The 2018 K & imath;lauea lower East Rift Zone (KLERZ) eruption was one of the most voluminous eruptions on the Island of Hawai'i in the past 200 years, leading to major disruption and destroying over 700 homes and structures. The majority of the erupted magma was emitted as a lava flow from Ahu'ail & amacr;'au (fissure 8), which was active from late May to early August. To better understand the evolution of long-lived channelized lava flows, we examined the evolution of velocity, texture, and inferred rheology of the fissure 8 lava in space and time. We quantified lava flow surface velocities using particle image velocimetry in more than 200 aerial videos that span the lava flow duration and length. Velocity measurements were analyzed together with vesicularity and crystallinity measurements from 9 co-located post-eruptive field samples to understand the textural evolution of this flow and its impact on lava rheology and flow velocity. The fissure 8 flow was highly vesicular, with 79%-88% vesicularity at the vent, decreasing to 16%-26% vesicularity 12.5 km from the vent. The volume fraction occupied by crystals >50 mu m in size increased from 6% at the vent to about 18% at 12.5 km downstream. We find that the effective flow viscosity increased at a quadratic rate with distance. Using experimentally determined liquid viscosity and applying established models to account for the effect of crystals and bubbles, we attribute this increase primarily to textural evolution driven initially by the near-vent loss of deformable bubbles and later by cooling and crystal growth. We demonstrate the importance of accounting for the evolution of vesicularity and the role of vesicles by showing that utilizing this capability in the open-source thermo-rheological lava flow propagation model PyFLOWGO allows for more accurate predictions of the observed flow velocities. Our modeling results suggest that small bubbles behaving rigidly are required to simulate the observed flow length, speed, and viscosities. Flow velocities of the fissure 8 lava also varied with time, driven by near-daily collapse events of the summit caldera. Temporal velocity changes were characterized by a period of steep acceleration, with the volumetric flux peaking around 4 h after a caldera collapse, followed by a period of gradual deceleration lasting up to 40 h or until the next collapse event. We use this temporal behavior to estimate the compressibility of the magma inside the plumbing system between the summit reservoir and the lower East Rift Zone. Overall, quantifying the spatial and temporal evolution of the KLERZ eruption provides information about magma and lava properties that can inform predictive modeling and hazard assessment during an eruption.

As the Pacific Plate migrates over the mantle plume below Hawaiʻi, magma flux decreases, resulting in changes in eruptive volume, style, and composition. It is thought that melt storage becomes deeper and ephemeral with the transition from highly voluminous tholeiitic (shield stage) to the less voluminous alkaline (post-shield and rejuvenation stages) magmatism. To quantitatively test this, we applied high-precision fluid inclusion barometry via Raman spectroscopy to samples from representative volcanoes of different evolutionary stages. This suggests an evolution from shield-stage shallow magma storage (~1 to 2 kilometers) for Kīlauea to a post-shield stage that includes crustal magma storage within the volcanic edifice (~2 kilometers) and deeper storage below the Moho (~20 to 27 kilometers) for Haleakalā. The rejuvenation stage (Diamond Head) displays mantle-dominated storage (~22 to 30 kilometers). High melt fluxes likely form stable conduits from the mantle to a shallow reservoir in the shield volcanoes. As melt flux decreases, the Moho becomes the boundary controlling melt stagnation and evolution.

Nanometer-scale titanomagnetite crystals have been detected in nominally aphyric rhyolite pumice, but whether they are numerous enough to impact bubble nucleation in explosive silicic volcanism was unresolved. This study examines sub-micron crystals using rock magnetic techniques, Rhyolite-MELTS modeling, and physical characterization. We analyzed pumice from four eruptions spanning wide ranges in intensity, storage depth, and bubble number density (1016 to 1013 m-3 liquid): 1060 CE Glass Mountain, 1912 CE Novarupta, 232 CE Taupo, and 0.45 Ma Pudahuel. Calculations assuming monospecific assemblages of 10 and 1,000 nm cubic particles yield titanomagnetite number densities of 1021 to 1013 m-3 dense rock equivalent, respectively. In all cases, titanomagnetite is thermodynamically stable at pre-eruptive storage conditions and magnetic susceptibility (chi LF) is independent of vesicularity and permeability, indicating that crystals likely formed prior to vesiculation. The existence of nm-scale Fe-Ti oxides in four diverse cases suggests that heterogeneous bubble nucleation is a general feature of explosive rhyolite volcanism.

