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Gravity Observation During 2021-2023 and Magma Activity in Changbaishan-Tianchi Volcano,China

Yaxuan Hu,  Guoqing Zhang, Guohua Xiong,Bing Feng

Abstract

The Changbaishan-Tianchi volcano(CBV) is one of the most active and hazardous volcanoes,which has experienced one of the largest Holocene eruptions around the year 946 CE. A series of volcanic unrest events in 2002-2005. Another low-level unrest occurred from December 2020 to June 2021. The Second Monitoring and Application Center, CEA selected and measured 29 gravity stations in the north and northwest flanks. The surveys were conducted with 2 Burris gravimeters in July 2021, August 2022, and August 2023. The results show that the gravity changes during 2021-2022 is -161.4uGal to 23.4uGal. The most of them are negative and the values are greater than 50uGal. The variations during 2022-2023 is -37.8uGal to 135.7uGal. The most of them are positive. The majority are less than 50uGal. The values of the several stations located in the northern flank are greater than 50uGal. The stations with more than 100uGal are generally located within 12km of the volcano center. The station with the largest gravity variations is located on the west flank, indicating a fault passing nearby. The variations during 2021-2023 are from -90.6uGal to 56.0uGal, mainly with negative values. According to the observed results of earthquake and deformation, the CBV activity is weak. Based on the magma structures in the crust and mantle, we speculate that the magma activity mainly occurred between the interconnected magma conduits,sills and faults. The conjoint analysis of gravity and deformation results also indicates that magma intrude/drain in existing void/space of chambers or faults.