Geology topics

Donald A. Swanson

Publications and source records attributed to Donald A. Swanson.

At least 19 recordsLinked to original sources

USGS2023

Complex styles of phreatomagmatic explosions at Kīlauea Volcano, Hawaii, controlled by magma structure

Explosive eruptions at basaltic volcanoes remain poorly understood. Kīlauea Volcano is a type locality for basaltic eruptions and is well-known for effusive activity. However, more than 7 m of phreatomagmatic Keanakākoʻi Tephra unit D deposits from explosive eruptions crown the southern rim of the summit caldera and provide a stark reminder of Kīlauea’s explosive past and future potential. We used detailed field observations as well as granulometric and morphological analysis of 100 samples from two proximal sections to assess the eruption style and fragmentation mechanism. The deposits can be divided into four subunits, six different lithofacies, and contain three juvenile tephra components. Each juvenile component shows distinct shape variability resulting from molten fuel-coolant interaction (MFCI) explosions of magma of variable vesicularity. Fragmentation of dense glass generates olive-green ash, fragmentation of low to moderately vesicular magma generates a dark gray ash-lapilli component, and fragmentation of highly vesicular magma generates light-yellow pumice. Our work shows that magma structure impacts MFCI explosion efficiency. Small-scale planar bedding throughout most of the deposit points to a general eruption style of small, frequent explosions generating low plumes. Thicker beds of accretionary lapilli of fine-extremely fine ash are related to very efficient magma-water mixing. Pyroclastic density current (PDC) deposits in the upper part of the stratigraphy contain at least three flows but show no significant dune or cross-bedding structures. We suggest that this is a function of the vent being situated in a caldera that was then ∼600 m deep, where the caldera wall acted as a barrier and changed the flow dynamics to very dilute overspills and co-PDC plume falls over the wall. Deconvolution modeling of the polymodal grain size distributions is used to assess grain size changes of each juvenile component for this deposit, which greatly improves interpretation of lithofacies generation and eruption dynamics. Size-correlated shape parameters show that shape data across a wide size range are needed to accurately track grain shapes. This study demonstrates how careful examination of grain size and shape of juvenile tephra clasts can help volcanologists understand how effusive basaltic volcanoes can become violently explosive.

Hawaii↗

USGS2023

The 2018 eruption of Kīlauea: Insights, puzzles, and opportunities for volcano science

The science of volcanology advances disproportionately during exceptionally large or well-observed eruptions. The 2018 eruption of Kīlauea Volcano (Hawai‘i) was its most impactful in centuries, involving an outpouring of more than one cubic kilometer of basalt, a magnitude 7 flank earthquake, and the volcano’s largest summit collapse since at least the nineteenth century. Eruptive activity was documented in detail, yielding new insights into large caldera-rift eruptions; the geometry of a shallow magma storage-transport system and its interaction with rift zone tectonics; mechanisms of basaltic tephra-producing explosions; caldera collapse mechanics; and the dynamics of fissure eruptions and high-volume lava flows. Insights are broadly applicable to a range of volcanic systems and should reduce risk from future eruptions. Multidisciplinary collaboration will be required to fully leverage the diversity of monitoring data to address many of the most important outstanding questions.

Hawai‘i↗

USGS2022

Olivine and glass chemistry record cycles of plumbing system recovery after summit collapse events at Kīlauea Volcano, Hawai‘i

