Eruption Site Research Articles

Constraining Spatiotemporal Characteristics of Magma Migration at Piton De La Fournaise Volcano From Pre-eruptive Seismicity.

Volcano‐tectonic seismicity has been recorded for decades on various volcanoes and is linked with the magma transport and reservoir pressurization. Yet earthquakes often appear broadly distributed such that magma movement is difficult to infer from its analysis. We explore the seismicity that occurred before eruptions at Piton de la Fournaise in the last 5 years. Using template matching and relocation techniques, we produce a refined image of the summit seismicity, demonstrating that most earthquakes are located on a ring structure. However, only a portion of this structure is activated before each eruption, which provides an indication as to the direction of the future eruptive site. Furthermore, we show that the delay between the pre‐eruptive swarm and the eruption onset is proportional to the distance of the eruptive fissures relative to the summit cone. This reveals that the beginning of the intrusion already bears information regarding the future eruption location.

Posteruptive Thermoelastic Deflation of Intruded Magma in Usu Volcano, Japan, 1992–2017

AbstractSecular ground subsidence at Usu volcano (Japan) has been reported around the eruption vents following the four eruptions in 1910, 1943, 1977, and 2000. However, the mechanisms accounting for the subsidence have not been well understood. In this study, we systematically investigated the posteruptive deformation at Usu volcano using interferometric synthetic aperture radar based on 111 JERS, ALOS‐1, and ALOS‐2 images acquired from 1992 to 2017. We also calculated quasi east‐west and vertical ground displacements between 2006 and 2017. Our results show three localized deformation regions from west to east of Usu volcano with their locations corresponding to the 2000, 1977, and 1943 eruption vents, respectively. All the deformation sites show patterns of east‐west contraction and subsidence. The extent and rate of posteruptive subsidence declined dramatically at the vent of the 2000 eruption site from 2006 to 2017, decreased gradually at the 1977 vent, and show a steady pattern for the 1943 site during 1992–2017. We ascribed the observed posteruptive subsidence to thermoelastic contraction of a sphere intruded at the time of the eruptions to constrain locations, depths, and volumes of heat sources with the assumption of the spherical source shapes. Thermoelastic modeling reveals that the heat sources are embedded at shallow depths not deeper than 400 m below sea level with volumes of about (8.72 ± 0.19) × 106, (132.18 ± 5.21) × 106, and (49.51 ± 2.02) × 106 m3 for the 2000, 1977, and 1943 eruption sites, respectively. The modeling also highlights the importance of underground water in assessing the thermal diffusion process and the associated posteruptive deformation.

Explosive volcanoes in the Mediterranean area: hazards from future eruptions at Vesuvius (Italy) and Santorini (Greece)

Santorini is the site of the famous Minoan eruption of the late Bronze Age and Vesuvius is the type locality for Plinian eruptions. Hazards from the eruption most likely to occur in the near future at these volcanoes are discussed. Downwind zones of Santorini can be affected by minor ash fallout and gas emission from a Vulcanian eruption of Nea Kameni, the most active post-caldera vent. More dangerous would be a sub-Plinian eruption from Columbus, a submarine volcano located 8 km NE of Santorini, whose eruption in 1649-1650 A.D. caused several casualties in Santorini, mostly by wind transported poisoning gas. Vesuvius last erupted in 1944 and its eruptive history includes periods of long quiescence, lasting centuries or tens of centuries, interrupted by violent Plinian or sub-Plinian eruptions. A sub-Plinian eruption is the reference event in the Civil Protection emergency plan. The scenario includes a Red Zone exposed to the risk of being invaded by pyroclastic flows and that should be entirely evacuated before the eruption onset, together with some nearby areas where there is a high risk of roofs collapse by overloading of fallout tephra (nearly 700,000 persons in total). The Red Zone is encircled by the Yellow Zone exposed to pyroclastic fallout and related risk maps are here commented. Another serious risk is associated with earthquakes of the pre-eruptive unrest phase. Because of the high seismic vulnerability of the buildings within the Red Zone, many of them might collapse before the evacuation order of the Red Zone be issued. Finally, the scientific difficulty of forecasting the time evolution of the eruption precursory phenomena is discussed together with the related civil protection implications.

