Numerical simulations of the influence of the magmatic system beneath Changbaishan volcano on surface deformation

The Changbaishan volcano (CBV) located on the border of China and North Korea, is one of the most dangerous active volcanoes on Earth. The CBV has experienced two “unrest periods” since 2000C.E. with uplift, increased ³He/⁴He ratio gas emissions and increased seismicity frequencies. During the intermediate “rest period”, subsidence occurred particularly on the eastern part of the Tianchi caldera. Whereas the magmatic system beneath the volcano is likely responsible for the surface deformation, several factors can significantly influence the surface deformation field such as the geometry, physical properties, and connection between separate magma or mush chambers. The mechanism of uplift surface at CBV is interpreted as magma recharge and the mechanism of subsidence is still under debate. Previous geophysical investigations and satellite data indicate that a shallow magma chamber might exist at 5 km depth, and the shallow magma chamber plays an important role in producing the surface deformation field. Understanding the magmatic system beneath CBV will improve the assessment of the risk of CBV.

Here, we utilized a new approach to construct a 3D thermo-mechanical model of the magmatic system beneath CBV developed on the basis of seismic velocity data collected during the “rest period”. We compare model output with InSAR data of the same period, to analyze the mechanism of the surface velocity field during the “rest period”. We test the influence of the shallow magma chamber at 5km, the connection of the magma system and physical properties of the magma chamber and surrounding host rock. Our results are consistent with there being four interconnected magma chambers beneath the CBV compared with InSAR observation. They support that a shallow magma chamber exists at 5km depth. This shallow magma chamber depth causes a convection field, and the convection field induced a downward flow at CBV area. Magma channels connecting the different magma batches play an important role in producing the uprise velocity to the surface. The higher temperature of the magma channels, the lower viscosity of the surrounding host rock and the higher density contrast with the surrounding host rock can increase the uprise velocity magnitude.