Eruption Conditions Research Articles

SURGICAL UNCOVERING AND STIMULATION OF PHYSIOLOGICAL ERUPTION OF PALATALLY IMPACTED MAXILLARY CANINES: Case reports

Introduction. The orthodontist treating patients with palatally impacted canines usually strives to build a complex treatment plan, based on uncomplicated and biological orthodontic and surgical techniques. The aim of the present report was to demonstrate by case reports the potential of the open surgical technique for stimulation of physiological eruption of palatally impacted canines. Material and methods. Three patients aged 13 to 20 years with various degrees of unilateral and bilateral palatal impaction of maxillary canines were managed by the described technique. Results and discussion. All canines underwent autonomous eruption after all soft- and hard-tissue obstructions on their paths were removed. Conclusion. The described method of surgical uncovering and autonomous eruption created conditions for biological eruption of the palatally impacted canines into the oral cavity and facilitated considerably the subsequent orthodontic treatment for their proper alignment in the dental arch.

Unique event plumes from a 2008 eruption on the Northeast Lau Spreading Center

The creation of ocean crust by lava eruptions is a fundamental Earth process, involving immediate and immense transfers of heat and chemicals from crust to ocean. This transfer creates event plumes (“megaplumes”), massive ellipsoidal eddies with distinctive and consistent chemical signatures. Here we report the discovery of unique event plumes associated with a 2008 eruption on the Northeast Lau Spreading Center. Instead of a large plume hundreds of meters thick, we detected at least eight individual plumes, each ∼50 m thick and apparently only 1–3 km in diameter, yet still rising 200–1000 m above the eruption site. Low and uniform 3He/heat (0.041 × 10−17 mol/J) and dissolved Mn/heat (0.04 nmol/J) ratios in water samples were diagnostic of event plumes. High H2 concentrations (up to 9123 nM) and basalt shards confirmed extensive interactions between molten lava and event plume source fluids. Remote vehicle observations in 2009 mapped a new, small (1.5–5.8 × 106 m3) lava flow. Our results suggest that event plumes are more variable, and thus perhaps more common, than previously recognized. Small event plumes may be preferentially associated with small or sheet-flow eruptions, and massive event plumes with slowly extruding pillow mounds 25–75 m thick. Despite this correlation, and high H2 concentrations, existing theory and seafloor observations argue that cooling lava cannot transfer heat fast enough to create the buoyancy flux required for event plumes. The creation of event plumes under a broad range of eruption conditions provides new constraints for any theory of their formation.

Evolution of the mechanics of the 2004–2008 Mt. St. Helens lava dome with time and temperature

The 2004–2008 eruption of Mount St. Helens, Washington, USA, formed a typical example of a Pelean spiny lava dome, with solid spines of crystalline silicic lava extruded along shear zones bounded by fault gouge (Cashman et al., 2008; Iverson et al., 2006). Creation of and movement along shear zones in this erupting lava, recorded as shallow micro-earthquakes, were thus key controls on eruption style and rate, in addition to dome stability. As eruption style and lava dome stability often change within individual eruptions, it is important to identify how the strength of dome rocks changes with temperature, time, texture and extrusion rate. However, critical values of the shear strength of dome lava at eruptive temperatures have never been measured. We have found in controlled laboratory experiments simulating eruption conditions that dome lava strength increased during the course of the 2004–2008 eruption of Mount St. Helens, as the textures became more crystalline and less porous. Increasing lava strength during the eruption would lead to deformation becoming increasingly localised to shear zones, explaining why the extrusion style and centre were so consistent. Acoustic emissions and microstructure analysis indicate that fracturing was more localised at higher temperatures, resulting in higher strengths at eruptive temperature compared to ambient temperatures for later erupted samples. The strength of these later erupted samples at eruptive temperatures increased markedly with strain rate. This would damp any increases in effusion rate that may result from changes in magma pressure, explaining the steady effusion rate at Mount St. Helens from 2004 to 2008.

A thin predominantly cold-based Late Miocene East Antarctic ice sheet inferred from glaciovolcanic sequences in northern Victoria Land, Antarctica

