Geology topics

Rebecca J. Carey

Publications and source records attributed to Rebecca J. Carey.

9 recordsLinked to original sources

USGS2025

How did westward volcaniclastic deposits accumulate in the deep sea following the January 2022 eruption of Hunga Volcano ?

Most volcanic eruptions on Earth take place below the ocean surface and remain largely unobserved. Reconstruction of past submerged eruptions has thus primarily been based on the study of seafloor deposits. Rarely before the 15 January 2022 eruption of Hunga volcano (Kingdom of Tonga) have we been able to categorically link deep-sea deposits to a specific volcanic source. This eruption was the largest in the modern satellite era, producing a 58-km-tall plume, a 20-m high tsunami, and a pressure wave that propagated around the world. The eruption induced the fastest submarine density currents ever measured, which destroyed submarine telecommunication cables and traveled at least 85 km to the west to the neighboring Lau Basin. Here we report findings from a series of remotely operated vehicle dives conducted 4 months after the eruption along the Eastern Lau Spreading Center-Valu Fa Ridge. Hunga-sourced volcaniclastic deposits 7–150 cm in thickness were found at nine sites, and collected. Study of the internal structure, grain size, componentry, glass chemistry, and microfossil assemblages of the cores show that these deposits are the distal portions of at least two ∼100-km-runout submarine density currents. We identify distinct physical characteristics of entrained microfossils that demonstrate the dynamics and pathways of the density currents. Microfossil evidence suggests that even the distal parts of the currents were erosive, remobilizing microfossil-concentrated sediments across the Lau Basin. Remobilization by volcaniclastic submarine density currents may thus play a greater role in carbon transport into deep sea basins than previously thought.

Hunga volcano↗

USGS2025

The crystalline silica respiratory hazard from rhyolitic lava dome eruptions in New Zealand's Taupo Volcanic Zone: A case study from the 1315 CE Kaharoa eruption

The rhyolitic Kaharoa 1315 CE eruption was a complex, long-lived event from Tarawera volcano, New Zealand. Explosive phases were followed by around 5 years of lava dome extrusion and collapse which produced block-and-ash flows (BAF). Lava domes generate crystalline silica in the form of cristobalite, and rhyolitic magmas often contain quartz phenocrysts. Fine-grained ash containing crystalline silica can be formed through dome collapses or explosions, generating a respiratory health hazard for communities affected by ashfall. The aims of this study are to: i) determine whether the Kaharoa eruption dome-forming phase generated substantial quantities of crystalline silica and, therefore, to determine the potential for future dome-forming eruptions of Tarawera to do the same; ii) consider the potential hazard of the crystalline silica by studying the crystal habit and chemistry compared to other lava domes, globally; and iii) assess the particle size and crystalline silica content of the Kaharoa ash, to inform a respiratory hazard assessment. Five co-BAF ash samples and one co-ignimbrite (explosive) ash sample from the Kaharoa pyroclastic deposits were analysed for health-pertinent factors: particle size distribution and crystalline silica content. Eight dome-rock samples were collected from the dome complex and associated BAF deposits and groundmass texture (especially forms of crystalline silica) and quantity of crystalline silica were assessed. Cristobalite was present in the 4 ash samples analysed by X-ray diffraction (XRD; 1.3–3.7 wt%) as was quartz (5.7–12.5 wt%). For the 4 dome samples analysed by XRD, all samples contained quartz (4.1–10.4 wt%) and two contained significant quantities of cristobalite (24.7 and 27.3 wt%). Of the two dome samples with minimal cristobalite (visible as individual vapour-phase crystals by SEM but not quantifiable by XRD), one was from the non-devitrified dome carapace and the other was from the compacted interior but had not undergone devitrification. The two dome samples with substantial cristobalite were from dome interiors and were highly devitrified, with well-developed spherulitic textures. Using energy-dispersive X-ray spectroscopy, cristobalite in all samples contained minor aluminium, as has been seen for volcanic cristobalite from other lava domes, which may ameliorate its toxicity. By laser diffraction, the quantities of ash in the health pertinent size fractions varied, with a range of 1.3–8.1 vol% for particles of <4 μm diameter and 1.7–15.6 vol% for particles of <10 μm diameter, which is lower than measured in ash from large-scale dome collapse events at other volcanoes. The findings suggest a potential for substantial crystalline silica to be formed in future Kaharoa-style eruptions, but that cristobalite generation is site-specific, depending on location within the dome and whether the dome remains sufficiently hot for spherulite formation and glass devitrification. Respiratory hazard will therefore vary depending on the collapse of (or explosions through) individual lobes – although all lava is expected to contain quartz phenocrysts – as well as the size and energy of those collapses, which will influence particle size and quantity of ash generated and dispersed.

