Caldera Research Articles

Caldera-Like Delineation and Geological Resources Identification of Majenang Area, Indonesia by Gravity and Magnetic Data Inversions

Indonesia’s archipelago formed by the tectonic evolution proceeded with subduction, which was accompanied by volcanism. The systematic subduction zones produce the magmatic arcs with different periods since the Permian up to the Tertiary. However, only the recent Quaternary volcanic arc is recognized and lacked of information about the ancient volcanic environment. Calderas are a crucial feature in any volcanic environment due to the prospect site of geological resources. The Gravity and Magnetic methods are commonly used for preliminary study in almost any cases due to their light-weight, low-cost, and ability to map a wide area rapidly. The inverse-modeling scheme was invoked to estimate the sub-surface situation during the interpretation processes. The study intended to show the ability of both gravity and magnetic method for delineating of caldera-like environment including geological resources prospective site identification. According to the research, a northwest-southeast dextral strike-slip fault found in the area and belongs to the Pamanukan-Cilacap Fault Zone (PCFZ). A circular caldera-like anomaly delineated and interpreted as the ring fault of an ancient volcanic caldera in the study area. Several high gravity anomalies found within the caldera rims are interpreted as lava domes or intrusion rocks, while the high-density found following the outer part of the ring-fault terrain is interpreted as the buried lava. The ancient eruption point inferred around Majenang city, thus the study area proposed as the Majenang Caldera. A mineralization zone identified around the study area, which is comparable with the Cihonje people’s gold mining site as the proven prospective area.

Object-Oriented Remote Sensing Approaches for the Detection of Terrestrial Impact Craters as a Reconnaissance Survey

The purpose of this study is to employ a remote sensing reconnaissance survey based on optimal segmentation parameters and an object-oriented random forest approach to the identification of possible terrestrial impact craters from the global 30-m resolution SRTM DEM. A dataset consisting of 94 confirmed and well-preserved terrestrial impact craters, 104 volcanic calderas, and 124 valleys were extracted from real-world surface features. For craters with different sizes, eight optimal scale parameters from 80 to 3000 have been identified using multi-resolution segmentation, where the scale parameters have a positive correlation (R2 = 0.78) with the diameters of craters. The object-oriented random forest approach classified the tested impact craters, volcanic calderas, and valleys with an overall accuracy of 88.4% and a Kappa coefficient of 0.8. The investigated terrestrial impact craters, in general, have relatively lower rim circularity, higher length-to-width ratio, and lower relief, slope, and elevation than volcanic calderas. The topographic characteristics can be explained by geological processes associated with the formation and post-deformation of impact craters. The excavation and ejection by initial impact and rebound of excavated materials contribute to low elevation. The post-impact deformation, including inward collapse and slump of unstable rims, weathering, erosion, and sediment deposition, further reduces elevation and relief and modifies shapes resulting in lower circularity and higher length-to-width ratio. Due to the resolution limitation of the source DEM data and the number of real-world samples, the model has only been validated for craters of 0.88 to 100 km in diameter, which can be generalized to explore undiscovered terrestrial impact craters using cloud computing with global datasets provided by platforms such as Google Earth Engine and Microsoft Planetary Computer.

The 2022 Eruption of Wolf Volcano, Galápagos: The Role of Caldera Ring‐Faults During Magma Transfer From InSAR Deformation Data

AbstractThe basaltic caldera volcanoes in the Galápagos Islands characteristically erupt lavas via summit circumferential and radial flank dike intrusions, but the underlying magma plumbing systems remain enigmatic. Here, we document surface displacements of Wolf volcano using interferometric synthetic aperture radar (InSAR) data from 2015 to 2022. We show that Wolf volcano experienced 6‐years of continuous inflation after the 2015 eruption, followed by a shallow flank eruption in January 2022. The deformation is modeled with a vertical caldera ring‐fault and a radial dike on the southeast flank. The ring‐fault underwent opening and reverse faulting during the inflation period, and closure and normal faulting during and after the eruption. Stress interactions between the ring‐fault and the flank dike suggest the asymmetric opening of the ring‐fault promotes flank eruptions. The best‐fit deformation model differs from the previous models and offers an alternative view of how magma is fed into radial dikes during flank eruptions.