The Relationship Between Lava Fountaining and Vent Morphology for the 2014–2015 Holuhraun Eruption, Iceland, Analyzed by Video Monitoring and Topographic Mapping

Fissure eruptions are associated with lava fountains which often show complex distinct venting activity, in pulsating form, and the development of characteristic morphologic expressions such as scoria or spatter cones. Most morphological studies are based on observations of old structures and are not related to direct observations and systematic records of vents activity, which are rare. The 2014 - 2015 Holuhraun eruption site, Iceland, offered an exceptional opportunity to study with unprecedented details the location and evolution of those cones and their relationship to the venting dynamic. Here we analyse records from lava fountains activity at distinguished vents, captured during the 2014-2015 Holuhraun eruption, and compare them with the developing morphology of spatter cones. We conducted a fieldwork mapping project combining Terrestrial Laser Scanning (TLS) and Unmanned Aerial Vehicle (UAV) aerophoto techniques to characterize the cone morphologies. We recorded videos of the eruption and used edge detection and particle image velocimetry to estimate venting heights and particle velocities. We find that at those locations where spatter cone morphology developed the strongest, the highest lava fountains and larger ejection velocities were recorded, already at the very first days of the eruption. Instead, those sites that finally developed moderate or weak morphologies are also identified as less active lave fountain locations during the early stage of the eruption. The comparison of our topographic datasets shows that spatter cones remain similar in shape but increase in size as the eruption progress. In addition, we suggest that the observed changes in morphology may affect lava ponding in the crater, which in turn is strongly affecting eruption heights. Our results improve the general understanding of landscape evolution at rift zones, and demonstrate the close relationship between the cone morphology and the lava fountain activity at the onset of an eruption.

Eruptions in sync: Improved constraints on Kīlauea Volcano's hydraulic connection

Kīlauea Volcano is an archetype for the complex interactions that can occur between a volcano's summit and flanks. Decades of monitoring at Kīlauea have demonstrated that magma rises beneath the summit and flows laterally at shallow depths to erupt along the rift zones. Kīlauea's recent eruptions at Halema‘uma‘u and Pu‘u ‘Ō‘ō mark the first time in the historic record that long-term (>1 year) eruptions have been concurrent at the summit and a rift zone, offering a new opportunity to improve our understanding of the relationship between these two segments of the magmatic system. While magma supply rate beneath the summit has been shown in previous studies to be a primary control on magmatic system pressure and eruptive activity, the role of the eruptive vent has been less clear. Our study shows that a dynamic equilibrium is maintained between Kīlauea's summit and East Rift Zone (ERZ) eruptive vent—and lava lake level fluctuations are closely coupled at the two eruption sites—providing new constraints on the hydraulic connection and ERZ conduit. We show that localized changes at the ERZ eruption site during 2010–2011 regulated summit behavior in an uprift direction over distances of ∼20 km. Changes in the elevation and efficiency of the ERZ vent affect pressure in Kīlauea's magmatic system and impact summit behavior. Thus, the hydraulic connection between the summit and rift zone is a “two-way street” that transmits both downrift- and uprift-directed changes. Our results support recent work at other volcanoes that shows a complex interplay between a volcano's summit reservoir and flank conduit during flank eruptions, and suggest that explosive summit activity may in some cases be triggered by changes far away on a volcano's rift. These concepts were reinforced by the historic eruptive activity on Kīlauea that occurred during May–August 2018, when the manuscript was being revised.

A Recent Volcanic Eruption Discovered on the Central Mariana Back-Arc Spreading Center

