An Unprecedented Experiment to Map Kīlauea’s Summit Magma System

Kīlauea volcano, on the island of Hawaiʻi, is fed by the Hawaiian sizzling spot, a plume of buoyant rock and magma that rises by way of Earth’s mantle and crust. As one of the energetic volcanoes on the planet, it has for hundreds of years drawn scientific observers to the island, which grew to become the location of one of many earliest volcano observatories.

Kīlauea has been probed, interpreted, and studied intensively, revealing a lot in regards to the internal workings of basaltic volcanoes. However, regardless of complete analysis on practically each side of this volcano, a transparent image of the scale and configuration of Kīlauea’s magmatic plumbing system has proved elusive.

Previous efforts to estimate or not directly picture the extent of Kīlauea’s magmatic system have yielded broad ranges of prospects. The quantity of the magma system from geodetic, seismic, geologic, and petrologic information has been estimated to be anyplace from 0.2 to 240 cubic kilometers [Decker, 1987; Denlinger, 1997; Fiske and Kinoshita, 1969; Pietruszka et al., 2015; Poland et al., 2014]. Storage techniques interpreted from various information have assorted from a plexus of dikes and sills with little connectivity amongst them to a number of massive, subterranean our bodies with well-established connections. No dominant consensus emerged from these research.

Then a catastrophic change occurred. In early Could 2018, an enormous dike propagated 20 kilometers eastward from the volcano’s energetic Puʻu ʻŌʻō vent on the East Rift Zone to Leilani Estates, adopted quickly by a magnitude 6.9 earthquake as the huge south flank of the volcano abruptly lurched seaward [Neal et al., 2019]. The dike and flank motion opened a steady conduit from Leilani Estates to the summit, and from Could to August this conduit drained 15 years of magma provide (1.5 cubic kilometers) from the East Rift Zone and summit magma storage techniques.

This drainage was pushed by a piston-like collapse of the caldera inside Kīlauea’s summit area (Figures 1 and a pair of) [Anderson et al., 2019]. The ensuing voluminous lava flows broken main infrastructure and destroyed practically 2,000 properties. Scientists’ capability to forecast the amount and period of each the key summit collapse and accompanying eruptions was inhibited by the shortage of a definitive understanding of Kīlauea’s subsurface construction and the way it might function.

The 2018 eruption was probably the most catastrophic occasion on Hawaiian volcanoes prior to now 200 years and essentially modified our understanding of the amount of magma saved in Kīlauea’s summit area. The storage quantity is far bigger than beforehand accepted, however we’re nonetheless at midnight as to precisely how this magma is distributed inside the volcano. This distribution has implications for geologic hazards on the volcano.

In latest geologic historical past Kīlauea’s summit eruptions have largely been effusive, or nonexplosive. This conduct stands in distinction to geologic proof for the formation of Kaluapele (Kīlauea’s caldera) round 1500 CE, which was adopted by about 3 centuries of explosive volcanism. Though extra eruptions since 2018 have proven {that a} extra explosive future is very unlikely for Kīlauea, move and faulting hazards persist. Having correct subsurface details about magma storage is essential to bettering our forecast capabilities and responses to volcanic occasions because the volcano evolves.

Following the 2018 eruption, Congress offered supplemental funding beneath the Catastrophe Reduction Act of 2019 (see Acknowledgments) to the U.S. Geological Survey (USGS) to switch the devices and amenities of the Hawaiian Volcano Observatory (HVO) misplaced within the eruption and to assist analysis to raised perceive Kīlauea and its hazards. USGS scientists (together with three of the authors) proposed a passive imaging experiment to assist present key info and in addition joined with educational colleagues (the remaining authors) to acquire extra assist from the Nationwide Science Basis for energetic supply seismic imaging.

The following mission—one of many largest and most formidable ever performed on the summit of an energetic volcano—required years of planning and a powerful partnership with the Nationwide Park Service (virtually the entire survey space is inside Hawaiʻi Volcanoes Nationwide Park). Harm associated to the 2018 summit collapse together with different technical and logistical hurdles related to the train of deploying an enormous quantity of apparatus and marshaling assist from quite a few contributors from a number of establishments difficult this effort. Nonetheless, the deployment and information acquisition for the research have been easily and efficiently accomplished in April–June 2023. Ongoing evaluation of the large trove of information acquired (virtually 200 million waveforms) will present the sharpest look but into the core of this iconic volcano.

Pondering Massive

Our plan for the array referred to as for procuring practically 2,000 self-contained seismic stations, or nodes, deploying them throughout the summit (Determine 3), after which retrieving them following the info assortment. Every node included a three-component seismometer with an onboard energy provide, information storage, and GPS locator. Networked collectively, the seismic imaging they supply is equivalent in idea to CT (computed tomography) scans that picture the inside anatomy of the human physique. Nonetheless, as an alternative of finding out penetrating X-rays we used variations in penetrating seismic wavefronts to light up Kīlauea’s inner summit construction.