Modelling the post-caldera plumbing system of Changbaishan volcano (China) from integrated geochemical, isotopic, geobarometric, and geophysical data

The Changbaishan Tianchi volcano is the largest active volcano of China and the 946 CE VEI 6 “Millennium eruption” (ME) is responsible for the formation of its summit caldera. After the ME, the volcanic activity is characterized by smaller eruptions most of which are recorded only in historical documents. Here we analyze the deposits of the ME and 1403 CE eruption outcropping in the Heishigou section, which is located east of the Chagbaishan Tianchi caldera. We present whole-rock, glass, mineral, isotopic, and geobarometric data to obtain information on the vertical extent of the caldera and post-caldera plumbing system of the volcano. Results show that the plumbing system of the 1403 CE eruption is located between 1.9 and 5.4 km depth, which is also the depth range of the shallower reservoir of the ME. Therefore, the magma reservoir of the ME was active also after the caldera collapse. The 1403 CE magma stored in the ME reservoir evolved by fractional crystallization of the residual ME trachytic magma and underwent the contamination of upper crust material. The 1403 CE event was triggered by the injection of less evolved, mafic magma from depth. The inferred depth of the shallower ME reservoir and that of the 1403 CE eruption is the same of the present-day main geophysical anomalies (low seismic velocity and low resistivity) recorded below the Changbaishan Tianchi caldera. In addition, the source of the deformations related to the uplift during unrest episodes between 2002 and 2020 suggests a refilling of the 1403 CE plumbing system. We conclude that the plumbing system of the 1403 CE, post-caldera activity at Changbaishan Tianchi volcano is the same of the ME eruption and it is still active. This system may be recharged from the arrival of less evolved magma from depth. The proposed conceptual model of the post-caldera volcanism at Changbaishan Tianchi represents a reference framework to interpret the signals of unrest and decipher the dynamics of the present-day plumbing system.

New geological and geochronological constraints on the evolution of the Cotacachi - Cuicocha volcanic complex (Ecuador)

Extensive fieldwork at the Cotacachi-Cuicocha Volcanic Complex (CCVC, North of Ecuador) resulted in a new collection of geological data including cartography, chronology, petrography, geochemistry, and morphology. This volcanic complex is formed by a central volcano (Cotacachi: 4939 m asl, current bulk volume of 56 ± 4 km3), several peripheral domes, and a 3 km wide volcanic caldera (Cuicocha: 4.2 ± 0.1 km3). CCVC comprises three stratigraphic members: The first, Cotacachi Basal, represents the initial phase of construction, which started at 173 ± 4 ka with a basal andesitic lava flow succession (∼500 m-thick) including isolated basaltic-andesitic lavas (Verde Tola unit; NE: 113 ± 6 ka, SE: 133 ± 9 ka), the construction of some peripheral amphibole-bearing andesitic domes, such as Muyurcu and Loma Negra (138 ± 4 ka and <108 ka, respectively), and a debris-avalanche deposit to the north-west (0.5–1.8 km3, older than 108 ka). The second member, Upper Cotacachi, consists of an andesitic lava flow succession (∼300 m-thick), younger than 108 ± 6 ka. A gap of activity occurred afterwards from 100 to 70 ka, during which a second debris-avalanche (0.2–1.1 km3, 108 to 65 ka) occurred to the NE, followed by the effusion of the dacitic Piribuela dome (65 ± 2 ka). Afterwards, several superimposed andesitic lava flows were emplaced at the summit, possibly around 15–10 ka since they lack glacial erosion. The third member includes the extrusion of the andesitic Cuicocha pre-caldera domes, which marks the beginning of a new eruptive stage of activity of CCVC during the Holocene, resulting in a violent eruption (3525 ± 35 to 2980 ± 30 a BP; VEI = 5) that partially destroyed the young dome and formed a funnel-shaped caldera (Cuicocha Caldera-Lake), ending with the emplacement of the Wolf and Yerovi post-caldera domes.

