Large Volcanoes Research Articles

Magma flow paths and strain patterns in magma chambers growing by floor subsidence: a model based on magnetic fabric study of shallow-level plutons in the Štiavnica volcano–plutonic complex, Western Carpathians

The Miocene Stiavnica volcano–plutonic complex, Western Carpathians, exposes two nearly coeval intra-caldera plutons, their roof (basement of a stratovolcano), and associated volcanic rocks. The complex thus provides insights into mechanisms of magma chamber growth beneath large volcanoes. As inferred from the anisotropy of magnetic susceptibility (AMS), these plutons were emplaced through significantly different processes: the diorite as a discordant stock with steep fabric and the granodiorite as a tabular, bell-jar pluton. In detail, we interpret that the latter was assembled in two stages. First, an upper “layer” intruded as a thin sill along a major subhorizontal basement/cover detachment. The subhorizontal magnetic fabric and strongly oblate AMS ellipsoid in this layer record intrusive strain where the magma flow paths were subparallel to the pluton roof. Second, in the lower “layer” of the pluton, magnetic foliations dip moderately to the ∼NW and ∼WNW to vertical and are associated with down-dip to subhorizontal lineations and prolate to weakly oblate shapes of the AMS ellipsoids. Such a fabric pattern is compatible with piecemeal floor subsidence, where magma flowed along multiple subsiding fault-bounded blocks. Based on this case example, we develop a conceptual model for magma flow paths and strain patterns for four main modes of floor subsidence: (1) piston (cauldron) subsidence is characterized by convergent flow and radial principal stretching above the magma chamber floor; (2) the piecemeal floor subsidence leads to steep to inclined magma flow paths in conduits along fault-bounded blocks; (3) asymmetric (trapdoor) subsidence produces first divergent flow paths near the conduit sides, changing into convergent paths in the narrower space near the kinematic hinge; and (4) symmetric cantilever (funnel) subsidence will lead to divergent flow from a central feeder and thus circumferential principal stretching of the magma. If the growing pluton develops a “two-layer” structure, all the flow paths and associated strains are affected by the flat-lying pluton roof and will convert into horizontal flattening as the roof is approached.

Impact of volcanism on the evolution of Lake Van (eastern Anatolia) III: Periodic (Nemrut) vs. episodic (Süphan) explosive eruptions and climate forcing reflected in a tephra gap between ca. 14 ka and ca. 30 ka

Fifteen Lateglacial to Holocene rhyolitic, dominantly primary tephra layers piston-cored and drilled (ICDP Paleovan drilling project) in western Lake Van (eastern Anatolia, Turkey) were precisely correlated to either of the two adjacent and active large volcanoes Nemrut and Süphan based on shard textures, mineralogy and mineral and glass compositions. The young peralkaline (comenditic to pantelleritic) primary rhyolitic Nemrut tephras are characterized by anorthoclase, hedenbergitic to augitic clinopyroxene, fayalitic olivine, minor quartz, and rare accessory chevkinite and zircon. Phenocrysts in subalkaline primary rhyolitic Süphan tephras are chiefly oligoclase-labradorite, with minor K-rich sanidine in some, biotite, amphibole, hypersthene, rare augitic clinopyroxene, relatively common allanite and rare zircon.Two contrasting explosive eruptive modes are distinguished from each other: episodic (Süphan) and periodic (Nemrut). The Lateglacial Süphan tephra swarm covers a short time interval of ca. 338years between ca. 13,078vy BP and 12,740vy BP, eruptions having occurred statistically every ca. 42years with especially short intervals between V-11 (reworked) and V-14. Causes for the strongly episodic Süphan explosive behavior might include seismic triggering of a volcano–magma system unable to erupt explosively without the benefit of external triggering, as reflected in pervasive faulting preceding the Süphan tephra swarm. Seismic triggering may have caused the rise of more mafic (“trachyandesitic”) parent magma, heating near-surface pockets of highly evolved magma – that might have formed silicic domes during this stage of volcano evolution – resulting in ascent and finally explosive fragmentation of magma essentially by external factors, probably significantly enhanced by magma–water/ice interaction.Explosive eruptions of the Nemrut volcano system, interpreted to be underlain by a large fractionating magma reservoir, follow a more periodic mode of (a) long-term relatively constant supply of parent magma, (b) evolution by low pressure crystal fractionation resulting in sporadic relatively low-volume eruption of trachytic and minor rhyolitic magmas, (c) evolution of a large magma reservoir to the point of highly explosive large-volume peralkaline rhyolitic Plinian eruptions at temporal intervals of ca. 20–40ky, some accompanied by ignimbrites and inferred caldera collapse.A striking tephra gap between ca. 14ka and ca. 30ka, i.e. during glacial climate conditions, is postulated to be due to climate-forcing via lithosphere unloading following deglaciation.

