Geology topics

Research about Kilauea Volcano

Source-linked reports with geographic coverage including Kilauea Volcano.

At least 37 records · Page 2Linked to original sources

USGS2019

Communication strategy of the U.S. Geological Survey Hawaiian Volcano Observatory during the lava-flow crisis of 2014–2015, Kilauea Volcano, Hawaii

In 2014–2015, a slow-moving pāhoehoe lava flow from the remote Pu‘u ‘Ō‘ō vent on Kīlauea Volcano advanced 20 km into populated areas of the Puna District on the Island of Hawai‘i. The staff of the U.S. Geological Survey’s (USGS) Hawaiian Volcano Observatory (HVO) mobilized their resources to closely monitor the flow and provide up-to-date information to the Hawai‘i County Civil Defense (HCCD) agency, the public, and the news media. Scientists issued formal USGS notifications about the flow and Kīlauea’s two eruptions, prepared maps and annotated photographs, infrared images, and videos for dissemination online, and wrote weekly “Volcano Watch” articles for local newspapers. They also provided regular briefings for federal, state, and county agency representatives, answered questions during near-daily briefings with local and national media, and offered information through an established lecture series and participation in community emergency preparedness fairs. Noteworthy among the communication activities was a series of public meetings organized by the Hawai‘i County mayor’s office and led by the HCCD administrator. The meetings were a regular forum for many HVO scientists to talk directly and frequently with residents, business owners, elected officials, and other stakeholders about their concerns, the evolving status of the eruptions, and the uncertain prognosis of the flow’s advance and extent. The dialogue was essential for HVO staff to describe their observations and insights about the lava flow’s behavior and to gain credibility with the community during the crisis. This experience suggests that personal engagement with people at risk from future lava flows in Hawai‘i and elsewhere in the world will remain a crucial part of an eruption response, even with greater capability to disseminate warnings and information digitally via the Internet.

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USGS2018

A retrospective look at the February 1993 east rift zone intrusion at Kīlauea volcano, Hawaii

The February 1993 dike intrusion in the East Rift Zone (ERZ) of Kīlauea Volcano, Hawai'i, was recognized from tilt and seismic data, but ground-based geodetic data were too sparse to constrain the characteristics of the intrusion. Analysis of Interferometric Synthetic Aperture Radar (InSAR) from the Japan Aerospace Exploration Agency (JAXA) JERS-1 satellite reveals a maximum of ~30 cm of line-of-sight (LOS) displacement occurring near Makaopuhi Crater in the middle ERZ of Kīlauea. We model this deformation signal as a subvertical dike using a 3D-Mixed Boundary Element Method (3D-MBEM) paired with a nonlinear inversion algorithm to find the best-fit model. The best-fit dike is located just to the west of Makaopuhi Crater striking N50°W, extends to within 100 m of the surface, is ~1.3 km in length by ~4.2 km in width along strike, and has a total volume of ~7.4 × 10 6 m 3 . In addition, a post-intrusion interferogram from JERS-1 spanning 1993–1997 was analyzed. Guided by previous results, our model for the 4-year period consists of opening of the deep rift zones by about 0.5 m at 3–8.5 km depth beneath the Southwest Rift Zone (SWRZ), ERZ and the summit. A sub-horizontal detachment fault is connected to the seaward side of the vertical dike-like source to mimic the décollement known to exist beneath the volcano. We classify the 1993 dike intrusion as a passive intrusion similar to those that occurred in 1997 and 1999. Passive intrusions lack precursory inflation at Kīlauea's summit, and the likely triggering mechanism is persistent deep rift opening combined with seaward motion of the south flank along the basal décollement. Passive intrusions make forecasting and hazard assessment difficult since they are not preceded by inflation nor by large increases in seismicity.

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USGS2018

Gravity signature of basaltic fill in Kīlauea caldera, Island of Hawai‘i

Characterization of the subsurface structure of a volcanic edifice is essential to understanding volcanic behavior. One of the best-studied volcanoes is Kīlauea (Island of Hawai‘i). Geological evidence suggests that the formation of the summit caldera of Kīlauea is cyclic, with repeated collapse followed by filling with lava. The most recent collapse occurred ca. 1500 CE, producing a basin that is several hundred meters deeper than the current caldera. In this study, we used two- and three-dimensional gravity modeling of spatially dense gravity data covering the summit area to suggest that, since its formation in 1500 CE, the caldera has been progressively filled by lava flows that are slightly denser than those found in the rim and outboard of the caldera. The geometry of this fill, inferred from gravity data, enables us to reconstruct the morphology of the 1500 CE caldera before its subsequent filling. The coincidence of fumarolic zones and thermal anomalies observed at the surface with the interpreted 1500 CE caldera rim suggests that hydrothermal fluid circulation is guided by the more permeable inner faults bounding the main caldera.