HVO had solely a restricted variety of seismic nodes obtainable, so we borrowed an extra 1,580 from the Integrated Analysis Establishments for Seismology (IRIS) Consortium’s Moveable Array Seismic Research of the Continental Lithosphere (PASSCAL) Instrument Middle to construct the dense array wanted for our survey.

For energetic (managed supply) seismic surveying, we used a 34-ton triaxial vibroseis shaker truck referred to as T-Rex that’s managed by the Pure Hazards Engineering Analysis Infrastructure (NHERI) on the College of Texas at Austin (UT-Austin). This huge beast needed to be shipped from Texas to Hawaii, saved at a particular facility within the park, after which pushed every day to predetermined areas to generate floor vibrations utilizing a roughly 6-square-meter baseplate mounted to its underbelly. These vibrations propagated by way of the volcano, offering the seismic indicators essential to picture the inside.

Such an experiment, involving hundreds of seismic nodes unfold throughout an energetic volcanic summit like Kīlauea’s, not solely is dear but in addition requires a big, professional workforce in addition to car and helicopter assist. Moreover, as a result of the PASSCAL nodes used can function for under 30 days at a time, the whole surveying effort needed to be accomplished in that brief timeframe. Redeployment for longer was not attainable as a result of we lacked accessible infrastructure for retrieving, recharging, and shortly downloading tens of terabytes of information from the nodes. Even with a single deployment, the method of deploying and retrieving the nodes, working T-Rex, and coordinating helicopter flights, all inside 30 days, required a well-orchestrated, collaborative effort among the many group of USGS and educational scientists with collective expertise in each passive and energetic seismic imaging.

By way of scale and complexity, this mission is the biggest area experiment ever carried out on an energetic volcano, involving much more seismic nodes, a bigger energetic supply part, and tighter logistical constraints than earlier experiments similar to a 2020 deployment at Yellowstone caldera or the 2014–2016 Imaging Magma Beneath St. Helens (iMUSH). Given its dimension and complexity, park officers have been rightfully involved in regards to the potential bodily impacts of our experiment on the area, which hosts a number of endangered species and which had already been rattled by greater than 60,000 earthquakes in the course of the 2018 collapse sequence that considerably broken park roads and different infrastructure.

Crew members thus labored carefully with the Nationwide Park Service to develop a plan to attenuate injury from our seismic surveying actions. For instance, on the idea of outcomes from preliminary ground-penetrating radar (GPR) surveys finished for this mission, which revealed options similar to shallow underground cavities, we tremendously diminished the variety of areas the place we had initially deliberate to make use of T-Rex to generate shaking. Particularly, we eradicated sampling websites on street sections close to or over lava tubes, recognized faults, and pure or human-made voids to keep away from inflicting additional injury. With enter from the Hawaii Division of Transportation, we additionally outlined a threshold for extreme floor vibrations (2.5 centimeters per second) on their engineered roads. In the course of the mission, we deployed accelerometers at every sourcing web site in order that we might monitor the shaking and shut down instantly when this threshold was approached.

To cut back the impression on guests to Hawaiʻi Volcanoes Nationwide Park, we additionally considerably diminished the quantity of helicopter flight time we’d deliberate to succeed in distant websites contained in the park. As an alternative, we made extra use of current four-wheel-drive-accessible roads in closed areas, and we enlisted extra folks and automobiles to extend the variety of survey websites situated adjoining to each paved and unpaved roads.

Because the mission was underway, we stored the general public knowledgeable about our progress with interpretive indicators and we stationed scientists at key customer websites within the summit space. Additional, we coordinated with the park to carry on-site coaching for scientists concerned within the fieldwork to make sure their consciousness of the cultural sensitivities and endangered species within the park, and we timed the experiment so it might not intrude with the nesting season for nēnē, the Hawaiian state hen.

So Many Nodes, So Little Time

With permissions secured and our plan in place, floor crews deployed the nodes throughout the volcano’s summit. Along with 1,580 PASSCAL nodes, we used two other forms of nodes: eighty-three 0.2-hertz nodes from SmartSolo and 100 fifty-two 2-hertz nodes from Geophysical Expertise, Inc. (GTI). Because the latter two varieties have longer-lasting batteries than the PASSCAL nodes, we set them up first. These nodes have been first distributed in caches through helicopter in a single morning after which deployed to particular websites by a skeleton crew over a few week’s time.

Whereas this preliminary week of deployments was pretty relaxed, the following stage of establishing the PASSCAL nodes was decidedly unrelaxed. Timing was essential to our technique, and we needed to coordinate street crews, off-road car crews, and helicopter crews concurrently to maintain to the schedule. As soon as these nodes arrived in Hawaii in a big sea container and have been transported to the park, we had simply 5 days budgeted to deploy them earlier than we started surveying with T-Rex.