Ring fault creep drives volcano-tectonic seismicity during caldera collapse of Kīlauea in 2018

Basaltic caldera collapses are episodic, producing very-long-period (VLP) earthquakes up to Mw 5.4, with prolific inter-collapse (between collapses) volcano-tectonic (VT) seismicity. During the 2018 caldera collapse of Kīlauea Volcano, VT seismicity ceased following each collapse, and then accelerated to a quasi-steady rate prior to the next collapse, marking a temporal pattern distinct from typical foreshock/aftershock sequences. There is currently no consensus on the mechanism(s) that generates the VT seismicity. Here we demonstrate that inter-collapse ring fault creep, induced by chamber depressurization, was the main driver of VT seismicity at Kīlauea in 2018. This is evidenced by: 1) the correlation between cumulative number of VT events and GNSS-derived ring fault creep; 2) agreement between repeating earthquake and GNSS derived creep rates; and 3) consistency between the time dependence of mechanically modeled, creep-driven seismicity and observations. We further show that, ring fault creep can be explained by velocity strengthening friction alone or in conjunction with viscous shear zone rheology. The simultaneous occurrence of creep and seismicity highlights the spatially heterogeneous velocity weakening/strengthening friction on the ring fault. If the VT seismicity-creep correlation can be replicated at other basaltic volcanoes, it would demonstrate that VT seismicity can be used as a proxy for ring fault creep in the absence of GNSS measurements on subsiding caldera block(s).

Developing an Integrated Petrogenetic Model for Understanding REE Deportment of the Ampasibitika Intrusion and Associated Ion Adsorption Deposits

Abstract Alkaline–peralkaline igneous systems are promising sources of rare earth elements (REEs). Preservation bias has resulted in a gap in the geological record for alkaline–peralkaline magmatic systems, with the hypabyssal plumbing system linking magma chambers to extrusive volcanic rocks poorly represented. Large plutonic varieties of these systems are often proposed to have fed (now eroded) volcanoes, and current peralkaline volcanic systems obscure the plutonic system at depth. The alkaline to peralkaline Ampasibitika Intrusion in Madagascar is a rare example where the magmatic–volcanic interface between a deeper level magma reservoir and its genetically related caldera volcano is exposed. This c. 24 Ma sub-volcanic intrusive system comprises silica-undersaturated to silica-oversaturated units, of peralkaline to metaluminous and peraluminous characters, with varying styles of REE mineralisation, including supergene ion adsorption-style REE occurrences in the overlying weather profiles. There are two main intrusive suites: (1) the concentric Marginal Dyke Swarm (MDS) formed of quartz–microsyenite and peralkaline granite dykes (PGDs), and (2) the Ampasibitika Ring Dyke (ARD) comprising alkali feldspar syenites and subordinate nepheline syenites, trachytes and phonolites. We present new field observations and geochemical data to indicate that the MDS was emplaced as a series of low-viscosity, volatile-rich melt batches, which coalesced in the magma reservoir roof zone and intruded prior to caldera collapse, whereas the ARD was emplaced into the ring fault as a heterogeneous mix of variably evolved syenitic crystal mushes and phonolitic to trachytic-melt batches. As such, we suggest the MDS represents the residual melt fraction of the magma reservoir, whereas the ARD contains portions of the fractionating, silica-neutral to silica-undersaturated syenite, cumulate assemblage. In this revised framework, we assess the major and trace element geochemistry of amphibole- and clinopyroxene-group minerals to gain insight into the magmatic evolution of the Ampasibitika Intrusion and partitioning of REE between early cumulate and residual melt phases. Ultimately, the most REE-enriched units, the PGDs of the MDS, are identified as the product of the most volatile-rich, highly evolved melts from the roof zone of the magma reservoir. However, although REE enriched, the mineralogy does not always enable efficient release of REE for ion adsorption-style mineralisation; instead, lower REE-content protoliths with REE-host phases more amenable to decomposition release a greater proportion of REE.