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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

Relative seismic velocity variations correlate with deformation at Kilauea volcano

Seismic noise interferometry allows the continuous and real-time measurement of relative seismic velocity through a volcanic edifice. Because seismic velocity is sensitive to the pressurization state of the system, this method is an exciting new monitoring tool at active volcanoes. Despite the potential of this tool, no studies have yet comprehensively compared velocity to other geophysical observables on a short-term time scale at a volcano over a significant length of time. We use volcanic tremor (~0.3 to 1.0 Hz) at Kīlauea as a passive source for interferometry to measure relative velocity changes with time. By cross-correlating the vertical component of day-long seismic records between ~230 station pairs, we extract coherent and temporally consistent coda wave signals with time lags of up to 120 s. Our resulting time series of relative velocity shows a remarkable correlation between relative velocity and the radial tilt record measured at Kīlauea summit, consistently correlating on a time scale of days to weeks for almost the entire study period (June 2011 to November 2015). As the summit continually deforms in deflation-inflation events, the velocity decreases and increases, respectively. Modeling of strain at Kīlauea suggests that, during inflation of the shallow magma reservoir (1 to 2 km below the surface), most of the edifice is dominated by compression—hence closing cracks and producing faster velocities—and vice versa. The excellent correlation between relative velocity and deformation in this study provides an opportunity to understand better the mechanisms causing seismic velocity changes at volcanoes, and therefore realize the potential of passive interferometry as a monitoring tool.

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USGS2016

Insights into shallow magmatic processes at Kīlauea Volcano, Hawaiʻi, from a multiyear continuous gravity time series

Continuous gravity data collected near the summit eruptive vent at Kīlauea Volcano, Hawaiʻi, during 2011–2015 show a strong correlation with summit-area surface deformation and the level of the lava lake within the vent over periods of days to weeks, suggesting that changes in gravity reflect variations in volcanic activity. Joint analysis of gravity and lava level time series data indicates that over the entire time period studied, the average density of the lava within the upper tens to hundreds of meters of the summit eruptive vent remained low—approximately 1000–1500 kg/m 3 . The ratio of gravity change (adjusted for Earth tides and instrumental drift) to lava level change measured over 15 day windows rose gradually over the course of 2011–2015, probably reflecting either (1) a small increase in the density of lava within the eruptive vent or (2) an increase in the volume of lava within the vent due to gradual vent enlargement. Superimposed on the overall time series were transient spikes of mass change associated with inflation and deflation of Kīlauea's summit and coincident changes in lava level. The unexpectedly strong mass variations during these episodes suggest magma flux to and from the shallow magmatic system without commensurate deformation, perhaps indicating magma accumulation within, and withdrawal from, void space—a process that might not otherwise be apparent from lava level and deformation data alone. Continuous gravity data thus provide unique insights into magmatic processes, arguing for continued application of the method at other frequently active volcanoes.

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USGS2016

Joint analysis of geodetic and earthquake fault-plane solution data to constrain magmatic sources: A case study from Kīlauea Volcano

A joint analysis of geodetic and seismic datasets from Kīlauea Volcano during a period of magmatic unrest in 2006 demonstrates the effectiveness of this combination for testing and constraining models of magma dynamics for a complex, multi-source system. At the end of 2003, Kīlauea's summit began a four-year-long period of inflation due to a surge in magma supply to the volcano. In 2006, for the first time since 1982, Kīlauea's Southwest Rift Zone (SWRZ) also experienced inflation. To investigate the characteristics of active magma sources and the nature of their interactions with faults in the SWRZ during 2006, we integrate, through Coulomb stress modeling, contemporary geodetic data from InSAR and GPS with a new catalogue of double-couple fault-plane solutions for volcano-tectonic earthquakes. We define two periods of inflation during 2006 based on the rate of deformation measured in daily GPS data, spanning February to 15 March 2006 (Period 1) and 16 March to 30 September 2006 (Period 2). InSAR data for these two periods are inverted to determine the position, change in size, and shape of inflation sources in each period. Our new models are consistent with microseismic activity from each period. They suggest that, during Period 1, deformation in the SWRZ can be explained by pressurization of magma in a spherical reservoir beneath the south caldera, and that, during Period 2, magma was also aseismically intruded farther to the southwest into the SWRZ along a sub-horizontal plane. Our Coulomb stress analysis shows that the microseismicity recorded in the SWRZ is induced by overpressurization of the south caldera reservoir, and not by magma intrusion into the SWRZ. This study highlights the importance of a joint analysis of independent geophysical datasets to fully constrain the nature of magma accumulation.

