摘要
地貌学和沉积学证据表明,山东蒙山地质灾害遗迹分布广泛,通常以砾石堆积堤及河谷堆积阶地的形式保留在现代河床之上。其中,峨峪口砾石堤在蒙山具有典型性和代表性。探明峨峪口砾石堤的成因类型和发生历史,对中国东部(105°E以东)第四纪环境变化、气候地貌过程具有重要的科学研究和科普教育价值。2020年10月和2021年2月,笔者团队两次赴蒙山考察,野外工作主要是砾石组构测量,寻找砾石埋压的断木等有机14C测年材料,以及历史洪水调查、地方文献资料收集等。研究结果表明:(1)峨峪口砾石堤不连续、不对称分布于凹岸(弯道),砾石组构、石线构造、叠置空洞构造和砾石群构造等成因专属性特征,以及砾石表面擦痕的明度,揭示其可能为数百年前所形成的一次性历史泥石流堆积垄岗,且被后期山洪改造过;(2)年代学和遥感资料显示,1991年夏季峨峪口等地曾暴发大型山洪泥石流,这一结果与蒙山泥石流的历史记载具有一致性,从证据链上进一步增强了峨峪口砾石堤泥石流成因的确然性;(3)峨峪口砾石堤可能是低频、短历时快速地貌灾害过程,属于暴雨直接类特大型历史泥石流堆积,其物源主要是峨峪口上游谷地的重力崩积物;(4)峨峪口砾石堤缺少冰缘现象的地貌组合证据,不存在全新世早期冰缘地貌的年代学依据,当地不具备发育全新世早期“石河”和“冻土环境”的气候条件;(5)蒙山地区分布有丰富的碎屑物质和比较陡的沟谷纵剖面,暴雨频繁、水分充足,具有泥石流暴发的形成条件,周边居民点、公路和登山步道应加强山洪泥石流地质灾害防治工作。
Geomorphology and sedimentology evidences show that the relics of geological disasters in Shandong Mengshan Mountains are prevalent.They are usually distributed along the channels in the form of debris levees and accumulation terraces.Among them,Eyukou boulder levee is one of the most typical and representative le⁃vees.To gain a deeper understanding of the Quaternary environmental change process in Eastern China(east of 105°E)and to improve geo-science education better,it is of critical significance to clarify the formation history and genetic type of the Eyukou boulder levee.During the two field trips to Mengshan Mountains in October 2020 and February 2021,a series of data was collected,several sets of gravel fabric measurement data and four AMS14C dating samples of dead tree trunks which was found in the crevices of boulders were reported here.The results show that:(1)The Eyukou Levee distributed on the cut bank at downstream Eyu Valley discontinuously and asymmetrically.Its depositional features including gravel fabric,roundness,stone-trace structure,cavern⁃ous structure of stacked boulders and structure of boulders group along with the brightness of scratches on the sur⁃face of boulders can definitely attribute Eyukou Levee to a debris flow genesis occurred several hundred years ago and was transformed by the later mountain floods.(2)According to the AMS 14C dating results and remote sensing data,a catastrophic flood was occurred in Eyukou Levee about 30 years ago,which is consistent with a recorded geological disaster happened in Summer 1991.It further enhances the possibility that the Eyukou Levee was formed by catastrophic debris flows.(3)The historical debris flows may be a rapid geomorphological disas⁃ter process which is induced by torrential rain.The materials mainly come from the mass movement process,which occurred in the upper of Eyukou.This result is consistent with the fresh scratches on the surface of boul⁃ders and supported by the historical records of modern debris flows.(4)The formation of Eyukou Levee is irrel⁃evant to frost-action,additionally the levee is not a block stream.The reported“block stream”in Mengshan Mountains is unreliable due to the lack of reliable evidence of combined geomorphological features,and chrono⁃logical or sedimentological evidence.The local climate does not have the conditions for the formation of block stream or permafrost environment in the Early Holocene.(5)The Mengshan region is rich in detrital materials with steep longitudinal profiles.During torrential rains,debris flows have a high possibility to occur.There⁃fore,surrounding residential areas,roads and hiking trails should strengthen the prevention of geological disas⁃ter,especially debris flows.
作者
王乃昂
安东
孙德浩
刘啸
陆晨遨
孟楠
杨丹
王媛媛
席振鑫
WANG Nai’ang;Antuk;SUN Dehao;LIU Xiao;LU Chen’ao;MENG Nan;YANG Dan;WANG Yuanyuan;XI Zhenxin(Center for Glacier and Desert Research,College of Earth and Environmental Sciences,Lanzhou University,Lanzhou 730000,China)
出处
《冰川冻土》
CSCD
北大核心
2021年第4期1228-1242,共15页
Journal of Glaciology and Geocryology
基金
国家自然科学基金项目(41871021)资助。
关键词
砾石堆积堤
成因类型
定居期
洪水事件
历史泥石流
蒙山
峨峪口
boulder levee
genetic type
ecesis time
flood events
historical debris flows
Mengshan Moun⁃tains
Eyukou
