Evidence for Episodic Magma Injection at Cordón Caulle Volcano (Southern Andes, Chile) During 2004-2019: New Insights from InSAR Time Series and Finite Element Models

Despite the strong geological evidence for episodic injection of magma over thousands of years, there are very few case studies where this process can be observed over short time scales (1-10 years). The 9 month long VEI 4 rhyolitic eruption of Cordón Caulle volcano in 2011-2012 was immediately followed by ∼1 m of uplift and constitutes a prime example of the episodic nature of magma injection over very short time scales.

In this study, we use InSAR time series to characterize a sequence of three transient pulses of ground uplift during March 2012 - May 2019. InSAR time series from COSMO-SkyMED, RADARSAT-2, Sentinel-1 and ALOS-2 detected ∼77 cm of exponential uplift during March 2012 - May 2015, ∼12 cm during July 2016 - February 2017 and ∼12 cm during May 2017 - May 2019. The three uplift episodes have very similar spatial wavelength and can be modeled with the same inflating sill at a depth of 6 km with a volume change of 0.17 km³, but their time evolution is different, from linear to exponential. Numerical models of a pressurized reservoir surrounded by a viscoelastic shell do not have a better fit than a magma injection model to the exponential signal recorded during 2012-2015, indicating that magma injection is the most likely mechanism to explain this uplift signal and that viscoelastic effects are negligible. The episodic time series of ground deformation can be explained by a coupled model of reservoir pressurization with magma flow in a conduit and variations of ∼5 MPa in the pressure of a deep magma source are enough to explain the transient signals observed in the time series. These magma injection pulses provide the heat to remobilize the crystal mush beneath the volcano on timescales of a few months, but the end of the uplift is not predicted by existing models. None of these uplift pulses were related to abnormal seismicity, and we speculate that they are mostly aseismic because they caused stresses of lower magnitude than the co-eruptive stresses. The meter scale displacement observed at Cordón Caulle between 2004 and 2019 suggests that the volcano undergoes episodic cycles of inflation like those observed in silicic calderas.