Glaciovolcanic sequences are widespread in northern Victoria Land and their interpretation enables estimates of past ice thicknesses and other defining parameters of the coeval ice sheet to be made with considerable certainty. The terrestrial sequences are mainly Late Miocene in age (c. 12–5 Ma) and conform to five main types: aa lava-fed deltas, volcanic sheet-like sequences, a glaciolacustrine sequence, scoria cones and tuff cones. Apart from the environmentally undiagnostic pyroclastic cones, the volcanic sequences were erupted in association with a glacial cover that was typically, and possibly never much more than, a few hundred metres thick (< 300 m). Despite gaps in the record, no evidence was observed for prolonged subaerial (i.e. fully ice-free) eruptive conditions, suggesting either that ice-free conditions did not occur or else were of such limited areal extent or short duration that they left no record. These observations are consistent with the presence of a thin persistent Late Miocene ice dome or icefield draping the pre-Miocene topography in northern Victoria Land for the period, although it may have been confluent with the greater East Antarctic Ice Sheet similar to conditions present today. The presence of glacially emplaced sequences right down to present datum suggests that the Transantarctic Mountains in the region were already uplifted to their current elevation prior to the volcanism. The high terrain would have helped the ice sheet to establish and persist. The glacial thermal regime varied from wet-based and dynamic, to cold-based (frozen to its bed) and presumably relatively stable. A major transition from wet-based ice to cold-based ice might have occurred between 9.7 and 7.5 Ma consistent with published interpretations of the regional landscape evolution. Alternatively, the glacial thermal regime was dominantly polar since the earliest eruptions but with several temporary changes to a wet-based (sub-polar or temperate) more dynamic regime.

Volcanic and atmospheric controls on ash iron solubility: A review

The ash material produced by volcanic eruptions carries important information about the underground magma eruptive conditions and subsequent modifications in the volcanic plume and during atmospheric transport. Volcanic ash is also studied because of its impacts on the environment and human health. In particular, there is a growing interest from a multidisciplinary scientific community to understand the role that ash deposition over open ocean regions may play as a source of bioavailable Fe for phytoplankton production. Similar to aeolian mineral dust, the processes that affect the mineralogy and speciation of Fe in ash may promote solubilisation of Fe in ash, and thus may increase the amount of volcanic Fe supplied to ocean surface waters. Our knowledge of these controls is still very limited, a situation which has hindered quantitative interpretation of experimental Fe release measurements. In this review, we identify the key volcanic and atmospheric controls that are likely to modulate ash Fe solubility. We also briefly discuss existing data on Fe release from ash and make some recommendations for future studies in this area.

Geomorphometric variability of “monogenetic” volcanic cones: Evidence from Mauna Kea, Lanzarote and experimental cones

Volcanic cones are the most common volcanic constructs on Earth. Their shape can be quantified using two morphometric ratios: the crater/cone base ratio (W cr/W co) and the cone height/width ratio (H co/W co). The average values for these ratios obtained over entire cone fields have been explained by the repose angle of loose granular material (i.e. scoria) controlling cone slopes. The observed variability in these ratios between individual cones has been attributed to the effect of erosional processes or contrasting eruptive conditions on cone morphometry. Using a GIS-based approach, high spatial resolution Digital Elevation Models and airphotos, two new geomorphometry datasets for cone fields at Mauna Kea (Hawaii, USA) and Lanzarote (Canary Islands, Spain) are extracted and analyzed here. The key observation in these datasets is the great variability in morphometric ratios, even for simple-shape and well-preserved cones. Simple analog experiments are presented to analyze factors influencing the morphometric ratios. The formation of a crater is simulated within an analog cone (i.e. a sand pile) by opening a drainage conduit at the cone base. Results from experiments show that variability in the morphometric ratios can be attributed to variations in the width, height and horizontal offset of the drainage point relative to the cone symmetry axis, to the dip of the underlying slope or to the influence of a small proportion of fine cohesive material. GIS analysis and analog experiments, together with specific examples of cones documented in the field, suggest that the morphometric ratios for well-preserved volcanic cones are controlled by a combination of 1) the intrinsic cone material properties, 2) time-dependent eruption conditions, 3) the local setting, and 4) the method used to estimate the cone height. Implications for interpreting cone morphometry solely as either an age or as an eruption condition indicator are highlighted.

Eruptive history and magmatic evolution of the 1.9 kyr Plinian dacitic Chiltepe Tephra from Apoyeque volcano in west-central Nicaragua

