Study On Volcanic Stack Succession And Disaster Pre-warning In Longgang Region, Jilin Province

Longgang region is one of the most dangerous volcanic clusters in China. According to volcanic stratum and isotope age, it is divided into eight volcanic eruptive periods. They are the periods of lava mesa in Early-Pleistocene (Q₁), volcanic eruption in early middle-Pleistocene (Q₂¹), volcanic eruption in late middle-Pleistocene (Q₂³), early eruption of Jinlongdingzi in early late-Pleistocene (Q₃¹), Dawengquan eruption in late late-Pleistocene (Q₃³), Hongqilinchang eruption in Holocene(Q₄¹), late Jinlongdingzi eruption in Holocene(Q₄²) and the latest Jinlongdingzi eruption in Holocene(Q₄³). We found two pieces of carbonized wood in the basesurge deposit and pumice stratum of Dawengquan. The age of these carbonized woods are about 15965±145a.BP and 17120±145a.BP. It is the first time to get the ages of ¹⁴C before the Holocene. These ages can limit the time of the Dawengquan eruption and have a great sense in the study of volcanic period in LongGang region. Based on the periods we set up the stack succession of Quaternary volcanic eruptions. Transformation of phreatic eruption - phreatomagmatic eruption -magmatic explosive eruption - lava diffusing is the common eruptive mode in LongGang region. The explosive eruption can also be divided into four types which are phreatic eruption, phreatomagmatic eruption , magma explosive eruption and lava diffuse.According to the volcanic eruptive types, density and scale, the main Volcanic disasters in LongGang region are fall deposit, lava diffuse and basesurge etc. In the case of fall deposit, within 2km from the vent is the area of high danger, while from 2-9km is the area of middle danger, and more than 9km far away from the vent is of relative low danger. Lava flows from Jinlongdingzi are about 10 km. The range of basesurge is about 2-4km. these data will be useful for future volcanic eruption.