Submarine volcanic eruptions are difficult to detect because they are hidden from view at the bottom of the ocean and far from land-based sensors. However, most of Earth’s volcanic activity is in the oceans along tectonic plate boundaries, and modern tools of oceanography now allow us to find and study recent eruptions in the deep sea. The first known historical eruption on the Mariana back-arc spreading center was discovered in December 2015 during exploration of the southern back-arc for new hydrothermal vent sites. A water-column survey along the axis of the back-arc showed hydrothermal plumes over the site characterized by low particle concentrations and relatively high reduced chemical anomalies. A dive with the autonomous underwater vehicle Sentry collected high-resolution (1 m) multibeam sonar bathymetry over the site, followed by a near-bottom photographic survey of a smaller area. The photo survey revealed the presence of a pristine, dark, glassy lava flow on the seafloor with no sediment cover. Venting of milky hydrothermal fluid indicated that the lava flow was still warm and therefore very young. A comparison of multibeam sonar bathymetry collected by R/V Falkor in December 2015, to the most recent previous survey of the area by R/V Melville in February 2013, revealed large depth changes in the same area, effectively bracketing the timing of the eruption within a window of less than 3 years. The bathymetric comparison shows the eruption produced a string of lava flows with maximum thicknesses of 40–138 m along a distance of 7.3 km (from latitude 15∘22.3′ to 15∘26.3′N) between depths of 4050–4450 m bsl (meters below sea level), making this the deepest known historical submarine volcanic eruption on Earth. The cross-axis width of the lava flows is 200–800 m. The Sentry bathymetry shows that the new lava flows are constructed of steep-sided hummocky pillow mounds and are surrounded by older flows with similar morphology. In April and December 2016, two dives were made on the new lava flows by remotely operated vehicles Deep Discoverer and SuBastian. The pillow lavas have many small glassy buds on the steep flanks of the mounds, locally thick accumulations of hydrothermal sediment near the tops of mounds, and small cones of radiating pillows at their summits. The 2015–2016 observations show a rapidly declining hydrothermal system on the lava flows, suggesting that the eruption had occurred only months before its discovery in December 2015. The morphology of the pillow lavas is similar to other historical eruption sites, so the greater depth and ambient pressure of this site had no apparent effect on the processes of lava extrusion and emplacement. This study reveals that some segments of the Mariana back-arc have active magmatic systems despite the relatively low spreading rate, and that other eruptions are possible in the near future.

Detecting and Locating Precursory Signals During the 2011 El Hierro, Canary Islands, Submarine Eruption

AbstractForecasting and monitoring submarine volcanic eruptions represent a particular challenge due to the lack of direct surface observations. In the present study, we investigate the dynamics of the 2011 El Hierro submarine eruption using phase autocorrelation and cross‐correlation from 2 years of continuous seismic records. Time evolution analysis of the waveform similarity allows us to clearly identify different preeruptive phases of this new volcano, as well as three magmatic intrusions that occurred in 2012. We use probabilistic sensitivity kernels to locate the places of the highest dynamics within the magmatic accumulation zone and the extinct volcanic area of Tiñor that might have acted as stress barriers, guiding the magma from the North of El Hierro Island to the final eruption site at the South. Our results highlight the potential of ambient noise methods to monitor volcanic hazard and unrest even with sparse data sets and limited knowledge of the region.

Lithostratigraphy, geology and geochemistry of the volcanic rocks of the Maligât Formation and associated intrusions on Disko and Nuussuaq, Paleocene of West Greenland