Monitoring the Mauna Loa (Hawaii) eruption of November–December 2022 from space: Results from GOES-R, Sentinel-2 and Landsat-8/9 observations

Mauna Loa, one of the most actives volcanoes on Earth, is a shield volcano, located on the Island of Hawaii (USA). On 27 November 2022, after about 38 years of quiescence, a new eruptive activity took place at the Moku‘āweoweocaldera, continuing in the following days (i.e. until 10 December) from the fissure vents opening on the Northeast Rift Zone.In this work, we investigate the Mauna Loa November − December 2022 eruption from space, integrating the information from different satellite sensors. The analysis of short-wave infrared (SWIR) data, at 10 min temporal resolution, from the Advanced Baseline Imager (ABI), aboard the Geostationary Operational Environmental Satellites − R series (GOES-R), performed through the Normalised Hotspot Indices (NHI), indicates that the Mauna Loa eruption started on 27 November in between 23:10–23:20 LT (28 November at 09:10–09:20 UTC). The same analysis shows the increase of thermal activity and its progressive reduction from the early morning of 28 November, in agreement with the eruption migration from the summit caldera to the Northeast Rift Zone. By analysing the second phase of eruption through SWIR data from the Multispectral Instrument (MSI) and Operational Land Imager (OLI), respectively aboard Sentinel-2 and Landsat 8/9 satellites, we estimated a maximum lava flow length of 17 km. Moreover, we retrieved values of the volcanic radiative power (VRP) up to 65 GW, and a time-averaged discharge rate (TADR) of ∼1000 (±500) m3/s. These results show that SWIR observations, at different spatial and temporal resolution, may give an important contribution to the monitoring, mapping and characterisation of intense lava effusions.

The role of decompression history in gas bubble formation in crystal-rich silicic magma: Gas retention versus segregation

In crystal-rich magma, gas bubble formation causes magma lubrication by loosening the connected crystal framework. In contrast, if the crystal framework behaves as rigid, the gas bubbles segregate. In this study, we experimentally investigated the bifurcation between retention and segregation of gas bubbles in crystal-rich magmas under decompression. In particular, we focused on the history of decompression such as continuous, single-step, and multi-step decompressions with various degrees of each decompression step to consider the processes in the natural system. For this, the decompression experiments for hydrous rhyolitic melts with 50 vol% crystal were conducted with average rates of 10 and 80 MPa h−1 at a temperature of 800 °C. Bubble and crystal microstructures were analyzed using micro X-ray CT. Our experiments observed both retention and expansion of gas bubbles in the crystal-rich zone and permeable gas segregation. At an average rate of 80 MPa h−1 under multistep decompression, the boundary between the retention and segregation was the stepwise decompression of 5 MPa. On the other hand, the gas bubbles are retained when the degree of the stepwise decompression is larger than 20 MPa under an average decompression rate of 10 MPa h−1, resulting in the collapse of the framework. At the decompression degree <10 MPa at the rate of 10 MPa h−1, permeable gas segregation becomes dominant. Based on the experimental results, we established a regime map that predicts gas bubble retention and segregation during decompression. By applying this map to decompression rates and numbers of caldera collapses (twice) during the 1912 Katmai and 1991 Pinatubo eruptions, we infer that the magma during these eruptions experienced gas bubble formation (retention) without permeable segregation.

Surface composition of Pluto's Kiladze area and relationship to cryovolcanism

A link between exposures of water (H2O) ice with traces of an ammoniated compound (e.g., a salt) and the probable effusion of a water-rich cryolava onto the surface of Pluto has been established in previous investigations. Here we present the results from the application of a machine learning technique and a radiative transfer model to a water-ice-rich exposure in a geographic feature on Pluto named Kiladze and its surroundings. We demonstrate the presence of an ammoniated material suggestive of an undetermined but relatively recent emplacement event. Kiladze lies in a region of Pluto's surface that is structurally distinct from that of the areas where similar evidence points to cryovolcanic activity at some undetermined time in the planet's history. Although the Kiladze depression superficially resembles an impact crater, a close inspection of higher-resolution images indicates that the feature lacks the typical morphology of a crater. Here we suggest that a cryolava consisting of water carrying an ammoniated component may have emerged onto the surface at the Kiladze area via one or more collapses, as in a resurgent volcanic caldera complex. Large regions east of Kiladze also exhibit the presence of H2O ice and have graben-like structures suggestive of cryovolcanic activity, but the existing data are not amenable to the detailed search that might reveal an ammoniated component.

