dating method，we conducted an indepth study on the formation mechanism and environmental effects of Tianchi Barrier Lake in Wenxian County.The results showed that Tianchi Lake was formed when a strong earthquake struck the Tianchi region （6450 ± 73） years ago，causing two high landslides in the right bank and left bank of Tiachi valley at the same time，blocking the Tianchi valley.The "inverse grading structure feature" of the landslide deposit causes the particle size structure of the landslide dam material to show the features of "smaller below and larger above" and "smaller in the middle and larger on the sides".This is the reason why the Tianchi Barrier Lake can stand long，becoming a natural reservoir，forming a unique microclimate，and generating a very rich，varied，and heterogeneous landscape type.The long existence of Tianchi Barrier Lake accelerated the erosion rate down the landslide dam，controlled the undercutting in the lake area，and had little effect on the undercut rate of the valley in the upper reaches of the lake，forming clearly contrasting landforms.
Key words：Tianchi Barrier Lake；landslide；cause analysis；environmental effects
強震作用下高位斜坡失稳（滑坡）形成堰塞湖在复杂山区是十分常见的[14]，有一些堰塞坝可以稳定存在数百年、数千年，甚至数万年[5]，对周围环境产生深刻的环境效应。许多学者对滑坡的形成机制及地质灾害效应[610]和滑坡堰塞湖的环境效应[1113]进行研究，提出了典型的斜坡（滑坡）变形破坏的地质力学模式，分析了堰塞坝存续期间对所在区域的地貌及地质环境演化的影响。
文县天池，又名洋汤天池，位于甘肃省陇南市文县天池乡境内（图 1（a）），为我国四大天池之一。由于研究区强震活动较为频繁，致使深切峡谷区高位山体滑坡[14]，天池沟谷被堵截，于是在海拔2 400余m的天魏山上，便汇成了状如葫芦的一湖碧水，古称“天魏湫”。文县旧志载，“文县天池，碧波万顷，如揩新绿，微风鼓浪，势若海潮，岩树倒影，隐如龙跃”。本文对文县天池堰塞坝两岸斜坡变形破坏模式分析，旨在阐明文县天池形成以及长期稳定存在的原因，并对其在水文、地貌和景观方面的环境效应进行初步探讨。
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