The Paleocene volcanic rocks in the Nuussuaq Basin on Disko and Nuussuaq comprise the picritic Vaigat Formation (c. 62–61 Ma) and the overlying basaltic Maligât Formation (c. 60 Ma). The Maligât Formation is up to 2000 m thick on western Disko where the top of the formation is least eroded. The formation is divided into four members, the Rinks Dal, Nordfjord, Niaqussat and Sapernuvik members, which are formally defined here. On central and eastern Disko and Nuussuaq the Maligât Formation lavas are interbedded with fluvial and lacustrine sandstones and mudstones of the Atanikerluk Formation.The Rinks Dal Member is the lowest member and originally constituted around 61% by volume of the formation. It is divided into 12 informal units based on chemically recognisable oscillations in the fractionation state of the basalts. The oldest units are present on central and south Disko close to the Disko Gneiss Ridge. The younger lavas spread farther to the east, north and west, filled the Assoq Lake basin east of the ridge and gradually onlapped the shield of the earlier Vaigat Formation that rose to the north. Only the lavas of the upper Rinks Dal Member reached far into Nuussuaq. The lavas are generally not crustally contaminated and comprise evolved basalts with 4.4–9.2 wt% MgO and a few picrites. The most evolved basalts with 3.2–4.8 wt% TiO2 occur in the middle part of the member where they form the Akuarut unit.
 The Nordfjord Member originally constituted around 6% by volume of the formation. It is not subdivided because the lithological variability is local. The member is widespread but has its depocentre on north-western Disko where thicknesses reach 350 m and eruption sites, intermediate lavas and acid tuffs are present. Over most of the area the member consists of just a few lava flows with combined thicknesses of 30–100 m. The member has a very diverse lithology with rock types ranging from silicic basalt with 5.3–10.0 wt% MgO through magnesian basaltic andesite and andesite with 2.4–10.6 wt% MgO to dacite with 1.2–2.2 wt% MgO. Rhyolite with 0.2–1.2 wt% MgO and up to 77 wt% SiO2 occur in tuffs and conglomerate clasts. All rocks are crustally contaminated and some are native-iron-bearing.
 The Niaqussat Member originally constituted around 33% by volume of the formation. It is subdivided into three informal units. The member is widespread, but much of it has been removed by erosion. Lithologies in the lower unit range from silicic picrite with up to 15 wt% MgO to basalt with 6–12 wt% MgO and a few basaltic andesite flows. The middle and upper parts of the Niaqussat Member comprise more evolved basalts with respectively 6.1–7.2 wt% MgO and 4.9–6.4 wt% MgO. All rocks are crustally contaminated and a few lava flows are native-iron-bearing.
 The Sapernuvik Member comprises three uncontaminated basalt flows with 7.5–10.7 wt% MgO. It is only preserved in a small area on western Disko.
 Dyke systems with up to 80 km long dykes and subvolcanic intrusions associated with the Nordfjord and Niaqussat members occur on western and north-eastern Disko. The rocks are crustally contaminated and range from silicic basalt with 4–13 wt% MgO to magnesian andesite with 3–10 wt% MgO. They commonly form composite intrusions, some of which contain accumulations of native iron and sulfides.
 The contaminants are carbon- and sulfur-bearing sediments of the Nuussuaq Group. Major contamination mechanisms were mixing with partial melts from the sediment sidewall and xenoliths and selective exchange of some elements, including carbon and sulfur, between magma and sediment. Degrees of contamination vary from 2−5% in the basalts to 10−50% in the more silicic rocks. No rocks more evolved than basalt were produced by ordinary fractional crystallisation.

Petrology and geochemistry of the 2014–2015 Holuhraun eruption, central Iceland: compositional and mineralogical characteristics, temporal variability and magma storage

The 2014–2015 Holuhraun fissure eruption provided a rare opportunity to study in detail the magmatic processes and magma plumbing system dynamics during a 6-month-long, moderate- to large-volume basaltic fissure eruption. In this contribution, we present a comprehensive dataset, including major and trace elements of whole-rock and glassy tephra samples, mineral chemistry, and radiogenic and oxygen isotope analyses from an extensive set of samples (n = 62) that were collected systematically in several field campaigns throughout the entire eruptive period. We also present the first detailed chemical and isotopic characterization of magmatic sulfides from Iceland. In conjunction with a unique set of geophysical data, our approach provides a detailed temporal and spatial resolution of magmatic processes before and during this eruption. The 2014–2015 Holuhraun magma is compositionally indistinguishable from recent basalts erupted from the Barðarbunga volcanic system, consistent with seismic observations for magma ascent close to the Barðarbunga central volcano, followed by dyke propagation to the Holuhraun eruption site. Whole-rock elemental and isotopic compositions are remarkably constant throughout the eruption. Moreover, the inferred depth of the magma reservoir tapped during the eruption is consistently 8 ± 5 km, in agreement with geodetic observations and melt inclusion entrapment pressures, but inconsistent with vertically extensive multi-tiered magma storage prior to eruption. The near constancy in the chemical and isotopic composition of the lava is consistent with the efficient homogenization of mantle-derived compositional variability. In contrast, occurrence of different mineral populations, including sulfide globules, which display significant compositional variability, requires a more complex earlier magmatic history. This may include sampling of heterogeneous mantle melts that mixed, crystallized and finally homogenized at mid- to lower-crustal conditions.