The eruptive activity of Kīlauea Volcano (Hawai‘i) in the past 2500 years has alternated between centuries-long periods dominated either by explosive or effusive eruptions. The onset of explosive periods appears to be marked by caldera collapse events at the volcano's summit accompanied by draining of Kīlauea's magmatic plumbing system. Here we leverage >1800 olivine forsterite (Fo) contents, >900 glass MgO contents, and estimated magma supply rates from the past six centuries to describe the relationships between summit collapse and the composition of erupted material. On a first order basis, the major element chemistry of the centuries-long eruptive periods largely originates from fundamental differences between fractional crystallization of shallowly stored magmas during high-supply effusive-dominated periods versus little evolution of mafic recharge magmas during low-supply explosive-dominated periods. The modern effusive period (1820s-present) is dominated by relatively evolved olivine forsterite contents (Fo81–82) for Kīlauea, which is interpreted to reflect a buffered crustal reservoir system in which shallow storage and fractional crystallization control the composition of magmas. In contrast, olivine crystals from the explosive Keanakāko‘i Tephra (1500 - early 1800s C.E.) are dominated by higher olivine forsterite contents (Fo89) which are interpreted to reflect more primitive compositions, are correlated with glass MgO compositions extending to high values (e.g.,11.0 wt%), and show signs of magma mixing (zoned olivine, bimodal Fo populations). These signatures reflect a disrupted reservoir system in which high-MgO recharge melts mix with melts left over from draining of the shallow (<5 km) magma plumbing. Superimposed on these explosive-effusive periods are three decades- to centuries long periods of progressively evolving olivine and glass compositions. Eruptions that occur after caldera collapse in ~1500C.E. and smaller scale crater collapse events in 1790 (inferred) and 1924 have heterogeneous olivine populations dominated by ≥Fo88 and typically high MgO glasses. These compositions reflect inefficient mixing of stored and primitive recharge magmas after the disruption of the shallow plumbing system. After these collapses, olivine Fo and glass MgO subsequently evolve to <Fo82 and <7.0 wt% compositions, reflecting the recovery of the crustal plumbing system to an end-member system state characterized by efficient mixing of recharge and stored magmas that serve to buffer the shallow magma reservoirs. These evolved signatures suggest that a mature and buffered reservoir system may be a key condition for significant disruptions of volcanic plumbing systems. Plumbing system recovery is slower following large-scale caldera collapse (hundreds of years) compared to recovery following smaller crater collapse (tens of years), which may be modulated by differences in magma supply rates. Following the 2018 crater collapse olivine populations have high-Fo but glasses are low MgO, suggesting that this collapse might have disrupted shallow magma pathways but not strongly impacted the reservoir(s). Ultimately, olivine and glass major element chemistry record the impacts of caldera and smaller but significant summit crater collapse events at Kīlauea and could be used to provide a framework for better characterizing long-term volcano evolution in Hawai‘i and shield volcanoes elsewhere.

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USGS2020

From lava to water: A new era at Kīlauea

No abstract available.

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USGS2019

Total grain size distribution of an intense Hawaiian fountaining event: Case study of the1959 Kīlauea Iki eruption

The 1959 eruption of Kīlauea Iki on the Island of Hawai’i is a principal example of powerful Hawaiian fountaining. Over 36 days (including repose periods), 16 fountaining episodes created a small cone, a downwind tephra blanket of approximately 0.003 km 3 and a lava lake of about 0.04 km 3 volume. During the explosive activity, the maximum fountain heights reached 600 m. Based on a dataset of more than 450 tephra grain size samples, we present both a total grain size distribution (TGSD) of the entire downwind tephra deposit, and also TGSDs for two eruptive subunits (the opening and the closing stages). The opening stage was characterized by persistent fountaining over a period of 8 days with fountain heights averaging ∼ 100 m; in contrast, the closing stage was characterized by two short (hours-long) but powerful fountaining episodes (up to 600 m). The significantly different fountaining intensities are reflected in the characteristics of the TGSDs. For the closing stages, we link bimodality of TGSDs to periods of simultaneous deposition of ballistics and fallout from the convective cloud, both of which are a function of the maximum fountain height. The 1959 Kīlauea Iki case study presents a well-constrained set of TGSD data linked with Hawaiian-style fountaining of two contrasting intensities and can be used as a valuable reference point for eruption source parameters in future modeling of pyroclast dispersal during Hawaiian fountaining eruptions.

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USGS2019

The Kulanaokuaiki-3 tephra, 900 CE: Products of a remarkably energetic pyroclastic eruption at Kīlauea Volcano, Hawaiʻi, USA

