Geology topics

Research about Kilauea Volcano

Source-linked reports with geographic coverage including Kilauea Volcano.

At least 19 recordsLinked to original sources

USGS2025

Social sensing a volcanic eruption: Application to Kīlauea, 2018

Protecting lives and livelihoods during volcanic eruptions is the key challenge in volcanology, conducted primarily by volcano monitoring and emergency management organisations, but it is complicated by scarce knowledge of how communities respond in times of crisis. Social sensing is a rapidly developing practice that can be adapted for volcanology. Here we use social sensing of Twitter (currently known as X) posts to track changes in social action and reaction throughout the 2018 eruption of Kīlauea on the island of Hawai`i. The volume of relevant posts very rapidly increases in early May, coincident with the beginning of the eruption; automated sentiment analysis shows a simultaneous shift towards more negative emotions being expressed in post text. Substantial negative trends in sentiment are evident in reaction to high-impact events, including the destruction of a popular residential area and injuries sustained by tourists viewing the eruption. Topics of local Twitter conversation reveal societal actions, including the sharing of hazard warnings, mitigation actions, and aid announcements. Temporal trends in societal actions reflect patterns in volcanic activity (e.g. the peak and waning of eruptive activity), civil protection actions (e.g. risk mitigation actions and the communication of official warnings), and socioeconomic pressures (e.g. the destruction of homes). Local tweets detailing eruption damage and disruption display a similar temporal trend to independent estimates of the number of buildings in contact with lava. We show how hazard and risk information is discussed and reacted to on Twitter, which helps inform our understanding of community response actions and aids situational awareness, and outline how our approach could be adapted for use in real time.

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USGS2024

Pulsing in the Ahu‘ailaʻau pond-spillway system during the 2018 Kilauea Eruption: A dynamical systems perspective

During the 2018 K ī "> ī ī lauea lower East Rift Zone eruption, lava from 24 fissures inundated more than 8000 acres of land, destroying more than 700 structures over three months. Eruptive activity eventually focused at a single vent characterized by a continuously fed lava pond that was drained by a narrow spillway into a much wider, slower channelized flow. The spillway exhibited intervals of ‘pulsing’ behaviour in which the lava depth and velocity were observed to oscillate on time scales of several minutes. At the time, this was attributed to variations in vesiculation originating at depth. Here, we construct a toy fluid dynamical model of the pond–spillway system, and present an alternative hypothesis in which pulsing is generated at the surface, within this system. We posit that the appearance of pulsing is due to a supercritical Hopf bifurcation driven by an increase in the Reynolds number. Asymptotics for the limit cycle near the bifurcation point are derived with averaging methods and compare favourably with the cycle periodicity. Because oscillations in the pond were not observable directly due to the elevation of the cone rim and an obscuring volcanic plume, we model the observations using a spatially averaged Saint-Venant model of the spillway forced by the pond oscillator. The predicted spillway cycle periodicity and waveforms compare favourably with observations made during the eruption. The unusually well-documented nature of this eruption enables estimation of the viscosity of the erupting lava.

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USGS2023

Dynamics of the December 2020 ash-poor plume formed by lava-water interaction at the summit of Kilauea Volcano, Hawaii

On 20 December 2020, after more than 2 years of quiescence at Kīlauea Volcano, Hawaiʻi, renewed volcanic activity in the summit crater caused boiling of the water lake over a period of ∼90 min. The resulting water-rich, electrified plume rose to 11–13 km above sea level, which is among the highest plumes on record for Kīlauea. Although conventional models would infer a high mass flux from explosive magma-water interaction, the plume was not associated with an infrasound signal indicative of “explosive” activity, nor did it produce a measurable ash-fall deposit. We use multisensor data to characterize lava-water interaction and plume generation during this opening phase of the 2020–21 eruption. Satellite, weather radar, and eyewitness observations revealed that the plume was rich in water vapor and hydrometeors but transported less ash than expected from its maximum height. Volcanic lightning flashes detected by ground-based cameras were confined to freezing altitudes of the upper cloud, suggesting that the ice formation drove the electrification of this plume. The low acoustic energy from lava-water interaction points to a weakly explosive style of hydrovolcanism. Heat transfer calculations show that the lava to water heat flux was sufficient to boil the lake within 90 min. Limited mixing of lava and water inhibited major steam explosions and fine fragmentation. Results from one-dimensional plume modeling suggest that the models may underpredict plume height due to overestimation of crosswind air-entrainment. Our findings shed light on an unusual style of volcanism in which weakly explosive lava-water interaction generated an outsized plume.