And there was one other wrinkle. The PASSCAL nodes have detachable spikes for anchoring them within the floor. Though we used most as is, we had requested that PASSCAL take away spikes from greater than 100 nodes so we might deploy them in buckets of sand to be positioned on exhausting surfaces (lava flows) that the spikes wouldn’t simply penetrate. Due to the burden and dimension of the bucketed sensors—roughly 12 kilograms apiece versus 3 kilograms for the standard spiked sensors—we couldn’t haul a lot of them at a time contained in the helicopter. So we designed and examined a extra environment friendly means to sling load the buckets to distant websites with out them tipping, in addition to a format sample facilitating deployment of those heavy sensors by area crews on foot.

We transported our assembled bucket nodes to a helicopter staging space, constructed the slings on web site, after which transported them to the place they’d be deployed. In all different instances, a number of node caches could possibly be transported contained in the helicopter together with the one who would place the nodes at every cache web site.

The node caches have been distributed to almost three dozen areas round Kīlauea’s summit. Though a bunch of 4 to 6 folks (the scale assorted each day) was in a position to cache and deploy the 235 SmartSolo and GTI nodes inside a few week, greater than two dozen folks have been wanted full-time to distribute and activate the 1,580 PASSCAL nodes within the 5 days we allotted for this work earlier than surveying might start. Retrieval of the nodes was roughly the reverse of the deployment operation, with the addition of a crew stationed on the sea container to facilitate cleansing and repacking of the PASSCAL nodes for cargo again to the U.S. mainland.

Because of our group’s detailed planning and to very good logistical assist from companions on the College of Hawai‘i at Hilo, USGS, and the College of Miami, all deployments and retrieval operations went easily and effectively. All recovered nodes collected information for his or her full time period. Solely two nodes—every of which had been put in close to lawns in residential areas—have been misplaced. (One succumbed to a lawnmower shortly after being deployed.)

Traversing a Fractured, Faulted Summit

The 2018 caldera collapse that disrupted Kīlauea’s summit infrastructure (Determine 2) created distinctive challenges for information acquisition. We couldn’t drive T-Rex fully across the summit, for instance, as a result of many roads that have been destroyed had not been rebuilt. And though T-Rex is a multiply articulated off-road car, we couldn’t drive it throughout the Kaʻū Desert south of Kīlauea’s summit crater as a result of it might injury delicate ecosystems. But we knew from complete advance testing that confining T-Rex to solely the paved roads remaining after 2018 would go away gaping holes in our sampling of the subsurface magma system, complicating our capability to piece collectively pictures of this technique from the seismic information we collected.

To assist fill these gaps, we relied on ambient seismicity recorded by the node array (Figures 3 and 4). The sensors recorded greater than 8,500 shallow earthquakes that occurred inside 5 kilometers of the middle of Kaluapele and greater than 25,000 earthquakes exterior the caldera. The detections of those earthquakes present extra illumination, significantly from the south and west, that we would have liked to picture the higher crustal construction of the summit. This seismicity mitigated the shortage of full floor protection with the T-Rex managed supply.

Even once we might use T-Rex to provide energetic supply seismicity (Determine 5), it was harder than anticipated. With the outcomes of our preliminary GPR survey, we had situated proposed websites the place T-Rex would shake the bottom or pavement, however in observe, many of those websites proved unusable.

Our preliminary foray with T-Rex was on unpaved roads over outdated pāhoehoe lava north of the park, in an space close to the Volcano Vineyard simply northwest of the city of Volcano. We presumed that strong coupling between T-Rex’s metal baseplate and the pāhoehoe, with its comparatively easy, ropy floor texture, would work effectively for inducing shaking. As well as, climate forecasts predicted daytime winds robust sufficient to jostle vegetation and vibrate the bottom however nighttime winds that have been docile. Consequently, we initially selected to run T-Rex on this space at night time.

Each of those plans proved untenable. Although the pāhoehoe on the unpaved street floor gave the impression to be practically flat, it was not flat sufficient to maintain from inconsistently loading T-Rex’s baseplate and punishing the truck’s hydraulic drive techniques. And the wind by no means did die down. So we adjusted our plan and began working T-Rex at daybreak, conserving it on pavement to keep up uniform loading of each the street floor and T-Rex’s hydraulic and mechanical techniques. Even so, we had to make use of care in working the huge T-Rex machine on pavement. To keep away from street injury, we coated T-Rex’s metal baseplate with rubber, monitored the bottom response throughout use, and instantly stopped shaking and moved to the following supply place if the height floor velocity approached the two.5 centimeter-per-second threshold.