Long-range transport of volcanic aerosols over South Africa: a case study of the Calbuco volcanic eruption in Chile during April 2015

ABSTRACTIn response to the observation of a large amount of sulphur dioxide (SO2) over the Republic of South Africa (RSA) during April 2015, the present study was formulated to explain the origin and contributing factors to such an increase. The Calbuco volcanic eruption in Chile occurred on 22 and 23 April 2015 and this study investigates the possible transport of SO2 and volcanic aerosols from the eruption site to RSA with the aid of model and satellite data. Time-averaged maps of SO2 and aerosol optical depth (AOD) from the Ozone Monitoring Instrument (OMI) and the Moderate Resolution Imaging Spectroradiometer (MODIS), showed SO2 and AOD leaving Calbuco and reaching RSA on 28 April 2015. The Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model forward trajectories showed that air masses, in the altitude range from 15 to 20 km, left the eruption site and travelled towards RSA. The zonal extinction coefficient profiles and total backscatter height-time-colour map from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) also confirmed the presence of volcanic aerosols from 28 April 2015 to 16 May 2015. The stratospheric feature observed by CALISO vertical feature mask (VFM) confirmed that these were indeed volcanic aerosols.

Temporal change of upper-crustal [formula omitted] ratios with volcanic evolution in Redoubt Volcano

Volcanic activities accompany changes in the physical and chemical properties of the medium. The ratio between P- and S-wave velocities, VP/VS, is sensitive to the medium property changes. We investigate temporal variations of the VP/VS ratios in the upper crust around Redoubt Volcano in the 1989–2014 time period using the traveltimes of local earthquakes. The VP/VS ratios reached ∼2.0 immediately prior to the 1989–1990 and 2009 eruptions. These high VP/VS ratios may be associated with partial melts in the edifice. The VP/VS ratios rapidly decreased to ∼1.7 during the 1989–1990 and 2009 eruptions due to decreasing temperatures, fluids, and pore pressures and increasing effective stresses after melt eruptions and gas emission. The change rates of the VP/VS ratios showed evident spatial distributions. The VP/VS ratios increased at a rate of 0.025 (±0.003) yr−1 below the 2009 vent during the inter-eruption period between the 1989–1990 and 2009 eruptions due to an increase in the temperature, which may be associated with the recharge of the magma in the lower crust. The increase rate of the VP/VS ratios was as low as 0.005 (±0.001) yr−1 in the regions located away from the eruption site. The VP/VS ratios appear to have increased consistently at a rate of 0.017 (±0.004) yr−1 since the 2009 eruption.

REFIR- A multi-parameter system for near real-time estimates of plume-height and mass eruption rate during explosive eruptions

Meaningful forecasting of the atmospheric concentration and ground accumulation of volcanic ash during explosive eruptions requires detailed knowledge of the eruption source parameters. However, due to the large uncertainties in observations and limitations of current models used to make inferences from these, monitoring an ongoing eruption and quantifying the mass eruption rate in real-time is a considerable challenge. Within the EU supersite project “FutureVolc”, an integrated approach has been applied to develop a quasi-autonomous multi-parameter system, denoted “REFIR”, for monitoring volcanic eruptions in Iceland and assessing the eruption mass flow rate by inverting the plume height information and taking account of these uncertainties. REFIR has the capability to ingest and process streaming plume-height data provided by a multitude of ground based sensors, including C– and X-band radars and web-cam based plume height tracking systems. These observational data are used with a suite of plume models that also consider the current wind and other atmospheric conditions, providing statistically assessed best estimates of plume height and mass eruption rate. Provided instrumental data is available, near real-time estimates are obtained (the delay corresponding to the scan rate of data-providing instruments, presently of the order of minutes). Using the Hekla 2000, and Eyjafjallajökull 2010 eruptions in Iceland, the potential of REFIR is demonstrated and discussed through application to three scenarios. The system has been developed to provide maximum flexibility. A setup script assists the user in adapting to local conditions, allowing implementation of REFIR for any volcanic eruption site worldwide. REFIR is designed to be easily upgradable, allowing future extension of monitoring networks, learning from new events, and incorporation of new technologies and model improvements. This article gives an overview of the basic structure, models implemented, functionalities and the computational techniques of REFIR.