Taupo Volcanic Zone↗

USGS2021

Patterns of bubble bursting and weak explosive activity in an active lava lake—Halema‘uma‘u, Kīlauea, 2015

The rise of the Halemaʻumaʻu lava lake in 2013–2018 to depths commonly 40 meters or less below the rim of the vent was an excellent opportunity to study outgassing and the link to associated eruptive activity. We use videography to investigate the rise and bursting of bubbles through the free surface of the lake in 2015. We focus on low-energy explosive activity (spattering) in which the ascent and bursting of meter-sized, mechanically decoupled bubbles trigger the ejection of fluidal bombs to tens of meters above the free surface. A decay in initial pyroclast velocity with time follows the same functional form as that observed for ejecta at Stromboli (Italy), suggesting a similar bubble-burst mechanism. We also find that the upward velocity of the bubble crust as it bursts is around 2.5 times higher than the velocity of the bubble as it rises through the lake surface, indicating that the bubbles are over-pressurized. Prior to bursting, bubbles emerge at velocities of 4 to 14 meters per second, suggesting rise from depths of at least tens of meters but unaffected by the deeper circulation of the lava lake. We identify three styles of bubble bursting: (1) isolated, widely spaced, single bursts, (2) recurring clusters of discrete bubbles, and (3) prolonged episodes of overlapping bubble bursts along elongate narrow sources typically parallel to the margins of the lava lake. We call these styles of bursting isolated events, clusters, and prolonged episodes, respectively. The frequency of bubble bursting and the mass fluxes of gas and pyroclasts increase from styles 1 to 3. The intensity (mass eruption rate) for single bubble bursts ranges from 280 to 3,500 kilograms per second. The total erupted mass of pyroclasts for a single burst is <4,000 kilograms (kg) and for a single well-constrained prolonged episode is about 10 7 kg. These numbers place the observed spattering at the lowest end of basaltic explosivity in terms of erupted mass (that is, magnitude). Most ejecta fell back into the crater; only strands of Pele’s hair rose to heights where they could be advected downwind from the vent. Collectively, the explosive activity accompanying the three styles of bubble bursting spans from impulsive, transient eruptive behaviors to sustained discharge; this shift represents progressively higher frequency and intensity of bubble bursting.

Hawaii↗

USGS2019

Decrease in seismic velocity observed prior to the 2018 eruption of Kilauea volcano with ambient seismic noise interferometry

The 2018 Kilauea eruption was a complex event that included deformation and eruption at the summit and along the middle and lower East Rift Zones. We use ambient seismic noise interferometry to measure time-lapse changes in seismic velocity of the volcanic edifice prior to the 2018 Kilauea Lower East Rift Zone eruption. Our results show that seismic velocities increase in relation to gradual inflation between 1 March and 20 April. In the ten days prior to the May 3rd eruption, a rapid seismic velocity decrease occurs even though the summit is still undergoing inflation. We show that inter-eruptive inflation/deflation is correlated with surface deformation, while the velocity decrease prior to East Rift Zone eruption is likely due to accumulating damage induced by the pressure exerted by the magma reservoir on the surrounding edifice. The accumulating damage and subsequent decrease in bulk edifice strength likely facilitates the transport of magma from the summit reservoir to the Middle East Rift Zone.

Hawaii↗

USGS2016

Stronger or longer: Discriminating between Hawaiian and Strombolian eruption styles

The weakest explosive volcanic eruptions globally, Strombolian explosions and Hawaiian fountaining, are also the most common. Yet, despite over a hundred years of observations, no classifications have offered a convincing, quantitative way of demarcating these two styles. New observations show that the two styles are distinct in their eruptive timescale, with the duration of Hawaiian fountaining exceeding Strombolian explosions by about 300 to 10,000 seconds. This reflects the underlying process of whether shallow-exsolved gas remains trapped in the erupting magma or whether it is decoupled from it. We propose here a classification scheme based on the duration of events (brief explosions versus prolonged fountains) with a cutoff at 300 seconds that separates transient Strombolian explosions from sustained Hawaiian fountains.

Geology↗

USGS2015

Reticulite‐producing fountains from ring fractures in Kīlauea Caldera ca. 1500 CE

A widely dispersed reticulite bed occurs close to the base of the Keanakākoʻi Tephra at Kīlauea Volcano. It can be divided into six subunits in the northern sector of the volcano; the reticulite also occurs in the southern sector, but outcrops are sparse owing to penecontemporaneous erosion and burial. Multilobate isopachs for each subunit and the total deposit suggest that multiple fountaining vents were distributed in the northern half of the caldera, possibly along ring fractures for the newly formed caldera. Isopach maps also show a sharp decline in thickness along the dispersal axis of each lobe, which could be explained by remobilization of tephra and/or inclined fountains. Despite such isopach characteristics, thinning rates calculated from the isopach data indicate that the fountains were among the most intense and powerful of all studied Kīlauea fountains. Density analyses of the pyroclasts suggest that fountaining was high (>600m) yet complex, possibly due to lava ponding and reentrainment. The calculated volume of the reticulite deposited around the caldera rim is approximately 0.2km 3 , more voluminous than the deposits of the 1959 Kīlauea Iki eruption; this volume is a minimum, however, as the low-density tephra is easily remobilized, and 600m high caldera walls probably trapped tephra within the caldera, which is deeply buried today and not accounted for in the volume calculations. The duration of this eruption was most likely at least a few days to weeks, based on the calculated volume and estimated discharge rates as seen during the Kīlauea Iki 1959 eruption.