Eruptions of Kīlauea Volcano, Hawaiʻi, USA, can be more powerful than previously recognized. The Kulanaokuaiki-3 (K-3) eruption, ca. 900 CE, consisted of two episodes that dispersed lithic wall-rock clasts (Episode 1) and dominantly scoria (Episode 2; VEI-3) across >65 km 2 southeast of the summit. Dense 12 cm blocks of Episode 1 fell 8–10 km from the summit vent, and 2–4 cm lithic lapilli reached the coastline, 17 km from the vent. The Episode 2 deposit is chemically zoned, indicating orderly eruption from a layered magma body analogous to the 1959 Kīlauea Iki lava lake. Olivine-hosted melt inclusions suggest a magma body within 1 km of the surface. Some Episode 1 lithic clasts have magmatic rinds chemically similar to the early Episode 2 scoria, suggesting a genetic link, although each had a distinct eruption mechanism. Southeastward tephra dispersal counter to NE trade winds implies dispersal by jet-stream winds. The dispersal of lithic clasts in Episode 1 cannot be explained by ballistic trajectories or by transport in a buoyant plume. Calculations instead indicate that a jet from a vent with a minimum diameter of 50 m, a velocity of at least 300 m/s, and a duration of ∼60 s could have lifted the lithic clasts into the jet stream. Isopach and isopleth maps for Episode 2 indicate a subplinian column height of 14–18 km and a duration of 2–3 h, assuming constant flux. The Episode 1 conduit probably intersected or otherwise lowered pressure within a compositionally zoned magma body, triggering eruption of the Episode 2 scoria.

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USGS2019

Controls on lava lake level at Halema‘uma‘u Crater, Kīlauea Volcano

The height of the lava column is a fundamental measure of open-vent volcanic activity, but little continuous long-term data exist to understand this parameter. The recent (2008-2018) lava lake activity at the summit of Kīlauea Volcano provides a unique opportunity to track and understand the processes that control lava level over timescales ranging from minutes to years. We review recently published data as well as analyze the long-term record of lava level at Kīlauea’s summit during 2009-2017. Longer timescale fluctuations, over days to months, have a strong positive linear correlation with ground deformation, suggesting they reflect pressure changes in the summit magma reservoir. Shorter timescale fluctuations, over minutes to hours, have an inverse relationship with spattering (i.e. outgassing) intensity at the lake surface – increased outgassing lowers the lake level and vice versa. Our analysis of the long-term lava level data thus confirms that lava level at Halemaʻumaʻu is controlled by these two types of processes: 1) those related to magma reservoir pressure changes (such as magma supply rate) and 2) shallow outgassing fluctuations (such as gas pistoning). Frequency filtering can isolate pressure- and outgassing-driven components of lava level change. Time series analysis indicates that there was no large, persistent periodicity in the lava level; a minor fortnightly oscillation might be related to Earth tides but was not continuously present. The remarkable correlation between lava level and deformation of the summit indicates that the lava lake acts as a reliable “piezometer”; tracking lava level over time may thus provide an indication of flank eruptive potential. We show that long-term interdisciplinary monitoring is necessary to discriminate the processes that control lava level.

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USGS2019

Geochemical evolution of Keanakāko‘i Tephra, Kīlauea Volcano, Hawai‘i

The Keanakāko‘i Tephra was deposited from 1500 to ca. 1820 CE, when Kīlauea’s magmatic output was ~2% of the average output during historical times (post–1823 CE). The tephra consists of deposits from numerous phreatomagmatic and phreatic eruptions, three episodes of high lava fountains, and one lava. Fresh glass is available from most tephra units. Major elements and trace elements were determined for glass from 49 tephra units and three pretephra lavas. Olivine crystals from 11 high-MgO tephra glasses were also analyzed. These results were compared to compositions from Kīlauea’s historical period to evaluate ~500 yr of Kīlauea geochemical evolution. Keanakāko‘i Tephra glass composition ranged widely (e.g., 3.4–11.2 wt% MgO). The observed large variations in FeO, CaO, TiO 2 , and K 2 O at a given MgO indicate numerous compositionally distinct parental magmas, with the two early nineteenth-century pumice eruptions showing the most diverse compositions. These two magmas were erupted on opposite sides of the caldera and probably tapped different magma bodies. The common occurrence of high-MgO olivine compositions (forsterite [Fo] 88%–89%) in MgO-rich tephra glasses indicates that primitive magma (Mg# 73–74) was routinely supplied to Kīlauea’s summit. Wide ranges and reverse zoning in olivine core compositions from some units show that magma mixing occurred before some eruptions. Modeling of compositional variations within Keanakāko‘i Tephra units using alphaMELTS showed that the most consistent trends for crystal fractionation involved shallow magma (1–2 km), with low water content (0.2 wt% in parental magma) and oxygen fugacity just below the quartz-fayalite-magnetite (QFM) buffer (–0.5 log units). Keanakāko‘i Tephra glasses have lower La/Yb and Nb/Y ratios than historical Kīlauea lavas. Low ratios have been observed during periods of high magma output for historical lava, which is inconsistent with the low magma output at Kīlauea’s summit during 1500–1820 CE. The most likely explanation for this inconsistency is endogenous growth within Kīlauea during this period, following formation of the modern summit caldera. No correlation was found between glass chemistry and eruption style for Keanakāko‘i Tephra deposits. Glass samples from many explosive units have lower Nb/Y and La/Yb ratios compared to glass from high lava-fountain units and historical effusive eruptions. The explosive character of Keanakāko‘i Tephra eruptions was probably caused by interaction of magma with shallow or surface water.

