Caldera Research Articles

Piercement mechanisms for mobile shales

AbstractWe have identified seven mechanisms by which mobile shales can pierce their roofs. The operative piercement mechanism depends on mobile‐shale viscosity, roof strength and stress state. For mobile shales at depths of several kilometres, three mechanisms are possible: fracture piercement, thrust piercement and ductile “piercement.” However, injection up fractures and faults appears to be the dominant mechanism by which mobile shales rise towards the surface. In this process, mobile shales behave similar to magmas rising through the Earth's crust. Nearer the surface, a wider range of piercement mechanisms becomes possible: passive piercement, reactive piercement, active piercement and erosional piercement. These mechanisms all have salt‐tectonics analogues. Although shale tectonics and salt tectonics share common piercement mechanisms, in many cases the resulting structures are different. This is because near‐surface mobile shales can have much lower viscosities than salt. Mobile shales that reach the surface extrude very rapidly, in many cases leading to caldera collapse of the underlying shale chamber. This instability in the near‐surface means that long‐term, stable growth of passive shale diapirs is unlikely, in contrast with the behaviour of salt. A key question in seismic interpretation of mobile‐shale structures is whether large‐volume mobile‐shale diapirs exist. We show that both active piercement and ductile “piercement” can create such structures. Both of these mechanisms create steeply upturned beds on diapir flanks, which are diagnostic. However, active shale diapirs appear to be rare, and ductile “piercements” are not documented. We therefore suggest that large‐volume shale diapirs should be interpreted with caution on seismic data.

Hydrothermal Alteration at the San Vito Area of the Campi Flegrei Geothermal System in Italy: Mineral Review and Geochemical Modeling

The Campi Flegrei geothermal system sets in one of the most famous and hazardous volcanic caldera in the world. The geothermal dynamics is suspected to have a crucial role in the monitored unrest phases and in the eruption triggering as well. Numerical models in the literature do not properly consider the geochemical effects of fluid-rock interaction into the hydrothermal circulation and this gap limits the wholly understanding of the dynamics. This paper focuses on fluid-rock interaction effects at the Campi Flegrei and presents relevant information requested for reactive transport simulations. In particular, we provide: (1) an extensive review of available data and new petrographic analyses of the San Vito cores rearranged in a conceptual model useful to define representative geochemical and petrophysical parameters of rock formations suitable for numerical simulations and (2) the implemented thermodynamic and kinetic data set calibrated for the San Vito 1 well area, central in the geothermal reservoir. A preliminary 0D-geochemical model, performed with a different contribution of CO2 at high (165 °C) and low (85 °C) temperatures, firstly allows reproducing the hydrothermal reactions over time of the Campanian Ignimbrite formation, the most important deposits in the case study area.

Repeating caldera collapse events constrain fault friction at the kilometer scale

Fault friction is central to understanding earthquakes, yet laboratory rock mechanics experiments are restricted to, at most, meter scale. Questions thus remain as to the applicability of measured frictional properties to faulting in situ. In particular, the slip-weakening distance [Formula: see text] strongly influences precursory slip during earthquake nucleation, but scales with fault roughness and is challenging to extrapolate to nature. The 2018 eruption of K̄ılauea volcano, Hawaii, caused 62 repeatable collapse events in which the summit caldera dropped several meters, accompanied by [Formula: see text] 4.7 to 5.4 very long period (VLP) earthquakes. Collapses were exceptionally well recorded by global positioning system (GPS) and tilt instruments and represent unique natural kilometer-scale friction experiments. We model a piston collapsing into a magma reservoir. Pressure at the piston base and shear stress on its margin, governed by rate and state friction, balance its weight. Downward motion of the piston compresses the underlying magma, driving flow to the eruption. Monte Carlo estimation of unknowns validates laboratory friction parameters at the kilometer scale, including the magnitude of steady-state velocity weakening. The absence of accelerating precollapse deformation constrains [Formula: see text] to be [Formula: see text] mm, potentially much less. These results support the use of laboratory friction laws and parameters for modeling earthquakes. We identify initial conditions and material and magma-system parameters that lead to episodic caldera collapse, revealing that small differences in eruptive vent elevation can lead to major differences in eruption volume and duration. Most historical basaltic caldera collapses were, at least partly, episodic, implying that the conditions for stick-slip derived here are commonly met in nature.