Insights into the dynamics of planetary interiors obtained through the study of global distribution of volcanoes II: Tectonic implications from Venus

The distribution of volcanic features is ultimately controlled by processes taking place beneath the surface of a planet. For this reason, characterization of volcano distribution at a global scale can be used to obtain insights concerning dynamic aspects of planetary interiors. Until present, studies of this type commonly have focused on volcanic features of a specific type (e.g., large volcanoes in Venus or hot-spot volcanism on Earth), or have concentrated on relatively small regions (i.e., vent distribution within individual volcanic fields), but no comparison of extensive databases has been made by using the same tools in both planets. In this work, the description of the distribution of volcanic features observed over the entire surface of Venus is made using the same tool used for Earth, and is applied to an extensive database. The analysis is based on density contours obtained with the Fisher kernel. As a result, several groupings of volcanoes are identified refining the already documented concentration of volcanoes on the BAT zone. In particular some doughnut-like patterns are observed that might be related to the action of mantle plumes. The occurrence of such features on Earth, as well as the existence of a uniform distribution of background volcanism on both planets, suggests similarities on their geodynamic behavior that had not been identified previously.

New constraints on volcano-tectonic evolution of large volcanic edifices on Venus from stereo topography–derived strain estimates

Research Article| January 01, 2014 New constraints on volcano-tectonic evolution of large volcanic edifices on Venus from stereo topography–derived strain estimates Patrick J. McGovern; Patrick J. McGovern 1Lunar and Planetary Institute, USRA (Universities Space Research Association), Houston, Texas 77058, USA Search for other works by this author on: GSW Google Scholar Gerald A. Galgana; Gerald A. Galgana 1Lunar and Planetary Institute, USRA (Universities Space Research Association), Houston, Texas 77058, USA2AIR Worldwide, 131 Dartmouth Street, Boston, Massachusetts 02116, USA Search for other works by this author on: GSW Google Scholar Katelyn R. Verner; Katelyn R. Verner 1Lunar and Planetary Institute, USRA (Universities Space Research Association), Houston, Texas 77058, USA3Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Indiana 47907, USA Search for other works by this author on: GSW Google Scholar Robert R. Herrick Robert R. Herrick 4Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska 99775-7320, USA Search for other works by this author on: GSW Google Scholar Geology (2014) 42 (1): 59–62. https://doi.org/10.1130/G34919.1 Article history received: 08 Jul 2013 rev-recd: 13 Sep 2013 accepted: 25 Sep 2013 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 Patrick J. McGovern, Gerald A. Galgana, Katelyn R. Verner, Robert R. Herrick; New constraints on volcano-tectonic evolution of large volcanic edifices on Venus from stereo topography–derived strain estimates. Geology 2014;; 42 (1): 59–62. doi: https://doi.org/10.1130/G34919.1 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 Radial fracture systems at large volcanoes on Venus offer opportunities to unravel the tectonic and magmatic evolution of such edifices. However, the relatively low spatial resolution (10–20 km) of altimetry data for Venus has hampered previous efforts at quantitative analysis of fault systems. Recently released stereo-derived topography enables kilometer-scale strain estimates to be made at tectonic features. The new data resolve fault valleys (grabens) that cut the summit regions of two large volcanoes, showing them to be deeper than previously assumed. The grabens formed after most edifice building was complete. We demonstrate that inflation of oblate sill-like magma chambers is consistent with the magnitudes and distributions of strain at these volcanoes, and estimate chamber depth, radius, and overpressure. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Benevolence, Charity, and Duty: Urban Relief and Domain Society during the Tenmei Famine