Geochemistry and Petrology of the Bellecombe Lava Sequence, Enclos Fouqué Caldera, Piton de la Fournaise Volcano (Réunion, France)

Piton de la Fournaise is an active shield volcano located in the eastern area of the Réunion Island (Indian Ocean) whose activity is characterized by effusive and explosive episodes with the emission of scarcely differentiated magmas with mostly tholeiitic affinity. The presently active edifice has grown within the Enclos Fouqué caldera, a polylobate plain bounded on its western side by the 80–200 m high Bellecombe vertical cliffs. This escarpment exposes a vertical sequence of 12 lava flows cut by a dike with an age &gt; 5.5 kyrs. In this work, the Bellecombe products were investigated by X-ray fluorescence, Inductively Coupled Plasma Mass Spectroscopy, a Scanning Electron Microscope and X-ray computed microtomography in order to characterize the evolution over time of the magmatic system feeding the eruptive activity prior to the Enclos Fouqué caldera collapse. The results indicate that lava flows share a geochemical affinity with the two main series documented at Piton de la Fournaise, namely, Steady State Basalts (SSB) at the bottom and top of the sequence and Abnormal basalt Group (AbG) with different degrees of differentiation in the central part. The emission of these two different products in both a restricted area and timespan testifies to the dynamic activity of the plumbing system, capable of shifting rapidly from central to eccentric activity in the recent past.

Partial Melting under Shallow-Crustal Conditions: A Study of the Pleistocene Caldera Eruption of Mendeleev Volcano, Southern Kuril Island Arc

Abstract The southern part of the Kuril Island Arc is one of the world’s most active modern volcanic zones, with widespread felsic caldera volcanism, but it has been less well studied compared with other arcs. The Mendeleev caldera-forming eruption (40 ka) on Kunashir Island, southern Kurils, is one of the most explosive Pleistocene eruptions to have occurred in this region. This study aimed to establish the origin and storage conditions of magma preceding the Pleistocene caldera eruption of Mendeleev volcano. Mineralogical and melt inclusion analyses reveal that the primary melts had felsic compositions and that the early stage of magmatic evolution involved amphibole breakdown into a two-pyroxene, plagioclase, and Fe–Ti oxide assemblage under pressure–temperature conditions of 107–314 MPa and 807–932°C. The caldera-forming products are represented by dacitic pumice composed of plagioclase + augite + hypersthene+ quartz + Fe–Ti oxides and melt with uniform low-K rhyolite composition. Pre-eruptive magma was stored in a reservoir at 77–195 MPa (3.0–7.6 km depth) and 830–890°C under H2O-saturated conditions. The mechanism of magmatic evolution implies the following two-step scenario: (1) generation of magma by the partial melting of an amphibole-bearing substrate accompanied by the formation of early Mg-rich clino- and orthopyroxene, plagioclase, Fe–Ti oxides, and peritectic rhyolitic melt; and (2) crystallization of late plagioclase and quartz directly from these partial melts. Local or regional extension during the Pleistocene, accompanied by increasing heat flow in the supra-subduction mantle, generated an active mafic intrusion into the upper crust. This process was accompanied by abundant subaerial eruptions of basaltic volcanoes and could have caused intense heating and partial melting of upper-crustal rocks. Our results indicate that the partial melting of amphibole-bearing substrates in island arcs may serve as a universal mechanism for the generation of silicic magmas during powerful caldera eruptions in young island arcs.

Caldera collapse thresholds correlate with magma chamber dimensions

Explosive caldera-forming eruptions eject voluminous magma during the gravitational collapse of the roof of the magma chamber. Caldera collapse is known to occur by rapid decompression of a magma chamber at shallow depth, however, the thresholds for magma chamber decompression that promotes caldera collapse have not been tested using examples from actual caldera-forming eruptions. Here, we investigated the processes of magma chamber decompression leading to caldera collapse using two natural examples from Aira and Kikai calderas in southwestern Japan. The analysis of water content in phenocryst glass embayments revealed that Aira experienced a large magmatic underpressure before the onset of caldera collapse, whereas caldera collapse occurred with a relatively small underpressure at Kikai. Our friction models for caldera faults show that the underpressure required for a magma chamber to collapse is proportional to the square of the depth to the magma chamber for calderas of the same horizontal size. This model explains why the relatively deep magma system of Aira required a larger underpressure for collapse when compared with the shallower magma chamber of Kikai. The distinct magma chamber underpressure thresholds can explain variations in the evolution of caldera-forming eruptions and the eruption sequences for catastrophic ignimbrites during caldera collapse.

