Caldera Formation Research Articles

Cycles of explosive and effusive eruptions at Kīlauea Volcano, Hawai‘i

Research Article| July 01, 2014 Cycles of explosive and effusive eruptions at Kīlauea Volcano, Hawai‘i Donald A. Swanson; Donald A. Swanson 1U.S. Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, Hawaii 96718, USA Search for other works by this author on: GSW Google Scholar Timothy R. Rose; Timothy R. Rose 2Department of Mineral Sciences, Museum of Natural History, Smithsonian Institution, Washington, D.C. 20013, USA Search for other works by this author on: GSW Google Scholar Adonara E. Mucek; Adonara E. Mucek 3Department of Geology and Geophysics, SOEST (School of Ocean and Earth Science and Technology), University of Hawai‘i, Honolulu, Hawai‘i 96822, USA Search for other works by this author on: GSW Google Scholar Michael O. Garcia; Michael O. Garcia 3Department of Geology and Geophysics, SOEST (School of Ocean and Earth Science and Technology), University of Hawai‘i, Honolulu, Hawai‘i 96822, USA Search for other works by this author on: GSW Google Scholar Richard S. Fiske; Richard S. Fiske 2Department of Mineral Sciences, Museum of Natural History, Smithsonian Institution, Washington, D.C. 20013, USA Search for other works by this author on: GSW Google Scholar Larry G. Mastin Larry G. Mastin 4U.S. Geological Survey, Cascades Volcano Observatory, Vancouver, Washington 98683, USA Search for other works by this author on: GSW Google Scholar Geology (2014) 42 (7): 631–634. https://doi.org/10.1130/G35701.1 Article history received: 21 Mar 2014 rev-recd: 10 May 2014 accepted: 13 May 2014 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Donald A. Swanson, Timothy R. Rose, Adonara E. Mucek, Michael O. Garcia, Richard S. Fiske, Larry G. Mastin; Cycles of explosive and effusive eruptions at Kīlauea Volcano, Hawai‘i. Geology 2014;; 42 (7): 631–634. doi: https://doi.org/10.1130/G35701.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The subaerial eruptive activity at Kīlauea Volcano (Hawai‘i) for the past 2500 yr can be divided into 3 dominantly effusive and 2 dominantly explosive periods, each lasting several centuries. The prevailing style of eruption for 60% of this time was explosive, manifested by repeated phreatic and phreatomagmatic activity in a deep summit caldera. During dominantly explosive periods, the magma supply rate to the shallow storage volume beneath the summit dropped to only a few percent of that during mainly effusive periods. The frequency and duration of explosive activity are contrary to the popular impression that Kīlauea is almost unceasingly effusive. Explosive activity apparently correlates with the presence of a caldera intersecting the water table. The decrease in magma supply rate may result in caldera collapse, because erupted or intruded magma is not replaced. Glasses with unusually high MgO, TiO2, and K2O compositions occur only in explosive tephra (and one related lava flow) and are consistent with disruption of the shallow reservoir complex during caldera formation. Kīlauea is a complex, modulated system in which melting rate, supply rate, conduit stability (in both mantle and crust), reservoir geometry, water table, and many other factors interact with one another. The hazards associated with explosive activity at Kīlauea’s summit would have major impact on local society if a future dominantly explosive period were to last several centuries. The association of lowered magma supply, caldera formation, and explosive activity might characterize other basaltic volcanoes, but has not been recognized. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Tephrostratigraphy and eruptive history of post-caldera stage of Toya Volcano, Hokkaido, northern Japan

A detailed tephrostratigraphy of Toya Volcano in Hokkaido, northern Japan has been constructed to evaluate the post-caldera eruptive history of the volcano. The tephrostratigraphic sequence preserved above the Toya ignimbrite reaches a total thickness of 8m southeast of the caldera. After the caldera formation (115–112ka), there was a long quiescent period of more than 60kayears. The first post-caldera activity started with Nakajima Osarugawa pumice-fall deposit (Nj-Os) inside the caldera at 48ka. Eruptive activity at Nakajima Volcano resumed at 30ka with Nakajima Sekinai pumice-fall deposit (Nj-Sk), and was followed by continuous emission of fine ash including abundant accretionary lapilli. Soon after the Nakajima pyroclastic eruption Usu Volcano began its activity with discharges of basaltic ash and scoria (forming the Usu prehistoric tephra) and extrusion of homogeneous lavas namely Usu somma lava, resulting in the formation of the initial volcanic edifice. Subsequently, a large sector collapse occurred between 30 and 20ka that emplaced the Zenkoji debris avalanche with little break after the formation of the initial Usu volcanic edifice. After the sector collapse, the volcano remained dormant for about 20–30kayears. Eruptive activity at Usu Volcano resumed in 1663AD with the most explosive plinian eruption in the post-caldera stage of Toya Volcano. Since then, seven eruptions have been recorded in 1769, 1822, 1853, 1910, 1943–1945, 1977–1978 and 2000 at multi-decadal interval. Total tephra volume during the post-caldera stage is estimated at about 0.9km3 (dense rock equivalent: DRE), whereas total lava volume is calculated at about 2.3km3. Therefore, the average magma discharge rate during the post-caldera stage of Toya Volcano is estimated at about 0.03km3/ky, which is one or two order smaller than those of other Quaternary volcanoes in Japan.