Deep hydrothermal activity driving the Lusi mud eruption

The Lusi mud eruption in East Java continues unabated after more than a decade of activity as a pulsating geyser system bursting mud, clasts, water, and gas. The origin of the fluids and their properties at depth are not well constrained, thus hampering our understanding and modelling of the system. Previous geochemical and geophysical studies show that Lusi is a sediment-hosted hydrothermal system with two sources of mud at depths between 0.3–2 km and another between 3.5–4.75 km. Here, we present results of mineral thermometry using Raman spectroscopy and chlorite composition on clasts erupted at Lusi. The results show that some of these specimens originate from the two main fluid sources, and at depths consistent with the geochemical and geophysical interpretation. Two main clast lithotypes erupt at Lusi. The first lithotype is a light grey shale returned to the surface from the Upper Kalibeng Formation (the primary mud source) and equilibrated at temperatures below 200 °C. The second lithotype is a black shale, whose source is the Ngimbang Formation at >3800 m depth. Two distinct temperature clusters are recorded in these black shales: one at 179±17 °C, consistent with the temperature estimate at 3800 m depth with the pre-eruption geothermal gradient, while younger minerals in the same specimen recorded substantial anomalous heating at ∼250 °C. These high temperatures indicate interaction with a heat source associated with the eruption through mixing with hydrothermal fluids. This temperature jump suggests rapid heating at ∼4000 m depth, consistent with a scenario of a magmatic intrusion and hydrothermal fluids circulation. This rapid and significant temperature increase would initiate devolatilisation reactions of hydrous minerals within the deep sedimentary package and generate substantial (highly overpressured) fluids at depths significantly below the main source of erupted mud. We infer that reactive and thermal pressurisation led to a deep and metastable system susceptible to e.g. seismic activity ultimately opening fluid pathways towards the surface along the Watukosek fault system. The two temperatures clusters recorded in the clasts show that conductive heat flow was the dominant heat transport prior to the eruption, while the system is now driven by large-scale convection and advective heat transport. The Lusi eruption occurred in a highly populated area forcing the evacuation of several tens of thousands of people. This system appears unstoppable and poses a real and present hazard for the settlements still surrounding the eruption site. Continuous research is necessary to understand this spectacular phenomenon, both for its important scientific relevance, and the societal impact of this natural disaster.

Thermal power of Grímsvötn, Iceland, from 1998 to 2016: Quantifying the effects of volcanic activity and geothermal anomalies

Grímsvötn lies beneath the centre of the Vatnajökull ice cap, Iceland, and has for centuries been one of the most geothermally active calderas in the world as well as being Iceland's most active volcano. Calorimetric studies of its heat output have suggested long-term heat release of 2–4 GW. We have performed a detailed study of the heat release at Grímsvötn over the period 1998–2016, which includes the eruptions of 1998, 2004 and 2011. Annual mapping of the ice surface is used to monitor ice volume changes, combined with results of mass-balance monitoring over this same period. We estimate an average heat release of 1800 ± 200 MW, whereof about ~1200 MW is the base geothermal heat flux. The remaining ~600 MW is an average over the study period, composed of peaks above the base flux from melting during eruptions and geothermal anomalies. The most intense melting occurred at eruption sites during eruptions. Less intense signals lasting several months to years were due to increased geothermal melting creating new ice cauldrons and deepening pre-existing ones. Such thermal anomalies were observed both as precursors to the eruptions, and in the 2–3 years following. The strongest signal followed the 1998 eruption which produced an average of 650 MW in the two years following. After the 2004 eruption a thermal anomaly of 500 MW was observed in the following years, and an average signal of 450 MW followed the 2011 eruption. These thermal signals demonstrate a post-eruption link to increased geothermal activity at the caldera walls.

Mass transfer processes in a post eruption hydrothermal system: Parameterisation of microgravity changes at Te Maari craters, New Zealand