Benevolence, Charity, and DutyUrban Relief and Domain Society during the Tenmei Famine Maren Ehlers (bio) In the fifth lunar month of 1783, the people of Ōno 大野 were startled by a roll of thunder that returned over several weeks and reminded them of giant drums or cannon shots.1 The source of this menacing noise was Mt. Asama 浅間, a large volcano in neighboring Shinano 信濃 province, which subsequently erupted later in the summer. A small domain set within the mountainous hinterland of Echizen 越前 province, Ōno was too far away to be directly affected by the eruption, but the noise proved an unlucky omen nonetheless. In 1783, after a cold and rainy summer, the peasants of the Ōno plain suffered what they called a “crop failure” (fusaku 不作). This came in the wake of a meager harvest the previous year and was followed by two more years of dearth in 1784/85 and 1786/87.2 Ōno, together with many other parts of eastern and central Japan, had entered one of the worst and longest food crises of the Tokugawa period: the Tenmei 天明 Famine.3 [End Page 55] This article discusses how Ōno’s domain authorities and the people of the castle town (also known as Ōno) organized hunger relief for the town’s commoner population during the Tenmei Famine. Relief institutions for townspeople in Tokugawa Japan differed from those for villagers because governments were particularly eager to prevent unrest around their seats of power, and because towns were centers of commerce and home to a very diverse mix of nonagricultural livelihoods. Most previous research on urban famine relief has focused on the “three capitals,” Edo, Osaka, and Kyoto.4 Consideration of the situation in Ōno adds a new dimension to such studies by exploring how different schemes of hunger aid were managed, funded, and modified in a much smaller setting. The article argues that famine relief in Ōno was structured by the local social order, especially the roles assumed by urban status groups, which served as a coordinating framework for charitable interactions. As such it also addresses the question of what relief activities reveal about society and domain rule in a small castle town in the late Tokugawa period. The shogunate and domain lords administered their territories by relying on the self-governing capacities of groups such as peasant villages, neighborhoods (which were largely occupation based), guilds, and fraternities of various kinds. Although the warrior authorities expected these groups to submit to their control and could impose their will by force if necessary, they also allowed such entities autonomy in many situations and secured their allegiance by granting them privileges and protection. In return, status groups provided the rulers with duties in the form of goods and services that reflected their particular expertise. Famine relief was shaped by this style of governance, which relied on powerful bonds of mutual obligation and group cohesion. Much of what may at first appear like individual acts of charity actually hinged on the givers’ status ties with the authorities, while the government exercised “benevolent rule” by relying on the contributions of commoners. Commoner and seigneurial interventions in hunger relief were closely intertwined and cannot be understood in isolation from one another. [End Page 56] Two types of status entities stand out as particularly relevant for urban famine relief in Ōno and elsewhere: neighborhoods (chō 町) and various forms of guilds (nakama 仲間). Chō were small, self-governing units of house-owning townspeople through which warrior governments exercised their rule over the town population. They typically comprised the two rows of houses on either side of a block-long street section. Mutual help, including assistance to needy neighbors or tenants, is often identified as one of two major responsibilities of the chō, and especially the five-household groups within them—the second being mutual supervision and control.5 By comparison, the involvement in famine relief of other officially recognized groups in Tokugawa society, such as guilds, has not received much scholarly attention. In Ōno, the sake brewer guild, the purveyor guild, and the beggar guild (a group of mendicant outcastes) all played important roles in the organization and funding of town-wide systems of relief. Their participation in these...

