Magmas with matrix glass compositions ranging from basalt to dacite erupted from a series of 24 fissures in the first 2 weeks of the 2018 Lower East Rift Zone (LERZ) eruption of Kīlauea Volcano. Eruption styles ranged from low spattering and fountaining to strombolian activity. Major element trajectories in matrix glasses and melt inclusions hosted by olivine, pyroxene and plagioclase are consistent with variable amounts of fractional crystallization, with incompatible elements (e.g., Cl, F, and H2O) becoming enriched by 4–5 times as melt MgO contents evolve from 6 to 0.5 wt%. The high viscosity and high H2O contents (∼2 wt%) of the dacitic melts erupting at Fissure 17 account for the explosive Strombolian behavior exhibited by this fissure, in contrast to the low fountaining and spattering observed at fissures erupting basaltic to basaltic‐andesite melts. Saturation pressures calculated from melt inclusion CO2‐H2O contents indicate that the magma reservoir(s) supplying these fissures was located at ∼2–3 km depth, which is in agreement with the depth of a dacitic magma body intercepted during drilling in 2005 (∼2.5 km) and a seismically imaged low
The most explosive basaltic scoria cone eruption yet documented (>20 km high plumes) occurred at Sunset Crater (Arizona) ca. 1085 AD by undetermined eruptive mechanisms. We present melt inclusion analysis, including bubble contents by Raman spectroscopy, yielding high total CO2(approaching 6000 ppm) and S (~2000 ppm) with moderate H2O (~1.25 wt%). Two groups of melt inclusions are evident, classified by bubble vol%. Modeling of post-entrapment modification indicates that the group with larger bubbles formed as a result of heterogeneous entrapment of melt and exsolved CO2and provides evidence for an exsolved CO2phase at magma storage depths of ~15 km. We argue that this exsolved CO2phase played a critical role in driving this explosive eruption, possibly analogous to H2O exsolution driving silicic caldera-forming eruptions. Because of their distinct gas compositions relative to silicic magmas (high S and CO2), even modest volume explosive basaltic eruptions could impact the atmosphere.
more » « less- Award ID(s):
- 1642569
- NSF-PAR ID:
- 10209423
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Vp /Vs anomaly (∼2 km depth). Nb/Y ratios in erupted products are similar to lavas erupted between 1955 and 1960, indicating that melts were stored and underwent variable amounts of crystallization in the LERZ for >60 years before being remobilized by a dike intrusion in 2018. We demonstrate that extensive fractional crystallization generates viscous and volatile‐rich magma with potential for hazardous explosive eruptions, which may be lurking undetected at many ocean island volcanoes. -
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Abstract Magmatic volatiles drive pressure, temperature, and compositional changes in upper crustal magma chambers and alter the physical properties of stored magmas. Previous studies suggest that magmatic H2O content influences the growth and longevity of silicic chambers through regulating the size and frequency of eruptions and impacting the crystallinity‐temperature curve. However, there has been comparatively little exploration of how CO2impacts the evolution of magma chambers despite the strong influence of CO2on H2O solubility and the high concentrations of CO2often present in mafic systems. In this study, we integrate the thermodynamic effects of dissolved and exsolved H2O and CO2with the mechanics of open‐system magma chambers that interact thermally and mechanically with the crust. We applied this model to investigate how intrinsic variations in magmatic H2O‐CO2content influence the growth and longevity of silicic and mafic magma chambers. Our findings indicate that even with a tenfold increase in CO2content (up to 10,000 ppm), CO2plays a minimal role in long‐term chamber growth and longevity. While CO2content affects the magma compressibility, the resulting changes in eruption mass are balanced out by a commensurate change in eruption frequency so that the time‐averaged eruptive flux and long‐term chamber behavior remain similar. In contrast, H2O content strongly influences chamber growth and longevity. In silicic systems, high H2O contents hinder magma chamber growth by increasing the total eruptive flux and steepening the slope of the crystallinity‐temperature curve. In mafic systems, high H2O contents promote magma chamber growth by flattening the slope of the crystallinity‐temperature curve.