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USGS2019

A new perspective on the 19th century golden pumice deposit of Kilauea volcano

The golden pumice deposit (unit K1) represents one of the latest episodes of Hawaiian fountaining in the Keanakāko‘i Tephra and is the product of the first high fountaining eruption at Kīlauea summit in ~300 yr, since the caldera formed in ca. 1500 CE. We present a new physical characterization of the deposit based on over 200 field sites, all affected by severe erosion, alteration, and silicic encrusting. We detail the deposit geometry, stratigraphic and structural relationships, and componentry to constrain its volume and reconstruct the eruptive sequence. The deposit is then discussed and set against other young episodes of high fountaining at Kīlauea. We interpret the golden pumice as the product of a days-long eruptive sequence with a source located inside a caldera much deeper than that of today. The eruption probably started along a NE-SW–oriented fissure and migrated toward a single vent in the southwestern part of the caldera, where at least two high Hawaiian-style fountains produced a tephra deposit of ~6 × 10 6 m 3 . Stratigraphic contacts reveal that erosion occurred not only between, but also during the fountaining episodes, suggesting heavy rainfall during deposition. Field observations during this study also led to the discovery of the first stratigraphic evidence that the eastern pumice postdates the golden pumice, which contributes to the new definition of the stratigraphy of the Keanakāko‘i Tephra presented in this volume.

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USGS2019

Dikes in the Koaʻe fault system, and the Koaʻe-east rift zone structural grain at Kīlauea Volcano, Hawaii

Two small scoria vents were discovered in the Koa‘e fault system, an extensional regime connecting the east and southwest rift zones of Kīlauea that was previously considered to be noneruptive. The chemical composition of the scoria suggests an early to middle nineteenth-century age. The vents prove that magma can intrude several kilometers into the central part of the Koa‘e fault system from the nearest rift zone, supporting previous seismic and geodetic inferences of intrusions into the Koa‘e fault system in the twentieth century. Geodetic studies for the past 50 yr document widening of the Koa‘e fault system at a time-averaged rate of ~4.5 cm/yr, involving mostly coseismic strains, but also creep and displacement related to dike intrusions. These rates are consistent with a longer-term widening rate for the past ~700 yr calculated from crack widths in a lava flow of about that age. The Koa‘e fault system blends into, and is a structural continuation of, the east rift zone. We interpret the locus of intrusion in the east rift zone to have migrated ~6.5 km SE during the past 100,000–125,000 yr, as estimated from linear extrapolation of measured displacement rates across the Koa‘e fault system and east rift zone. The inception of migration is consistent with the onset of the tholeiitic stage at Kīlauea as interpreted by previous studies. As the rift zone moved away from the summit, a marked curvature in the transport pathway developed in order for the rift zone to maintain its connection to the summit magma reservoir. The migration resulted in development of the SE-trending east rift connector, a term we prefer instead of the upper east rift zone. The connector supplies magma to the ENE-trending rift zone from the summit storage complex but is not itself the site of significant magma storage or eruption. The Koa‘e fault system merges into the southwest rift zone, which has been migrating southeastward for an uncertain period of time. Some magma that enters it passes from the summit reservoir complex through the southwest rift connector (seismic southwest rift zone), analogous to the east rift connector. Both connectors reflect the response of magma-transport pathways to asymmetric volcano spreading away from a relatively fixed summit magma reservoir. The ENE structural grain of the Koa‘e fault system and east rift zone pervades Kīlauea’s entire edifice. Most eruptions take place along this trend. The major exception is the southwest rift zone, which may reflect the stresses of Mauna Loa spreading and the Ka‘ōiki fault system. The dominant ENE grain emphasizes the importance of SSE-directed volcano spreading in controlling most of Kīlauea’s tectonic and eruptive behavior.

