Active Volcanic Vents Research Articles

Automatic Detection of the Explosive Activity of the Mt. Etna Volcano through Doppler Radar Monitoring

Improving the capability to detect volcanic explosive activity could be strategic for the task of a volcano observatory to inform civil protection authorities and air traffic controllers. The detection of explosive volcanic activity can be done in real time and also under bad visibility conditions by using the radar remote sensing technique. Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo (INGV-OE) installed an S-band pulse Doppler radar in a shelter located at about 3 km south of the active volcanic vents in order to enhance the Etna volcano’s surveillance. Here, we describe the realisation of a system that exploits such device, aimed at continuously monitoring the explosive eruptive activity at the Mt. Etna summit craters through an automatic processing flow of the radar data. We analysed the signals recorded during 23 eruptive episodes that occurred at the Etna South-East Crater during the second half of 2021; these episodes were characterised by an opening Strombolian activity and the subsequent evolution into a lava fountain. To identify the onset of both volcanic phenomena, empirical thresholds of radar time series were extracted with the help of thermal and visible images acquired by the INGV-OE cameras’ network. The resulting monitoring tool automatically operates 24/7 for volcanic surveillance, providing real-time data to the INGV-OE control room.

Maximum-Likelihood Retrieval of Volcanic Ash Concentration and Particle Size From Ground-Based Scanning Lidar

An inversion methodology, named maximum-likelihood (ML) volcanic ash light detection and ranging (Lidar) retrieval (VALR-ML), has been developed and applied to estimate volcanic ash particle size and ash mass concentration within volcanic plumes. Both estimations are based on the ML approach, trained by a polarimetric backscattering forward model coupled with a Monte Carlo ash microphysical model. The VALR-ML approach is applied to Lidar backscattering and depolarization profiles, measured at visible wavelength during two eruptions of Mt. Etna, Catania, Italy, in 2010 and 2011. The results are compared with those of ash products derived from other parametric retrieval algorithms. A detailed comparison among these different retrieval techniques highlights the potential of VALR-ML to determine, on the basis of a physically consistent approach, the ash cloud area that must be interdicted to flight operations. Moreover, the results confirm the usefulness of operating scanning Lidars near active volcanic vents.

Features of Large Magmatic–Hydrothermal Systems in Japan: Characteristics Similar to the Tops of Porphyry Copper Deposits

AbstractVolcanic complexes in Japan such as Kusatsu Shirane, Honshu, and Kuju‐Hatchobaru and Kirishima, Kyushu, host active magmatic–hydrothermal systems that are several kilometers in diameter and typically asymmetric to the intrusive center. Their heat flow is driven by multiple intrusions at <5–10 km depth over a period on the order of ~105 years. These hydrothermal systems consist of advecting fluids of magmatic origin (either vapor with acidic components condensed into meteoric water, or a subsequent liquid of varying reactivity) that interact with convecting meteoric water. The amount of the magmatic component depends on location relative to the intrusive center, local controls on permeability, and the temporal evolution of the intrusions. The proportion of meteoric water diluent typically increases from proximal to distal locations (over several kilometer distance), and with time after intrusion (> several thousands of years). Some of the neutral pH solutions in these large hydrothermal systems, up to ~5 km from volcanic vents, support geothermal energy developments, with strong structural control on fluid flow. Near active volcanic vents, the magmatic vapor component of hydrothermal systems can form acidic condensates (pH ~ 1.5) that are responsible for strong alteration of the host rock. The resulting residual quartz and advanced argillic minerals are typical of shallow‐formed lithocap alteration that is associated with deeper porphyry copper deposits in similar arc‐hosted volcanic settings. Around the world, this near‐surface lithocap alteration, influenced by structures as well as lithology, may be barren in metals, even where associated with mineralized porphyry intrusions at depth. Such intrusion‐proximal alteration is widespread in both active and extinct settings in Japan. In addition, distal geothermal hot springs typically have a magmatic water component, albeit minor, with a pH that varies from ~3 to near‐neutral; deep alteration intersected in drill holes is characterized by alunite–dickite–pyrophyllite or chlorite–wairakite, respectively. These alteration assemblages are typical of their extinct equivalents, intermediate sulfidation epithermal veins, with mineralogical complexities caused by temporal evolution as well as spatial variation (e.g. along different structures). Such active and extinct magmatic–hydrothermal systems signify the presence of shallow degassing or degassed intrusions, respectively. Where similar intrusions in volcanic arcs around the world are eroded to ~1 to 2 km depth, the tops of porphyry copper deposits are commonly exposed, marked by a transition of white mica upward to pyrophyllite‐dominant alteration. Active magmatic–hydrothermal systems on the flanks of arc volcanoes in Japan are dynamic – both cycling as well as evolving – and share characteristics with extinct systems that host epithermal and porphyry ore deposits.

