Characteristics And Chronology Of Mountain Torrent And Mudflow Events In Jianzha-Xunhua Basin In The Upper Reaches Of The Yellow River

In the context of global warming,extreme climate change often leads to frequent extreme disasters,which have attracted the attention and research of many scholars due to their sudden and harmful characteristics.The Gansu province and Qinghai province in the upper reaches of the Yellow River is located in the transition zone between the Tibet Plateau and the Loess Plateau,and is the transition zone between the eastern monsoon region,the northwestern arid region and the Tibet Plateau.This paper studies the characteristics of mudflows and dammed lake in the upper reaches of the Yellow River in the Jianza basin and the Xunhua basin,and discusses the relationship between climate change and disaster events,which is of great significance for further understanding the response law of the regional monsoon climate change.On the basis of field survey,this paper select the CGT profile and DBC profile in Jianzha basin,TJC-R profile,DTC profile,TJC-R profile and XTC-W-R profile in Xunhua basin as the research profiles.In the laboratory,the magnetic susceptibility,particle size and chemical elements of the samples were analyzed,and the age data of the section strata were obtained by using the OSL dating technology.The field data and experimental data were comprehensively analyzed and discussed,and the following main conclusions were obtained:(1)Since the late pleistocene,there have been many mudflows in the upper reaches of the Yellow River in the Jianzha basin and the Xunhua basin,but the mudflows in the two basins are not happened in the same time.By combining the OSL dating data with the profiles,it was determined that the mudflow event in the Jianza basin started at 27 ka and ended at 4.5 ka.The mudflow events in Xunhua basin occurred between 6.3 to 4.5 ka,and the mudflow activity was during the holocene warm period.(2)The typomorphic characteristics of mountain torrents are studied.The mountain flood mud flow sediments have the same basic characteristics as tertiary red clay and are the products of tertiary red clay near-source transportation in the northern red layer hilly area of Jianzha Basin and Xunhua Basin.The sediment of mountain torrents is turbidized red-brown and turbidized orange,which is in a mass structure,mainly composed of clay and fine silt.It is fine and sticky,dense and hard when dry,with a high degree of cementation.In case of rain,secondary liquefaction flows easily occur,resulting in ground collapse and collapse,and dense dark holes,forming a large and poor land.(3)The mechanism of mountain torrents.The mudflow events in Jianzha Basin and Xunhua basin may be related to the regional climate change.In the abrupt or transitional phase of the global climate,the monsoon is unstable and extreme rainfall occurs,resulting in an unusually warm and humid climate.Spring snow and permafrost melt accelerated the tertiary red clay layer liquefaction,caused a large number of loose material flows along the slope,summer storm will form quickly flash floods,heavy rains and flash floods carry plenty of tertiary red clay mixed with gravel,the sand is loose sediment together to form mud flow valleys,position along the channel in the lower Yellow River terrace accumulation,formed in the piedmont pluvial fan,the formation of large-scale mountain torrent of mud flow event,due to the effect of incised and lateral erosion of the Yellow River,the mountain torrent of mud flow fan front become steep platform.Both of these events occurred at the abrupt or transitional stage of global climate.