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USGS2022

Lava fountain jet noise during the 2018 eruption of fissure 8 of Kīlauea volcano

Real-time monitoring is crucial to assess hazards and mitigate risks of sustained volcanic eruptions that last hours to months or more. Sustained eruptions have been shown to produce a low frequency (infrasonic) form of jet noise. We analyze the lava fountaining at fissure 8 during the 2018 Lower East Rift Zone eruption of Kīlauea volcano, Hawaii, and connect changes in fountain properties with recorded infrasound signals from an array about 500 m from the fountain using jet noise scaling laws and visual imagery. Video footage from the eruption reveals a change in lava fountain dynamics from a tall, distinct fountain at the beginning of June to a low fountain with a turbulent, out-pouring lava pond surrounded by a tephra cone by mid-June. During mid-June, the sound pressure level reaches a maximum, and peak frequency drops. We develop a model that uses jet noise scaling relationships to estimate changes in volcanic jet diameter and jet velocity from infrasound sound pressure levels and peak frequencies. The results of this model indicate a decrease in velocity in mid-June which coincides with the decrease in fountain height. Furthermore, the model results suggest an increase in jet diameter, which can be explained by the larger width of the fountain that resembles a turbulent lava pond compared to the distinct fountain at the beginning of June. The agreement between the infrasound-derived and visually observed changes in fountain dynamics suggests that jet noise scaling relationships can be used to monitor lava fountain dynamics using infrasound recordings.

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USGS2022

Infrasound observations and constraints on the 2018 eruption of Kīlauea Volcano, Hawaii

The 2018 eruption of Kīlauea Volcano was a dynamic event involving explosions, collapses, and fountaining at multiple vents spread over tens of kilometers. The permanent infrasound network operated by the USGS Hawaiian Volcano Observatory (HVO) was well prepared to observe the collapse of the summit, and additional deployments permitted infrasound observations during fissuring in the lower East Rift Zone (LERZ). We provide a summary of infrasound observations, including lava lake spattering, collapses, explosions, rockfall, and lava fountaining, using seismicity and tilt at times to help constrain our interpretations. At the summit of Kīlauea Volcano, we document the process of partial caldera collapse and examine a set of “proto-collapse” events that precede the widely observed events but share many of the same qualities as the larger collapses. For the initial twelve collapse events, we compare the timing of collapse onset to other observations and illustrate the repeatable characteristics of the recorded waveforms and infrasound characteristics associated with each episode of caldera collapse. In the LERZ, we match the acoustic signals with visual observations, including fissure migration, explosions near fissures, and littoral explosions. Lastly, we document and discuss the performance of infrasound alarms during the 2018 Kīlauea eruption. In general, alarming became successful in detecting collapse events at the summit of the volcano after tuning and became a key discriminant in the initial determination of collapse events, especially when visual observations were not available.

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USGS2022

Synthetic aperture radar volcanic flow maps (SAR VFMs): A simple method for rapid identification and mapping of volcanic mass flows

Volcanic mass flows, including lava, pyroclastic density currents, and lahars, account for the bulk of fatalities and infrastructure damage caused by volcanic eruptions. Mapping these flows soon after their emplacement is vital to understanding their impact and to forecasting the likely behavior of potential future flows. Synthetic aperture radar (SAR) can provide useful information about surface properties and changes regardless of environmental conditions or time of day, but no individual SAR product can unambiguously detect and map surface mass flows in all conditions. Combining SAR products, however, can capitalize on the strengths and compensate for the weaknesses of individual data types. SAR volcanic flow maps (SAR VFMs) merge cross-polarized amplitude imagery from two different dates with interferometric coherence spanning those dates. The combination of amplitude change with coherence provides a means of detecting volcanic mass flows regardless of surface conditions, and data collected by satellite provide the spatial coverage needed to detect changes over broad areas. Application to eruptions of Kīlauea (Hawaiʻi), Nyiragongo (Democratic Republic of Congo), Sinabung (Indonesia), and Fuego (Guatemala) demonstrate the value of SAR VFMs for monitoring hazardous volcanic activity, and the importance of acquiring cross-polarized satellite SAR imagery for volcano applications. The ever-growing number of public and private satellite SAR missions will provide for improved temporal resolution in SAR VFMs in the future, and the technique may be suitable for automated analysis that is capable of timely identification of changes due to volcanic activity, even in areas that are otherwise unmonitored.