Evaluating volumes for magma chambers and magma withdrawn for caldera collapse

We develop an analytical model to infer the total volume of a magma chamber associated with caldera collapse and the critical volume of magma that must be withdrawn to induce caldera collapse. The diameter of caldera border fault, depth to the magma chamber, and volumes of magma erupted before the onset of collapse and of entire eruption are compiled for 14 representative calderas. The volume of erupted magma at the onset of collapse aligns between the total erupted volume of the other representative caldera-forming eruptions and the volume of eruptions without collapse during the post-caldera stage, correlating with the structural diameter of the calderas.The total volume of magma chamber is evaluated using a piston-cylinder collapse model, in which the competition between the decompression inside magma chamber and friction along the caldera fault controls the collapse. Estimated volumes of the magma chambers associated with caldera collapse are 3–10 km3 for Vesuvius 79 A.D. to 3000–10 500 km3 for Long Valley, correlating with the cube of caldera diameters. The estimated volumes of magma chamber are always larger than the total volume of erupted magma for caldera formation, suggesting that the magma chambers are never completely emptied by the caldera-forming eruptions. The minimum volumes of erupted magma to trigger collapse are calculated from the correlation between the caldera diameters and the evaluated volume of magma chambers. The minimum eruptive volume for the collapse correlates with the square of the caldera radius r and the square of the depth to the magma chamber h, and inversely correlates with the bulk modulus of magma, which is mainly controlled by the bubble fraction in the magma. A bubble fraction between 5 and 10% at the onset of collapse may explain the distribution of the erupted volumes at the onset of collapse of the calderas in nature.

Zircon trace element chemistry at sub-micrometer resolution for Tarawera volcano, New Zealand, and implications for rhyolite magma evolution

Zoned crystals can be important recorders of magmatic processes in space and time. However, in most situations, the temporal dimension is difficult to quantify. Here, we have employed secondary ion mass spectrometry depth profiling to excavate parallel pits into non-polished crystal faces of zircon to obtain ~5 μm resolution U–Th disequilibrium ages (one pit) that can be correlated with trace element zoning at sub-μm resolution derived from a second pit. Data from 17 crystals representing each of the four rhyolite eruptions of Tarawera volcano, an intra-caldera edifice within the Okataina Volcanic Centre, reveal diverse zircon growth conditions over time. Most crystals display rimward depletions in Zr/Hf and Ti, broadly consistent with cooling and crystallization. However, a significant fraction of crystals lacks these patterns and displays rimward trace element variations consistent with isothermal or prograde crystallization. Oscillatory zonation patterns in Y, Th, and U are superimposed on the Zr/Hf and Ti trends. Despite the limited number of crystals analyzed in this way, the striking lack of ubiquitous trace element zoning patterns in crystals from the same hand sample implies that fractional crystallization upon cooling was punctuated by magma recharge and crystal mixing affecting different parts of the magma reservoir. By combining data from all crystals, a systematic change to more heterogeneous trace element abundances is revealed by zircon crystal domains 100 ka prior to caldera formation and is best explained by the post-caldera system consisting of small, isolated melt pockets that evolved independently. An important conclusion is that the zircon ‘cargo’ in volcanic rocks reflects thermally and compositionally divergent processes that act near simultaneously in a magma storage region and not exclusively the conditions in the eruptible magma.