Trapdoor Fault Activation: A Step Toward Caldera Collapse at Sierra Negra, Galápagos, Ecuador

AbstractThe 2018 Sierra Negra eruption resulted in meter‐scale subsidence due to basaltic magma extraction from a deflating reservoir. The eruption was also characterized by dike intrusions, &gt;4 MW earthquakes, and sulfur dioxide emissions. We use a combination of Interferometric Synthetic Aperture Radar, Digital Elevation Model, Global Positioning System and seismic data to assess conditions required to trigger episodic caldera collapse at Sierra Negra. The 2018 effusive eruption was mainly sourced from a horizontal sill located at ∼2 km depth, with a minimum erupted bulk volume of 0.19 km3. The modeled reservoir is bound by a C‐shaped ring of seismicity, suggesting trapdoor fault slip. Two &gt;4.5 MW earthquakes (5 and 22 July 2018) produced localized subsidence north of the southern trapdoor fault. After removing the modeled subsidence signal, distributed normal trapdoor fault slip explains the location of residual displacement. Furthermore, distributed fault models indicate slip occurred along the northern, central and southern segments of the trapdoor fault during the entire eruption, until 25 August 2018. Theoretical models of caldera collapse estimate that an erupted volume of 0.19 km3 is too small to trigger full‐scale caldera collapse, given the caldera aspect ratio (depth/diameter) of 0.22. Nonetheless, the spatial distribution and duration of seismicity and slip suggest trapdoor fault activation is the initial stage of caldera collapse at Sierra Negra, which may lead to full‐scale caldera collapse during larger eruptions. Alternatively, hundreds of medium‐sized eruptions, similar to that of 2018, may have triggered fault slip events over the past millennia.

Gas Emissions and Subsurface Architecture of Fault‐Controlled Geothermal Systems: A Case Study of the North Abaya Geothermal Area

AbstractEast Africa hosts significant reserves of untapped geothermal energy. Exploration has focused on geologically young (&lt;1 Ma) silicic calderas, yet there are many sites of geothermal potential where there is no clear link to an active volcano. The origin and architecture of these systems are poorly understood. Here, we combine remote sensing and field observations to investigate a fault‐controlled geothermal play located north of Lake Abaya in the Main Ethiopian Rift. Soil gas CO2 and temperature surveys were used to examine permeable pathways and showed elevated values along a ∼110 m high fault, which marks the western edge of the Abaya graben. Ground temperatures are particularly elevated where multiple intersecting faults form a wedged horst structure. This illustrates that both deep penetrating graben bounding faults and near‐surface fault intersections control the ascent of hydrothermal fluids and gases. Total CO2 emissions along the graben fault are ∼300 t d−1; a value comparable to the total CO2 emission from silicic caldera volcanoes. Fumarole gases show δ13C of −6.4‰ to −3.8‰ and air‐corrected 3He/4He values of 3.84–4.11 RA, indicating a magmatic source originating from an admixture of upper mantle and crustal helium. Although our model of the North Abaya geothermal system requires a deep intrusive heat source, we find no ground deformation evidence for volcanic unrest or recent volcanism along the graben fault. This represents a key advantage over the active silicic calderas that typically host these resources and suggests that fault‐controlled geothermal systems offer viable prospects for geothermal exploration.

Numerical modeling of caldera formation using Smoothed Particle Hydrodynamics (SPH)

SUMMARYCalderas are kilometer-scale basins formed when magma is rapidly removed from shallow magma storage zones. Despite extensive previous research, many questions remain about how host rock material properties influence the development of caldera structures. We employ a mesh-free, continuum numerical method, Smoothed Particle Hydrodynamics (SPH) to study caldera formation, with a focus on the role of host rock material properties. SPH provides several advantages over previous numerical approaches (finite element or discrete element methods), naturally accommodating strain localization and large deformations while employing well-known constitutive models. A continuum elastoplastic constitutive model with a simple Drucker–Prager yield condition can explain many observations from analogue sandbox models of caldera development. For this loading configuration, shear band orientation is primarily controlled by the angle of dilation. Evolving shear band orientation, as commonly observed in analogue experiments, requires a constitutive model where frictional strength and dilatancy decrease with strain, approaching a state of zero volumetric strain rate. This constitutive model also explains recorded loads on the down-going trapdoor in analogue experiments. Our results, combined with theoretical scaling arguments, raise questions about the use of analogue models to study caldera formation. Finally, we apply the model to the 2018 caldera collapse at Kīlauea volcano and conclude that the host rock at Kīlauea must exhibit relatively low dilatancy to explain the inferred near-vertical ring faults.