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USGS2022

Rainfall an unlikely trigger of Kilauea’s 2018 rift eruption

If volcanic eruptions could be forecast from the occurrence of some external process, it might be possible to better mitigate risk and protect lives and livelihoods. Farquharson and Amelung 1 suggested that the 2018 lower East Rift Zone (ERZ) eruption of Kīlauea Volcano—the most destructive eruption in Hawai‘i in at least 200 years 2 —was triggered by extreme precipitation, which caused increased pore pressure that resulted in mechanical weakening of the volcano. Here we argue that Kīlauea’s 2018 eruption was instead caused by significant pre-eruptive pressurization, that pre-eruptive rainfall was not extreme, and that there is no significant correlation between rain and eruptions at Kīlauea. Understanding the causal mechanisms of volcanic eruptions is vital for hazard assessment and mitigation, and misattribution may compromise monitoring, preparedness, communication and response efforts.

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USGS2022

Trace elements in olivine fingerprint the source of 2018 magmas and shed light on explosive-effusive eruption cycles at Kīlauea Volcano

Understanding magma genesis and the evolution of intensive parameters (temperature, pressure, composition, degree of melting) in the mantle source of highly active volcanic systems is crucial for interpreting magma supply changes over time and recognizing cyclic behavior to anticipate future volcanic behavior. Major and trace elements in olivine are commonly used to study variations in mantle lithologies and melting conditions (e.g., temperature, pressure, oxygen fugacity) affecting the mantle over time. Here, we track the temporal evolution of primary melts through the most recent cycle of explosive and effusive eruptions at Kīlauea (Hawai‘i), which spans the last ∼500 years. We report major and trace elements in olivine from the last explosive period (∼1500 – early 1820’s Keanakāko‘i Tephra) and the most recent decade of the current effusive period (2018 LERZ, 2015–2018 Pu‘u‘ō‘ō, 2008–2018 lava lake and 2020 eruption in Halema‘uma‘u). Scandium concentrations in olivine allow characterizing changes in mantle source between 1500 and 2018, and suggest that the recent (2015–2018) magma feeding the Pu‘u‘ō‘ō cone did not significantly interact with the magma that erupted in the LERZ in 2018. The evolution of olivine and melt compositions over the past 500 years is not easily reconcilable with variations in mantle potential temperature, pressure of mantle melt pooling and storage, or oxygen fugacity. Instead, Sc, Mn, and Co concentrations and Ni/Mg ratio in high forsterite (Fo >87) olivine advocate for an increase in the proportion of clinopyroxene in the mantle source associated with a slightly higher degree of partial melting from 1500 to 2018. Changes in primitive melt compositions and degrees of mantle melting may well modulate magma supply to the crust and formation-replenishment of steady or ephemeral summit reservoirs, and thereby control transitions between explosive and effusive periods at Kīlauea. Analyzing trace elements in olivine at Kīlauea and elsewhere could therefore provide important clues on subtle changes occurring at the mantle level that might herald changes in volcanic behavior.

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USGS2021

Onset and evolution of Kilauea’s 2018 flank eruption and summit collapse from continuous gravity

Prior to the 2018 lower East Rift Zone (ERZ) eruption and summit collapse of Kīlauea Volcano, Hawai‘i, continuous gravimeters operated on the vent rims of ongoing eruptions at both the summit and Pu‘u ‘Ō‘ō. These instruments captured the onset of the 2018 lower ERZ eruption and the effects of lava withdrawal from both locales, providing constraints on the timing and style of activity and the physical properties of the lava lakes at both locations. At the summit, combining gravity, lava level, and a three-dimensional model of the vent indicates that the upper ∼200 m of the lava lake had a density of about 1700 kg m −3 , slightly greater than estimates from 2011–2015 and possibly indicating a gradual densification over time. At Pu‘u ‘Ō‘ō, gravity and vent geometry were used to model both the density and the rate of crater collapse, which was unknown owing to a lack of visual observations. Results suggest the withdrawal of at least 11×106 m 3 of lava over the course of two hours, and a material density of 1800–1900 kg m −3 . In addition, gravity data at Pu‘u ‘Ō‘ō captured a transient decrease and increase about an hour prior to crater collapse and that was probably related to a small, short-lived fissure eruption on the west flank of the cone and possibly to dike intrusion beneath Pu‘u ‘Ō‘ō. The fissure was the first event in the subsequent cascade that ultimately led to the extrusion of over 1 km 3 of lava from lower ERZ vents, collapse of the summit caldera floor by more than 500 m, and the destruction of over 700 homes and other structures. These results emphasize the importance of continuous gravity in operational monitoring of active volcanoes.