Hawaii↗

USGS2018

Lava lake activity at the summit of Kīlauea Volcano in 2016

The ongoing summit eruption at Kīlauea Volcano, Hawai‘i, began in March 2008 with the formation of the Overlook crater, within Halema‘uma‘u Crater. As of late 2016, the Overlook crater contained a large, persistently active lava lake (250 × 190 meters). The accessibility of the lake allows frequent direct observations, and a robust geophysical monitoring network closely tracks subtle changes at the summit. These conditions present one of the best opportunities worldwide for understanding persistent lava lake behavior and the geophysical signals associated with open-vent basaltic eruptions. In this report, we provide a descriptive and visual summary of lava lake activity during 2016, a year consisting of continuous lava lake activity. The lake surface was composed of large black crustal plates separated by narrow incandescent spreading zones. The dominant motion of the surface was normally from north to south, but spattering produced transient disruptions to this steady motion. Spattering in the lake was common, consisting of one or more sites on the lake margin. The Overlook crater was continuously modified by the deposition of spatter (often as a thin veneer) on the crater walls, with frequent collapses of this adhered lava into the lake. Larger collapses, involving lithic material from the crater walls, triggered several small explosive events that deposited bombs and lapilli around the Halema‘uma‘u Crater rim, but these did not threaten public areas. The lava lake level varied over several tens of meters, controlled primarily by changes in summit magma reservoir pressure (in part driven by magma supply rates) and secondarily by fluctuations in spattering and gas release from the lake (commonly involving gas pistoning). The lake emitted a persistent gas plume, normally averaging 1,000–8,000 metric tons per day (t/d) of sulfur dioxide (SO 2 ), as well as a constant fallout of small juvenile and lithic particles, including Pele’s hair and tears. The gas emissions created volcanic air pollution (vog) that affected large areas of the Island of Hawai‘i. The summit eruption has been a major attraction for visitors in Hawai‘i Volcanoes National Park. During 2016, the rising lake levels allowed the lake and its spattering to be more consistently visible from public viewing areas, enhancing the visitor experience. The U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) closely monitors the summit eruption and keeps emergency managers and the public informed of activity.

Hawai'i↗

USGS2017

Timescales of mixing and storage for Keanakāko‘i Tephra magmas (1500-1823 C.E.), Kīlauea Volcano, Hawai‘i

The last 2500 years of activity at Kīlauea Volcano (Hawai‘i) have been characterized by centuries-long periods dominated by either effusive or explosive eruptions. The most recent period of explosive activity produced the Keanakāko‘i Tephra (KT; ca. 1500–1820 C.E.) and occurred after the collapse of the summit caldera (1470–1510 C.E.). Previous studies suggest that KT magmas may have ascended rapidly to the surface, bypassing storage in crustal reservoirs. The storage conditions and rapid ascent hypothesis are tested here using chemical zoning in olivine crystals and thermodynamic modeling. Forsterite contents (Fo; [Mg/(Mg + Fe) × 100]) of olivine core and rim populations are used to identify melt components in Kīlauea’s prehistoric (i.e., pre-1823) plumbing system. Primitive (≥Fo 88 ) cores occur throughout the 300+ years of the KT period; they originated from mantle-derived magmas that were first mixed and stored in a deep crustal reservoir. Bimodal olivine populations (≥Fo 88 and Fo 83–84 ) record repeated mixing of primitive magmas and more differentiated reservoir components shallower in the system, producing a hybrid composition (Fo 85–87 ). Phase equilibria modeling using MELTS shows that liquidus olivine is not stable at depths >17 km. Thus, calculated timescales likely record mixing and storage within the crust. Modeling of Fe–Mg and Ni zoning patterns (normal, reverse, complex) reveal that KT magmas were mixed and stored for a few weeks to several years before eruption, illustrating a more complex storage history than direct and rapid ascent from the mantle as previously inferred for KT magmas. Complexly zoned crystals also have smoothed compositional reversals in the outer 5–20 µm rims that are out of Fe–Mg equilibrium with surrounding glasses. Diffusion models suggest that these rims formed within a few hours to a few days, indicating that at least one additional, late-stage mixing event may have occurred shortly prior to eruption. Our study illustrates that the lifetimes of KT magmas are more complex than previously proposed, and that most KT magmas did not rise rapidly from the mantle without modification during shallow crustal storage.