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Abstract Interpreting unrest at silicic volcanoes requires knowledge of the magma storage conditions and dynamics that precede eruptions. The Laguna del Maule volcanic field, Chile, has erupted ~40 km3of rhyolite over the last 20 ka. Astonishing rates of sustained surface inflation at >25 cm/year for >12 years reveal a large, restless system. Integration of geochronologic, petrologic, geomorphic, and geophysical observations provides an unusually rich context to interpret ongoing and prehistoric processes. We present new volatile (H2O, CO2, S, F, and Cl), trace element, and major element concentrations from 109 melt inclusions hosted in quartz, plagioclase, and olivine from seven eruptions. Silicic melts contain up to 8.0 wt. % H2O and 570 ppm CO2. In rhyolites melt inclusions track decompression‐driven fractional crystallization as magma ascended from ~14 to 4 km. This mirrors teleseismic tomography and magnetotelluric findings that reveal a domain containing partial melt spanning from 14 to 4 km. Ce and Cl contents of rhyolites support the generation of compositionally distinct domains of eruptible rhyolite within the larger reservoir. Heat, volatiles, and melt derived from episodic mafic recharge likely incubate and grow the shallow reservoir. Olivine‐hosted melt inclusions in mafic tephra contain up to 2.5 wt. % H2O and 1,140 ppm CO2and proxy for the volatile load delivered via recharge into the base of the silicic mush at ~14 to 8 km. We propose that mafic recharge flushes deeper reaches of the magma reservoir with CO2that propels H2O exsolution, upward accumulation of fluid, pressurization, and triggering of rhyolitic eruptions.
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Abstract Plagioclase microlites in a magma nucleate and grow in response to melt supersaturation (Δ
ϕ plag ). The resultant frozen plagioclase crystal size distribution (CSD) preserves the history of decompression pathways (dP/dt ). SNGPlag is a numerical model that calculates the equilibrium composition of a decompressing magma and nucleates and grows plagioclase in response to an imposed Δϕ plag . Here, we test a new version of SNGPlag calibrated for use with basaltic andesite magmas and modeldP/dt for the ca. 12.6 ka Curacautín eruption of Llaima volcano, Chile. Instantaneous nucleation (N plag ) and growth (G plag ) rates of plagioclase were computed using the experimental results of Shea and Hammer (J Volcanol Geotherm Res 260:127–145, 10.1016/j.jvolgeores.2013.04.018, 2013) and used for SNGPlag modeling of basaltic andesite composition. MaximumN plag of 6.1 × 105 cm h−1is achieved at a Δϕ plag of 44% and the maximumG plag of 27.4 μm h−1is achieved at a Δϕ plag of 29%. Our modeled logdP/dt avg range from 2.69 ± 0.09 to 6.89 ± 0.96 MPa h−1(1σ) with an average duration of decompression from 0.87 ± 0.25 to 16.13 ± 0.29 h assuming a starting pressureP i of 110–150 MPa. These rates are similar to those derived from mafic decompression experiments for other explosive eruptions. Using assumptions for lithostatic pressure gradients (dP/dz ), we calculate ascent rates of < 1–6 m s−1. We conducted a second set of Monte Carlo simulations usingP i of 15–30 MPa to investigate the influence of shallower decompression, resulting in logdP/dt avg from 2.86 ± 0.49 to 6.00 ± 0.86 MPa h−1. ThedP/dt modeled here is two orders of magnitude lower than those calculated by Valdivia et al. (Bull Volcanol, 10.1007/s00445-021-01514-8, 2022) for the same eruption using a bubble number density meter, and suggests homogeneous nucleation raisesdP/dt by orders of magnitude in the shallow conduit. Our modeling further supports the rapid-ascent hypothesis for driving highly explosive mafic eruptions. -
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