We discovered that the ground-shaking response was much more variable than we had anticipated from our GPR survey. Particularly, we discovered that resonances induced by the shaking and sign attenuation with distance from the T-Rex conspired to restrict our capability to gather usable information at many areas. Due to the unpredictable floor responses, we have been in a position to collect helpful information at fewer than 400 websites out of the greater than 700 we initially proposed.

For some areas the place we might obtain good coupling, we noticed first arrivals of compressional seismic waves (P waves) from vertical shaking throughout the whole deployed community of nodes (Figures 3, 4, and 5). At a lot of those self same websites, we noticed that the velocities of compressional waves generated by T-Rex have been persistently and astonishingly low within the first 100 meters of depth, probably ensuing from pervasive fractures and voids inside the floor lava flows. This low near-surface P wave velocity proved to be the norm at most websites we surveyed, and we discovered that by utilizing this info to change the prevailing velocity construction beneath Kīlauea’s summit, we might decide earthquake areas extra precisely.

Imaging Kīlauea’s Summit Construction Anew

Our imaging may have important penalties for continued research of Kīlauea. Earlier seismic and gravity research yielded a primary framework of the volcano’s magma system outlined by seismicity and by accumulation of dense olivine on this system [Denlinger and Flinders, 2022, 2024; Flinders et al., 2013; Lin et al., 2014]. We used this earlier work and the outcomes of quite a few geodetic research of eruptions to design this experiment, concentrating on areas within the higher 6 kilometers of the subsurface above a big, dense, high-velocity physique (with the density and velocity of olivine) that underlies the summit and its caldera.

The 2018 summit collapse enlarged the caldera (as proven in Determine 2), parts of which subsided by as a lot as 500 meters [Neal et al., 2019], and completely altered a minimum of the higher 2 kilometers of the summit construction [Shelly and Thelen, 2019]. Utilizing native earthquakes and the energetic supply T-Rex, we achieved unprecedented protection from the 1,815 seismometers we packed into the summit space. Working with these information and the prevailing HVO seismic community, we’ve got recognized roughly 35,000 earthquakes that occurred inside 30 kilometers of the middle of Kaluapele throughout our experiment, giving us probably 192 million waveforms to investigate throughout the community.

Inside the subsequent yr, we anticipate utilizing these seismic information to slice by way of the summit quantity from the floor downward (Determine 6), a lot as in a medical CT scan, and use this info to create a lot sharper and extra complete tomographic footage of the summit magma system. As of the publication of this text, we’ve got sliced right down to solely an elevation of about 1 kilometer beneath sea degree. These outcomes present distinctive info by illuminating the summit construction overlying the magma system. And as we proceed to slice down and refine these information, these pictures will ultimately reveal the transition to and the construction of the magma system itself.

The anticipated new view of the magmatic plumbing construction of Kīlauea will improve scientific understanding of one of many world’s most energetic volcanoes: the way it erupts, how and the place it shops magma, and the way it collapses on the summit whereas feeding voluminous lava flows erupting tens of kilometers away. Finding out this construction will even guarantee that we are going to extra successfully inform emergency managers, policymakers, and the general public in regards to the hazards they face as we watch this volcanic system evolve.

Acknowledgments

This survey went easily and effectively largely due to the comradery and professionalism of workers members of HVO, the Alaska Volcano Observatory, the California Volcano Observatory, and the Cascades Volcano Observatory, all beneath the auspices of USGS’s Volcano Hazards Program. The groups shortly solved issues as they arose, coordinated effectively, and moved effectively and intelligently over typically tough, bushy, and/or deeply crevassed terrain. Along with these working within the area, the remaining workers of Hawai‘i Volcanoes Nationwide Park went above and past to facilitate this operation, placing in extra radio hyperlinks, offering upkeep house for T-Rex, granting entry to closed areas, and serving to us function as a result of the truck proved to be a giant distraction for guests to the park. These contributions from the observatories and the park have been important to our success, as was the information and experience of the NHERI engineers at UT-Austin, who helped us with T-Rex and stored it operating throughout our survey. Particularly, we acknowledge Steve Brantley (USGS emeritus) for main allowing efforts and Lil DeSmither from the College of Hawai‘i at Hilo, Rebecca Kramer and Ashton Flinders from USGS, and Elizabeth Vinarski from the College of Miami for logistical assist associated to the instrument deployments. As well as, we acknowledge assist from the 2019 congressional complement to the USGS (Further Supplemental Appropriations for Catastrophe Reduction Act, 2019 (H.R. 2157)) and Nationwide Science Basis grants EAR-2218645 (College of Miami), EAR-2218646 (Rensselaer Polytechnic Institute), and CMMI-2037900 (NHERI at UT-Austin) to be used of T-Rex. Any use of commerce, agency, or product names is for descriptive functions solely and doesn’t suggest endorsement by the U.S. authorities.

References