Title

The Role of Magma Mixing in the 1968-2010 Eruption of Arenal Volcano, Costa Rica: Insights from Modelling of the Magma Chamber

Presenter Information

Jenna Adams
Martin Streck
Frank Spera

Document Type

Oral Presentation

Location

SURC 140

Start Date

21-5-2015

End Date

21-5-2015

Keywords

Magma Mixing, Thermodynamics, Eruptions

Abstract

Magmatic processes, such as magma mixing (mixing of two or more magmas), control compositional diversity of magmas (less to more silica-rich), eruption style (gentle to explosive), and can potentially catalyze eruptions, making documentation of mixing events at active volcanoes important for improving eruption prediction. Thousands of cases of magma mixing have been documented, but a new computational approach documents for the first time the relative size, frequency, and location beneath the volcano of mixing events. The 1968-2010 eruption of Arenal Volcano, Costa Rica, produced lava flows that are homogenous at the whole-rock (kg) scale but highly heterogeneous at the crystal (mg) scale. The hypothesis of Streck et al. (2005) that four distinct magmatic components mixed in a shallow subvolcanic magma reservoir to produce Arenal’s lavas was analyzed by the Magma Chamber Simulator, a new thermodynamic computer model (Bohrson et al., 2014). Based on several hundred simulations, model results constrain pre-mixing pressure, oxygen fugacity, temperature, and H2O contents of the four crystallization environments. Three reside 3-6 km below the surface and magmas are relatively oxidized (QFM to QFM+1) with moderate water concentrations (2-3.5 wt.%). The fourth is ~23 km below the surface with crystallization requiring oxidizing conditions (QFM+1) and H2O contents of 3-4 wt.%. Mixing simulations that best reproduce observed temperatures and lava and crystal compositions require high frequency, small volume intrusions that mix into a shallow subvolcanic magma chamber. Quantification of the size and frequency of mixing events should improve our understanding of eruption precursors, thereby improving volcanic hazard prediction.

Faculty Mentor(s)

Wendy Bohrson

Department/Program

Geological Sciences

Additional Mentoring Department

Geological Sciences

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May 21st, 12:40 PM May 21st, 1:00 PM

The Role of Magma Mixing in the 1968-2010 Eruption of Arenal Volcano, Costa Rica: Insights from Modelling of the Magma Chamber

SURC 140

Magmatic processes, such as magma mixing (mixing of two or more magmas), control compositional diversity of magmas (less to more silica-rich), eruption style (gentle to explosive), and can potentially catalyze eruptions, making documentation of mixing events at active volcanoes important for improving eruption prediction. Thousands of cases of magma mixing have been documented, but a new computational approach documents for the first time the relative size, frequency, and location beneath the volcano of mixing events. The 1968-2010 eruption of Arenal Volcano, Costa Rica, produced lava flows that are homogenous at the whole-rock (kg) scale but highly heterogeneous at the crystal (mg) scale. The hypothesis of Streck et al. (2005) that four distinct magmatic components mixed in a shallow subvolcanic magma reservoir to produce Arenal’s lavas was analyzed by the Magma Chamber Simulator, a new thermodynamic computer model (Bohrson et al., 2014). Based on several hundred simulations, model results constrain pre-mixing pressure, oxygen fugacity, temperature, and H2O contents of the four crystallization environments. Three reside 3-6 km below the surface and magmas are relatively oxidized (QFM to QFM+1) with moderate water concentrations (2-3.5 wt.%). The fourth is ~23 km below the surface with crystallization requiring oxidizing conditions (QFM+1) and H2O contents of 3-4 wt.%. Mixing simulations that best reproduce observed temperatures and lava and crystal compositions require high frequency, small volume intrusions that mix into a shallow subvolcanic magma chamber. Quantification of the size and frequency of mixing events should improve our understanding of eruption precursors, thereby improving volcanic hazard prediction.