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USGS2015

Delicate balance of magmatic-tectonic interaction at Kilauea Volcano, Hawai`i, revealed from slow slip events: Chapter 13

Eleven slow slip events (SSEs) have occurred on the southern flank of Kilauea Volcano, Hawai’i, since 1997 through 2014. We analyze this series of SSEs in the context of Kilauea’s magma system to assess whether or not there are interactions between these tectonic events and eruptive/intrusive activity. Over time, SSEs have increased in magnitude and become more regular, with interevent times averaging 2.44 ± 0.15 years since 2003. Two notable SSEs that impacted both the flank and the magmatic system occurred in 2007, when an intrusion and small eruption on the East Rift Zone were part of a feedback with a SSE and 2012, when slow slip induced 2.5 cm of East Rift Zone opening (but without any change in eruptive activity). A summit inflation event and surge in East Rift Zone lava effusion was associated with a SSE in 2005, but the inferred triggering relation is not clear due to a poorly constrained slip onset time. Our results demonstrate that slow slip along Kilauea’s décollement has the potential to trigger and be triggered by activity within the volcano’s magma system. Since only three of the SSEs have been associated with changes in magmatic activity within the summit and rift zones, both the décollement and magma system must be close to failure for triggering to occur.

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USGS2015

Two magma bodies beneath the summit of Kilauea Volcano unveiled by isotopically distinct melt deliveries from the mantle

The summit magma storage reservoir of Kīlauea Volcano is one of the most important components of the magmatic plumbing system of this frequently active basaltic shield-building volcano. Here we use new high-precision Pb isotopic analyses of Kīlauea summit lavas—from 1959 to the active Halema‘uma‘u lava lake—to infer the number, size, and interconnectedness of magma bodies within the volcano's summit reservoir. From 1971 to 1982, the 206 Pb/ 204 Pb ratios of the lavas define two separate magma mixing trends that correlate with differences in vent location and/or pre-eruptive magma temperature. These relationships, which contrast with a single magma mixing trend for lavas from 1959 to 1968, indicate that Kīlauea summit eruptions since at least 1971 were supplied from two distinct magma bodies. The locations of these magma bodies are inferred to coincide with two major deformation centers identified by geodetic monitoring of the volcano's summit region: (1) the main locus of the summit reservoir &sim;2–4 km below the southern rim of Kīlauea Caldera and (2) a shallower magma body <2 km below the eastern rim of Halema‘uma‘u pit crater. Residence time modeling suggests that the total volume of magma within Kīlauea's summit reservoir during the late 20th century (1959–1982) was exceedingly small (&sim;0.1–0.5 km 3 ). Voluminous Kīlauea eruptions, such as the ongoing, 32-yr old Pu‘u ‘Ō‘ō rift eruption (>4 km 3 of lava erupted), must therefore be sustained by a nearly continuous supply of new melt from the mantle. The model results show that a minimum of four compositionally distinct, mantle-derived magma batches were delivered to the volcano (at least three directly to the summit reservoir) since 1959. These melt inputs correlate with the initiation of energetic (1959 Kīlauea Iki) and/or sustained (1969–1974 Mauna Ulu, 1983-present Pu‘u ‘Ō‘ō and 2008-present Halema‘uma‘u) eruptions. Thus, Kīlauea's eruptive behavior is partly tied to the delivery of new magma batches from the volcano's source region within the Hawaiian mantle plume.

