Townsend, MeredithCarey, MarkHuang, Mong-HanO'Hara, Catherine2022-07-122022-07-122022https://hdl.handle.net/1794/27395An episode of ongoing uplift in the Three Sisters volcanic center in the Oregon Cascades was discovered in 2001 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. The combination of InSAR and continuous GPS data since 2001 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 (Riddick and Schmidt, 2011) . 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 (Le Mével et al., 2015), but it is unclear whether the pattern of uplift is due to magma recharge that varies with time and/or viscoelastic effects. I present a model for surface deformation due to a spherical magma chamber in a viscoelastic crust subject to recharge, cooling, crystallization, and volatile exsolution, and combine this model with InSAR and GPS data to test the recharge rates and magma chamber conditions that can best explain the variation in the uplift rates at Three Sisters. I found a spherical magma chamber at 6 km depth, a volume of 38 , and 0.04% water content. I also tested for a pulse-like recharge as a cause of the uplift. The best fit solution was the emplacement of kg of magma into the chamber, estimated to last for ~15 years with a maximum recharge rate of ~4,000 kg/s occurring ~7 years after the beginning of the recharge event.en-USCC BY-NC-ND 4.0VolcanologyGeophysicsGeologyGeodesyThree SistersThesis/Dissertation0000-0002-8982-6217