The 2011-2012 rhyolitic eruption of Cordon Caulle (Southern Andes, Chile): a complete silicic eruptive cycle observed by InSAR, petrology and numerical models

The Puyehue-Cordón Caulle (PCC) volcanic complex in Southern Chile has erupted a large volume of similar composition crystal poor rhyolite/rhyodacite (>2 km3) in a series of three major explosive-extrusive eruptions (1921-22, 1960, 2011-12) in the last 100 years. The 9-month 2011-12 eruption is the only highly silicic event with detailed geophysical observations before, during and after. InSAR data show several episodes of ground uplift in the years before the eruption, but also a temporal gap between the uplift and the time of eruption. The uplift was likely caused by pressurization of the magmatic system between 4-9 km depth and might related to magmatic intrusions with a mafic component that helped to remobilize either volatiles or melt in the crystal mush underlying PCC. The 2011 eruption began explosively on 4 June and after two weeks evolved into an hybrid explosive - effusive eruption. A large volume shallow laccolith or cryptodome was intruded near the eruptive vent during the first 2.5 months of the eruption. InSAR data spanning the first 3 days of the eruption show clear evidence for two distinct sources of deflation 18 km from each other and up to 10 km from the eruptive vent – suggesting hydraulic connectivity of a large magma mush zone. An additional co-eruptive source of deflation is observed during the ~8.5 months of the extrusive phase of the eruption. The eruption was immediately followed by three transient pulses of ~1 m of post-eruptive uplift ongoing as of May 2018, interpreted as being produced by magma recharge, although in a different area than any of the pre and co-eruptive ground deformation sources, and with very different amplitudes and time evolution. Despite the large magnitude of the post-eruptive inflation, these pulses did not led to an eruption because the source pressurization was one order of magnitude below the tensile strength of the rock.