Sensitivity to lunar cycles prior to the 2007 eruption of Ruapehu volcano

A long-standing question in Earth Science is the extent to which seismic and volcanic activity can be regulated by tidal stresses, a repeatable and predictable external excitation induced by the Moon-Sun gravitational force. Fortnightly tides, a ~14-day amplitude modulation of the daily tidal stresses that is associated to lunar cycles, have been suggested to affect volcano dynamics. However, previous studies found contradictory results and remain mostly inconclusive. Here we study how fortnightly tides have affected Ruapehu volcano (New Zealand) from 2004 to 2016 by analysing the rolling correlation between lunar cycles and seismic amplitude recorded close to the crater. The long-term (~1-year) correlation is found to increase significantly (up to confidence level of 5-sigma) during the ~3 months preceding the 2007 phreatic eruption of Ruapehu, thus revealing that the volcano is sensitive to fortnightly tides when it is prone to explode. We show through a mechanistic model that the real-time monitoring of seismic sensitivity to lunar cycles may help to detect the clogging of active volcanic vents, and thus to better forecast phreatic volcanic eruptions.

3‐D high‐speed imaging of volcanic bomb trajectory in basaltic explosive eruptions

AbstractImaging, in general, and high speed imaging in particular are important emerging tools for the study of explosive volcanic eruptions. However, traditional 2‐D video observations cannot measure volcanic ejecta motion toward and away from the camera, strongly hindering our capability to fully determine crucial hazard‐related parameters such as explosion directionality and pyroclasts' absolute velocity. In this paper, we use up to three synchronized high‐speed cameras to reconstruct pyroclasts trajectories in three dimensions. Classical stereographic techniques are adapted to overcome the difficult observation conditions of active volcanic vents, including the large number of overlapping pyroclasts which may change shape in flight, variable lighting and clouding conditions, and lack of direct access to the target. In particular, we use a laser rangefinder to measure the geometry of the filming setup and manually track pyroclasts on the videos. This method reduces uncertainties to 10° in azimuth and dip angle of the pyroclasts, and down to 20% in the absolute velocity estimation. We demonstrate the potential of this approach by three examples: the development of an explosion at Stromboli, a bubble burst at Halema'uma'u lava lake, and an in‐flight collision between two bombs at Stromboli.

Volcanic morphology of West Mata Volcano, NE Lau Basin, based on high-resolution bathymetry and depth changes

High-resolution (1.5 m) mapping from the autonomous underwater vehicle (AUV) D. Allan B. of West Mata Volcano in the northern Lau Basin is used to identify the processes that construct and modify the volcano. The surface consists largely of volcaniclastic debris that forms smooth slopes to the NW and SE, with smaller lava flows forming gently sloping plateaus concentrated along the ENE and WSW rift zones, and more elongate flows radiating from the summit. Two active volcanic vents, Prometheus and Hades, are located ∼50 and ∼150 m WSW of the 1159 m summit, respectively, and are slightly NW of the ridgeline so the most abundant clastic deposits are emplaced on the NW flank. This eruptive activity and the location of vents appears to have been persistent for more than a decade, based on comparison of ship-based bathymetric surveys in 1996 and 2008–2010, which show positive depth changes up to 96 m on the summit and north flank of the volcano. The widespread distribution of clastic deposits downslope from the rift zones, as well as from the current vents, suggests that pyroclastic activity occurs at least as deep as 2200 m. The similar morphology of additional nearby volcanoes suggests that they too have abundant pyroclastic deposits.

Major and trace element distributions around active volcanic vents determined by analyses of grasses: implications for element cycling and bio-monitoring

Samples of grass were collected at Masaya Volcano (Nicaragua; Rhynchelytrum repens and Andropogon angustatus) and the Piton de La Fournaise (around the April 2007 eruptive vent, La Reunion; Vetiveria zizanioides) to investigate the controls on major and trace element concentrations in plants around active volcanic vents. Samples were analysed using inductively coupled plasma mass spectrometry for a wide range of elements, and atomic absorption spectroscopy for Hg. At Masaya, As, Cu, Mo, Tl and K concentrations in both grass species showed a simple pattern of variability consistent with exposure to the volcanic plume. Similar variability was found in A. angustatus for Al, Co, Cs, Hg and Mg. At the Piton de La Fournaise, the patterns of variability in V. zizanioides were more complex and related to variable exposures to emissions from both the active vent and lava flow. These results suggest that exposure to volcanic emissions is, for many elements, the main control on compositional variability in vegetation growing on active volcanoes. Thus, vegetation may be an important environmental reservoir for elements emitted by volcanoes and should be considered as part of the global biogeochemical cycles.

