Constraining volcanic inflation at Three Sisters Volcanic Field in Oregon, USA, through microgravity and deformation modeling

Abstract

[1] Microgravity data were collected between 2002 and 2009 at the Three Sisters Volcanic Complex, Oregon, to investigate the causes of an ongoing deformation event west of South Sister volcano. Three different conceptual models have been proposed as the causal mechanism for the deformation event:(1) hydraulic uplift due to continual injection of magma at depth, (2) pressurization of hydrothermal systems and (3) viscoelastic response to an initial pressurization at depth. The gravitational effect of continual magma injection was modeled to be 20 to 33 mGal at the center of the deformation field with volumes based on previous deformation studies. The gravity time series, however, did not detect a mass increase suggesting that a viscoelactic response of the crust is the most likely cause for the deformation from 2002 to 2009. The crust, deeper than 3 km, in the Three Sisters region was modeled as a Maxwell viscoelastic material and the results suggest a dynamic viscosity between 10 18 to 5 Â 10 19 Pa s. This low crustal viscosity suggests that magma emplacement or stall depth is controlled by density and not the brittle ductile transition zone. Furthermore, these crustal properties and the observed geochemical composition gaps at Three Sisters can be best explained by different melt sources and limited magma mixing rather than fractional crystallization. More generally, low intrusion rates, low crustal viscosity, and multiple melt sources could also explain the whole rock compositional gaps observed at other arc volcanoes.

The origin of Mauna Loa's Nīnole Hills: Evidence of rift zone reorganization

“…The largest daily closures occurred when surveying over jungle paths, dirt roads, and large changes in elevation where the gravimeter was subject to vibration and opportunities to repeat base station measurements were limited. The travel‐induced data tares are the most probable cause for the large closure errors observed [e.g., Crider et al , ; Zurek et al , ]. Data reduction included terrain corrections, bathymetry, free air correction, removal of solid Earth tides, Earth curvature, and removal of the regional field.…”

Geodetic Constraints on a 25‐year Magmatic Inflation Episode Near Three Sisters, Central Oregon

“…Zurek et al. (2012) reported results of such measurements made between 2002 and 2009. Their modeling predicted a 20–30 µGal gravity increase at the center of uplift during that period if the observed surface deformation were caused by magma intrusion.…”

Time-Scales of Inter-Eruptive Volcano Uplift Signals: Three Sisters Volcanic Center, Oregon (United States)

“…This is compatible with the formation of viscoelastic aureoles as a result of the alteration of the mineralogical and rheological properties of the surrounding rocks. Previously, Zurek et al (2012) concluded, based on the lack of gravity change from [2002][2003][2004][2005][2006][2007][2008][2009], that deformation at Three Sisters reflects a viscoelastic response of the crust to an intrusion of magma. The estimated e-folding indicates viscosities of ∼10 18 Pa s of a viscoelastic shell surrounding the magmatic source with a pressure change which increases in finite time from 0 to a constant value, considering theoretical estimations on the time constants and viscoelastic medium parameters (e.g., Newman et al, 2001;Bonafede and Ferrari, 2009;Del Negro et al, 2009;Segall, 2016).…”

“…Interpretation of the temporal evolution of InSAR, leveling and GPS data suggests the beginning of deformation in late 1997 or 1998, with a maximum uplifting rate of 3-5 cm/year during 1998. Microgravity data collected between 2002 show no significant change in the mass flux across the deforming area (Zurek et al, 2012). No studies have been published about the uplift evolution over the last decade.…”