Potential field and bathymetric investigation of the Monowai volcanic centre, Kermadec Arc: implications for caldera formation and volcanic evolution

The dynamics of caldera formation are affected by internal factors, such as magma chamber structure and properties and regional tectonic stresses. Understanding their interrelationship is important for assessing volcanic hazard and reconstructing the evolution of a volcano. The Monowai volcanic centre, located at the Tonga–Kermadec Arc, is a basaltic–andesitic submarine stratovolcano and caldera. Recent surveys have shown that it is active, but little is known about its structure and evolution. Here we present a combined analysis of swath bathymetry and potential field data from Monowai, acquired during cruise SO215 on the R/V Sonne, in 2011 April–June. The Monowai caldera is associated with a 20–25 mGal Bouguer gravity anomaly high and a broad positive magnetic anomaly. Short-wavelength magnetic anomalies of up to +1400 and −800 nT are observed along the caldera rim and on the summit of Monowai cone. Inversion of the Bouguer gravity anomaly data shows that the caldera high is caused by a buried dense body with density contrast of up to +450 kg m−3 with respect to the surrounding arc crust. The body has a volume of ∼250 km3 and is divided into a main unit extending from 3 to 6 km depth and a shallower ring structure that underlies the rim of Monowai caldera. We estimate the density of the body to be 2650–2850 kg m−3, suggesting a mafic composition. The ring structure is interpreted as set of ring dykes and the main unit as a solidified or partly solidified magma chamber system (the Monowai pluton). The observed magnetic anomalies are consistent with pluton intrusion within the Bruhnes magnetic polarity. Analysis of the swath bathymetry data shows that Monowai is located in a 20-km-wide graben, part of an en-echelon, left-stepping horst and graben system that spans the length of the arc and backarc. The Monowai caldera is elongated perpendicular to the direction of rifting, suggesting that it is affected by the regional stress regime. Geomorphological analysis suggests that the caldera was created by repeated collapse of a single caldera structure and that its complex shape and multiple ring faults can be attributed to prolonged activity and multiple cycles of inflation and collapse. We propose a multiphase evolution of the Monowai volcanic centre comprising initial magma emplacement and crustal inflation; magma chamber evacuation and caldera collapse; caldera resurgence and mass waisting; southward migration of the eruptive vent; and formation of Monowai cone. It remains unclear whether the current eruption at the Monowai cone is fed directly from a small underlying magma chamber, or laterally from the Monowai pluton. Observation of radial fissure ridges on its flanks suggests that a shallow magma body may have been recently emplaced beneath the summit causing inflation and the formation of extensional cracks. The summit appears unstable and may be prone to lateral or vertical collapse. Therefore, the region remains a potential source of regional volcanic and tsunami hazard.

The magmatic evolution of three Venusian coronae

Abstract The volcanic and tectonic histories of Venusian coronae appear to be intricately linked. We explore that link through the construction of geological maps of three coronae using Magellan synthetic aperture radar (SAR) imagery and altimetry radar data. Each examined corona – Aramaiti, Bhumidevi and Zemire Coronae – is characterized by an annulus of concentric fractures, lava flows, tholi and clusters of small shields. Radial fractures occur at one corona (Bhumidevi Corona), whereas the other two coronae (Aramaiti and Zemire Coronae) occur within linear fracture belts. Based on observed timing relationships, we propose that the evolution of these three coronae is similar to large silicic caldera formation on Earth in that the formation of concentric fractures facilitated a mass evacuation of a magma reservoir residing underneath each corona resulting in subsequent corona collapse. Our model emphasizes the late-stage evolution of these coronae and predicts that all the erupted products could be basaltic. Such predictions are testable through continued geological mapping of coronae, as well as through in situ spectral analyses by Venusian landers.

Elastic models of magma reservoir mechanics: a key tool for investigating planetary volcanism

Abstract Understanding how shallow reservoirs store and redirect magma is critical for deciphering the relationship between surface and subsurface volcanic activity on the terrestrial planets. Complementing field, laboratory and remote sensing analyses, elastic models provide key insights into the mechanics of magma reservoir inflation and rupture, and hence into commonly observed volcanic phenomena including edifice growth, circumferential intrusion, radial dyke swarm emplacement and caldera formation. Based on finite element model results, the interplay between volcanic elements – such as magma reservoir geometry, host rock environment (with an emphasis on understanding how host rock pore pressure assumptions affect model predictions), mechanical layering, and edifice loading with and without flexure – dictates the overpressure required for rupture, the location and orientation of initial fracturing and intrusion, and the associated surface uplift. Model results are either insensitive to, or can readily incorporate, material and parameter variations characterizing different planetary environments, and they also compare favourably with predictions derived from rheologically complex, time-dependent formulations for a surprisingly diverse array of volcanic scenarios. These characteristics indicate that elastic models are a powerful and useful tool for exploring many fundamental questions in planetary volcanology.