The geologic evolution of Venus: Insights into Earth history

Through the clever use of stereo radargrammetric techniques on images from the Magellan mission to Venus in the 1990s, combined with recent quantitative analyses of magma reservoirs on Earth, McGovern et al. (2014, p. 59 in this issue of Geology) resolve an important outstanding question dating from that era: What forces are responsible for the graben extending radially from large shield volcanoes? They show that, in addition to radial dike emplacement, the larger graben are readily accounted for by magma reservoir infl ation, providing new insight into processes of magma ascent and eruption on Venus, and their relation to globally interconnected rift systems on Earth’s sibling planet. This new contribution serves as a reminder of the importance of Venus to our understanding of geological processes and history on Earth, and the need for new data to resolve some of the most fundamental problems in comparative planetology. HISTORY OF VENUS EXPLORATION The liftoff of Sputnik in 1957 launched a vigorous international program of planetary exploration and the fi eld of comparative planetology. How do our neighboring terrestrial (Earth-like) planets look, and what insights can they provide in understanding our own planet? Early missions to the Moon, Mercury, and Mars showed that these terrestrial planets with one-half or less the diameter of Earth looked very different from Earth. Their high surface area/volume ratio lets them conduct internal heat to the surface effi ciently and cool rapidly, becoming “one-plate planets” with thick, stable lithospheres. Their surfaces preserve evidence of geological processes from the fi rst half of solar system history. Intensely pockmarked by impact craters and resurfaced by volcanism, they reveal the roles of external forces (early accretion and high impact fl ux) and internal thermal evolution (conduction, convection, hot spot formation, magmatism, advection, and surface volcanism). But what about Venus, similar to Earth in size, density, and position in the Solar System? Is it Earth-like, with a young surface, plate tectonics, and tracks of hot-spot volcanoes, or like the smaller planets, with a heavily cratered surface? When imagination outstripped data, Venus was thought to have an Earth-like hot swampy surface, but we now know that its CO 2 atmosphere, sulfuric acid clouds, surface temperatures hot enough to melt lead, and very slow and retrograde rotation, are nothing like Earth. What about its surface and interior geology? Venera (Soviet Union) atmospheric probes and landers showed that the surface was littered with generally basaltic rocks and patchy soils (Hunten et al., 1983). A radar altimeter on the Pioneer Venus (PV, United States) orbiter (1978) provided a global topographic map, with a resolution of ~100 km, low by today’s standards. Its analysis showed many Earth-like features: evidence for continent-like highlands with marginal linear mountain belts, broad Iceland-like rises and plateaus, circular basins, and very long, linear lowlands, but with a global hypsometry different from that of current Earth. Instead of the latter’s bimodal distribution of global topography, the hypsometry of Venus was unimodal, skewed to higher elevations. Increasingly higher-resolution radar data provided additional evidence for Earth-like features. One of the rises in the PV data (Beta Regio) was cleaved by a rift zone, surmounted by volcanoes. The mountain belts surrounding a large continent-like plateau (Ishtar Terra) were composed of multiple parallel linear features analogous to Earth’s folded mountain belts. Often-circular features (coronae) were not impact structures, but complex deformation zones, more consistent with internal deformation origins. Higher-resolution radar imaging and more coverage were needed to fi out whether Venus was Earth-like. In 1983, Soviet Union orbiters Venera 15 and 16 surveyed the northern hemisphere (~30% of Venus), with radar imaging resolution of 1‐2 km (Barsukov et al., 1992), showing that many highlands consist of very highly deformed terrain (tesserae), and that organized linear folded mountain belts surround highland plateaus. Large volcanoes exist in abundance, but show little evidence for hot spot traces or convergent plate boundaries. Coronae looked like the fi ngerprints of mantle processes. Most remarkably, there were few impact craters, indicating an age on the order of only hundreds of millions of years. These results raised signifi cant, fundamental questions: Where is the ancient billions-of-years-old continent-like terrain on Venus? What is the average age of the surface? Is Venus characterized by Earth-like plate tectonics, or do its thermal regimes suggest another manifestation of plate tectonics? Is internal heat transferred mainly by conduction, advection, or plate tectonics? Are the fold belts global and if so, where is the corresponding extension and divergence? These questions guided the 1989 United States Magellan mission to Venus. THE MAGELLAN MISSION PROVIDES GLOBAL COVERAGE

The diverging volcanic rift system

Abstract Eruptions and volcano internal growth are mostly fed by dykes. The comprehension of the control factors on dyke paths is fundamental for the assessment of areas prone to vent formation and to the general understanding of how volcanoes work. We analyse an understudied magma path system; field data of nine volcanoes show they have a rectilinear rift zone in the central part passing into fan-arranged dykes at the two opposite volcano flanks. The geological, geomorphological and structural characteristics of these volcanoes and their substrate suggest that the formation of these “diverging rifts” is not specifically linked to substrate lithology and mechanical behaviour. The studied volcanoes have elongation V > 10 km 3 (mostly > 300 km 3 ). Eight volcanoes have the central rift that is normal to the regional tectonic least principal stress (σ 3reg ) and in one case it is sub-perpendicular. Field data have been combined with scaled analogue modelling, suggesting that if the σ 3reg is oblique to the volcano elongation axis, dyke geometry in the edifice axial zone is controlled by elongation and thus by local gravity σ 3 , but dyke strike becomes perpendicular to σ 3reg when dykes intrude the more external areas of the volcano. If a dyke is injected under the volcano flanks with slope inclination > 50°, it attains a geometry parallel to the slope. At lower slope inclinations at the edifice terminations, magma paths diverge outwards and crosscut slopes at high angle. Our data are in agreement with the assumption that regional tectonic stresses can affect large volcanoes up to the summit area guiding the development of a rectilinear thoroughgoing rift, both in extensional and transtensional regimes. The diverging pattern takes place due to reorientation of the local stress field guided by topography only when dyke inception localizes laterally respect to the edifice axis.