Seismic Monitoring during Crises at the NEIC in Support of the ANSS

Abstract Over the past two decades, the U.S. Geological Survey (USGS) National Earthquake Information Center (NEIC) has overcome many operational challenges. These range from minor disruptions, such as power outages, to significant operational changes, including system reconfiguration to handle unique earthquake sequences and the need to handle distributed work during a pandemic. Our ability to overcome crises is built on the development and implementation of a continuity of operations plan, well-designed infrastructure, adaptive software systems, experienced staff, and extensive collaboration. The NEIC does not operate in a vacuum but benefits from contributions of United States and international seismic networks. Similarly, the overall resilience of earthquake monitoring in the United States and around the globe benefits from the NEIC’s role as the national center for the Advanced National Seismic System (ANSS). Here, we highlight significant adaptations the NEIC has made in the face of crises. We discuss the COVID-19 pandemic, which represents the most significant operational crisis to impact the NEIC. The NEIC has maintained continuous operations during the ongoing COVID-19 pandemic by shifting from a fully onsite operations center to a distributed hybrid of onsite and telework staffing. We then discuss cases in which the NEIC has supported regional monitoring in the face of significant crises. In 2018, the NEIC assisted the Hawaiian Volcano Observatory with the Kīlauea volcano eruption by responding to large events, implementing contingency monitoring procedures, and calculating moment magnitudes for the low-frequency caldera collapses. Impacts of a crisis extend beyond the immediate response and often require a significant postevent assessment and a rebuilding phase. After the 2017 Hurricane Maria, the NEIC, the USGS National Strong-Motion Program, and the USGS Albuquerque Seismological Laboratory worked with the Puerto Rico Seismic Network and the Puerto Rico Strong-Motion program to assess, plan, and implement upgrades at sites that experienced storm damage.

Gold in Paleoproterozoic (2.1 to 1.77 Ga) Continental Magmatic Arcs at the Tapajós and Juruena Mineral Provinces (Amazonian Craton, Brazil): A New Frontier for the Exploration of Epithermal–Porphyry and Related Deposits

This review paper aims to integrate geological, tectonic and metallogenetic data, including new data, and propose a regional model for the gold (and base metal) mineralization in the south Amazonian Craton to support the mineral exploration concerning magmatic–hydrothermal deposits. The Proterozoic evolution of the Amazonian Craton comprises the accretion of terrains to the Archean Carajás Mineral Province. In the Tapajós and Juruena mineral provinces, located at the south part of the Amazonian craton, a long-lived ocean–continent subduction event produced ca. 2.0 to 1.77 Ga continental magmatic arcs. Extensive lava flows, volcaniclastic, sedimentary, and plutonic rocks were originated during at least four major orogenic magmatic events (ca. 2.1, 1.9, 1.88, and 1.80 Ga) and two post- to anorogenic events (ca. 1.87 and 1.77 Ga). Gold mineralization occurs in: (i) alluvial/colluvial occurrences, (ii) orogenic carbonate–sulfide-rich quartz veins in shear zones, (iii) stockworks, veins, and dissemination in granites, (iv) contact of basic dikes, (v) well-preserved high-, intermediate- and low-sulfidation epithermal mineralization, and (vi) porphyry-like and intrusion-related gold systems associated with late- to post-orogenic epizonal granites. The estimated historical gold production, mainly in secondary deposits, is over 27 Moz at the Tapajós and 6 Moz at the Juruena provinces. A total resource of over 5 Moz Au is currently defined in several small to large primary gold deposits. Andesite to rhyolite, volcaniclastic, and clastic sedimentary rocks (1.96–1.88 Ga) host epithermal (high-, intermediate-, and low-sulfidation) Au–(Ag–Pb–Zn) mineralization, whereas Au–Cu and Cu–Mo–Au mineralization is hosted in sub-volcanic tonalitic to granitic plutons. Advanced argillic alteration (alunite, pyrophyllite, enargite) associated with high-sulfidation mineralization occurs in ring volcanoes around nested volcanic calderas. This zone grades outward to propylitic or chlorite alteration, often covered by silica caps with vuggy silica. Lava flows and volcaniclastic rocks within faults or associated with volcanic edifices and rhyolitic domes host low- and intermediate-sulfidation mineralization. Low-sulfidation alteration zones typically have adularia and illite or sericite. Chalcopyrite, sphalerite, galena, pyrite, digenite, and manganiferous calcite are related to intermediate-sulfidation gold mineralization. Late- to post-orogenic evolved oxidized I-type granitoids host alkalic-type epithermal and porphyry-like gold mineralization. Porphyry-style hydrothermal alteration is analogous to those of modern systems, with inner sodic and potassic (potassic feldspar ± biotite or biotite) alterations grading to propylitic, muscovite-sericite, chlorite–sericite, and chlorite alterations. Potassic alteration zones are the locus of Cu–Mo mineralization, and gold-rich zones occur in muscovite/sericite–quartz–pyrite alteration. The Paleoproterozoic epithermal and porphyry-like mineralization in these large provinces defines a new frontier for the exploration of world-class gold deposits in the worldwide Proterozoic arc-related magmatic terrains.

