The magmatic-hydrothermal system of the Three Sisters volcanic cluster, Oregon, imaged from field gravity measurements
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Abstract
From 2019 to 2024, gravity surveys were conducted at the Three Sisters volcanic cluster (TSVC), measuring 246 gravity sites using a spring relative gravimeter. We calculated the residual Bouguer anomaly and identified three main zones with negative anomalies, ranging from −4 to −8 mGal, located southwest and west of South Sister, within an area that has been uplifting for the past two decades. After inversion, we obtain a 3D density model of the subsurface and identify low-density bodies extending from the surface down to 3 km. We estimate a total of 15 km3 of crustal bodies with density close to 2 g/cm3 that could store up to ~5 km3 of water, forming an extensive hydrothermal system beneath the TSVC. We explore the possible combinations of melt compositions and temperatures that could create a bulk density close to our reference crustal density (2.5 g/cm3) using MELTS thermodynamic simulations. Our results indicate that a magmatic mush with as little as 15% partial melt of bulk rhyolitic composition or as much as 52%–57% partial melt of a bulk dacitic composition could be stored in a magmatic system under TSVC without generating a detectable gravity anomaly. Episodic magma injections at the base of the magmatic system, such as the 1998–2000 intrusion at ~6 km depth, would bring heat and gas to the hydrothermal system while maintaining a low melt fraction in the magmatic mush, as imaged at other Cascade volcanoes.
Suggested Citation
Le Mevel, H., Andersen, N.L., Dechert, A.E., Dufek, J., 2026, The magmatic-hydrothermal system of the Three Sisters volcanic cluster, Oregon, imaged from field gravity measurements: JGR Solid Earth, v. 131, no. 1, e2025JB031886, 16 p., https://doi.org/10.1029/2025JB031886.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | The magmatic-hydrothermal system of the Three Sisters volcanic cluster, Oregon, imaged from field gravity measurements |
| Series title | JGR Solid Earth |
| DOI | 10.1029/2025JB031886 |
| Volume | 131 |
| Issue | 1 |
| Publication Date | January 14, 2026 |
| Year Published | 2026 |
| Language | English |
| Publisher | American Geophysical Union |
| Contributing office(s) | Volcano Science Center |
| Description | e2025JB031886, 16 p. |
| Country | United States |
| State | Oregon |
| Other Geospatial | Three Sisters volcanic cluster |