Processes and timescales of magmatic rejuvenation and residence prior to post-caldera rhyolitic eruptions: Ōkataina Volcanic Centre, Aotearoa New Zealand

Understanding the timescales and processes through which magma bodies form and develop in the crust prior to eruption is vital for volcanic monitoring and interpreting future unrest signals, particularly at caldera volcanoes. Here we present the results of a case study on Ōkataina Volcanic Centre, New Zealand, into the timescales of pre-eruptive processes operating during young intra-caldera eruptions, using Fe-Mg interdiffusion profiles in orthopyroxene. Three eruptions covering the three different vent regions, the 15.6 ka Rotorua episode from the Ōkareka Embayment, the 14.0 ka Waiohau episode from Tarawera, and the 5.5 ka Whakatāne episode from Haroharo have broadly similar rhyolitic compositions but show distinctions in their mineralogy and crystal zoning profiles. Back-scattered electron imaging coupled with major-element analyses of orthopyroxene cores and rims imply that open-system mixing and disequilibrium is a common process in the early stages of magma assembly at Ōkataina. Through interpreting mineral chemistry and zoning patterns, we infer that melt segregation, magma body assembly from the source mush and residence in the upper crust takes place on the order of decades up to several centuries, or (if prematurely triggered) as short as months. Priming events such as heating by basaltic injection (common in the Ōkataina rhyolite eruptions) occur over decades prior to eruption. Our findings highlight that multiple processes can dictate the assembly, residence and eruption of melt bodies from the crust and that most magmatic processes occur over timescales that are short enough to be directly relevant to geophysical imaging of magma reservoirs and monitoring initiatives.

The upper Pleistocene (1.8–0.7 Ma) explosive eruptive history of Las Cañadas, ocean-island volcano, Tenerife

While most ocean-island volcanism is effusive, recent evidence has demonstrated that intraplate ocean island volcanoes can exhibit protracted explosive histories, with catastrophic eruption styles and hazardous behaviour more typically associated with volcanoes in continental and plate-margin settings. Tenerife is the largest explosive ocean-island volcano on Earth, with a prolonged (∼2 Ma) post-erosional history of caldera-forming, plinian and ignimbrite eruptions of evolved composition. The 0.7–1.8 Ma succession with 20 newly defined formations is reported for southern Tenerife, Canary Islands. In the last 2 Myr, the Las Cañadas volcano has produced >42 pumice-fall eruptions, 21 with extensive ignimbrites, and 12 inferred caldera collapse events. Pyroclastic density currents have repeatedly travelled more than15 km from source to the ocean, filling valleys and burying extensive interfluves. A robust whole-rock chemistry dataset, selected mineral chemistry, coupled with new 40Ar/39Ar ages of units through the pyroclastic stratigraphy, allow recognition of magmatic trends within the system on the order of 100 ky. The catastrophic explosive eruptions form three, 0.2–0.5 Myr-duration clusters (the Ucanca, Guajara and Diego-Hernandez) that do not appear to correspond simply with geochemical cycles, or to cycles of increasing eruption size or explosivity as has been previously proposed. During the clusters, large eruption frequencies averaged 1 every 20–45 kyrs. The eruption clusters were separated by hiatuses of ∼240–260 kyr, recorded by soils and unconformities, and may reflect marked changes in geographic dispersals following giant landslide breaches in Las Cañadas caldera wall. Two concurrent evolutionary magmatic trends are distinguished: one producing crystal-rich magmas, the other formed the cooler crystal-poor magmas: both spanned over a million years until 0.66 Ma, when the former ceased.

