Summit Collapse Research Articles

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. ▪Unprecedented observations of a caldera collapse and coupled rift zone eruption yield new opportunities for advancing volcano science.▪Magma flow to a low-elevation rift zone vent triggered quasi-periodic step-like collapse of a summit caldera, which pressurized the magma system and sustained the eruption.▪Kīlauea's magmatic-tectonic system is tightly interconnected over tens of kilometers, with complex feedback mechanisms and interrelated hazards over widely varying timescales.▪The eruption revealed magma stored in diverse locations, volumes, and compositions, not only beneath the summit but also within the volcano's most active rift zone.

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.

Post Audit of Simulated Groundwater Flow to a Short-Lived (2019 to 2020) Crater Lake at Kīlauea Volcano.

About 14.5months after the 2018 eruption and summit collapse of Kīlauea Volcano, Hawai'i, liquid water started accumulating in the deepened summit crater, forming a lake that attained 51 m depth before rapidly boiling off on December 20, 2020, when an eruption from the crater wall poured lava into the lake. Modeling the growth of the crater lake at Kīlauea summit is important for assessing the potential for explosive volcanism. Our current understanding of the past 2500 years of eruptive activity at Kīlauea suggests a slight dominance of explosive behavior over effusive. The deepened summit crater and presence of the crater lake in 2019 raised renewed concerns about explosive activity. Groundwater models using hydraulic-property data from a nearby drillhole successfully forecast the timing and rate of lake filling. Here we compare the groundwater-model predictions with observational data through the demise of the crater lake, examine the implications for local water-table configuration, consider the potential role of evaporation and recharge (neglected in previous models), and briefly discuss the energetics of the rapid boil-off. This post audit of groundwater-flow models of Kīlauea summit shows that simple models can sometimes be used effectively to simulate complex settings such as volcanoes.

Onset and evolution of Kīlauea'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 kgm−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 m3 of lava over the course of two hours, and a material density of 1800–1900 kgm−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 km3 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.

Earthquake collapse mechanisms and periodic, migrating seismicity during the 2018 summit collapse at Kīlauea caldera

The 2018 Lower East Rift Zone eruption of Kīlauea volcano was accompanied by a remarkable and periodic succession of collapses in the summit region. Between May-August the eruption and collapse sequence included 54 earthquakes (M∼5; M5s) observed worldwide, and over 45,000 intervening earthquakes (M≥0). We estimated seismic full moment tensors for the M5s and analyzed the spatiotemporal evolution of the intervening seismicity. The hypocenters were concentrated between 0-3 km depths and reveal arcuate bands that migrated outward by ∼300 m (map view) and downward by ∼200 m. The temporal evolution reveals almost daily successions of escalating earthquake swarms, followed by an M5, followed by a quiescent period. The moment tensors reveal consistent collapse mechanisms with vertical P-axis orientations. Poisson's ratios estimated from the moment tensors were variable at first (ν=0.1−0.3) and from June 26 onward converged to ν∼0.28, similar to loading cycles observed in lab experiments. The shallower collapses approximately follow the expanding contour of the crater, while deeper collapses aggregate first to the north of the previous crater and later to the east and south. We interpret that the magma storage complex beneath the summit region comprises a distributed plexus of cracks that progressively evacuated and underwent collapse as magma drained from the summit region to feed the eruption.

Comprehensive High‐Precision Relocation of Seismicity on the Island of Hawai‘i 1986–2018

AbstractAbundant seismicity beneath the Island of Hawai‘i from mantle depths to the surface plays a central role in understanding how volcanoes work, grow, and evolve at this intraplate oceanic hotspot. We perform systematic waveform cross‐correlation, cluster analysis, and relative relocation of 347,445 events representing 32 years of seismicity on and around the island from 1986 to 2018. We successfully relocate 275,009 (79%) events using ∼1.7 billion differential times (P and S) from ∼128 million similar‐event pairs. The results reveal a dramatic sharpening of seismicity along faults, streaks, rings, rift zones, magma pathways, and mantle fault zones; seismicity delineating crustal detachments on the flanks of Kīlauea and Mauna Loa is particularly well‐resolved. The resulting high‐precision spatio‐temporal image of seismicity captures almost the entire 1983–2018 Pu‘u ‘Ō‘ō‐Kūpaianaha eruption of Kīlauea with its numerous distinct episodes and wide‐ranging activity, culminating in the 2018 lower East Rift Zone eruption and summit collapse.