Hawaii↗

USGS2015

Onset of a basaltic explosive eruption from Kīlauea’s summit in 2008

The onset of a basaltic eruption at the summit of Kīlauea volcano in 2008 is recorded in the products generated during the first three weeks of the eruption and suggests an evolution of both the physical properties of the magma and also lava lake levels and vent wall stability. Ash componentry and the microtextures of the early erupted lapilli products reveal that the magma was largely outgassed, perhaps in the preceding weeks to months. An increase in the juvenile:lithic ratio and size of ash collected from March 23 to April 3 records an increasing level of the magma within the conduit. After April 3 until the explosive eruption of April 9, a trend of decreasing juvenile:lithic ratio suggests that vent wall collapses were more frequent, possibly because lava level increased and destabilized the overhanging wall [Orr et al. 2013]. Despite increasing lake height, the microtextural characteristics of the lapilli suggest that the outgassed end-member was still being tapped between March 26 and April 8. The April 9 rockfall triggered an explosive eruption that produced a new component in the eruption deposits not seen in the preceding weeks; microvesicular juvenile lapilli, the first evidence of an actively vesiculating magma. Two additional dense end-member pyroclast types were also erupted during the April 9 explosion, likely related to outgassed magma with longer residence times than the microvesicular magma. We link these pyroclasts to a stagnant viscous crust at the top of the magma column or to convecting, downwelling magma. Our study of ash componentry and the textures of juvenile lapilli suggests that the April 9 explosive event effectively cleared the conduit of largely outgassed magma. The degassing processes during this eruption are complex and varied: in the period of persistent degassing during March 26-April 8 small resident bubbles at shallow levels in the lava lake were coupled to the magma whereas large bubbles ascended, expanded and fragmented. During the rockfall- triggered explosion of April 9, all bubbles were coupled to the host magma on the timescale of decompression, but additional exsolution, decompression and expansion of deeper, more gas-rich resident magma likely occurred [cf. Carey et al. 2012]. Where external conditions play a significant role in eruption dynamics, e.g., by triggering eruptions, vesiculation and degassing dynamics can be expected to be complex.

Hawai'i↗

USGS2013

Convection in a volcanic conduit recorded by bubbles

Microtextures of juvenile pyroclasts from Kīlauea’s (Hawai‘i) early A.D. 2008 explosive activity record the velocity and depth of convection within the basaltic magma-filled conduit. We use X-ray microtomography (μXRT) to document the spatial distribution of bubbles. We find small bubbles (radii from 5 μm to 70 μm) in a halo surrounding larger millimeter-size bubbles. This suggests that dissolved water was enriched around the larger bubbles—the opposite of what is expected if bubbles grow as water diffuses into the bubble. Such volatile enrichment implies that the volatiles within the large bubbles were redissolving into the melt as they descended into the conduit by the downward motion of convecting magma within the lava lake. The thickness of the small bubble halo is ∼100–150 μm, consistent with water diffusing into the melt on time scales on the order of 10 3 s. Eruptions, triggered by rockfall, rapidly exposed this magma to lower pressures, and the haloes of melt with re-dissolved water became sufficiently supersaturated to cause nucleation of the population of smaller bubbles. The required supersaturation pressures are consistent with a depth of a few hundred meters and convection velocities of the order of 0.1 m s −1 , similar to the circulation velocity observed on the surface of the Halema‘uma‘u lava lake.

Hawai'i↗

USGS2012

Externally triggered renewed bubble nucleation in basaltic magma: the 12 October 2008 eruption at Halema‘uma‘u Overlook vent, Kīlauea, Hawai‘i, USA

From October 2008 until present, dozens of small impulsive explosive eruptions occurred from the Overlook vent on the southeast side of Halema‘uma‘u Crater, at Kīlauea volcano, USA. These eruptions were triggered by rockfalls from the walls of the volcanic vent and conduit onto the top of the lava column. Here we use microtextural observations and data from clasts erupted during the well-characterized 12 October 2008 explosive eruption at Halema‘uma‘u to extend existing models of eruption triggering. We present a potential mechanism for this eruption by combining microtextural observations with existing geophysical and visual data sets. We measure the size and number density of bubbles preserved in juvenile ejecta using 2D images and X-ray microtomography. Our data suggest that accumulations of large bubbles with diameters of >50 μ m to at least millimeters existed at shallow levels within the conduit prior to the 12 October 2008 explosion. Furthermore, a high number density of small bubbles <50 μ m is measured in the clasts, implying very rapid nucleation of bubbles. Visual observations, combined with preexisting geophysical data, suggest that the impact of rockfalls onto the magma free surface induces pressure changes over short timescales that (1) nucleated new additional bubbles in the shallow conduit leading to high number densities of small bubbles and (2) expanded the preexisting bubbles driving upward acceleration. The trigger of eruption and bubble nucleation is thus external to the degassing system.

Hawaii↗