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USGS2017

Partitioning of pyroclasts between ballistic transport and a convective plume: Kīlauea volcano, 19 March 2008

We describe the discrete ballistic and wind-advected products of a small, but exceptionally well-characterized, explosive eruption of wall-rock-derived pyroclasts from Kīlauea volcano on 19 March 2008 and, for the first time, integrate the size distribution of the two subpopulations to reconstruct the true size distribution of a population of pyroclasts as it exited from the vent. Based on thinning and fining relationships, the wind-advected fraction had a mass of 6.1 × 10 5 kg and a thickness half distance of 110 m, placing it at the bottom end of the magnitude and intensity spectra of pyroclastic falls. The ballistic population was mapped, in the field and by using structure-from-motion techniques, to a diameter of > 10–20 cm over an area of ~0.1 km 2 , with an estimated mass of 1 × 10 5 kg. Initial ejection velocities of 50–80 m/s were estimated from inversion of isopleths. The total grain size distribution was estimated by using a mass partitioning of 98% of wind-advected material and 2% of ballistics, resulting in median and sorting values of −1.7 ϕ and 3.1 ϕ . It is markedly broader than those calculated for the products of magmatic explosive eruptions, because the grain size of 19 March 2008 clast population is unrelated to a volcanic fragmentation event and instead was “inherited” from a population of talus clasts that temporary blocked the vent prior to the eruption. Despite a conspicuous near-field presence, the ballistic subpopulation has only a minor influence on the grain size distribution because of its rapid thinning and fining away from source.

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USGS2016

Magma decompression rates during explosive eruptions of Kīlauea volcano, Hawaii, recorded by melt embayments

The decompression rate of magma as it ascends during volcanic eruptions is an important but poorly constrained parameter that controls many of the processes that influence eruptive behavior. In this study, we quantify decompression rates for basaltic magmas using volatile diffusion in olivine-hosted melt tubes (embayments) for three contrasting eruptions of Kīlauea volcano, Hawaii. Incomplete exsolution of H 2 O, CO 2 , and S from the embayment melts during eruptive ascent creates diffusion profiles that can be measured using microanalytical techniques, and then modeled to infer the average decompression rate. We obtain average rates of ~0.05–0.45 MPa s −1 for eruptions ranging from Hawaiian style fountains to basaltic subplinian, with the more intense eruptions having higher rates. The ascent timescales for these magmas vary from around ~5 to ~36 min from depths of ~2 to ~4 km, respectively. Decompression-exsolution models based on the embayment data also allow for an estimate of the mass fraction of pre-existing exsolved volatiles within the magma body. In the eruptions studied, this varies from 0.1 to 3.2 wt% but does not appear to be the key control on eruptive intensity. Our results do not support a direct link between the concentration of pre-eruptive volatiles and eruptive intensity; rather, they suggest that for these eruptions, decompression rates are proportional to independent estimates of mass discharge rate. Although the intensity of eruptions is defined by the discharge rate, based on the currently available dataset of embayment analyses, it does not appear to scale linearly with average decompression rate. This study demonstrates the utility of the embayment method for providing quantitative constraints on magma ascent during explosive basaltic eruptions.

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USGS2015

Lava lake level as a gauge of magma reservoir pressure and eruptive hazard

Forecasting volcanic activity relies fundamentally on tracking magma pressure through the use of proxies, such as ground surface deformation and earthquake rates. Lava lakes at open-vent basaltic volcanoes provide a window into the uppermost magma system for gauging reservoir pressure changes more directly. At Kīlauea Volcano (Hawaiʻi, USA) the surface height of the summit lava lake in Halemaʻumaʻu Crater fluctuates with surface deformation over short (hours to days) and long (weeks to months) time scales. This correlation implies that the lake behaves as a simple piezometer of the subsurface magma reservoir. Changes in lava level and summit deformation scale with (and shortly precede) changes in eruption rate from Kīlauea's East Rift Zone, indicating that summit lava level can be used for short-term forecasting of rift zone activity and associated hazards at Kīlauea.