DUCKS: Low cost thermal monitoring units for near-vent deployment

During 1999 we designed and tested a thermal monitoring system to provide a cheap, robust, modular, real-time system capable of surviving the hostile conditions encountered proximal to active volcanic vents. In November 2000 the first system was deployed at Pu'u 'O'o (Kilauea, Hawai'i) to target persistently active vents. Aside from some minor problems, such as sensor damage due to tampering, this system remained operational until January 2004. The success of the prototype system led us to use the blueprint for a second installation at Stromboli (Aeolian Islands, Italy). This was deployed, dug into a bomb-proof bunker, during May 2002 and survived the April 2003 paroxysmal eruption despite being located just 250 m from the vent. In both cases, careful waterproofing of connectors and selection of suitable protection has prevented water damage and corrosion in the harsh atmosphere encountered at the crater rim. The Pu'u 'O'o system cost ∼US$10,000 and comprises four modules: sensors, transmission and power hub, repeater station and reception site. The sensor component consists of three thermal infrared thermometers housed in Pelican™ cases fitted with Germanium–Arsenide–Selenium windows. Two 1° field of view (FOV) sensors allow specific vents to be targeted and a 60° FOV sensor provides a crater floor overview. A hard wire connection links to a Pelican™-case-housed microprocessor, modem and power module. From here data are transmitted, via a repeater site, to a dedicated PC at the Hawaiian Volcano Observatory. Here data are displayed with a delay of ∼3 s between acquisition and display. The modular design allows for great flexibility. At Stromboli, 1° and 15° FOV sensor modules can be switched depending changes in activity style and crater geometry. In addition a direct line of site to the Stromboli reception center negates the repeater site requirement, reducing the cost to US$5500 for a single sensor system. We have also constructed self-contained units with internal data loggers for US$1500/unit. These have been tested at Kilauea, Stromboli, Etna, Masaya, Santiaguito, Fuego, Pacaya, Poas, Soufriere Hills, Villarrica and Erta Ale. These instruments have proved capable of detecting thermal signals associated with: (1) gas emission; (2) gas jetting events; (3) crater floor collapse; (4) lava effusion; (5) lava flow in tubes; (6) lava lake activity; (7) lava dome activity; and (8) crater lake skin temperature.

Active Volcanism on Io as Seen by Galileo SSI

Active volcanism on Io has been monitored during the nominal Galileo satellite tour from mid 1996 through late 1997. The Solid State Imaging (SSI) experiment was able to observe many manifestations of this active volcanism, including (1) changes in the color and albedo of the surface, (2) active airborne plumes, and (3) glowing vents seen in eclipse.About 30 large-scale (tens of kilometers) surface changes are obvious from comparison of the SSI images to those acquired by Voyager in 1979. These include new pyroclastic deposits of several colors, bright and dark flows, and caldera-floor materials. There have also been significant surface changes on Io during the Galileo mission itself, such as a new 400-km-diameter dark pyroclastic deposit around Pillan Patera. While these surface changes are impressive, the number of large-scale changes observed in the four months between the Voyager 1 and Voyager 2 flybys in 1979 suggested that over 17 years the cumulative changes would have been much more impressive. There are two reasons why this was not actually the case. First, it appears that the most widespread plume deposits are ephemeral and seem to disappear within a few years. Second, it appears that a large fraction of the volcanic activity is confined to repeated resurfacing of dark calderas and flow fields that cover only a few percent of Io's surface.The plume monitoring has revealed 10 active plumes, comparable to the 9 plumes observed by Voyager. One of these plumes was visible only in the first orbit and three became active in the later orbits. Only the Prometheus plume has been consistently active and easy to detect. Observations of the Pele plume have been particularly intriguing since it was detected only once by SSI, despite repeated attempts, but has been detected several times by the Hubble Space Telescope at 255 nm. Pele's plume is much taller (460 km) than during Voyager 1 (300 km) and much fainter at visible wavelengths. Prometheus-type plumes (50–150 km high, long-lived, associated with high-temperature hot spots) may result from silicate lava flows or shallow intrusions interacting with near-surface SO2.A major and surprising result is that ∼30 of Io's volcanic vents glow in the dark at the short wavelengths of SSI. These are probably due to thermal emission from surfaces hotter than 700 K (with most hotter than 1000 K), well above the temperature of pure sulfur volcanism. Active silicate volcanism appears ubiquitous. There are also widespread diffuse glows seen in eclipse, related to the interaction of energetic particles with the atmosphere. These diffuse glows are closely associated with the most active volcanic vents, supporting suggestions that Io's atmopshere is dominated by volcanic outgassing.Globally, volcanic centers are rather evenly distributed. However, 14 of the 15 active plumes seen by Voyager and/or Galileo are within 30° of the equator, and there are concentrations of glows seen in eclipse at both the sub- and antijovian points. These patterns might be related to asthenospheric tidal heating or tidal stresses. Io will continue to be observed during the Galileo Europa Mission, which will climax with two close flybys of Io in late 1999.