Graben type calderas: The Bolaños case, Sierra Madre Occidental, Mexico

Graben calderas are volcano-tectonic structures that use the faults of a graben as main vents from which magma is massively erupted from a shallow magma chamber during collapse of intra-graben blocks. These eruptions are generally silicic and explosive and form large volume ignimbrite sheets without a previous Plinian major depressurization event. Graben calderas can be associated to tectonic settings ranging from pure extension to strike-slip transtension, including complete grabens, half-grabens or pull-apart grabens. The Sierra Madre Occidental (SMO) in western Mexico includes several of these graben type calderas with the corresponding large volume ignimbrite sheets that result from fissure type eruptions along the graben's border and interior faults. The Bolaños graben constitutes one of the best examples of these tectonically controlled collapse calderas and is the second largest caldera of the world after Toba caldera. It is a 90 × 25 km rectangular caldera and the vent of the 25.37 ± 0.36 Ma silicic Alacrán ignimbrite, with a minimum Dense Rock Equivalent volume of 2650 km3 (3800 km3 rock volume). Post-collapse silicic domes were emplaced just after the Alacrán ignimbrite from 25.02 ± 0.33 Ma to 23.94 ± 0.33 Ma, with a total minimum lava volume of 171 km3. Both ignimbrite and domes account for at least 2800 km3 rhyolitic magma output from Bolaños graben caldera, without considering the distal deposits, and in particular the co-ignimbrite ash-cloud deposit. We describe the characteristics of the Bolaños graben caldera focusing on its major products, the Alacrán ignimbrite and the post-collapse dome volcanism, providing the geological frame of the Bolaños graben area documented with 40Ar-39Ar ages. We finally propose a conceptual model to explain the dynamics of the Bolaños graben that can be applied to other similar volcano-tectonic depressions of the Sierra Madre Occidental and elsewhere in the world with similar geological settings.

Caldera Collapse as the Trigger of Chaos and Fractured Craters on the Moon and Mars

AbstractChaotic terrains are broad regions on Mars characterized by the disruption of the basaltic bedrock into polygonal blocks separated by deep fractures. To date, the proposed genetic scenarios often involve the occurrence of subsurface ice or liquid H2O. Nevertheless, similar features also occur within some craters on the Moon, namely floor‐fractured craters (FFCs), where water ice reservoirs are not present. We propose a new formation mechanism for Martian chaotic terrains as well as for lunar and Martian FFCs. The proposed mechanism does not require a major role of water but multiple cycles of inflation and deflation of a buried magma chamber. This process results in a particular type of caldera collapse, called the piecemeal (or chaotic) caldera collapse. A series of analog experiments show both geometrical and quantitative correspondence with natural case studies: Arsinoes Chaos (Mars), an unnamed FFC (Mars), and Komarov crater (FFC on the Moon).

