Constraining magma chamber and recharge conditions from surface uplift at Three Sisters volcanic center, Oregon Cascades

Abstract:

An episode of ongoing uplift in the Three Sisters volcanic center in the Oregon Cascades was discovered in 2000 from InSAR observations. The center of uplift is ~6 km west of the summit of South Sister, and the spatial pattern is consistent with a spheroidal source of inflation at ~5-7 km depth. The combination of InSAR and continuous GPS data since 2002 indicate a gradual onset of uplift beginning around 1996, reaching a peak of ~3-4 cm/yr between ~1998-2004, and declining since then to a current rate of ~0.5 cm/yr . This pattern of initially rapid uplift followed by an exponential decay has been observed at several other volcanoes, such as Yellowstone, Long Valley, and Laguna del Maule, but it is unclear whether the pattern of uplift is due to magma recharge that varies with time and/or viscoelastic effects. We present a model for surface deformation due to a spherical magma chamber in a viscoelastic crust subject to recharge, cooling, crystallization, and volatile exsolution. By combining this model with InSAR and GPS data we test the recharge rates and magma chamber conditions that can best explain the variation in the uplift rates at Three Sisters.