The influence of lithospheric flexure on magma ascent at large volcanoes on Venus

AbstractLarge volcanoes on Venus exert large vertical loads on the lithosphere, which responds by deflecting downward. Stresses induced by this lithospheric flexure can have a strong influence on magma ascent pathways from the mantle source region to the surface. Here we propose that flexural stresses exert control over the shapes of volcanic edifices on Venus, applying criteria for magma ascent expressed in terms of stress orientations (can vertical dikes form?) and gradients (is magma squeezed upward or downward in a vertical dike?) to determine favored magma ascent paths and locations. For conical edifices emplaced on lithosphere with high elastic thickness Te, (e.g., > 40 km) both sets of magma ascent criteria are satisfied over the entire lithosphere, allowing essentially unimpeded ascent of magma to the surface and the formation of relatively steep edifices. However, for lower values of Te, high adverse stress gradients tend to cut off magma ascent beneath the summit, instead favoring lateral transport of magma at depth to distal regions with gentler stress gradients, resulting in domical edifice shapes. At the lowest values of Te (< 10 km), large short‐wavelength deflections of the lithosphere tend to produce narrow and widely spaced zones of magma ascent: Such zones may produce annular ridges of volcanic material, thereby generating forms characteristic of a subset of features known as “coronae” on Venus. Another subset of coronae may form by intrusive‐based generation of annular fractures at the edge of the summit region of domical edifices, as proposed for Alba Mons on Mars.

Underwater geophysical monitoring for European Multidisciplinary Seafloor and water column Observatories

We present a review of our work on data acquired by GEOSTAR-class (GEophysical and Oceanographic STation for Abyssal Research) observatories deployed at three EMSO (European Multidisciplinary Seafloor and water-column Observatory; http://www.emso-eu.org) sites in southern European waters where strong geo-hazards are present: the Western Iberian Margin, the Western Ionian Sea, the Marmara Sea, and the Marsili basin in the Tyrrhenian Sea. A procedure for multiparameter data quality control is described. Then we explain why the seafloor is an interesting observation point for geophysical parameters and how it differs from land sites. We consider four interesting geophysical phenomena found at the EMSO sites that are related to geo-hazard. In the first case, we show how unknown seismicity and landslides in the Western Ionian Sea were identified and roughly localised through a single-sensor analysis based on the seismometer. In the second case, we concentrate on the problem of near-coast tsunami generation and describe a Tsunami Early Warning Detection (TEWD) system, tested in the Western Iberian Margin and currently operating in real time at the Western Ionian site. In the third case, we consider two large volcanoes in the central Mediterranean area, Mt. Etna and the Marsili seamount. Signals from the seismometer and gravimeter recorded at the seafloor at 2100m b.s.l. show various phases of Mt. Etna's 2002–2003 eruption. For the less-known Marsili we illustrate how several indicators coming from different sensors point to hydrothermal activity. A vector magnetometer at the two volcanic sites helps identify the magnetic lithospheric depth. In the fourth and final case, we present a multiparameter analysis which was focused on finding possible correlations between methane seepage and seismic energy release in the Gulf of Izmit (Marmara Sea).

Largest volcano on Earth found beneath Pacific

Largest volcano on Earth found beneath Pacific

Meet the world's largest volcano

Meet the world's largest volcano

Volcanic evolution of the South Sandwich volcanic arc, South Atlantic, from multibeam bathymetry