Sources of Volcanic Tremor Associated With the Summit Caldera Collapse During the 2018 East Rift Eruption of Kīlauea Volcano, Hawai'i

AbstractVolcanic tremor occurring at the beginning of the 2018 Kīlauea eruption is characterized using both seismic and tilt data recorded at the Kīlauea summit. An automatic seismic network‐based approach detects several types of tremor including (a) 0.5–1 Hz long‐period tremor preceding the eruption, located at the south‐southwest edge of Halema'uma'u Crater and attributed to the quasi‐steady radiation from a shallow hydrothermal system and (b) two sequences of gliding tremor at the beginning of the eruption, both with locations on the edges of the crater and within it. The first sequence is attributed to two swarms of low‐amplitude regularly repeating earthquakes induced by the jerky motions of a cylindrical rock piston with radius of 325 m, height of 250 m, and mass of 2.07 × 1011 kg, progressively intruding 12.3 m into the shallow hydrothermal system with volume of 108 m3 and depth extent of 300 m. The second sequence is attributed to a gradual evolution in the properties of a bubbly magma within an east‐striking dike below Halema'uma'u Crater, impacted by repeated roof collapses. A fluid‐filled crack model points to a decrease in gas volume fraction from 4.22% to 1.6 × 10−2% in the magma filling the dike, and a model of gas retro‐diffusion within the melt suggests a two orders of magnitude decrease in bubble number density from 7 × 108 m−3 down to 4 × 106 m−3. Both models feature a quasi to totally degassed magma by May 26.

Volcanic Unrest at Taupō Volcano in 2019: Causes, Mechanisms and Implications

AbstractTaupō volcano, New Zealand, is a large caldera volcano that has been highly active through the Holocene. It most recently erupted ∼1,800 years ago but there have been multiple periods of historic volcanic unrest. We use seismological and geodetic analysis to show that in 2019 Taupō underwent a period of unrest characterized by increased seismic activity through multiple swarms and was accompanied by ground deformation within the caldera. The earthquakes, which include non‐double‐couple events, serve to outline an aseismic zone beneath the most recent eruptive vents. This aseismic zone is coincident with an inflating source, based on forward modeling of ground deformation data. We infer that this aseismic and deforming region delineates the location of the present day magma reservoir that is ≥250 km3 in volume and has a melt fraction of >20%–30%, inhibiting seismic activity. Our analysis shows that the 2019 unrest at Taupō was volcanic in nature and origin, demonstrating that this is an active and potentially hazardous volcano, and that improving our monitoring and understanding of its behavior is important.

The Volcanic Relief within the Kos-Nisyros-Tilos Tectonic Graben at the Eastern Edge of the Aegean Volcanic Arc, Greece and Geohazard Implications

The active Kos-Nisyros-Tilos volcanic field is located in the eastern sector of the Aegean Volcanic Arc resulting from the subduction of the African plate beneath the Aegean plate. The volcanic activity is developed since Middle Pleistocene and it occurs within a tectonic graben with several volcanic outcrops both onshore and offshore. Data obtained from previous offshore geophysical surveys and ROV exploration, combined with geospatial techniques have been used to construct synthetic maps of the broader submarine area. The volcanic relief is analyzed from the base of the volcanic structures offshore to their summits onshore reaching 1373 m of height and their volumes have been computed with 24.26 km3 for Nisyros Island and a total volume of 54.42 km3 for the entire volcanic area. The volcanic structures are distinguished in: (1) volcanic cones at the islands of Nisyros (older strato-volcano), Pergousa, Yali and Strongyli, (2) volcanic domes at the islands of Pachia, East Kondeliousa and Nisyros (younger Prophitis Ilias domes), (3) submarine volcanic calderas (Avyssos and Kefalos). Submarine volcanic debris avalanches have been also described south of Nisyros and undulating features at the eastern Kefalos bay. Submarine canyons and channels are developed along the Kos southern margin contrary to the Tilos margin. Ground truth campaigns with submarine vessels and ROVs have verified the previous analysis in several submarine volcanic sites. The geohazards of the area comprise: (1) seismic hazard, both due to the activation of major marginal faults and minor intra-volcanic faults, (2) volcanic hazard, related to the recent volcanic structures and long term iconic eruptions related to the deep submarine calderas, (3) tsunami hazard, related to the seismic hazard as well as to the numerous unstable submarine slopes with potential of gravity sliding.

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.