The historic events at Kīlauea Volcano in 2018: summit collapse, rift zone eruption, and Mw 6.9 earthquake: preface to the special issue

The historic events at Kīlauea Volcano in 2018: summit collapse, rift zone eruption, and Mw 6.9 earthquake: preface to the special issue

Spatiotemporal Seismic Structure Variations Associated With the 2018 Kīlauea Eruption Based on Temporary Dense Geophone Arrays

AbstractDuring the 2018 Kīlauea volcanic eruption, lava erupted from a series of new fissures in the lower East Rift Zone more than 30 km away from the summit through a dike intrusion. Between late May and early August, variations in the effusion rate at the persistent eruptive vent (Fissure 8) were observed following near‐daily summit caldera collapse events. Targeting the ongoing eruptive activity and the subsurface magma movement, we deployed a temporary dense seismic array. The observed time‐lapse changes in seismic velocity associated with the response of the summit collapse in three areas are presented in this study. The results show (1) clear spatially dependent co‐collapse velocity reductions across the newly‐intruded dike structure, (2) a gradual post‐collapse velocity increase near Fissure 8 correlated with the surge of magma supply, and (3) a gradual post‐collapse velocity increase on the summit likely associated with reservoir pressurization and crustal welding.

The 2007 caldera collapse at Piton de la Fournaise: new insights from multi-temporal structure-from-motion

We produced new multi-temporal Digital Elevation Models (DEMs) of the April 2007 summit collapse at Piton de la Fournaise from previously unused aerial photographs. This dataset revealed the precise temporal evolution of collapsed volume and caldera morphological changes. Four days after the onset of an eruption at an unusually low elevation, the summit started to collapse (20:48 UTC April 5th). During the first 30 hours, collapsing was relatively fast (840 m3 s-1 average), and continued for at least the following 12 days, at a slower rate (46 m3 s-1 average). On April 19th, the collapse reached 96% of its final volume, while the remaining 4% were probably attained by May 1st (end of lava emission at the vent). The post-collapse hydrothermal activity in the caldera is closely associated with the main ring faults evidenced as active during the collapse, which are now preferential paths for fluids to reach the surface.

Post‐Collapse Gravity Increase at the Summit of Kīlauea Volcano, Hawaiʻi

AbstractWe conducted gravity surveys of the summit area of Kīlauea Volcano, Hawaiʻi, in November 2018 and March 2019, with the goal of determining whether there was any mass change at depth following the volcano's May–August 2018 caldera collapse. Surface deformation between the two surveys was minimal, but we measured a gravity increase (maximum 44 μGal) centered on the caldera that can be modeled as mass accumulation in a region ~1 km beneath the surface. We interpret this mass increase to be mostly magma accumulation in void space that was created during the summit collapse. Caldera uplift was evident by April 2019, indicating that the magma volume had reached a point where pressurization could be sustained. Modeled gravity change suggests a maximum magma storage rate at Kīlauea's summit during November 2018 to March 2019 that is much less than the pre‐2018 magma supply rate to the volcano.

Volcanic earthquake foreshocks during the 2018 collapse of Kīlauea Caldera

SUMMARYThe summit collapse of the Kīlauea Caldera—due to magma chamber drainage being directed to the Volcano's lower east rift zone—was accompanied by 50 large, nearly identical magnitude Mw 5 earthquakes between 29 May and 2 August 2 2018. I have examined the seismicity associated with these 50 primary earthquakes, and find that the typical pattern of earthquake aftershocks decaying in number and magnitude is not evident. Rather, immediately after the primary shock there is a hiatus of one-to-several hours before the associated earthquakes grow in number and magnitude up to the next primary shock. In essence, the associated seismicity consists of thousands of foreshocks. The magnitude of completeness is estimated at ML = 2.5. The trend of foreshocks does not fit an Omori power-law model. Rather, the pattern of foreshocks (number per hour) is fit well by a semi-Gaussian curve, which initially grows rapidly and slows hours prior to the primary earthquakes. The Gaussian fits (${r^2} &gt; 0.98$) for three different magnitude thresholds are self-similar with a common half-width, $\sigma \sim 13$ hr. The pattern of foreshock seismic moments aligned with and stacked for the 50 primary events is fit by an exponential trend, growing at the mean (stacked intervals) rate of 17 per cent per hour. The power of foreshocks measured within each interval also grows with time—the total foreshock power per interval (J hr–1) increases by a factor of 18 through the first half of the sequence (May 29 through June 26), and then declines by half through to the end.