Fluid transfer and ground deformation at hydrothermal systems occur both as a precursor to, or as a result of, an eruption. Typically studies focus on pre-eruption changes to understand the likelihood of unrest leading to eruption; however, monitoring post-eruption changes is important for tracking the return of the system towards background activity. Here we describe processes occurring in a hydrothermal system following the 2012 eruption of Upper Te Maari crater on Mt Tongariro, New Zealand, from observations of microgravity change and deformation. Our aim is to assess the post-eruption recovery of the system, to provide a baseline for long-term monitoring. Residual microgravity anomalies of up to 92 ± 11 μGal per year are accompanied by up to 0.037 ± 0.01 m subsidence. We model microgravity changes using analytic solutions to determine the most likely geometry and source location. A multiobjective inversion tests whether the gravity change models are consistent with the observed deformation. We conclude that the source of subsidence is separate from the location of mass addition. From this unusual combination of observations, we develop a conceptual model of fluid transfer within a condensate layer, occurring in response to eruption-driven pressure changes. We find that depressurisation drives the evacuation of pore fluid, either exiting the system completely as vapour through newly created vents and fumaroles, or migrating to shallower levels where it accumulates in empty pore space, resulting in positive gravity changes. Evacuated pores then collapse, causing subsidence. In addition we find that significant mass addition occurs from influx of meteoric fluids through the fractured hydrothermal seal. Long-term combined microgravity and deformation monitoring will allow us to track the resealing and re-pressurisation of the hydrothermal system and assess what hazard it presents to thousands of hikers who annually traverse the volcano, within 2 km of the eruption site.

EVIDENCE FOR THE MAGNETIC BREAKOUT MODEL IN AN EQUATORIAL CORONAL-HOLE JET.

Small, impulsive jets commonly occur throughout the solar corona, but are especially visible in coronal holes. Evidence is mounting that jets are part of a continuum of eruptions that extends to much larger coronal mass ejections and eruptive flares. Because coronal-hole jets originate in relatively simple magnetic structures, they offer an ideal testbed for theories of energy buildup and release in the full range of solar eruptions. We analyzed an equatorial coronal-hole jet observed by SDO/AIA on 09 January 2014, in which the magnetic-field structure was consistent with the embedded-bipole topology that we identified and modeled previously as an origin of coronal jets. In addition, this event contained a mini-filament, which led to important insights into the energy storage and release mechanisms. SDO/HMI magnetograms revealed footpoint motions in the primary minority-polarity region at the eruption site, but show negligible flux emergence or cancellation for at least 16 hours before the eruption. Therefore, the free energy powering this jet probably came from magnetic shear concentrated at the polarity inversion line within the embedded bipole. We find that the observed activity sequence and its interpretation closely match the predictions of the breakout jet model, strongly supporting the hypothesis that the breakout model can explain solar eruptions on a wide range of scales.

The structure of composite volcanoes unravelled by analogue modelling: A review

Volcanic edifices are unstable accumulations of eruptive and intrusive products with complex internal structures. A documentation of these structures facilitates the assessing of the various hazards associated with volcanoes, e.g. flanks instabilities and eruptive events. However, structures are not easily assessed in the field, as volcanoes are regularly covered by eruptive products and are rapidly eroded. In the case of recent and active volcanoes, internal structures are generally extrapolated from the external morphology of the edifice, which can be documented using Digital Elevation Models (DEM) and geodetic data. Interpretation of such data greatly benefits from analogue models, which are idealised representations of reality used to test the impact that various processes may have on the shape of a volcanic edifice. This short review focuses on the contribution of analogue models to our comprehension of the internal structure of composite volcanic cones. The other volcanic morphologies (e.g. caldera) are excluded from this review, as they have distinct structure and evolution that have already been thoroughly reviewed. The reviewed models were used to investigate the impact that regional faults, magma injections and ductile substratum, among other processes, have on the internal structure and surface morphology of many volcanic edifices. These models were also used to locate unstable flanks and eruption sites.

Melt inclusion constraints on petrogenesis of the 2014\u20132015 Holuhraun eruption, Iceland