Pityusa Patera, Mars: Structural analyses suggest a mega-caldera above a magma chamber at the crust-mantle interface

Pityusa Patera is the southernmost of four paterae in the 1.2 × 106 km2 wrinkle-ridged plains-dominated Malea Planum region of Mars. Based on their texture, morphology, and uniqueness to Pityusa Patera, we interpret layered, folded massifs as pyroclastic deposits emplaced during patera formation as a collapse caldera. Such deposits would not be expected in a previously suggested scenario of patera formation by subsidence from lithospheric loading. Our structural measurements and modeling indicate that the folding and high relief of the massifs resulted from ~1.3%–6.9% of shortening, which we show to be a reasonable value for a central plug sagging down into an assumed piston-type caldera. According to a previously published axisymmetric finite-element model, the extent of shortening structures on a caldera floor relative to its total diameter is controlled by the roof depth of the collapsed magma chamber beneath it, which would imply Pityusa Patera formed above a chamber at 57.5–69 km depth. We interpret this value to indicate a magma chamber at the crust-mantle interface, which is in agreement with crust-penetrating ring fractures and mantle flows expected from the formation of the Hellas basin. As such, the folded massifs in Pityusa Patera, which are partially superposed by ca. 3.8 Ga wrinkle-ridged plains, should consist of primordial mantle material, a theory that might be assessed by future hyperspectral observations. In conclusion, we do not favor a formation by load-induced lithospheric subsidence but suggest Pityusa Patera to be one of the oldest extant volcanic landforms on Mars and one of the largest calderas in the solar system, which makes the folded, likely mantle-derived deposits on its floor a prime target for future exploration.

The 2014–2015 complex collapse of the Bárðarbunga caldera, Iceland, revealed by seismic moment tensors

Between August 2014 and February 2015, a caldera collapse process in Bárðarbunga volcano accompanied a fissure eruption at the Holuhraun lava field after magma had propagated laterally 45 km from the Bárðarbunga magma chamber to the lava field. The Icelandic Meteorological Office (IMO) reported around 30,000 earthquakes at the caldera, including more than 70 earthquakes with moment magnitude MW ≥ 5.0. We built a moment tensor catalog of around 230 seismic events at the caldera with MW between 3.7 and 5.5 using a waveform inversion method. We identified five event families based on focal mechanisms, double couple (DC) and compensated linear vector dipole (CLVD) components, epicentral distribution relative to the caldera center, and time of occurrence. The main characteristics of these families are (1) DC to CLVD normal faulting events with steep (50°–70°) to near-vertical (>70°) dip angles on the northern side of the caldera; (2) DC to CLVD normal events with predominant steep (50°–70°) dip angles on the southern side of the caldera; (3) intra-caldera oblique strike-slip events; and (4) thrust events at the eastern side of the caldera with a horizontal tension axis compensated linear vector dipole (T-CLVD) component. Each family provided new insights about the Bárðarbunga collapse mechanism such as (1) a systematic increase in the CLVD component with magnitude, corroborating that the curvature in the ring fault is the likely cause for the vertical CLVD moment tensors observed for the largest events; (2) seismic evidence of near-vertical dip angles in agreement with the vertical faults observed in many calderas worldwide, and numerical and analog models of caldera collapse structures; (3) intra-caldera oblique and strike-slip events on the western side of the caldera occurred by asymmetric collapse; (4) thrust horizontal T-CLVD events observed at the last stage of the eruption, possibly related to a viscoelastic response.

Geology and history of the Malea Planum region: A new view of Mars’ oldest large volcanic province

Geology and history of the Malea Planum region: A new view of Mars’ oldest large volcanic province

A shout-out to middle authors: Opportunities for achieving clarity in editing.