Topographic Changes During the 2018 Kīlauea Eruption From Single‐Pass Airborne InSAR

AbstractThe 2018 eruption of Kīlauea volcano, Hawai‘i, was its most effusive in over 200 years. We apply the airborne Glacier and Ice Surface Topography Interferometer (GLISTIN‐A) interferometric synthetic aperture radar (InSAR) instrument to measure topographic change associated with the eruption. The GLISTIN‐A radar flew in response to the eruption, acquiring observations of Kīlauea on 7 days between 18 May and 15 September 2018. Topography differences were computed relative to GLISTIN‐A observations in 2017. Bare‐Earth topography and offshore bathymetry were used to correct for vegetation and creation of new coastal land within the lower East Rift Zone (LERZ) lava flow field. We estimate that the LERZ subaerial flows total bulk volume is 0.593 ± 0.011 km3 and that the summit collapse volume is −0.836 ± 0.002 km3. Within the temporal sampling and uncertainty from submarine flow volumes, we find that both the LERZ and caldera volume changes were approximately linear.

High 3He/4He ratios in lower East Rift Zone steaming vents precede a new phase of Kilauea 2018 eruption by 8 months

On May 1, 2018, a magnitude 5.0 earthquake heralded the collapse of the Pu’u O’o Vent on the middle East Rift Zone (ERZ) of Kilauea Volcano, active since 1983. Increased seismicity was recorded on the middle to lower ERZ from April 30 until May 2, 2018. The active lava lakes within both Pu’u O’o Vent and Halema’uma’u Crater began to drain and the summit caldera began to deflate, with the summit collapse ending on August 2, 2018 and lower ERZ eruptive lava activity ending by 4 September 2018. Herein we report on elevated 3He/4He ratios in steaming vents in the lower ERZ from samples collected in early September 2017. Gas isotopic measurements were made with a new, field-portable He isotope detector capable of sub-daily monitoring of the 3He/4He ratio. When corrected for air contamination, these values exceed those previously reported for Kilauea by nearly twofold, resembling a purer hotspot plume signature, such as those measured directly over the mantle plume at Loihi Seamount to the SE of Hawaii Island, and in older basalt flows when Kilauea and its sister Hawaiian shield volcanoes were located more directly over the plume. The discovery, which presages the eruption there by more than eight months, suggests that we either sampled a 3He/4He rich magma already in place in the lower ERZ or a shallow groundwater reservoir in the lower ERZ (Puna district) with anomalously low values of 4He relative to their 3He/4He ratio, similar to previous findings there and suggestive of a previously unknown He isotopic fractionation.

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

Abstract 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 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 207Pb/204Pb 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 207Pb/204Pb at a given 206Pb/204Pb 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.

The 2018 rift eruption and summit collapse of Kīlauea 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 kilometers. A 4 May earthquake [moment magnitude (M w) 6.9] produced ~5 meters of fault slip. Lava erupted at rates exceeding 100 cubic meters per second, eventually covering 35.5 square kilometers. The summit magma system partially drained, producing minor explosions and near-daily collapses releasing energy equivalent to M w 4.7 to 5.4 earthquakes. Activity declined rapidly on 4 August. Summit collapse and lava flow volume estimates are roughly equivalent-about 0.8 cubic kilometers. Careful historical observation and monitoring of Kīlauea enabled successful forecasting of hazardous events.

Newspaper reporting of the April 2007 eruption of Piton de la Fournaise part 1: useful information or tabloid sensationalism?

During March, April and May 2007 the local newspaper for the island of La Réunion, “Le Journal de L’Ile de La Réunion” (JIR), published 427 articles relating to natural hazards, with hazard-related articles occupying a total paper area of 21.94 m2 and appearing in all but four of the 90 editions of the newspaper. This high level of coverage was due to the passage of two cyclones in March, the largest historical eruption of Piton de la Fournaise in April, and a major rock fall event in May. The high level of coverage may also be due to the fact that JIR is a tabloid that follows tabloid news values. Cyclones, volcanic eruptions and rock falls fit the news values of a tabloid well, especially when the stories involve the power elite, feature stories of human interest, include surprise elements and rescues, and are of high impact, especially to the local population. Disasters also provide spectacular imagery and the opportunity for eye-catching headlines, which is another element of the tabloid format. These key parameters thus all flag stories about natural hazards and, in particular, volcanic eruptions as being newsworthy for a tabloid.Of the page space devoted to natural hazards, 9.24 m2 (42%) were set aside to reporting of volcanic activity, specifically the April 2007 eruption of Piton de la Fournaise. We completed a content analysis of these reports to understand the quality of information disseminated to the readership and to extract data regarding the impact of the eruption on local communities. We found the information to be of extremely high quality, with lava reporting being the most important issue covered by page area, mostly due to its photogenic nature. If we consider text-dominated reports, and exclude photo-montages, then the order of importance in terms of space set aside to reporting of a particular theme becomes: (i) general eruption details; (ii) summit collapse; (iii) lava flows; (iv) evacuation; (v) gas; (vi) ocean-entry; (v) air fall; (vi) vegetation fires (lit by lava contact); and (vii) volcano-seismicity. As the eruption and the nature of the hazard evolved (from lava flow through air-fall and gas, to summit collapse and ocean-entry) so too did the focus of the reporting. Once the eruption had finished, emphasis shifted from the hardships of the impacted community to sightseeing and tourism. We found that the quality of the reporting resulted from the use of journalists who were specialized in their reporting areas and who therefore knew the background and the correct sources to seek out for information. This shows that a well-informed journalist can be (i) a means to disseminate information and educate an impacted population, and (ii) a source of information for the volcanologist regarding societal impacts of, and population responses to, natural hazards.