AbstractNucleation of H2O vapor bubbles in magma requires surpassing a chemical supersaturation threshold via decompression. The threshold is minimized in the presence of a nucleation substrate (heterogeneous nucleation, <50 MPa), and maximized when no nucleation substrate is present (homogeneous nucleation, >100 MPa). The existence of explosively erupted aphyric rhyolite magma staged from shallow (<100 MPa) depths represents an apparent paradox that hints at the presence of a cryptic nucleation substrate. In a pair of studies focusing on Glass Mountain eruptive units from Medicine Lake, California, we characterize titanomagnetite nanolites and ultrananolites in pumice, obsidian, and vesicular obsidian (Brachfeld et al., 2024, https://doi.org/10.1029/2023GC011336), calculate titanomagnetite crystal number densities, and compare titanomagnetite abundance with the physical properties of pumice to evaluate hypotheses on the timing of titanomagnetite crystallization. Titanomagnetite crystals with grain sizes of approximately 3–33 nm are identified in pumice samples from the thermal unblocking of low‐temperature thermoremanent magnetization. The titanomagnetite number densities for pumice are 1018 to 1020 m−3, comparable to number densities in pumice and obsidian obtained from room temperature methods (Brachfeld et al., 2024, https://doi.org/10.1029/2023GC011336). This range exceeds reported bubble number densities (BND) within the pumice from the same eruptive units (average BND ∼4 × 1014 m−3). The similar abundances of nm‐scale titanomagnetite crystals in the effusive and explosive products of the same eruption, together with the lack of correlation between pumice permeability and titanomagnetite content, are consistent with titanomagnetite formation having preceded the bubble formation. Results suggest sub‐micron titanomagnetite crystals are responsible for heterogeneous bubble nucleation in this nominally aphyric rhyolite magma.

AbstractWe document the presence, composition, and number density (TND) of titanomagnetite nanolites and ultra‐nanolites in aphyric rhyolitic pumice, obsidian, and vesicular obsidian from the 1060 CE Glass Mountain volcanic eruption of Medicine Lake Volcano, California, using magnetic methods. Curie temperatures indicate compositions of Fe2.40Ti0.60O4 to Fe3O4. Rock‐magnetic parameters sensitive to domain state, which is dependent on grain volume, indicate a range of particle sizes spanning superparamagnetic (<50–80 nm) to multidomain (>10 μm) particles. Cylindrical cores drilled from the centers of individual pumice clasts display anisotropy of magnetic susceptibility with prolate fabrics, with the highest degree of anisotropy coinciding with the highest vesicularity. Fabrics within a pumice clast require particle alignment within a fluid, and are interpreted to result from the upward transport of magma driven by vesiculation, ensuing bubble growth, and shearing in the conduit. Titanomagnetite number density (TND) is calculated from titanomagnetite volume fraction, which is determined from ferromagnetic susceptibility. TND estimates for monospecific assemblages of 1,000 nm–10 nm cubes predict 1012 to 1020 m−3 of solid material, respectively. TND estimates derived using a power law distribution of grain sizes predict 1018 to 1019 m−3. These ranges agree well with TND determinations of 1018 to 1020 m−3 made by McCartney et al. (2024), and are several orders of magnitude larger than the number density of bubbles in these materials. These observations are consistent with the hypothesis that titanomagnetite crystals already existed in extremely high number‐abundance at the time of magma ascent and bubble nucleation.