Caldera structure of submarine Volcano #1 on the Tonga Arc at 21°09′S, southwestern Pacific: Analysis of multichannel seismic profiling

Volcano #1 is a large submarine stratovolcano with a summit caldera in the south central part of the Tonga Arc. We collected and analyzed multichannel seismic profiles in conjunction with magnetic data from Volcano #1 to investigate the structure of the intracaldera fill and processes of caldera formation. The intracaldera fill, exhibiting stratified units with a maximum thickness of 2 km, consists of at least four seismic units and a thick wedge of landslide debris derived from the caldera wall. The structural caldera floor, deepening toward the northwestern rim, suggests asymmetric collapse in the initial stage, which, in turn, appears to have contributed to the creation of a caldera elongated to the northwest by enhancing gravitational instability along the northwestern caldera boundary. Occasional, but repeated, eruptions resulted in a thick accumulation of the intracaldera fill and further subsidence in the mode of piston collapse. Magnetization lows are well-defined along the structural rim of the caldera that is interpreted as the inner principal ring fault. The magnetization lows indicate sites of submarine hydrothermal vents that caused an alteration of magnetic minerals. Faults recognized on the outer slope of the volcano are interpreted to be involved in hydrothermal fluid circulation.

Possible regional tectonic controls on mammalian evolution in western North America

Previous work has suggested that tectonically active regions act as speciation pumps for mammals and plant species, but little is known about how fast or widespread tectonism must be in order to directly influence evolution. Here, we use oxygen and hydrogen isotopic data from Miocene sedimentary deposits to characterize the topographic evolution of the southern Columbia Plateau/Snake River Plain and northern Rocky Mountain regions during the Yellowstone hotspot passage, with the ultimate goal of understanding whether topographic changes caused by the hotspot influenced mammalian evolution within those regions. We conducted oxygen isotope analyses of 130 samples of lacustrine, and paleosol carbonate from Miocene stratigraphic sections that span much of the northern Rocky Mountain region, and combined these data with previously published isotopic records. Collectively these isotopic data show that caldera formation associated with the Yellowstone hotspot has modified regional topography and rearranged drainages along the track of the hotspot, and that the hotspot has left a topographic depression in its wake.We explore the extent to which these topographic changes influenced or are decoupled from diversity changes exhibited by the local mammal faunas and conclude that the passage of the hotspot and consequent surface uplift created rainshadows in the lee of high-elevation calderas and/or generated large volumes of volcanic materials, influencing soils and vegetation. Collectively, that may explain a possible rise in mammal diversity in the CP/SRP region at ~14Ma, coincident with a drop in diversity in the NRM. It is still unclear, however, how different taphonomic pathways and sample-standardization problems are influencing apparent diversity peaks at this temporal and geographic resolution.

The shallow structure of Kīlauea caldera from high‐resolution Bouguer gravity and total magnetic anomaly mapping: Insights into progressive magma reservoir growth

AbstractWe conducted total magnetic field and Bouguer gravity measurements to investigate the shallow structure beneath the summit caldera of Kīlauea Volcano, Hawai'i. Two significant and distinctive magnetic anomalies were identified within the caldera. One is interpreted to be associated with a long‐lived prehistoric eruptive center, the Observatory vent, located ~1 km east of the Hawaiian Volcano Observatory. The second magnetic anomaly corresponds to a set of eruptive fissures that strike northeast from Halema'uma'u Crater, suggesting this is an important transport pathway for magma. The Bouguer gravity data were inverted to produce 3‐D models of density contrasts in the upper 2 km beneath Kīlauea. The models detect 3.0 km3 of material, denser than 2800 kg m−3, beneath the caldera that may represent an intrusive complex centered northeast of Halema'uma'u. Recent temporal gravity studies indicate continual addition of mass beneath the caldera during 1975–2008 centered west of Halema'uma'u and suggest this is due to filling of void space. The growth of a large intrusive complex, apparent cyclical caldera formation, and continual mass addition without inflation, however, can also be explained by extensional rifting caused by the continual southward movement of Kīlauea's unstable south flank.