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USGS2014

Gravity changes and deformation at Kīlauea Volcano, Hawaii, associated with summit eruptive activity, 2009-2012

Analysis of microgravity and surface displacement data collected at the summit of Kīlauea Volcano, Hawaii (USA), between December 2009 and November 2012 suggests a net mass accumulation at ~1.5 km depth beneath the northeast margin of Halema‘uma‘u Crater, within Kīlauea Caldera. Although residual gravity increases and decreases are accompanied by periods of uplift and subsidence of the surface, respectively, the volume change inferred from the modeling of interferometric synthetic aperture radar deformation data can account for only a small portion (as low as 8%) of the mass addition responsible for the gravity increase. We propose that since the opening of a new eruptive vent at the summit of Kīlauea in 2008, magma rising to the surface of the lava lake outgasses, becomes denser, and sinks to deeper levels, replacing less dense gas-rich magma stored in the Halema‘uma‘u magma reservoir. In fact, a relatively small density increase (<200 kg m −3 ) of a portion of the reservoir can produce the positive residual gravity change measured during the period with the largest mass increase, between March 2011 and November 2012. Other mechanisms may also play a role in the gravity increase without producing significant uplift of the surface, including compressibility of magma, formation of olivine cumulates, and filling of void space by magma. The rate of gravity increase, higher than during previous decades, varies through time and seems to be directly correlated with the volcanic activity occurring at both the summit and the east rift zone of the volcano.

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USGS2014

Time-averaged discharge rate of subaerial lava at Kīlauea Volcano, Hawai‘i, measured from TanDEM-X interferometry: Implications for magma supply and storage during 2011-2013

Differencing digital elevation models (DEMs) derived from TerraSAR add-on for Digital Elevation Measurements (TanDEM-X) synthetic aperture radar imagery provides a measurement of elevation change over time. On the East Rift Zone (EZR) of Kīlauea Volcano, Hawai‘i, the effusion of lava causes changes in topography. When these elevation changes are summed over the area of an active lava flow, it is possible to quantify the volume of lava emplaced at the surface during the time spanned by the TanDEM-X data—a parameter that can be difficult to measure across the entirety of an ~100 km 2 lava flow field using ground-based techniques or optical remote sensing data. Based on the differences between multiple TanDEM-X-derived DEMs collected days to weeks apart, the mean dense-rock equivalent time-averaged discharge rate of lava at Kīlauea between mid-2011 and mid-2013 was approximately 2 m 3 /s, which is about half the long-term average rate over the course of Kīlauea's 1983–present ERZ eruption. This result implies that there was an increase in the proportion of lava stored versus erupted, a decrease in the rate of magma supply to the volcano, or some combination of both during this time period. In addition to constraining the time-averaged discharge rate of lava and the rates of magma supply and storage, topographic change maps derived from space-based TanDEM-X data provide insights into the four-dimensional evolution of Kīlauea's ERZ lava flow field. TanDEM-X data are a valuable complement to other space-, air-, and ground-based observations of eruptive activity at Kīlauea and offer great promise at locations around the world for aiding with monitoring not just volcanic eruptions but any hazardous activity that results in surface change, including landslides, floods, earthquakes, and other natural and anthropogenic processes.

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USGS2014

Electron microprobe analyses of glasses from Kīlauea tephra units, Kīlauea Volcano, Hawaii

This report presents approximately 2,100 glass analyses from three tephra units of Kīlauea Volcano: the Keanakākoʻi Tephra, the Kulanaokuaiki Tephra, and the Pāhala Ash. It also includes some new analyses obtained as part of a re-evaluation of the MgO contents of glasses in two of the three original datasets; this re-evaluation was conducted to improve the consistency of glass MgO contents among the three datasets. The glass data are a principal focus of Helz and others (in press), which will appear in the AGU Monograph Hawaiian Volcanoes—From Source to Surface. The report is intended to support this publication, in addition to making the data available to the scientific community.