The 2014–2015 Holuhraun eruption, on the Bárðarbunga volcanic system in central Iceland, was one of the best-monitored basaltic fissure eruptions that has ever occurred, and presents a unique opportunity to link petrological and geochemical data with geophysical observations during a major rifting episode. We present major and trace element analyses of melt inclusions and matrix glasses from a suite of ten samples collected over the course of the Holuhraun eruption. The diversity of trace element ratios such as La/Yb in Holuhraun melt inclusions reveals that the magma evolved via concurrent mixing and crystallization of diverse primary melts in the mid-crust. Using olivine–plagioclase–augite–melt (OPAM) barometry, we calculate that the Holuhraun carrier melt equilibrated at 2.1 ± 0.7 kbar (7.5 ± 2.5 km), which is in agreement with the depths of earthquakes (6 ± 1 km) between Bárðarbunga central volcano and the eruption site in the days preceding eruption onset. Using the same approach, melt inclusions equilibrated at pressures between 0.5 and 8.0 kbar, with the most probable pressure being 3.2 kbar. Diffusion chronometry reveals minimum residence timescales of 1–12 days for melt inclusion-bearing macrocrysts in the Holuhraun carrier melt. By combining timescales of diffusive dehydration of melt inclusions with the calculated pressure of H2O saturation for the Holuhraun magma, we calculate indicative magma ascent rates of 0.12–0.29 m s−1. Our petrological and geochemical data are consistent with lateral magma transport from Bárðarbunga volcano to the eruption site in a shallow- to mid-crustal dyke, as has been suggested on the basis of seismic and geodetic datasets. This result is a significant step forward in reconciling petrological and geophysical interpretations of magma transport during volcano-tectonic episodes, and provides a critical framework for the interpretation of premonitory seismic and geodetic data in volcanically active regions.

Hydrothermal Alteration of Basaltic Rocks at Eruptive Vents on Mount Cameroon Volcano, West Africa

The study of changes in rocks due to interaction with hydrothermal fluids at active volcanoes provides insights into wall rock alteration associated with ore deposits formed in the geological past. Therefore, the nature of mineral alteration and chemical changes experienced by wall rocks can be investigated at eruptive sites on active volcanoes and the results used to better constrain ore-forming processes. In this study, we investigated the alteration at eruptive sites at Mount Cameroon volcano. These eruptive vents lie along NE-SW-trending fissures that define the Mount Cameroon rift. The vents are surrounded by cones composed largely of pyroclastic materials and to a lesser extent lava. Fumaroles (volcanic gases) rising through the vents during and after the 1999 eruption have resulted in the alteration of the pyroclastic robble along the fissures and the inner walls of the cones. Consequently, altered basaltic materials are covered with thin films of reddish, yellowish to whitish secondary minerals. These coatings result from an interaction between the surfaces of the basaltic glass with volcanically-derived acidic fluids. Petrographic investigations and XRD analysis of the basalts have identified primary mineral phases, such as olivine, pyroxene (mainly augite) and feldspars. Alteration products revealed include ubiquitous silica as well as gypsum, magnetite, feldspar, alunite and jarosite. Jarosite occurrence indicates that SO2 is the primary volcanically-derived acid source involved in coating formation. High contents of sulfur identified in the basalts indicate that melts at Mount Cameroon can be sulfur saturated as backed by previous melt inclusion data. Whole rock geochemical analysis shows a gain in silica in the altered samples and this ties with the mass balance calculations although minor gains of Al2O3, , MgO, MnO, CaO and K2O are shown by some samples.

Seismic Amplitude Ratio Analysis of the 2014–2015 Bárarbunga‐Holuhraun Dike Propagation and Eruption

AbstractMagma is transported in brittle rock through dikes and sills. This movement may be accompanied by the release of seismic energy that can be tracked from the Earth's surface. Locating dikes and deciphering their dynamics is therefore of prime importance in understanding and potentially forecasting volcanic eruptions. The Seismic Amplitude Ratio Analysis (SARA) method aims to track melt propagation using the amplitudes recorded across a seismic network without picking the arrival times of individual earthquake phases. This study validates this methodology by comparing SARA locations (filtered between 2 and 16 Hz) with the earthquake locations (same frequency band) recorded during the 2014–2015 Bár arbunga‐Holuhraun dike intrusion and eruption in Iceland. Integrating both approaches also provides the opportunity to investigate the spatiotemporal characteristics of magma migration during the dike intrusion and ensuing eruption. During the intrusion SARA locations correspond remarkably well to the locations of earthquakes. Several exceptions are, however, observed. (1) A low‐frequency signal was possibly associated with a subglacial eruption on 23 August. (2) A systematic retreat of the seismicity was also observed to the back of each active segment during stalled phases and was associated with a larger spatial extent of the seismic energy source. This behavior may be controlled by the dike's shape and/or by dike inflation. (3) During the eruption SARA locations consistently focused at the eruptive site. (4) Tremor‐rich signal close to ice cauldrons occurred on 3 September. This study demonstrates the power of the SARA methodology, provided robust site amplification; Quality Factors and seismic velocities are available.