New multibeam bathymetry data are presented for the South Sandwich intra-oceanic arc which occupies the small Sandwich plate in the South Atlantic, and is widely considered to be a simple end-member in the range of intra-oceanic arc types. The images show for the first time the distribution of submarine volcanic, tectonic and erosional–depositional features along the whole length of the 540km long volcanic arc, allowing systematic investigation of along-arc variations. The data confirm that the volcanic arc has a simple structure composed of large volcanoes which form a well-defined volcanic front, but with three parallel cross-cutting seamount chains extending 38–60km from near the volcanic front into the rear-arc. There is no evidence for intra-arc rifting or extinct volcanic lines. Topographic evidence for faulting is generally absent, except near the northern and southern plate boundaries. Most of the volcanic arc appears to be built on ocean crust formed at the associated back-arc spreading centre, as previously proposed from magnetic data, but the southern part of the arc appears to be underlain by older arc or continental crust whose west-facing rifted margin facing the back-arc basin is defined by the new bathymetry. The new survey shows nine main volcanic edifices along the volcanic front and ca. 20 main seamounts. The main volcanoes form largely glaciated islands with summits 3.0–3.5km above base levels which are 2500–3000m deep in the north and shallower at 2000–2500m deep in the south. Some of the component seamounts are interpreted to have been active since the last glacial maximum, and so are approximately contemporaneous with the volcanic front volcanism. Seven calderas, all either submarine or ice-filled, have been identified: Adventure volcano, a newly discovered submarine volcanic front caldera volcano is described for the first time. All but one of the calderas are situated on summits of large volcanoes in the southern part of the arc, and most are associated with current or historic volcanic or hydrothermal activity. Shallow shelves around the islands are generally 1–10km wide. Submerged banks up to 1100m deep are interpreted as subsided erosional surfaces. Seamounts and emergent volcanoes experienced a range of mass wasting processes including by landsliding and smaller mass flows.

K-Ar and Rb-Sr geochronology and evolution of the Štiavnica Stratovolcano (Central Slovakia)

Abstract The Štiavnica Stratovolcano in Central Slovakia is the largest volcano in the Neogene to Quaternary Carpathian volcanic arc. A large caldera, an extensive subvolcanic intrusive complex and a resurgent horst with late stage rhyolite volcanites are the most characteristic features. The results of new K-Ar and Rb-Sr isotope dating using more sophisticated methodical approaches have changed our view on the timing of volcanic and intrusive activity. K-Ar dating of groundmass fractions combined with Rb-Sr isochron dating in the cases of possible rejuvenation has provided highly reliable results. The lifespan of the stratovolcano is apparently shorter than assumed earlier. Evolution of the stratovolcano took place in five stages during the Early Badenian to beginning of Early Pannonian time: (1) construction of the extensive andesite stratovolcano during the interval 15.0-13.5 Ma; (2) denudation of the volcano concluded with the initial subsidence of a caldera and the contemporaneous emplacement of a subvolcanic intrusive complex of diorite, granodiorite, granodiorite porphyries and quartz-diorite porphyries during the interval 13.5-12.9 Ma; (3) subsidence of the caldera and its filling by differentiated andesites during the interval 13.1-12.7 Ma - volcanic activity overlapping with the emplacement of the youngest intrusions; (4) renewed explosive and effusive activity of less differentiated andesites during the interval 12.7-12.2 Ma; (5) uplift of the resurgent horst in the central part of the caldera accompanied by rhyolite volcanic/intrusive activity during the interval 12.2-11.4 Ma. Extensive epithermal mineralization was contemporaneous with the uplift of the resurgent horst and rhyolite volcanic activity and continued till 10.7 Ma

Volcanoes of the Diamante cross-chain: evidence for a mid-crustal felsic magma body beneath the Southern Izu–Bonin–Mariana arc

Abstract Three submarine Diamante cross-chain volcanoes in the southern Mariana arc mark a magma-healed zone of along-arc (north–south) extension that allows either mafic mantle-derived basalts or felsic magmas from the middle of thickened arc crust to erupt. The largest volcano is East Diamante, with a well-developed (5×10 km) caldera that formed via violent felsic submarine eruptions beginning nearly 0.5 Ma. One or more of these eruptions also formed a giant submarine dune field extending 30 km to the NW of the volcano. Felsic igneous activity continues at least as recently as c. 20 000 years ago, with emplacement of resurgent dacite domes, some hot enough to power the only black smoker hydrothermal system known in the Mariana arc. In contrast, felsic eruptions do not occur on the two volcanoes to the west, implying that the mid-crustal felsic zone does not underlie the thinner crust of the Mariana Trough back-arc basin. Diamante cross-chain lavas define a medium K suite; mafic lava phenocryst assemblages show arc-like associations of anorthite-rich plagioclase with Fe-rich olivine. Magmatic temperatures for a basaltic andesite and three dacites are c. 1100 °C and c. 800 °C, respectively, typical for cool, wet, subduction-related felsic magmas. Felsic magmas formed under low-P crustal conditions. The Diamante cross-chain is the southernmost of at least seven and perhaps eight Mariana arc volcanoes in a c. 115 km long arc segment characterized by felsic eruptions. This is the ‘Anatahan Felsic Province’, which may have formed above a mid-crustal tonalite body that formed by fractionation or was re-melted when heated by c. 1200 °C mafic, mantle-derived magmas. Across- and along-arc variations suggest that felsic eruptions and dome emplacement occurred when midcrustal tonalite was remobilized by intrusions of mafic magma, while north–south extension facilitated the development of conduits to the surface. Supplementary material: Detailed Hyperdolphin ROV dive tracks, Cook 7 dredge locations, 40 Ar/ 39 Ar analytical data, analytical methods, major and selected trace element analyses of whole rock samples, and compositional data for minerals are available at http://www.geolsoc.org.uk/SUP18611