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USGS2014

The June-July 2007 collapse and refilling of Puʻu ʻŌʻō Crater, Kilauea Volcano, Hawaiʻi

Episode 57 of Kīlauea’s long-lived east rift zone eruption was characterized by lava effusion and spattering within the crater at Puʻu ʻŌʻō that lasted from July 1 to July 20, 2007. This eruptive episode represented a resumption of activity following a 12-day eruptive hiatus on Kīlauea associated with the episode 56 intrusion and eruption near Kāne Nui o Hamo cone, uprift from Puʻu ʻŌʻō, on June 17–19, 2007. The withdrawal of magma from beneath Puʻu ʻŌʻō led to the collapse of Puʻu ʻŌʻō’s crater floor, forming a concave depression ~85 m deep. After the hiatus, episode 57 lava began to erupt from two vents within Puʻu ʻŌʻō, quickly constructing a lava lake and filling the crater to within 5 m of the precollapse lava level (25 m of the pre-collapse crater floor). Starting July 8, effusion waned as the crater floor began to rise. As uplift progressed, new vents opened along a circumferential fracture that accommodated the displacement. The bulk volume of filling within the Puʻu ʻŌʻō crater and flank pits during episode 57, including both surficial lava accumulation and endogenous growth, is estimated at 1.3×106 m 3 . This volume equates to a time-averaged dense rock equivalent accumulation rate of 0.6 m3 s -1 , which is an order of magnitude less than the supply rate to the volcano at that time, suggesting that most of the magma entering the volcano was being stored. Eruptive activity in Puʻu ʻŌʻō ended late on July 20, and the floor of the crater began to subside rapidly. Shortly afterward, early on July 21, a new fissure eruption started on the northeast flank of Puʻu ʻŌʻō, marking the onset of episode 58. The June–July 2007 collapse and refilling of the Puʻu ʻŌʻō crater, culminating in a new breakout outside of Puʻu ʻŌʻō, illustrates the response of a long-lived eruptive center in Kīlauea’s East Rift Zone to an uprift intrusion. Variations of this pattern occurred several times at Puʻu ʻŌʻō before 2007 and have occurred again since. Recognition of this pattern has improved the monitoring capability of the Hawaiian Volcano Observatory and will aid in future eruption response efforts.

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USGS2013

Moderate-magnitude earthquakes induced by magma reservoir inflation at Kīlauea Volcano, Hawai‘i

Although volcano-tectonic (VT) earthquakes often occur in response to magma intrusion, it is rare for them to have magnitudes larger than ~ M 4. On 24 May 2007, two shallow M 4+ earthquakes occurred beneath the upper part of the east rift zone of Kīlauea Volcano, Hawai‘i. An integrated analysis of geodetic, seismic, and field data, together with Coulomb stress modeling, demonstrates that the earthquakes occurred due to strike-slip motion on pre-existing faults that bound Kīlauea Caldera to the southeast and that the pressurization of Kīlauea's summit magma system may have been sufficient to promote faulting. For the first time, we infer a plausible origin to generate rare moderate-magnitude VTs at Kīlauea by reactivation of suitably oriented pre-existing caldera-bounding faults. Rare moderate- to large-magnitude VTs at Kīlauea and other volcanoes can therefore result from reactivation of existing fault planes due to stresses induced by magmatic processes.

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USGS2013

Very long period conduit oscillations induced by rockfalls at Kilauea Volcano, Hawaii

Eruptive activity at the summit of Kilauea Volcano, Hawaii, beginning in 2010 and continuing to the present time is characterized by transient outgassing bursts accompanied by very long period (VLP) seismic signals triggered by rockfalls from the vent walls impacting a lava lake in a pit within the Halemaumau pit crater. We use raw data recorded with an 11-station broadband network to model the source mechanism of signals accompanying two large rockfalls on 29 August 2012 and two smaller average rockfalls obtained by stacking over all events with similar waveforms to improve the signal-to-noise ratio. To determine the source centroid location and source mechanism, we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous medium that takes topography into account. We apply a new waveform inversion method that accounts for the contributions from both translation and tilt in horizontal seismograms through the use of Green's functions representing the seismometer response to translation and tilt ground motions. This method enables a robust description of the source mechanism over the period range 1–1000 s. The VLP signals associated with the rockfalls originate in a source region ∼1 km below the eastern perimeter of the Halemaumau pit crater. The observed waveforms are well explained by a simple volumetric source with geometry composed of two intersecting cracks including an east striking crack (dike) dipping 80° to the north, intersecting a north striking crack (another dike) dipping 65° to the east. Each rockfall is marked by a similar step-like inflation trailed by decaying oscillations of the volumetric source, attributed to the efficient coupling at the source centroid location of the pressure and momentum changes induced by the rock mass impacting the top of the lava column. Assuming a simple lumped parameter representation of the shallow magmatic system, the observed pressure and volume variations can be modeled with the following attributes: rockfall volume (200–4500 m 3 ), length of magma column (120–210 m), diameter of pipe connecting the Halemaumau pit crater to the subjacent dike system (6 m), average thickness of the two underlying dikes (3–6 m), and effective magma viscosity (30–210 Pa s). Most rockfalls occur during episodes of sustained deflation of the Kilauea summit. The mass loss rate in the shallow magmatic system is estimated to be 1400–15,000 kg s −1 based on measurements of the temporal variation of VLP period in the two large rockfalls that occurred on 29 August 2012.