Insights into caldera and regional structures and magma body distribution from lava domes at Rotorua Caldera, New Zealand

Lava domes emplaced after caldera-forming eruptions are often the only clue to the structure of the caldera and to the regional structure at the time of caldera formation. This is because the deposits from the subsequent eruptions commonly bury subsidence-controlling caldera faults and regional cross faults within calderas. Other calderas and lava domes in the Taupo Volcanic Zone (TVZ), New Zealand, have been previously reported to show strong regional control. At Rotorua Caldera there is a general lack of surface expression of faults, but rhyolite lava domes are well exposed and aligned with regional structures that have been mapped outside of the caldera. Our summary of published data and new observations allows these lava domes to be subdivided into three groups based upon their petrology, geochemistry, relative age and spatial distribution: (1) the Kaikaitāhuna Group of pre-collapse (451ka), crystal-rich domes at the caldera boundary, (2) the Utuhina Group of crystal-poor, high alkali, post-collapse domes (c. 200ka) surrounding the locus of collapse and directly related to the earlier (240ka) Mamaku ignimbrite eruption, and (3) The Ruamata Group of crystal-rich, more calcic, less devitrified post-collapse (60–36ka) domes further out from the collapse locus. Mapping of the morphology and internal structures of the Utuhina Group domes shows an ENE–WSW elongation direction and vent alignment, which is parallel to and down strike of (a) the extensional rift orientation independently mapped either side of the caldera, (b) the local caldera morphology and (c) structures mapped at nearby Okataina Caldera Complex. A second NW–SE trending orientation in the caldera morphology is parallel to a pre-collapse basement fabric, and has partially controlled the locations of the domes. A third orientation is hinted at through consistent N–S striking flow bands within Ngongotaha Dome, which are parallel with a gravity anomaly. We suggest that this orientation is a N–S section of a caldera ring fault that links regional structures and was utilised during caldera collapse. A subsequent dike intrusion also used this structure, erupting a fissure-style dome that contains radiating flow bands which mimic the orientation of the feeder dike. However, the structure, morphology and location of post-collapse lava domes generally echo the unburied regional structures outside the caldera indicating that dike intrusion also occurred along regional structures. We suggest that the regional structures at Rotorua Caldera, which are similar to those at Okataina Caldera Complex, show that the kink in the orientation of the rift across the TVZ to the SE of Rotorua was active to at least 240ka, and possibly earlier. This kink is significant due to its proximity and influence on both Rotorua and Okataina caldera systems and their associated geothermal fields. We conclude that internal structures, such as flow bands and morphology of lava domes are direct consequences of the shape and location of the feeder dike, which in turn is controlled by the structure of the caldera and region. We also suggest that lava dome eruptions at Rotorua were from a series of small, related nestled magma bodies. A key outcome of this study is the reconstruction of the wider structure of the caldera and surrounding structure based upon the localised internal features, distribution, and morphology of related lava domes.

Temporal and chemical connections between plutons and ignimbrites from the Mount Princeton magmatic center

The Mount Princeton magmatic center, located in central Colorado, consists of the epizonal Mount Princeton batholith, the nested Mount Aetna caldera, and volumetrically minor leucogranites. New CA-TIMS U/Pb zircon ages indicate the majority of the Mount Princeton batholith was emplaced during a period of regional ignimbrite quiescence. The structurally highest unit of quartz monzonite yields a 206Pb/238U age of 35.80 ± 0.10 Ma, and the youngest dated unit of the quartz monzonite is a porphyritic unit that yields a 206Pb/238U age of 35.37 ± 0.10 Ma. Using the exposed, dated volume of the quartz monzonite and new geochronology yields an estimated pluton filling rate of ~0.002 km3/a. This rate is comparable to the accumulation rates published for other plutons, and at least an order of magnitude slower than fluxes necessary to support accumulation of large eruptible magma volumes. Geochronology for the two large ignimbrites spatially associated with the batholith indicates a temporal disconnect between the vast majority of pluton building and explosive eruption of magma. The Wall Mountain Tuff erupted from a source in the same geographic area as the Mount Princeton batholith at 37.3 Ma (Ar/Ar sanidine), but no structural evidence of a caldera or temporally associated plutonic rocks is known. The Badger Creek Tuff erupted at 34.3 Ma (Ar/Ar sanidine) during the formation of the Mount Aetna caldera in the southern portion of the batholith. Our 206Pb/238U age for the Badger Creek Tuff is 34.47 ± 0.05. The only analyzed plutonic rocks of similar age to the Badger Creek Tuff are an extra-caldera dike with a 206Pb/238U age of 34.57 ± 0.08 Ma, a ring dike with a 206Pb/238U age of 34.48 ± 0.09 Ma, and a portion of the Mount Aetna pluton with a 206Pb/238U age of 34.60 ± 0.13 Ma. The small volume intrusions related to the eruption of the Badger Creek Tuff are chemically similar to the ignimbrite and show no signature of crystal–liquid separation in the shallow crust.