A sagging-spreading continuum of large volcano structure

Gravitational deformation strongly infl uences the structure and eruptive behavior of large volcanoes. Using scaled analog models, we characterize a range of structural architectures produced by volcano sagging and volcano spreading. These arise from the interplay of variable basement rigidity and volcano-basement (de-)coupling. From comparison to volcanoes on Earth (La Reunion and Hawaii) and Mars (Elysium and Olympus Montes), the models highlight a structural continuum in which large volcanoes throughout the Solar System lie.

Lead Isotope composition and origin of the quaternary lavas of Elbrus Volcano, the Greater Caucasus: High-precision MC-ICP-MS data

A systematic study of Pb isotope composition was carried out for Elbrus Volcano, one of the Europe’s largest volcanoes, using high-precision method of multi-collector inductively coupled plasma mass spectrometry. The measurement error of Pb isotope ratios was estimated from the results of replicate analyses of international BCR-1 and AGV-1 standards as ±0.03% (±2SD). The study of a representative collection showed that dacites of all three phases of the Elbrus eruptive activity are characterized by relatively small-scale variations of Pb isotope composition: 206Pb/204Pb 18.621–18.670, 207Pb/204Pb 15.636–15.659, and 208Pb/204Pb 38.762–38.845. New Pb isotope geochemical characteristics in combination with existing Sr-Nd data indicate that the parental magmas of Elbrus are of mixed mantle-crust origin. They were formed by interaction of mantle-derived melts with continental crust of the Greater Caucasus during continental collision between the Eurasian, Arabian, Turkish, and Iranian plates.

Quantitative Size Classification of Scoria Cones: The Case of Tenerife (Canary Islands, Spain)

Monogenetic volcanoes are the most abundant volcanic structures on the Earth's surface. Thousands of them exist in different tectonic contexts (e.g., subduction zones, intraplate areas, and divergent boundaries), appearing in groups forming volcanic fields. Tenerife, the largest and highest island of the Canarian archipelago, started to form about 14 million years ago (Ma), as a result of a complex eruptive history and a varied geomorphological evolution, including shield-building stages, volcanic rifts, stratovolcanoes, and monogenetic cones. Tenerife is an active, volcanic, oceanic island, where the last eruption occurred in 1909. In this paper, we propose a methodology for calculating the size of monogenetic basaltic volcanoes based on morphometric parameters, as well as a classification of the size of the volcanoes through the study of 297 scoria cones of Tenerife. Morphometric techniques, based mainly on height (Hco), volume (Vco), and area (Aco), were used together with correlations between different morphological parameters. The result is a simple quantitative classification, easy to use for estimating the size of monogenetic volcanoes. Of the monogenetic basaltic volcanoes of Tenerife, 98.98% fit into this classification, which distinguishes between large (Hco >200; Vco >0.1; Aco >0.5), medium (Hco >100 to <200; Vco >0.01 to <0.1; Aco >0.2 to <0.5), and small (Hco <100; Vco <0.01; Aco <0.2) volcanoes. There is a strong correlation between the size of cinder cones and their age: the more recent scoria cones are smaller in size than the older ones. This relationship supports suggestions by other researchers that eruptions have decreased in magnitude and the volume of available magma has become smaller. The results obtained by calculating the size of the scoria cones of Tenerife make possible the extrapolation of this technique to other insular or continental monogenetic volcanic fields.