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USGS2020

Very‐long‐period (VLP) seismic artifacts during the 2018 caldera collapse at Kīlauea, Hawaii

Throughout the 2018 eruption of Kīlauea volcano (Hawai‘i), episodic collapses of a portion of the volcano’s summit caldera produced repeated M w "> M w 4.9–5.3 earthquakes. Each of these 62 events was characterized by a very‐long‐period (VLP) seismic signal ( ⁠ > 40    s "> > 40 s ⁠ ). Although collapses in the later stage of the eruption produced earthquakes with significant amplitude clipping on near‐summit broadband seismometers, the first 12 were accurately recorded. For these initial collapse events, we compare average VLP seismograms at six near‐summit locations to synthetic seismograms derived from displacements at collocated Global Positioning System stations. We show that the VLP seismic signal was generated by a radially outward and upward ramp function in displacement. We propose that at local distances the period of the VLP seismic signal is solely dependent on the duration of this ramp function and the instrument transfer function, that is, the seismic VLP is an artifact of the bandlimited instrument response and not representative of real ground motion. The displacement ramp function imposes a sinc‐function velocity amplitude spectrum that cannot be fully recovered through standard seismic instrument deconvolution. Any near‐summit VLP signals in instrument‐response‐corrected velocity or displacement seismograms from these collapse events are subject to severe band limitation. Similarly, the seismic amplitude response is not flat through the low‐frequency corner, for example, instrument‐response‐uncorrected seismograms scaled by instrument sensitivity are equally prone to band limitation. This observation is crucial when attempting to clarify the different contributions to the VLP source signature. Not accounting for this effect could lead to misunderstanding of the magmatic processes involved.

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USGS2020

Caldera collapse geometry revealed by near‐field GPS displacements at Kilauea Volcano in 2018

We employ near‐field GPS data to determine the subsurface geometry of a collapsing caldera during the 2018 Kīlauea eruption. Collapse occurred in 62 discrete events, with “inflationary” deformation external to the collapse, similar to previous basaltic collapses. We take advantage of GPS data from the collapsing block and independent constraints on the magma chamber geometry from inversion of deflation prior to collapse onset. This provides an unparalleled opportunity to constrain the collapse geometry. Employing an axisymmetric finite element model, the co‐collapse displacements are best explained by piston‐like subsidence along a high angle ( ∼ 85°) normal ring fault that may steepen to vertical with depth. Reservoir magma has compressibility of 2→15 × 10 −10 Pa −1 , indicating bubble volume fractions from 1% to 7% (lower if fault steepens with depth). Magma pressure increases during collapses are 1 to 3 MPa, depending on compressibility. Depressurization of a triaxial point source in a homogeneous half‐space fits the data well but provides a biased representation of the source depth and process.

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USGS2019

Groundwater inflow toward a preheated volcanic conduit: Application to the 2018 eruption at Kīlauea Volcano, Hawai’i

The many successes in volcano forecasting over the past several decades owe mainly to pattern recognition, both in monitoring data and the geologic record. During the early stages of the 2018 Kīlauea eruption, the conceptual model of Stearns (1925), based on the explosive 1924 Kīlauea eruption, was highly influential. This model postulates that explosions are triggered by liquid-water inflow into a recently vacated magma conduit. Modern quantitative modeling approaches, supplemented by hydrogeologic data unavailable in 1925, yield a more nuanced view. Results demonstrate that liquid-water inflow would likely be delayed by months to years, owing to the inability of liquid water to transit a zone of very hot rock surrounding the conduit. The exercise demonstrates the use of physically based modeling to supplement traditional volcano-forecasting approaches during an ongoing event.

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USGS2019

Explosive summit collapse of Kīlauea Volcano in 1924 preceded by a decade of crustal contamination and anomalous Pb isotope ratios