The youngest dacitic Plinian eruption in west-central Nicaragua, forming the 18 km3 Chiltepe Tephra (CT), occurred about nineteen hundred years ago at Apoyeque stratovolcano, which dominates the Chiltepe volcanic complex 15 km north of the capital Managua, where the CT is 2 m thick. We have traced the CT from its proximal facies at the crater rim, through the medial facies in the lowlands around Apoyeque, and to the distal facies up to 550 km offshore in the Pacific. While medial and distal facies consist of widespread Plinian fall deposits, the proximal facies reveals the complexity of this eruption, which we divide into four phases (I–IV). Interaction of rising magma with a pre-existing crater lake generated the phreatomagmatic opening phase I of the eruption, which produced ash fall with accretionary lapilli. Phase II marked a rapid change to persistent magmatic activity that yielded several large Plinian eruptions, declining through a period of unstable eruption conditions, followed by a short hiatus. Phase III began with unstable conditions, probably as a result of eastward migration and widening of the vent, leading to a second period of Plinian eruptions with three major events reaching magma discharge rates five times larger than those of phase II. Phase III again declined through unstable eruption conditions before magmatic activity terminated. Numerous explosions in the shallow hydrothermal system during the final phase IV resulted in the formation of a phreatic tuff ring on the rim of Apoyeque crater. The white, highly-vesicular, dacitic CT pumice contains plagioclase (An45–68), orthopyroxene, clinopyroxene, and minor hornblende, apatite and titanomagnetite phenocrysts. A very subordinate fraction of gray pumice has the highest crystal content, the least evolved bulk-rock, but the most evolved matrix-glass composition. The CT dacite has two unusual compositional features: (1) all white dacite has the same melt (matrix-glass) composition such that variations in bulk-rock compositions (64–68 wt% SiO2) simply reflect different phenocryst contents of 10–35%, interpreted as the result of gradual phenocryst settling in the magma chamber. (2) Abundant olivine crystals with a bimodal distribution in Mg# (modes at Mg# = 0.75 and Mg# = 0.8) are dispersed throughout the erupted dacite. These are clearly out of equilibrium with the dacitic melt and are interpreted as xenocrysts derived from the basaltic Nejapa-Miraflores volcanic lineament that intersects the Chiltepe volcanic complex and was contemporaneously active. Thermobarometric estimates place the dacitic CT magma reservoir in the upper crust (<250 MPa), with a temperature of about 890°C and about 5 wt% water dissolved in the melt. Comparing water and chlorine contents with respective solubility models suggests that volatile degassing began in the magma reservoir and triggered the CT eruption. From the vertical compositional variation pattern of the CT we deduce that the conduit tapped the magma chamber not at the top but from the side, at some deeper level, and that subsequent magma withdrawal was governed by both variations in discharge rate and possible upward migration and/or widening of the conduit entrance.

Immunolocalization and activity of the MMP-9 and MMP-2 in odontogenic region of the rat incisor tooth after post shortening procedure

MMP-9 and MMP-2 are metalloproteinases which degrade the denatured collagen fibers. However, there is no report about roles of these MMPs in the odontogenic region of the adult rat incisor tooth under different eruption conditions. Male Wistar rats were divided in a normofunctional group (NF) in which their lower teeth remained in a normal eruption. In a hypofunctional group (HP) rats underwent shortening of their lower left incisor tooth every 2days during 12days. The eruption rate as well as the expression and activities of MMP-9 and MMP-2 were evaluated using imunohistochemistry and zymography. Although the shortening increased the eruption rate, no changes in the MMP-9 and MMP-2 were observed. We conclude that in adult rats, in opposite to development of tooth, the MMP-9 and MMP-2 present in the odontogenic region does not seem to play a direct role in the remodeling matrix, even after post-shortening procedures which to lead an acceleration of the eruption process in the incisor.

Modeling of unrest signals in heterogeneous hydrothermal systems

Monitoring of quiescent volcanoes, such as Campi Flegrei (Italy), involves the measurement of geochemical and geophysical parameters that are expected to change as eruptive conditions approach. Some of these changes are associated with the hydrothermal activity that is driven by the release of heat and magmatic fluids. This work focuses on the properties of the porous medium and on their effects on the signals generated by the circulating fluids. The TOUGH2 porous media flow model is applied to simulate a shallow hydrothermal system fed by a source of magmatic fluids. The simulated activity of the source, with periods of increased fluid discharge, generates changes in gas composition, gravity, and ground deformation. The same boundary conditions and source activity were applied to simulate the evolution of homogeneous and heterogeneous systems, characterized by different rock properties. Phase distribution, fluid composition, and the related signals depend on the nature and properties of the rock sequence through which the fluids propagate. Results show that the distribution of porosity and permeability affects all the observable parameters, controlling the timing and the amplitude of their changes through space and time. Preferential pathways for fluid ascent favor a faster evolution, with larger changes near permeable channels. Slower changes over wider areas characterize less permeable systems. These results imply that monitoring signals do not simply reflect the evolution of the magmatic system: intervening rocks leave a marked signature that should be taken into account when monitoring data are used to infer system conditions at depth.