Heterogeneities in the phosphorus (P) content of olivine are relatively resistant to diffusive homogenization when compared with other compositional heterogeneities. Thus, heterogeneities in the spatial distribution of P can preserve petrological information about olivine crystals from the earliest stages of crystallization which have been otherwise eliminated. However, compared to independent determinations of protracted cooling timescales in slowly cooled rocks, P enrichments are so sharp as to suggest a rate of diffusive mobility that is many orders of magnitude slower than previously suggested. Here, we heat single natural olivine crystals with sharply defined P heterogeneities (0.02-0.15 wt% P2O5 over 0.5 mu m spatial scale) in a 1-atmosphere gas-mixing furnace for durations of 10-20 days at 1400 degrees C, thus exposing them to conditions that should be sufficient for complete diffusive relaxation according to published P diffusivity values. However, high-precision chemical analysis of the same interior section before and after heating reveals no discernable difference in the sharpness of phosphorus concentration patterns. Therefore, diffusion chronometry applied to skeletal P enrichments in olivine currently provides erroneously short diffusive timescales. We discuss several possible causes for these discrepancies and the implications for diffusion chronometry as applied to phosphorus in olivine.

Rocks produced by diverse processes, from condensation in space to impacts on planetary surfaces to volcanism, contain both crystals and amorphous material. Crystallinity provides information on the thermal history of the sample and is especially important in characterizing volcanic rocks and pyroclasts because lava rheology is profoundly influenced by the crystal content. Crystallinity is typically quantified via microscopy, using transmitted light or backscattered electrons. However, many samples present visibly ambiguous textures such as intimate intergrowth of crystal phases, and/or crystal sizes extending down to the nanometer scale. Here, we apply calorimetric methods involving heat capacity and enthalpy to assess the crystallinity of a series of volcanic samples. We tested three different approaches, using differential scanning calorimetry, on 30-40 mg aliquots of powdered basalts from the 2018 K & imacr;lauea lower East Rift Zone. The first approach involves determining the magnitude of the increase in heat capacity at the glass transition, which can determine crystallinity to a 1 sigma precision of +/- 3%. The second approach is based on the enthalpy of fusion, which requires a longer more complex procedure with results that are typically more uncertain than for the heat capacity method, with a 1 sigma of +/- 6%. A final method utilizing differences in enthalpies calculated from the heat capacities required the most complex procedure and has the greatest uncertainty of +/- 18%. Preliminary results for lavas with microscopically determined crystallinities ranging from 11 to 98% indicate that crystallinity based on calorimetric data can be tens of percent higher than the average value identified using microscopy and petrographic analysis. Image-based methodologies applied to sections of samples reveal spatial heterogeneity and details in texture and crystallinity, whereas calorimetry-based methodologies capture the overall 'bulk sample' properties, unbiased by section effects or imaging resolution limits. These techniques are a powerful combination that can present complementary views of crystallinity.

Recharges of magma underneath basaltic volcanoes can occur as precursory events prior to an eruption but are not always revealed in geophysical data streams or erupted lavas compositions. In contrast, phosphorus within primitive, Mg-rich (Fo(89-90)), olivine can preserve recharge information lost by the mixed melt. Evidence of rapid growth and dissolution are preserved only in phosphorus X-ray intensity maps, which reveal that Mg-rich olivine from eruptions occurring between 2008 and 2020 at Kilauea Volcano (HawaiModified Letter Turned Commai) experienced at least two episodes of magma intrusion. We develop numerical diffusion models that evaluate the fidelity of the Fe-Mg compositional archive by quantifying three factors that influence Fo population distributions: (a) the frequency at which an Mg-rich basaltic liquid (in equilibrium with Fo(90) olivine) intrudes the reservoir, (b) the pre-existence of a polymodal distribution of olivine crystal sizes and their shapes (c) the effects of sectioning on apparent olivine core compositions. We find that most crystals lose their initial Mg-rich composition if they are held at temperatures relevant to summit magma storage conditions (1,160-1,190?) for more than 10 years. Thus, previous assertions that Mg-rich olivine crystals at Kilauea are scavenged from centuries-old stored magmas are unrealistic. Our method permits critical evaluation of contrasting explanations of heterogeneous Fe-Mg contents of olivine cargo: (a) different total durations of mush storage with partial diffusive erasure of compositional traits, or (b) coexistence of multiple chemically distinct magmas. Our approach provides general guidance for the conservative interpretation of temporal information preserved within olivine Fe-Mg compositional archives.