A geochemical time-series analysis of lavas from frequently active basaltic volcanoes has the potential to reveal the enigmatic mantle controls on volcanic behavior and hazards. In May 1924, the century-long lava lake within Halemaʻumaʻu pit crater at the summit of Kīlauea Volcano drained and the floor of Halemaʻumaʻu collapsed, triggering ∼3 weeks of phreatic explosions due to the interaction of groundwater with hot rock. For the next three decades, eruptions at Kīlauea were sporadic (the longest hiatus was from 1934 to 1952), small in volume, and short (typically <1 month long). Here, we show that the Pb isotope ratios of Kīlauea lava groundmass and tephra glass samples erupted from 1912 to 1954 are anomalous and unusually variable. Many of the samples have elevated 207 Pb/ 204 Pb ratios (at a given 206 Pb/ 204 Pb), ranging up to ∼0.05 higher than is typical for Kīlauea lavas. The variations in 206 Pb/ 204 Pb for samples from 1912–1913 (∼0.055), 1917–1921 (∼0.120), 1923 (∼0.065), and 1952–1954 (∼0.037) are larger over short time periods (∼1–4 yr) than observed during the Puʻu ʻŌʻō rift eruption (only ∼0.031 from 1986 to 2012). These Pb isotopic signatures resulted from variable amounts of crustal contamination (most likely by Pb-rich hydrothermal sulfide minerals with high 207 Pb/ 204 Pb ratios) as the parental magmas transited the ∼110 Ma Pacific oceanic crust. This crustal contamination was not directly related to the shallow volcanic events of 1924. Instead, mantle-driven processes at Kīlauea during the previous century—a factor of ∼2 decrease in the degree of partial melting of an increasingly refractory source—led to a decline in the magma supply rate, a major disruption of the magmatic plumbing system, and, for at least a decade prior to 1924, crustal contamination at or below the base of the volcanic edifice (>10 km). The Pb isotopic heterogeneity of the samples on short length (hand specimen to lava flow) and time (∼1–4 yr) scales can be explained by inefficient mixing as small batches of contaminated magma were delivered to the remnants of Kīlauea’s summit magma storage reservoir. Our results confirm that the Pb isotope ratios of basalts from ocean-island volcanoes may be significantly modified by assimilation of materials from the underlying oceanic crust. In particular, the 207 Pb/ 204 Pb ratio may be a sensitive tracer of such crustal contamination at Hawaiian shield volcanoes. Mauna Loa lavas display a factor of ∼5 more scatter towards higher 207 Pb/ 204 Pb at a given 206 Pb/ 204 Pb ratio than most Kīlauea lavas (excluding the samples from 1912 to 1954). This might be caused by more pervasive crustal contamination at Mauna Loa due to its lower magma supply rate over the last ∼4 kyr.

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USGS2019

3D electrical conductivity imaging of Halema‘uma‘u lava lake (Kīlauea volcano)

Before the 2018 collapse of the summit of Kīlauea volcano, a ca. 200 m in diameter lava lake inside of Halema‘uma‘u crater was embedded in a very active hydrothermal system. In 2015, we carried out an electrical conductivity survey and the data were inverted in 3D. The lack of conductivity contrast precludes distinguishing the lava column from the surrounding hydrothermal zones. Laboratory measurements on samples from the lava lake show that the conductivity of magma is significantly lower than that of hydrothermal zones but the high vesicularity of the upper part of the lava lake may decrease its macroscopic conductivity. Based on the 3D conductivity model, we distinguish at least two types of hydrothermal circulations: 1) one guided by the collapse faults of Halema‘uma‘u crater and by the magmatic column of the lava lake, and 2) another guided by previous caldera faults and fractures related to intrusions. We observe that the location of the faults formed during the 2018 collapse of the summit was greatly influenced by the hydrothermally altered zones.

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USGS2019

The 2018 rift eruption and summit collapse of Kilauea Volcano

In 2018, Kīlauea Volcano experienced its largest lower East Rift Zone (LERZ) eruption and caldera collapse in at least 200 years. After collapse of the Pu'u 'Ō'ō vent on 30 April, magma propagated downrift. Eruptive fissures opened in the LERZ on 3 May, eventually extending ~6.8 km. A 4 May earthquake (M6.9) produced ~5 m of fault slip. Lava erupted at rates exceeding 100 m3/s, eventually covering 35.5 km2. The summit magma system partially drained, producing minor explosions and near-daily collapses releasing energy equivalent to M4.7-M5.4 earthquakes. Activity declined rapidly on 4 August. Summit collapse and lava flow volume estimates are roughly equivalent--about 0.8 km3. Careful historical observation and monitoring of Kīlauea enabled successful forecasting of hazardous events.

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USGS2019

The tangled tale of Kīlauea’s 2018 eruption as told by geochemical monitoring

Changes in magma chemistry that affect eruptive behavior occur during many volcanic eruptions, but typical analytical techniques are too slow to contribute to hazard monitoring. We used rapid energy-dispersive X-ray fluorescence analysis to measure diagnostic elements in lava samples within a few hours of collection during the 2018 Kīlauea eruption. The geochemical data provided important information for field crews and civil authorities in advance of changing hazards during the eruption. The appearance of hotter magma was recognized several days before the onset of voluminous eruptions of fast-moving flows that destroyed hundreds of homes. We identified, in near-real time, interactions between older, colder, stored magma – including the unexpected eruption of andesite – and hotter magma delivered during dike emplacement.

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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

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.

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