Detailed Morphology and Structure of an Active Submarine Arc Caldera: Brothers Volcano, Kermadec Arc

A survey of the Brothers caldera volcano (Kermadec arc) with the autonomous underwater vehicle ABE has revealed new details of the morphology and structure of this submarine frontal arc caldera and the geologic setting of its hydrothermal activity. Brothers volcano has formed between major SW-NEtrending faults within the extensional field of the Havre Trough. Brothers may be unique among known submarine calderas in that it has four active hydrothermal systems, two high-temperature sulfide-depositing sites associated with faulting on the northwestern and western walls (i.e., the NW caldera and W caldera hydrothermal sites, respectively), and gas-rich sites on the summits of the constructional cones that fill most of the southern part of the caldera (i.e., the Upper and Lower cone sites). The 3.0- × 3.4-km caldera is well defined by a topographic rim encompassing ~320° of its circumference and which lies between the bounds of two outer half-grabenshaped faults in the northwest and southeast sectors. There is not a morphologically well defined continuous ring fault (at the map resolution), although near-vertical scarps are present discontinuously at the base of sections of the wall. The width of the wall varies from <200 m at its southwest portion to ~750 m on its northern section. The widest part of the wall is its northwest sector, which also has the largest documented area of hydrothermal alteration and where sea-floor magnetization is lowest. In addition to primary northwest-southeast elongation and southwest-northeast structures caused by faulting within the regional back-arc strain field, there are also less well developed west-southwestnorth-northeast regional structures intersecting the volcano that is appar- ent on the ABE bathymetry and at outcrop scale from submersible observations. Asymmetrical trap-doorstyle caldera collapse is considered a possible mechanism for the formation of the Brothers caldera.

Intermittent inflations recorded by broadband seismometers prior to caldera formation at Miyake-jima volcano in 2000

Very-long-period (VLP) pulses with widths of 20s on velocity seismograms were observed during volcanic activity at Miyake-jima Volcano, Japan in 2000. The VLP events occurred repeatedly during a few days prior to caldera formation and essentially vanished following the onset of caldera collapse. Waveform inversions of the pulse-like signals point to a source offset 3.5km beneath and 1km south of the summit. A candidate for the source mechanism is the inflation of an elliptical cylinder with axis tilted 20–30° from vertical and major axis of the elliptical cross section oriented northeast-southwest. The inferred mechanism appears consistent with a step-like pressurization of a magma reservoir impacted by a falling rock mass in response to gravitational instability. The repeated occurrences of the rock collapses lead to the caldera formation at Miyake-jima.

Spatio-temporal changes in seismic velocity associated with the 2000 activity of Miyakejima volcano as inferred from cross-correlation analyses of ambient noise

Miyakejima volcano, Japan, showed strong and interesting volcanic activities in 2000 with the occurrence of dike intrusions, caldera formation and a large amount of gas emission. To understand temporal changes of the volcanic structure associated with this activity, we apply ambient noise correlation analyses to the seismic records of five seismic stations at Miyakejima volcano from July 1999 to December 2002. We calculate cross-correlation functions (CCFs) for eight available station pairs at frequency bands of 0.4–0.8Hz and 0.8–1.6Hz, and retrieve the Rayleigh waves propagating with a group velocity of about 1.0km/s. Comparing CCFs obtained for each day with the reference CCFs that are calculated from a few months of data, we estimate seismic velocity changes before and after the 2000 activity. Results at the two frequency bands show seismic velocity increase and decrease. Shallow structure at the volcanic edifice on the flanks experienced a seismic velocity increase up to 3.3%. On the other hand, the regions located close to the collapsed caldera show a seismic velocity decrease down to 2.3%. To understand the mechanisms that may introduce these seismic velocity increase and decrease, we examine several possible mechanisms of the velocity changes: stress changes due to volcanic pressure sources and caldera formation, and topographic changes. By using the deflation sources previously determined from GPS data, we calculate the stresses at depths of 0km and 1km at the volcano. The results suggest that the seismic velocity increases observed at seismic paths on the volcanic flank are explained by the compression caused by the deflation sources associated with magma activity in 2000. Stress sensitivities of the seismic velocity changes are estimated to be 1.5×10−2 to 2.2×10−2MPa−1 and 4.6×10−3 to 2.4×10−2MPa−1 at frequency bands of 0.4–0.8Hz and 0.8–1.6Hz, respectively, which are in the range of the previously reported results. Our three dimensional numerical calculations on seismic wave propagation show that the seismic velocity decreases observed at seismic paths crossing the collapsed caldera can be explained by topographic changes introduced by a caldera. We further suggest that the seismic velocity decreases detected around the regions close to the caldera may originate from the dilated regions cause by formation of the caldera.