Quantitative textural analysis of crystals, including their number density, shapes, sizes, overall abundance and size distribution can be used to shed light on magmatic processes and the timescales over which they operate. At Merapi, textural analysis of phenocrysts in dome lavas, lava flows, tephra, and in plutonic cumulates has revealed that open system steady state conditions prevail throughout the crustal magma plumbing system over short time periods, with non-steady state conditions prevailing over the longer term. Phenocryst crystallisation likely takes place over tens to hundreds of years prior to eruption. Quantitative textural analysis of feldspar microlites, in conjunction with compositional data, elucidate magma ascent and degassing processes within the conduit during dome forming eruptions, and additionally reveal the driving forces behind transitions between effusive and explosive eruptive behaviour. For example, microlite textures from different stages of the 2010 eruption show that transitions between explosive and effusive activity in 2010 were driven primarily by the dynamics of magma ascent in the shallow conduit.

Abundant small titanomagnetite particles, on the edge and/or below conventional observation methods, may be responsible for the heterogenous nucleation of bubbles in crystal-poor systems. Prior experimental studies revealed that bubble number densities (BND) are higher in the presence of such particles

How to build a legacy of scientific leadership: the HR formula PROF. JULIA HAMMER, PHD1, LESLIE BAKER2, JENNI BARCLAY3, MICHAEL R. CARROLL4, MICHELLE COOMBS5, ELIZABETH COTTRELL6, NICHOLAS J DYGERT7, LINDA ELKINS-TANTON8, EMILY FIRST9, JAMES GARDNER10, DAVID GOLDSBY11, JAMES GREENWOOD12, MARIE JOHNSON13, MIKE KRAWCZYNSKI14, CHARLES MANDEVILLE15, MOLLY MCCANTA16, MICHELLE E. MINITTI17, WILLIAM NELSON18, TABB PRISSEL19, DINA VENEZKY20, CATHERINE WEITZ21 AND DIANE WOODRUFF22 1University of Hawaiʻi 2University of Idaho 3University of East Anglia 4Camerino University 5U.S. Geological Survey 6National Museum of Natural History, Smithsonian Institution 7University of Tennessee, Knoxville 8Arizona State University 9Cornell University 10University of Texas at Austin 11University of Pennsylvania 12Wesleyan University 13Cal State Fullerton 14Washington University in St. Louis 15US Geological Survey 16University of Tennessee at Knoxville 17Framework, Silver Spring 18University of Hawaii at Manoa 19NASA 20Smith College 21Planetary Science Institute 22Anadarko Petroleum Company Presenting Author: jhammer@hawaii.edu