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USGS2013

TerraSAR-X interferometry reveals small-scale deformation associated with the summit eruption of Kilauea Volcano, Hawai‘i

On 19 March 2008, a small explosive eruption at the summit of Kīlauea Volcano, Hawai‘i, heralded the formation of a new vent along the east wall of Halema‘uma‘u Crater. In the ensuing years, the vent widened due to collapses of the unstable rim and conduit wall; some collapses impacted an actively circulating lava pond and resulted in small explosive events. We used synthetic aperture radar data collected by the TerraSAR-X satellite, a joint venture between the German Aerospace Center (DLR) and EADS Astrium, to identify and analyze small-scale surface deformation around the new vent during 2008-2012. Lidar data were used to construct a digital elevation model to correct for topographic phase, allowing us to generate differential interferograms with a spatial resolution of about 3 m in Kīlauea's summit area. These interferograms reveal subsidence within about 100 m of the rim of the vent. Small baseline subset time series analysis suggests that the subsidence rate is not constant and, over time, may provide an indication of vent stability and potential for rim and wall collapse -- information with obvious hazard implications. The deformation is not currently detectable by other space- or ground-based techniques.

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USGS2013

Seismic detection of increased degassing before Kīlauea's 2008 summit explosion

The 2008 explosion that started a new eruption at the summit of Kīlauea Volcano, Hawai‘i, was not preceded by a dramatic increase in earthquakes nor inflation, but was associated with increases in SO 2 emissions and seismic tremor. Here we perform shear wave splitting analysis on local earthquakes spanning the onset of the eruption. Shear wave splitting measures seismic anisotropy and is traditionally used to infer changes in crustal stress over time. We show that shear wave splitting may also vary due to changes in volcanic degassing. The orientation of fast shear waves at Kīlauea is usually controlled by structure, but in 2008 showed changes with increased SO 2 emissions preceding the start of the summit eruption. This interpretation for changing anisotropy is supported by corresponding decreases in V p /V s ratio. Our result demonstrates a novel method for detecting changes in gas flux using seismic observations and provides a new tool for monitoring under-instrumented volcanoes.

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USGS2013

Evolution of dike opening during the March 2011 Kamoamoa fissure eruption, Kīlauea Volcano, Hawai`i

The 5–9 March 2011 Kamoamoa fissure eruption along the east rift zone of Kīlauea Volcano, Hawai`i, followed months of pronounced inflation at Kīlauea summit. We examine dike opening during and after the eruption using a comprehensive interferometric synthetic aperture radar (InSAR) data set in combination with continuous GPS data. We solve for distributed dike displacements using a whole Kīlauea model with dilating rift zones and possibly a deep décollement. Modeled surface dike opening increased from nearly 1.5 m to over 2.8 m from the first day to the end of the eruption, in agreement with field observations of surface fracturing. Surface dike opening ceased following the eruption, but subsurface opening in the dike continued into May 2011. Dike volumes increased from 15, to 16, to 21 million cubic meters (MCM) after the first day, eruption end, and 2 months following, respectively. Dike shape is distinctive, with a main limb plunging from the surface to 2–3 km depth in the up‐rift direction toward Kīlauea's summit, and a lesser projection extending in the down‐rift direction toward Pu`u `Ō`ō at 2 km depth. Volume losses beneath Kīlauea summit (1.7 MCM) and Pu`u `Ō`ō (5.6 MCM) crater, relative to dike plus erupted volume (18.3 MCM), yield a dike to source volume ratio of 2.5 that is in the range expected for compressible magma without requiring additional sources. Inflation of Kīlauea's summit in the months before the March 2011 eruption suggests that the Kamoamoa eruption resulted from overpressure of the volcano's magmatic system.

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