Redistribution of Pb and other volatile trace metals during eruption, devitrification, and vapor-phase crystallization of the Bandelier Tuff, New Mexico

A diverse suite of micron-scale minerals was deposited from vapor during eruption and post-emplacement crystallization of the Bandelier Tuff, New Mexico. The mineral suite is rich in sulfides, oxides, and chlorides of both common and rare metals (e.g., Fe, Pb, Bi, Cu, Ag, Re), and oxides and silicates of incompatible elements (e.g., P, Zr, Y, Nb, Ba and LREE). Minerals preserved in glassy samples grew from magmatic vapor trapped during emplacement, or from vapor migrating along contacts with more impermeable rocks; minerals observed in devitrified samples also grew from crystallization of glass and vapor liberated during this process. In devitrified samples, mafic silicate phenocrysts were partially replaced by an assemblage dominated by smectite and hematite. The syn- to post-eruptive mineral assemblage observed in upper Bandelier Tuff (UBT) samples bears striking similarity to those deposited by cooling gases near active volcanic vents. However, several differences exist: (1) the mineral suite in the UBT is disseminated throughout the unit, and formed over a broad temperature range (> 700 to < 150 °C) at higher rock:gas ratios; (2) the highly evolved composition of the UBT yielded a greater abundance of minerals rich in incompatible elements compared to sublimates from less evolved volcanoes; and (3) the UBT has suffered over 1 million years of post-emplacement exposure, which resulted in solution (or local re-precipitation in fractures) of soluble compounds such as halite, sylvite, and gypsum. Pb was enriched toward the roof of the UBT magma body due to its affinity for the melt and vapor phases relative to crystals (Bulk D pb < 0.2). Micron-scale Pb minerals appear to have grown from vapor exsolved during eruption, as well as vapor liberated during later devitrification. Additional Pb was scavenged by smectite and hematite that probably formed during the later stages of the devitrification and cooling process. Up to ten-fold increases in Pb concentrations are seen in zones of fumarolic concentration in the UBT, however, most bulk tuff samples have Pb values that appear to preserve magmatic values, indicating only very local trace-metal redistribution. The concentration of Pb and other heavy metals in micron-scale mineral coatings in porous tuff indicates that these metals could be readily mobilized and transported by acidic groundwaters or hydrothermal fluids, and thus locally concentrated into ore-grade deposits in long-lived systems.

Geochemical and structural studies of the Lamont seamounts: seamounts as indicators of mantle processes

A chain of seamounts located just west of the East Pacific Rise (EPR) axis at 09°55′N (herein called the Lamont seamounts) have been investigated using Sea MARC I and Sea Beam sonar surveys, “Alvin” submersible dives, deep-sea camera tows and dredging. The most recently active volcanic vents on the summits of these volcanoes are located at the periphery of each caldera or crater rim or at the margins of caldera floors. The distribution of recent volcanic vents and the morphology of the summit plateaus suggest the possible existence of ring fractures on these seamounts. Ring fractures could be important in focusing post-caldera collapse eruptions around summit craters and building summit plateaus. Structural and morphological data and the petrology of recovered lavas suggest that calderas in the Lamont seamounts probably formed by collapse associated with magma withdrawal into large, primary vertical magma conduit systems, rather than by repeated inflation/deflation cycles associated with steady-state shallow-level magma chambers. Calderas in the Lamont seamounts have evolved through coalescence of adjoining craters and the plan-view shape and morphology of each caldera suggest that primary magma conduits have migrated beneath the summit of each seamount through time. Compared to lavas from the adjacent EPR, the majority of Lamont seamount and cone lavas are more primitive, depleted in incompatible elements and compositionally heterogeneous. Variations in light rare earth elements relative to major elements (e.g. TiO 2, Na 2O/(Na 2O + CaO) ) and radiogenic isotopes cannot be ascribed to differences in the amount of partial melting of a single N-type MORB source. Rather it appears that Lamont seamount lavas were derived from heterogeneous mantle sources variably depleted in highly incompatible elements. Comparison with lavas from the adjacent ridge crest suggests that magma plumbing and ascent mechanisms beneath the Lamont seamounts are separate from those along the EPR. In particular seamount magmas appear to reflect near-primary melting events in the mantle whereas EPR lavas are the products of shallow-level crystallization and mixing in crustal magma chambers. Absence of long-lived magma chambers within the Lamont seamounts may account for the low level of hydrothermal activity observed throughout the chain. Furthermore, because of the tight control on sample location and the recovery of lavas having distinct parents from individual volcanoes as well as the Lamont chain as a whole, we propose that the scale of mantle chemical heterogeneities is less than 5 km.