Latest Pleistocene and Holocene glacier fluctuations on Mount Baker, Washington

Glaciers on stratovolcanoes of the Pacific Northwest of North America offer opportunities for dating late Pleistocene and Holocene glacier advances because tephra and fossil wood are common in lateral moraines and in glacier forefields. We capitalize on this opportunity by examining the Holocene glacial record at Mount Baker, an active stratovolcano in northwest Washington. Earlier workers concluded that glaciers on Mount Baker during the early Holocene were more extensive than during the Little Ice Age and hypothesized that the explanation lay in unusual climatic or hypsometric effects peculiar to large volcanoes. We show that the main argument for an early Holocene glacier advance on Mount Baker, namely the absence of ca 10,000-year-old tephra on part of the south flank of the mountain, is incorrect. Moreover, a lake-sediment core indicates that a small cirque moraine previously thought be of early Holocene age is also likely older than the tephra and consequently of late Pleistocene age.Lateral and end moraines and wood mats ca 2 km downvalley of the present snout of Deming Glacier indicate that an advance during the Younger Dryas interval was little more extensive than the climactic Little Ice Age advance. Tephra and wood between tills in the left lateral moraine of Easton Glacier suggest that ice on Mount Baker was restricted in the early Holocene and that Neoglaciation began ca 6 ka. A series of progressively more extensive Neoglacial advances, dated to about 2.2, 1.6, 0.9, and 0.4 ka, are recorded by stacked tills in the right lateral moraine of Deming Glacier. Intervening retreats were long enough to allow establishment of forests on the moraine. Wood mats in moraines of Coleman and Easton glaciers indicate that Little Ice Age expansion began before 0.7 ka and was followed by retreat and a readvance ca 0.5 ka. Tree-ring and lichen data indicate glaciers on the south side of the mountain reached their maximum extents in the mid-1800s.The similarity between glacier fluctuations at Mount Baker and those elsewhere in the Cascades and in British Columbia suggests a coherent history of Holocene climate change over a broad area of the western Cordillera. We found no evidence that glaciers on stratovolcanoes behave differently than glaciers elsewhere.

Structural control on volcanism in intraplate post collisional settings: Late Cenozoic to Quaternary examples of Iran and Eastern Turkey

Volcanic activity focuses along plate boundaries. However, large volcanoes are also found in intraplate settings. For these volcanoes, geodynamic processes responsible for magma generation and structural controls on magma rise and extrusion need to be evaluated. We merge original (field and remote sensing) and available (geodetic, geophysical, and petrological) data to consider the tectono‐magmatic relationships of three large intraplate volcanoes in the E‐Anatolian‐Iranian plateau; Sar'akhor (NE Iran), Damavand (Central Alborz) and Ararat (E Anatolia). In NE Iran, a Miocene‐Pliocene NW‐trending compression activated E‐W dextral faults to the NW of Sar'akhor and N‐S sinistral faults to the SE, creating an extruding wedge to the west of this volcano. Since Quaternary, NE‐trending compression inverted fault movement, hindering further block extrusion and volcanism terminated. The adakitic composition of the Sar'akhor rocks suggests post‐collisional melting of oceanic slab and/or mafic lower crust, possibly triggered by an asthenospheric rise after slab break‐off or intramantle delamination. For the active Damavand and Ararat volcanoes, available data suggest magma generation due to rising hot asthenosphere, following lithospheric delamination or slab break‐off in a transtensional environment. The features common to Sar'akhor, Damavand and Ararat allow proposing a model, where transtension focuses the rise of magma in intraplate settings overlying hot asthenosphere produced by delamination or slab break‐off.

Hf-Nd isotope variation in Mariana Trough basalts: The importance of “ambient mantle” in the interpretation of subduction zone magmas

In the study of geochemical mass balances at subduction zones, the composition of the mantle wedge prior to additions from the slab is a critically important yet poorly constrained parameter. Deconvolving the influence of ancient versus modern enrichments is particularly difficult, especially when considering elements that are highly mobile. Here we provide an alternative approach, using less mobile elements, and a filter to remove the effects of recent slab additions. We provide new Hf isotope data for 30 Mariana Trough (MT) backarc basin lavas. Once filtered, Hf and Nd isotope ratios are highly correlated, of Indian mid-oceanic ridge basalt character, and display variations similar to ocean ridges of comparable lengths. The isotopic variability observed in this “ambient mantle” provides a new paradigm for the interpretation of the varied volcanic products of the arc. Thus, shoshonites associated with the northern termination of the backarc basin rift axis reflect the interaction of a subducted sediment melt with an isotopically enriched mantle source. In contrast, the large volcanoes of the Central Island province have a consistent offset in Nd isotope compositions from the MT array resulting from fluid addition. Existing data for smaller edifices in the submarine portion of the arc have larger variations resulting from fluid addition on a more local scale. We suggest that the similar characterization of ambient mantle elsewhere may help to resolve many conflicting geochemical observations in arc lavas worldwide.