Dynamics of episodic magma injection and migration at Yellowstone caldera: revisiting the 2004-2009 episode of caldera uplift with InSAR and GPS data

The 2004-2009 caldera uplift is the largest instrumentally recorded episode of unrestat Yellowstone caldera. We use GPS and InSAR time series spanning 2004-2015, witha focus in the aforementioned event to understand the mechanisms of unrest. InSARdata recorded∼25 and∼20 cm of uplift at the Sour Creek (SCD) and Mallard Lake(MLD) resurgent domes during 2004-2009, and∼8 cm of subsidence at the NorrisGeyser Basin (NGB) during 2004-2008. The SCD/MLD uplift was followed by sub-sidence across the caldera floor with a maximum at MLD of∼1.5-2.5 cm/yr and nodeformation at NGB. The best-fit source models for the 2004-2009 period are two hori-zontal sills at depths of∼8.7 and 10.6 km for the caldera source and NGB, respectively,with volume changes of 0.354 and -0.121 km3, and an overpressure of∼0.1 MPa. TheInSAR and GPS time series record exponentially increasing followed by exponentiallydecreasing uplift between 2004 and 2009, which is indicative of magma injection intothe caldera reservoir. However, magma extractionfrom NGB to the caldera is unable to explain the subsidence coeval with the calderauplift. Models of magma injection can also explain other episodes of caldera uplift likethat in 2014-2015. Distributed sill opening models show that magma is stored acrossthe caldera source with no clear boundary between MLD and SCD. Since the magmaoverpressure is orders of magnitude below the tensile strength of the encasing rock,historical episodes of unrest like these are very unlikely to trigger an eruption.