Epiclastic deposits associated with large-scale landslides and the formation of erosive calderas in oceanic islands: The example of the La Palma Island (Canary Archipelago)

The growth and evolution of the La Palma Island has frequently been punctuated by high magnitude mass-wasting events triggered by gravitational collapses of volcanic edifices and by the erosion of the Caldera de Taburiente. These episodes are evidenced by voluminous debris accumulations in the submarine vicinity of the island and the presence of six very-coarse epiclastic units in the geological record of the island. In this paper we study these epiclastic units in order to characterize their stratigraphic architecture and facies associations, and the mechanisms involved in the transport and emplacement of the material associated with large failures and the erosion of volcanic edifices. Emphasis is also placed on characterising the temporal sequence of processes that have occurred on the island and discussing the origin of the Caldera de Taburiente.Three of the units described — La Cumbrecita Breccias and Megabreccias, La Pared de la Caldera Breccias and Conglomerates and La Viña Breccias – are overlying the detachment surfaces of the Santa Cruz de La Palma, Playa de la Veta and Cumbre Nueva landslides, respectively. They mainly represent the products of debris avalanches and debris flows with subordinate stream-flows filling the scars of the landslides. Unit 4, Las Angustias Breccias and Conglomerates, is interpreted as debris-flow or lahar deposits generated by landslides during the growth of the Bejenado Volcano. The uppermost units, the Tazacorte Conglomerates and El Riachuelo Conglomerates, represent water-laid deposits related to the excavation and erosion of the Caldera de Taburiente, and the incision of a valley between the Bejenado Volcano and the Cumbre Nueva scarp, respectively.Our results provide new and valuable data about cyclic events of construction–destruction of volcanic edifices worldwide, and their related processes and deposits.

Growth, destruction and volcanic facies architecture of three volcanic centres in the Miocene Uşak–Güre basin, western Turkey: Subaqueous–subaerial volcanism in a lacustrine setting

Early to Mid-Miocene extension in western Anatolia, related to plate tectonic motions, resulted in the development of a number of normal fault-bounded sedimentary basins as well as different styles and compositions of volcanic activity. The Uşak and Güre basins accumulated a thick fluvio-lacustrine fill in which three distinct volcanic edifices (Elmadağ, İtecektepe and Beydağı) and their deposits can overlap with each other and with the sediments produced by the background sedimentation. In addition, complete facies architectures of small-volume (monogenetic) volcanoes have been recognised in association with the three large complex (polygenetic) volcanoes providing a complex mixed siliciclastic and volcaniclastic basin infill in the respective basins where volcanism took place.All three volcanic centres display a complex succession of effusive and explosive volcanisms and their reworked deposits, with abundant evidences of magma–water interaction such as peperites for non-explosive magma-water interaction with the lacustrine water-saturated sediment and standing water body in a large alkaline lake. During the constructive phase, proximal successions of pyroclastic flows, pyroclastic falls, and rarely surge deposits are associated with distally-emplaced debris flow deposits, sometimes of mixed volcanogenic and terrestrial origins, and are interbedded with lacustrine sediments of the Inay Group. All three volcanic centres then experienced a phase of volcano growth and degradation between 17 and 15Ma ago, most likely related to a combination of tectonic movements on NE–SW-trending basement faults, which triggered multiple flank collapses and volcanic debris avalanches (Elmadağ), and voluminous ignimbrite eruptions that triggered caldera formation (İtecektepe and Beydağı volcanic centres). Lacustrine conditions persisted during the destruction and post-destruction stages of the volcano's evolution, as evidenced by indications of magma–water interactions within the central collapse structures, which also contain uplifted basement metamorphic rocks now exhumed in their eroded cores.