The ∼1000-years BP explosive eruption of Caldeira Volcano (Faial, Azores): the first stage of incremental caldera formation

The ∼1000-years BP eruption of Caldeira Volcano (Faial Island) was one of the last major explosive events recorded in the Azores. It produced a complex succession of pyroclastic deposits, known as the C11, divided into three members. At the base is the Brejo Member, a sequence of fine- to coarse-grained parallel-bedded ash layers found in the NW sector of the island. The middle part corresponds to the Inverno Member, a coarse-grained massive pumice fall deposit, restricted to the north flank of Caldeira Volcano. The top is dominated by the Cedros Member which includes massive to diffuse-stratified lapilli-ash and lithic breccias, exposed along the north and east flanks of the volcano. A minimum bulk volume of at least 0.22 km3 (>0.1 km3 dense rock equivalent (DRE)) is estimated for the C11 eruption, although a large portion may have been deposited offshore. The juvenile products are trachytic (59 wt% SiO2) with a homogenous whole-rock composition and mineral assemblage throughout the pyroclastic succession. However, petrographic and groundmass glass analyses indicate magma mingling/mixing processes between two trachytic batches. The C11 eruption history is divided into three phases (following the member division) with distinct eruptive styles: (1) an initial phreatomagmatic phase caused by rising magma (∼950 °C) encountering a crater pond or aquifer, (2) a fall-dominated phase which established a sub-Plinian column up to 14 km high (mass eruption rate (MER) of 1.2 × 107 kg/s) and (3) prolonged pyroclastic fountaining and sustained quasi-steady pyroclastic density current generation followed by summit collapse. The C11 eruption is interpreted as the first stage in the formation of an incremental caldera. This study provides valuable insights for a better understanding of small but complex explosive eruptions and their impact on ocean islands.

Magma degassing during the April 2007 collapse of Piton de la Fournaise: The record of semi-volatile trace elements (Li, B, Cu, In, Sn, Cd, Re, Tl, Bi)

This study reports the concentrations of trace elements, including fluid mobile and semi-volatile species (e.g., Li, B, Cu, Re, In, Sn, Cd, Tl, Bi) in lavas erupted before and during the April 2007 collapse of the Piton de la Fournaise summit. Lavas erupted just prior to the collapse (April 5) display anomalous abundances in semi-volatile elements, with both depletion in Li, Cu and Tl (mostly on April 2) and enrichment in Cd, Bi, In and Sn (on April 3 and 4). These transient anomalies are thought to record unusual degassing conditions. Between March 30 and April 2, static decompression caused by magma withdrawal from the shallow magma reservoir might have triggered massive exsolution of a H2O- and S-rich phase in which Li and Cu might have partitioned. Alternatively, the Li–Cu depletion could record the degassing of a magma body that intruded at shallow depth during the same period. The Bi–Cd–In–Sn enrichment observed in the April 3–4 magmas requires conditions that prevent magma outgassing. In the absence of evidence for the pressurisation of the reservoir or the onset of collapse before April 5, it is suggested that the occurrence of less degassed lavas on April 3 and 4 reflects a high rate of magma transfer from the shallow magma reservoir to the eruption site just prior to summit collapse.The kinetic (diffusive) fractionation of elements accounts for the observed anomalies. The short time-scales required to fractionate Li from Cd diffusively (minutes to hours) and Cd from Bi (few hours to two days) support the idea that the magmas underwent rapid pressure variations a few days before the summit collapse.