For the May 2021 issue of BJUI Compass, I want to give a shout-out to middle authors of our manuscripts. Obviously, we need first authors to take the lead on collecting data and writing up a project and we need last/senior authors for guidance, design and funding. But we often need strong contributions from middle authors who recruit patients to studies, assist in design/execution of trials/studies, and provide critical editorial work for drafting manuscripts. I was inspired to write this editorial from two different experiences. On the academic front, my research team had a manuscript reviewed by a journal and offered major revisions. They were tough ones—requiring additional analyses and statistical work. One of our strategies for revisions was to invite another urologic oncology fellow to the team to give us a fresh look at the manuscript and help us with the revision steps and getting the paper not only revised but back to word limits. The revised version completed peer review and is now published. Another point of inspiration came from a recent trip I made with my family—yes, a trip during pandemic times! Many of the photographs I’ve published with this editorial series were from pre-pandemic academic trips—I have a large inventory, but in theory could run into slim pickings if this pandemic keeps dragging on. Our family loves to ski at Jackson Hole, Wyoming, and rather than sit out another season, we made the journey with a long drive from Houston to Wyoming—a solid full 2 days of driving each way (I’m not quite ready for aeroplanes). In addition to the challenging skiing at Teton Village, another opportunity for winter sports is snowmobiling in Yellowstone national park—famous for its geysers and multiple volcanic activities. The whole park is actually a giant volcanic caldera—last erupted over 630,000 years ago but in theory could blow again. In Figure 1, I will demonstrate a fun photography editorial trick from Adobe's Lightroom photo-editing software. It is called the “dehaze” feature and it does an amazing job of getting rid of hazy appearing backgrounds—especially grey/dull skies, or city smog. Specific to geysers—it's a fun feature to tone down a lot of the steam coming out of these volcanic entities. Figure 2 shows another example from a hydrothermal pool—again with editing of the steam and colours for a more dramatic look. The analogy for our middle authors is that their editing efforts and fresh look at our papers can be effective methods for improving a manuscript. A primary writer can certainly edit and revise a paper, but sometimes another set of eyes can take it to the next level. These collaborative efforts can pay off in peer review. As Prokar Dasgupta, previous editor of the BJUI, used to say at lectures on publishing: “You have one good chance to make a good first impression.”

Provenance and compositional variations of intra-caldera lake sediments at La Primavera, Jalisco, Western Mexico

The multi-proxy provenance analyses carried out in the Upper Pleistocene sediments of the La Primavera intra-caldera paleolake in western Mexico document the evolution of source areas. This lake formed a few thousand years after the caldera collapse (~95 ka) and lasted until the intra-caldera resurgence process that ended 75 ka ago. Between 93.8 and 71 ka the sedimentary succession that filled the lake was affected by the extrusion of domes at its central part and the constant influx of volcaniclastic debris. Ring-fault domes and extra-caldera activity sourced at San Miguel volcano provided additional volcanic debris into the lake. Based on our multi-proxy studies and recent age determinations of the post-caldera activity is likely that the paleolake was coggled at 78 ka in the central sector of the caldera, synchronously with the caldera resurgence. The resulting deposits (volcaniclastic debris) are tuffaceous sands characterized by lithoarenites rich in neo-volcanic grains, mainly vitrophyric and felsitic volcanic fragments with similar characteristics to the rocks of the Ixtahuantonte, El Nejahuete composite dome, Cerro Alto, Las Pilas, and Dos Coyotes domes. Geochemically, the sediments of the La Primavera caldera exhibit concentrations and elemental relationships of major and trace elements similar to the average of the upper continental crust. However, the high concentrations of some elements, such as La, Th, Ti, and Zr are related to the hyperalkaline nature of the magmatism that originated this volcanic caldera. The concentrations of SiO2/Al2O3, Na2O/K2O, Th, Sc, and Zr/10 indicate a passive margin tectonic setting deposition under low weathering conditions.

Formation of Stanley Patch volcanic cone: New insights into the evolution of Deception Island caldera (Antarctica)

Deception Island (South Shetland Islands) is one of the most active volcanoes in Antarctica, with more than 20 explosive eruptive events registered over the past centuries. Recent eruptions (1967, 1969, and 1970) and volcanic unrest episodes (1992, 1999, and 2014–2015) demonstrate that volcanic activity is likely occurring in the future. This is of special concern for scientists, logistic personnel, and tourists, since the South Shetland Islands are an important tourist destination and host numerous year-round and seasonal scientific stations and base camps. Significant efforts have been made to understand the complex magmatic and volcanic evolution of Deception Island with special interest on its subaerial part. However, studies on submerged volcanic cones within Port Foster, the sea-flooded part of Deception Island's caldera depression, are comparatively scarce. Here, we provide a full characterization of Stanley Patch volcano, the largest of these volcanic edifices. Estimated morphometric parameters based on new multibeam bathymetric data, supported by petrographic and chemical observations from rock samples collected on the crater rim, reveal that Stanley Patch volcano grew in a subaerial environment. This result, combined with previous findings and new sedimentological evidence from our ultra-high resolution seismic profiles, allow to further detail the island's geologic evolution since the caldera collapse. We conclude that the complete flooding of Port Foster could have only occurred after the formation of Stanley Patch volcano, i.e. during the last ~2000 years, and in a time period of a few days or less.