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USGS2015

Hawaiian fissure fountains: Quantifying vent and shallow conduit geometry, episode 1 of the 1969-1974 Mauna Ulu eruption

Geometries of shallow magmatic pathways feeding volcanic eruptions are poorly constrained, yet many key interpretations about eruption dynamics depend on knowledge of these geometries. Direct quantification is difficult because vents typically become blocked with lava at the end of eruptions. Indirect geophysical techniques have shed light on some volcanic conduit geometries, but the scales are too coarse to resolve narrow fissures (widths typically 1 m). Kīlauea's Mauna Ulu eruption, which started with <50 m high Hawaiian fountains along a 4.5 km fissure on 24 May 1969, provides a unique opportunity to measure the detailed geometry of a shallow magmatic pathway, as the western vents remain unobstructed to depths >30 m. Direct measurements at the ground surface were augmented by tripod-mounted lidar measurements to quantify the shallow conduit geometry for three vents at a resolution <4 cm. We define the form of the fissure in terms of aspect ratio, flaring ratio, irregularity, sinuosity, and segmentation and discuss the factors influencing these parameters. In the past, simplified first-order fissure geometries have been used in computational modeling. Our data can provide more accurate conduit shapes for better understanding of shallow fissure fluid dynamics and how it controls eruptive behavior, especially if incorporated into computer models.

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USGS2014

The dynamics of Hawaiian-style eruptions: A century of study

This chapter, prepared in celebration of the Hawaiian Volcano Observatoryʼs centennial, provides a historical lens through which to view modern paradigms of Hawaiian-style eruption dynamics. The models presented here draw heavily from observations, monitoring, and experiments conducted on Kīlauea Volcano, which, as the site of frequent and accessible eruptions, has attracted scientists from around the globe. Long-lived eruptions in particular—Halema‘uma‘u 1907–24, Kīlauea Iki 1959, Mauna Ulu 1969–74, Pu‘u ‘Ō‘ō-Kupaianaha 1983–present, and Halema‘uma‘u 2008–present—have offered incomparable opportunities to conceptualize and constrain theoretical models with multidisciplinary data and to field-test model results. The central theme in our retrospective is the interplay of magmatic gas and near-liquidus basaltic melt. A century of study has shown that gas exsolution facilitates basaltic dike propagation; volatile solubility and vesiculation kinetics influence magma-rise rates and fragmentation depths; bubble interactions and gas-melt decoupling modulate magma rheology, eruption intensity, and plume dynamics; and pyroclast outgassing controls characteristics of eruption deposits. Looking to the future, we anticipate research leading to a better understanding of how eruptive activity is influenced by volatiles, including the physics of mixed CO 2 -H 2 O degassing, gas segregation in nonuniform conduits, and vaporization of external H 2 O during magma ascent.

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USGS2013

Contrasting patterns of vesiculation in low, intermediate, and high Hawaiian fountains: A case study of the 1969 Mauna Ulu eruption

Hawaiian-style eruptions, or Hawaiian fountains, typically occur at basaltic volcanoes and are sustained, weakly explosive jets of gas and dominantly coarse, juvenile ejecta (dense spatter to delicate reticulite). Almost the entire range of styles and mass eruption rates within Hawaiian fountaining occurred during twelve fountaining episodes recorded at Mauna Ulu, Kīlauea between May and December 1969. Such diversity in intensity and style is controlled during magma ascent by many processes that can be constrained by the size and shape of vesicles in the 1969 pyroclasts. This paper describes pyroclast vesicularity from high, intermediate, and low fountaining episodes with eruption rates from 0.05 to 1.3 × 10 6 m 3 h − 1 . As each eruptive episode progressed, magma ascent slowed in and around the vent system, offering extended time for bubbles to grow and coalesce. Late ejected pyroclasts are thus characterized by populations of fewer and larger vesicles with relaxed shapes. This progression continued in the intervals between episodes after termination of fountain activity. The time scale for this process of shallow growth, coalescence and relaxation of bubbles is typically tens of hours. Rims and cores of pumiceous pyroclasts from moderate to high fountaining episodes record a second post-fragmentation form of vesicle maturation. Partially thermally insulated pyroclasts can have internal bubble populations evolve more dynamically with continued growth and coalescence, on a time scale of only minutes, during transport in the fountains. Reticulite, which formed in a short-lived fountain 540 m in height, underwent late, short-lived bubble nucleation followed by rapid growth of a uniform bubble population in a thermally insulated fountain, and quenched at the onset of permeability before significant coalescence. These contrasting patterns of shallow degassing and outgassing were the dominant controls in determining both the form and duration of fountaining episodes at Mauna Ulu, and probably for many other Hawaiian-style eruptions.

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