Silicate-metallic spherules and the problem of the ignimbrite eruption mechanism: The Yakutinskaya volcanic depression

In the course of detailed mineralogical, geochemical, and petrological studies of volcanic rocks in the Yakutinskaya volcanic depression of the Eastern Sikhote-Alin volcanic belt (Primorye) silicate-metallic formations (small balls) were found to occur widely. This suggests a new approach to the evaluation of the mechanism that is responsible for the formation of specific large-volume “hot” explosions. The metallic nuclei (whose compositions vary from low-carbon cast iron to cohenite) are surrounded by symplectite, which consists of quartz, magnetite, and siliceous-potassic glass (without Na); thus, the entire formation can be considered as a siliceous-metallic spherule. Based on analyses of the gas phase, the spherules consist of hydrogen and methane. The calculation of oxidation reactions that involve these gases shows that the process entails a significant decrease of volume and heat release. This suggests that the mechanism of “hot” ignimbrite explosions consists of the collapse of the roof of the magma chamber into the explosion zone and the formation of a collapse caldera with the ejection of the melt and its subsequent dispersion on the surface. This is facilitated by significant overheating of magma and its saturation with hydrogen, which is accompanied by a sharp decrease in viscosity by several orders of magnitude, even for such highly siliceous melts.

A new comprehensive classification of the Piton de la Fournaise activity spanning the 1985–2010 period. Search and analysis of short-term precursors from a broad-band seismological station

Piton de la Fournaise volcano (La Réunion Island) is one of the most active basaltic volcanoes, with an average of one eruption every 10months. This study provides the first exhaustive compilation of all volcanic events (intrusions, eruptions, seismic crises) and related parameters at Piton de la Fournaise in the 1985–2010 period. This compilation has been correlated with the analysis of the records from the very broad-band seismological RER station (Geoscope network), located 8.5km north of the summit. Our approach allowed us to identify short-term long period seismic precursors for most eruptions and intrusions. After a signal filtering process that consists in removing the instrumental response and the theoretical Earth tides effect, these precursors can be distributed into 4 classes that depend on their waveform and are globally considered as tilt related with magma transfer inside the sub-aerial part of the volcano edifice. The shapes and characteristics of these transient phenomena (time delay, duration or class) exhibit particular features that can be partly related to other simple eruption or intrusion parameters (location, altitude, volume). Statistical analyses of all events (intrusions and eruptions) are then derived. Estimates of acceleration rates of tilt signal at the RER station have been retrieved for eruptions and intrusions, with the challenge of providing a way to differentiate one from the other in real-time. Acceleration rates seem to correlate with eruptive lava flow volume and a threshold value can be determined allowing us to discriminate between intrusions and eruptions, illustrating the interest of analyzing them for real‐time monitoring. The correlation with the initial seismic crisis marking the opening of magma ascent path was investigated, showing that the delay between the RER transient phenomenon and the start of the seismic crisis has been increasing since the major caldera formation event of 2007. This longer delay may be due to a combination of drastic changes in the internal structure of the edifice: a concomitant decrease in volume of magma batches and a deeper origin of magma setting off volcanic unrest. Our study highlights the additional role of external factors like loading and unloading related to the rainy season and stress field evolution due to Earth tides in influencing magma propagation and volcanic activity.

Formation of Öskjuvatn caldera at Askja, North Iceland: Mechanism of caldera collapse and implications for the lateral flow hypothesis

The Öskjuvatn caldera at Askja volcano, North Iceland, was formed as a result of an explosive eruption at Askja on 28th–29th March 1875. Öskjuvatn is one of the youngest collapse calderas on Earth, and its initiation and growth were observed and documented by explorers and geologists working in the Askja region between 1875 and 1932. It is an example of caldera formation where the volume of the caldera collapse far exceeds the volume of associated erupted products. The discrepancy between the collapse volume and associated erupted products has been used by previous workers as a justification for the hypothesis that the injection of lateral dykes from Askja fed the February to October 1875 Nýjahraun fissure eruptions at the Sveinagjá graben, some 60km north of Askja. However, historical accounts documenting the caldera formation in sufficient detail show clearly that Öskjuvatn formed by piecemeal collapse, taking over 40years to reach its current form. We use these accounts to undertake a detailed examination of the stages of caldera collapse and to compare them with the known magmatic output of Askja in the years following the 1875 eruption. ArcGIS software was used to calculate the volume of Öskjuvatn during the various stages of collapse, and the volume of material erupted after 1875. While a dyke extending between Askja and Sveinagjá may be implied to account for the ‘missing’ volume, our results demonstrate that the volume of Öskjuvatn in July 1875 closely corresponds to the volume of rhyolitic material erupted on 28th–29th March 1875. In addition, geochemical evidence indicates that the Nýjahraun magmas were sourced from a deeper reservoir rather than by lateral injection from Askja's shallow crustal magma chamber. We therefore suggest that the injection of sills and dykes in a coherent intrusion complex beneath Askja central volcano, combined with background deflation of the magma storage zone beneath Öskjuvatn caldera over 30 to 40years following 1875, satisfactorily accommodates the volume required to form Öskjuvatn caldera.