Dynamics of large effusive eruptions driven by caldera collapse.

The largest effusive basaltic eruptions are associated with caldera collapse and are manifest through quasi-periodic ground displacements and moderate-size earthquakes1-3, but the mechanism that governs their dynamics remains unclear. Here we provide a physical model that explains these processes, which accounts for both the quasi-periodic stick-slip collapse of the caldera roof and the long-term eruptive behaviour of the volcano. We show that it is the caldera collapse itself that sustains large effusive eruptions, and that triggering caldera collapse requires topography-generated pressures. The model is consistent with data from the 2018 Kīlauea eruption and allows us to estimate the properties of the plumbing system of the volcano. The results reveal that two reservoirs were active during the eruption, and place constraints on their connectivity. According to the model, the Kīlauea eruption stopped after slightly more than 60 per cent of its potential caldera collapse events, possibly owing to the presence of the second reservoir. Finally, we show that this physical framework is generally applicable to the largest instrumented caldera collapse eruptions of the past fifty years.

Postcaldera intrusive magmatism at the Platoro caldera complex, Southern Rocky Mountain volcanic field, Colorado, USA

The Oligocene Platoro caldera complex of the San Juan volcanic locus in Colorado (USA) features numerous exposed plutons both within the caldera and outside its margins, enabling investigation of the timing and evolution of postcaldera magmatism. Intrusion whole-rock geochemistry and phenocryst and/or mineral trace element compositions coupled with new zircon U-Pb geochronology and zircon in situ Lu-Hf isotopes document distinct pulses of magma from beneath the caldera complex. Fourteen intrusions, the Chiquito Peak Tuff, and the dacite of Fisher Gulch were dated, showing intrusive magmatism began after the 28.8 Ma eruption of the Chiquito Peak Tuff and continued to 24 Ma. Additionally, magmatic-hydrothermal mineralization is associated with the intrusive magmatism within and around the margins of the Platoro caldera complex. After caldera collapse, three plutons were emplaced within the subsided block between ca. 28.8 and 28.6 Ma. These have broadly similar modal mineralogy and whole-rock geochemistry. Despite close temporal relations between the tuff and the intrusions, mineral textures and compositions indicate that the larger two intracaldera intrusions are discrete later pulses of magma. Intrusions outside the caldera are younger, ca. 28–26.3 Ma, and smaller in exposed area. They contain abundant glomerocrysts and show evidence of open-system processes such as magma mixing and crystal entrainment. The protracted magmatic history at the Platoro caldera complex documents the diversity of the multiple discrete magma pulses needed to generate large composite volcanic fields.

Exploring fault propagation and the role of inherited structures during caldera collapse through laboratory experiments

Caldera collapse received large attention during the last decades and was widely studied using various approaches, spanning from field-geology to numerical and analogue modelling. Analogue models allow to reproduce caldera collapse deformation, providing information otherwise difficult to obtain during such an extremely transient geological process. A wide range of analogue studies is available in literature, nonetheless, some aspects are still barely known, particularly the propagation of caldera faults and the role of inherited structures during caldera collapse. We have thus addressed the above research questions through analogue models. Our models show how calderas may experience asymmetry due to the lateral propagation of caldera-related faults. Furthermore, inherited discontinuities may affect caldera collapse by inducing rectilinear caldera faults that generate non-circular ring faults. Finally, sub-vertical discontinuities may be able, in specific conditions, to inhibit the formation of standard caldera structures that have been commonly observed in previous experimental series (i.e., early inward-dipping reverse faults followed by peripheral normal ring faults). Our models were then compared with four natural examples (the Acoculco and Los Humeros caldera complexes in Mexico, the Tuscolo-Artemisio caldera in the Colli Albani volcanic district, Italy and the Glencoe Caldera in Scotland), suggesting a relevant control exerted by inherited faults during caldera collapse. On the basis of the modelling results, we propose an evolutionary model that can be generalized and likely applied to many other caldera settings worldwide.