The 2018 lower East Rift Zone (LERZ) eruption and contemporaneous summit collapse of Kīlauea raised fundamental questions about how the volcano would respond following such a major disruption to its magmatic plumbing system. Kīlauea's summit erupted on December 20, 2020, after only two years of quiescence, and poured around 40 million m 3 of lava into the new crater until mid-May 2021. A second eruption began on September 29, 2021, and added another 45 million m 3 of lava by the end of January 2022. Both eruptions were initially highly energetic, ejecting tephra high enough to accumulate on the crater rim for collection. Preliminary whole-rock, glass, and mineral chemistry revealed similarities between 2020–21 lava and late 2018 LERZ phase 3 (LERZ-3) lavas. The 2020–21 whole-rock samples are significantly different in incompatible elements and fractionation-resistant ratios (e.g., TiO 2 , K 2 O, Zr, CaO/TiO 2 , Nb/Y) compared to 2008–18 Halemaʻumaʻu summit (HMM) and Puʻuʻōʻō eruptions, but correspond well with LERZ-3. Previous work demonstrated that magma supplying Kīlauea eruptions has been shifting to higher TiO 2 and K 2 O (relative to fixed MgO) since around 2011. The 2020–21 eruptions have similar TiO 2 and K 2 O concentrations to the LERZ-3 values, implying this magma is from the same source. Olivine phenocrysts with high-Fo cores, common in LERZ-3 lava, are also found in the 2020–21 samples.

The 2018 lower East Rift Zone (LERZ) eruption of Kīlauea, Hawai’i, provides an excellent natural laboratory with which to test models of lava flow propagation. During early stages of eruption crises, the most useful lava flow propagation equations utilize readily determined parameters and require fewer a priori assumptions about future behavior of the flow. Here, we leverage the numerous observations of lava flows collected over the duration of the eruption crisis at Kīlauea in 2018 to test simple lava flow propagation models. These models track the one-dimensional propagation of the flows according to three main rheological restraining forces: bulk viscosity, yield strength, and growth of a surface crust. We calculate the predicted changes in length through time of three flows that vary in bulk composition, crystal content, and total flow length. Cooler flows that are more crystal-rich tend to be more dominated by crust growth, though early stages of propagation can be controlled by bulk viscosity. We find that variations in effusion rate significantly impact flows that are short-lived; flows that are produced during steady-state effusion are readily approximated by average values for the entire flow. Thus, accurate knowledge of variations in effusion rate are critical to accurate lava flow propagation forecasting.

The Pudahuel Ignimbrite is a rhyolitic, crystal poor deposit associated with the formation of the Diamante caldera in the Southern Volcanic Zone of the Andes. This Quaternary ignimbrite is the result of a massive eruption in what is now a densely populated area. The goal of this study is to understand the origin of this caldera-forming eruption by determining the pre-eruptive magmatic conditions through analytical and experimental approaches. The Fe-Ti oxide geothermometer and the plagioclase hygrometer were used to determine the temperature-X-H2O(fl) conditions that produce the glass, feldspar, and Fe-Ti oxide compositions observed in the natural sample. The results were combined with a composition-dependent water solubility model to constrain the magma storage pressure. This methodology was extended to temperatures up to 850 degrees C to define a band of P-T-H2O conditions that satisfy the natural plagioclase and glass compositional pairs, from 700 degrees C at 310 MPa to 850 degrees C at 85 MPa. Phase equilibrium experiments were performed at conditions within the band at H2O-vapor saturated and undersaturated conditions using a representative pumice sample as the starting material. The purely analytical approach, based on Fe-Ti oxide geothermometry and plagioclase hygrometry of the pumice phases, suggests pre-eruptive temperatures of 717 +/- 7 degrees C, P-H2O of 200-360 MPa and between 6.9 and 7.6 wt% H2O. The natural phase assemblage and the glass composition was best reproduced by experiments performed at low temperatures (700-750 degrees C) and high P-Total (>275 MPa, more likely 300-350 MPa), with water contents of at least 6 wt%. A compositional match between synthetic and natural glasses occurred in some H2O-undersaturated experiments, suggesting that the melt was not necessarily saturated with H2O-rich fluid. Overall, our work highlights that the source region related to the caldera-forming Pudahuel ignimbrite was relatively deep (> 10 km). This depth, combined with the low crystallinity of the magma, and the possibility of an H2O-undersaturated melt, suggest that caldera formation was likely initiated by an external trigger rather than internal pressurization due to volatile buildup in the reservoir. The storage conditions determined in this study lay the groundwork for continuing work to understand the Maipo volcanic complex and the future hazards it poses.