| There are more than 40 volcanoes in Shishan Volcanic Group of Haikou,Hainan Province.Up to now,more than 30 lava tunnels have been found.The lava tunnel group is large in scale and in large quantity,and rich in volcanic geological relics.It is an ideal place to study the genesis of lava tunnel and explore the tourism value of lava tunnel.This paper takes the Shishan Volcanic Group as the research area,through the field investigation and special survey,studies several typical lava tunnels exposed in the main scenic area of Shishan Volcanic Group Geological Park,including Seventy-two lava tunnel,Xianren lava tunnel,Ruhua lava tunnel and Huolong lava tunnel.Going deep into lava tunnels,a large number of micro-landscapes including lava stalactites and lava rock shoots were discovered,and the reasons for their formation and structural characteristics were analyzed.Based on paleomagnetism,K-Ar method,thermoluminescence,geomorphological characteristics,and stratigraphic dissolution,we have reorganized the Cenozoic volcanic rocks exposed on the surface in the North of Hainan area,and the characteristics of the volcanic rocks have been reorganized.The summary is divided into 6 periods from morning to late,namely Penglai period(Miocene),Jinniuling period(Pliocene),Duowenling period(Early Pleistocene),Dongying period(Mid Pleistocene),Daotang period(late Pleistocene),Leihuling period(Holocene),of which Leihuling period can be subdivided into Leihuling subperiod,Changdao subperiod and Maanling subperiod.According to the comparison between the distribution range of the lava flow,the stages and characteristics of the volcanic rock of the spread form and the location,the spread form,the internal structure and the characteristics of the volcanic rock of the lava tunnel,it is believed that Ruhua Cave and Huolong Cave were formed in the late Maanling sub-period,The cave and the Seventy-two cave were formed in the Pre and mid term of the Ma’anling subperiod.Based on the analysis of dating data,we judge that several lava tunnels should be formed in the Holocene Ma’anling period of the Quaternary 8-10 ka.Based on previous research results and field investigations,the formation mechanism and influencing factors of lava tunnels are analyzed.The formation mechanism is mainly controlled by topographic and geomorphic conditions,volcanic rock types and lava flow characteristics.Through the comparison and comprehensive analysis of lava flow characteristics,tunnel morphology,structural characteristics,etc,it is concluded that the formation patterns of Xianren Cave,Ruhua Cave and Huolong Cave are consistent with the stable flow restricted topography mode,and the seventy-two caves are consistent with the steady flow unrestricted topography.The model matches.Corresponding explanations are also given for other special structural features in the tunnel.In China,it has obvious characteristic advantages compared with the lava tunnels discovered in Jingbo Lake and Wudalianchi,and compared with the Thurston lava tunnel of Kilauea volcano in Hawaii,the lava tunnel of Jeju Island in South Korea,the lava tunnel of Iceland volcano,etc.On the famous lava tunnel,Hainan Haikou Shishan volcanic group lava tunnel also has its world-class tourism value and scientific research value. |