Keanakākoʻi Tephra produced by 300 years of explosive eruptions following collapse of Kīlauea's caldera in about 1500 CE

The Keanakākoʻi Tephra at Kīlauea Volcano has previously been interpreted by some as the product of a caldera-forming eruption in 1790 CE. Our study, however, finds stratigraphic and 14C evidence that the tephra instead results from numerous eruptions throughout a 300-year period between about 1500 and 1800. The stratigraphic evidence includes: (1) as many as six pure lithic ash beds interleaved in sand dunes made of earlier Keanakākoʻi vitric ash, (2) three lava flows from Kīlauea and Mauna Loa interbedded with the tephra, (3) buried syneruptive cultural structures, (4) numerous intraformational water-cut gullies, and (5) abundant organic layers rich in charcoal within the tephra section. Interpretation of 97 new accelerator mass spectrometry (AMS) 14C ages and 4 previous conventional ages suggests that explosive eruptions began in 1470–1510 CE, and that explosive activity continued episodically until the early 1800s, probably with two periods of quiescence lasting several decades. Kīlauea's caldera, rather than forming in 1790, predates the first eruption of the Keanakākoʻi and collapsed in 1470–1510, immediately following, and perhaps causing, the end of the 60-year-long, 4–6km3 ʻAilāʻau eruption from the east side of Kīlauea's summit area. The caldera was several hundred meters deep when the Keanakākoʻi began erupting, consistent with oral tradition, and probably had a volume of 4–6km3. The caldera formed by collapse, but no eruption of lava coincided with its formation. A large volume of magma may have quickly drained from the summit reservoir and intruded into the east rift zone, perhaps in response to a major south-flank slip event, leading to summit collapse. Alternatively, magma may have slowly drained from the reservoir during the prolonged ʻAilāʻau eruption, causing episodic collapses before the final, largest downdrop took place. Two prolonged periods of episodic explosive eruptions are known at Kīlauea, the Keanakākoʻi and the Uwēkahuna Tephra (Fiske et al., 2009), and both occurred when a deep caldera existed, probably with a floor at or below the water table, and external water could readily interact with the magmatic system. The next period of intense explosive activity will probably have to await the drastic deepening of the present caldera (or Halemaʻumaʻu Crater) or the formation of a new caldera.

Geology, tectonics, and the 2002–2003 eruption of the Semeru volcano, Indonesia: Interpreted from high-spatial resolution satellite imagery

The paper illustrates the application of high-spatial resolution satellite images in interpreting volcanic structures and eruption impacts in the Tengger–Semeru massif in east Java, Indonesia. We use high-spatial resolution images (IKONOS and SPOT 5) and aerial photos in order to analyze the structures of Semeru volcano and map the deposits. Geological and tectonic mapping is based on two DEMs and on the interpretation of aerial photos and four SPOT and IKONOS optical satellite images acquired between 1996 and 2002. We also compared two thermal Surface Kinetic Temperature ASTER images before and after the 2002–2003 eruption in order to delineate and evaluate the impacts of the pyroclastic density currents. Semeru's principal structural features are probably due to the tectonic setting of the volcano. A structural map of the Tengger–Semeru massif shows four groups of faults orientated N40, N160, N75, and N105 to N140. Conspicuous structures, such as the SE-trending horseshoe-shaped scar on Semeru's summit cone, coincide with the N160-trending faults. The direction of minor scars on the east flank parallels the first and second groups of faults. The Semeru composite cone hosts the currently active Jonggring-Seloko vent. This is located on, and buttressed against, the Mahameru edifice at the head of a large scar that may reflect a failure plane at shallow depth. Dipping 35° towards the SE, this failure plane may correspond to a weak basal layer of weathered volcaniclastic rocks of Tertiary age. We suggest that the deformation pattern of Semeru and its large scar may be induced by flank spreading over the weak basal layer of the volcano. It is therefore necessary to consider the potential for flank and summit collapse in the future. The last major eruption took place in December 2002–January 2003, and involved emplacement of block-and-ash flows. We have used the 2003 ASTER Surface Kinetic Temperature image to map the 2002–2003 pyroclastic density current deposits. We have also compared two 10 m-pixel images acquired before and after the event to describe the extent and impact of an estimated volume of 5.45 × 10 6 m 3 of block-and-ash flow deposits. An ash-rich pyroclastic surge escaped from one of the valley-confined block-and ash flows at 5 to 8 km distance from the crater and swept across the forest and tilled land on the SW side of the Bang River Valley. Downvalley, the temperature of the pyroclastic surge decreased and a mud-rich deposit coated the banks of the Bang River Valley. Thus, hazard mitigation at Semeru should combine: (1) continuous monitoring of the eruptive activity through an early-warning system, and (2) continuous remote sensing of the morphological changes in the drainage system due to the impact of frequent pyroclastic density currents and lahars.