The characteristics of the 2022 Tonga volcanic tsunami in the Pacific Ocean

Abstract. On 15 January 2022, an exceptional eruption of the Hunga Tonga–Hunga Ha'apai volcano generated atmospheric and tsunami waves that were widely observed in the oceans globally, gaining remarkable attention from scientists in related fields. The tsunamigenic mechanism of this rare event remains enigmatic due to its complexity and lack of direct underwater observations. Here, to explore the tsunamigenic mechanisms of this volcanic tsunami event and its hydrodynamic processes in the Pacific Ocean, we conduct statistical analysis and spectral analysis of the tsunami recordings at 116 coastal gauges and 38 deep-ocean buoys across the Pacific Ocean. Combined with the constraints of some representative barometers, we obtain the plausible tsunamigenic origins of the volcano activity. We identify four distinct tsunami wave components generated by air–sea coupling and seafloor crustal deformation. Those tsunami components are differentiated by their different propagating speeds or period bands. The first-arriving tsunami component with an ∼ 80–100 min period was from shock waves spreading at a velocity of ∼ 1000 m s−1 in the vicinity of the eruption. The second component with extraordinary tsunami amplitude in the deep ocean was from Lamb waves. The Lamb wave with a ∼ 30–40 min period radically propagated outward from the eruption site with spatially decreasing propagation velocities from ∼ 340 to ∼ 315m s−1. The third component with a ∼ 10–30 min period was probably from some atmospheric-gravity-wave modes propagating faster than 200 m s−1 but slower than Lamb waves. The last component with a ∼ 3–5 min period originated from partial caldera collapse with dimension of ∼ 0.8–1.8 km. Surprisingly, the 2022 Tonga volcanic tsunami produced long oscillation in the Pacific Ocean which is comparable with that of the 2011 Tohoku tsunami. We point out that the long oscillation is associated not only with the resonance effect with the atmospheric acoustic-gravity waves but more importantly with their interactions with local bathymetry. This rare event also calls for more attention to the tsunami hazards produced by an atypical tsunamigenic source, e.g. volcanic eruption.

A newly recorded Cryogenian-Ediacaran Dokhan Volcanic caldera with resurgent uplift in the Arabian-Nubian Shield, southwest Safaga, Egypt

The late Neoproterozoic Dokhan Volcanics (DV) of the Egyptian Eastern Desert (northern Arabian-Nubian Shield), were investigated at Gebel Nuqara, near the boundary between the Northern and Central Eastern Deserts. In particular, the nature of the peculiar circular and annular regional structures at Nuqara, were targeted for study. This included exploring the relationships of DV and intrusive units to each other and to regional dikes and faults. The central part of the Nuqara DV exposures consists of two volcanic units: 1) “Older DV” (intermediate varieties, dominantly andesites; 659 ± 16 Ma), with associated arc granitoids (663.2 ± 8.4 Ma), followed by andesite dikes (636.9 ± 7.2 Ma); and 2) “Younger DV” (acidic varieties; 602.3 ± 4.4 Ma for rhyolites, and 589.4 ± 6.1 Ma for rhyolite porphyry). This central area of DV units is enclosed within an annular intrusion of granite. The geochemical data for the Nuqara DV reveal intermediate low-silica adakitic (basaltic-andesite and andesite) and acidic high-silica adakitic (rhyolite and rhyolite porphyry). Both adakite groups share a common geochemical trend, and show evidence for magma diversification via fractional crystallization. The Nuqara DV is identified as a caldera sequence, with resurgent uplift, based on a positive comparison of the volcanic morphology, lithology, structure and mechanism of DV eruptions in the study area with those of other resurgent calderas. The geodynamic setting, volcanic architecture, and geochemistry of the DV, as well as its in-situ zircon LA–ICP–MS estimated ages, allow recognition of a series of eruptive stages, leading to collapse to form the Nuqara caldera, followed by resurgent uplift of the caldera floor during intrusion of rhyolite porphyry domes. The resurgent caldera model assigns a greater significance for the rhyolite porphyry as the exposed top of a sub-volcanic magma chamber. Resurgence is viewed as resulting from increased pressure or volume changes in the magma reservoir. A consequence of resurgence was uplift and erosion of the previous collapse-related topography.