Linking experimental and natural vesicle textures in Vesuvius 79AD white pumice

Vesicle populations in volcanic pumice provide a partial record of shallow magma ascent and degassing. Here we compare pumice textures from the well-characterized 79AD Vesuvius eruption to those generated during isothermal decompression experiments. Three series of experiments were conducted using starting material from the first two phases of the eruption (eruptive units EU1 and EU2). Samples were decompressed from 100 or 150 MPa to final pressures of 10–25 MPa using conditions appropriate for simulating eruption conditions ( T = 850 °C, d P/d T = 0.25 MPa/s). The experiments differed not only in starting material but also in temperature at which samples were annealed prior to decompression, which determined the initial number of crystals present in the melt. Results show that experiments approach the vesicle number densities and sizes of pumice samples, but show narrower size distributions. The wider size range of pumice samples suggests continuous, rather than instantaneous nucleation, which may reflect non-linear rates of decompression. All experiments exhibited equilibrium degassing, a process that was probably aided by heterogeneous bubble nucleation on oxide microlites. We conclude that delayed bubble nucleation cannot explain the explosivity of the Vesuvius eruption, which instead appears to require high rates of magma decompression.

Textural studies of vesicles in volcanic rocks: An integrated methodology

Vesicles in volcanic rocks are frozen records of degassing processes in magmas. For this reason, their sizes, spatial arrangements, numbers and shapes can be linked to physical processes that drive magma ascent and eruption. Although numerous techniques have been derived to describe vesicle textures, there is no standard approach for collecting, analyzing, and interpreting vesicular samples. Here we describe a methodology for techniques that encompass the entire data acquisition process, from sample collection to quantitative analysis of vesicle size and number. Carefully chosen samples from the lower, mean and higher density/vesicularity endmembers are characterized using image nesting strategies. We show that the texture of even microvesicular samples can be fully described using less than 20 images acquired at several magnifications to cover efficiently the range of existing vesicle sizes. A new program (FOAMS) was designed to perform the quantification stage, from vesicle measurement to distribution plots. Altogether, this approach allows substantial reduction of image acquisition and processing time, while preserving enough user control to ensure the validity of obtained results. We present three cameo investigations — on basaltic lava flows, scoria deposits and pumice layers — to show that this methodology can be used to quantify a wide range of vesicle textures, which preserve information on a wide range of eruptive conditions.

Magma storage conditions of the last eruption of Teide volcano (Canary Islands, Spain)

Phase equilibrium experiments were performed to determine the pre-eruptive conditions of the phonolitic magma responsible for the last eruption (about 1,150 yr B.P.) of Teide volcano. The Lavas Negras phonolite contains 30 to 40 wt% of phenocrysts, mainly anorthoclase, diopside, and magnetite. We have investigated pressures from 100 to 250 MPa, temperatures from 750 to 925°C, water contents from 1.3 to 10 wt%, at an oxygen fugacity (fO2) of 1 log unit above the Ni-NiO solid buffer. Comparison of the natural and experimental phase proportions and compositions indicates that the phonolite was stored at 900 ± 20°C, 150 ± 50 MPa, 3 ± 0.5 wt% dissolved H2O in the melt. The fO2 was probably close to the fayalite-magnetite-quartz solid buffer judging from results of other experimental studies. These conditions constrain the magma storage depth at about 5 ± 1 km below current summit of Teide volcano. Given that the island has not suffered any major structural or topographic changes since the Lavas Negras eruption, any remaining magma from this event should still be stored at such depth and probably with a similar thermal and rheological state.

Rugged lava flows on the Moon revealed by Earth‐based radar

Basaltic volcanism is widespread on the lunar nearside, and returned samples suggest that the mare‐forming magmas had low viscosity that led to primarily sheet‐like deposits. New 70‐cm wavelength radar observations that probe several meters beneath the lunar surface reveal differences in mare backscatter properties not explained by age or compositional variations. We interpret areas of high backscatter and high circular polarization ratio in Maria Serenitatis, Imbrium, and Crisium as having an enhanced abundance of decimeter‐scale subsurface rocks relative to typical mare‐forming flows. The 3.5 b.y survival of these differences implies an initial platy, blocky, or ridged lava flow surface layer with thickness of at least 3–5 m. Such rugged morphology might arise from episodic changes in magma effusion rate, as observed for disrupted flood basalt surfaces on the Earth and Mars, very high flow velocities, or increased viscosity due to a number of factors. Significant information on lunar mare eruption conditions may thus be obtained from long‐wavelength radar probing of the shallow subsurface.

Tephra dispersal and eruption dynamics of wet and dry phases of the 1875 eruption of Askja Volcano, Iceland

The 1875 rhyolitic eruption of Askja volcano in Iceland was a complex but well-documented silicic explosive eruption. Eyewitness chronologies, coupled with examination of very proximal exposures and historical records of distal deposit thickness, provide an unusual opportunity for study of Plinian and phreatoplinian eruption and plume dynamics. The ∼ 17 hour-long main eruption was characterized by abrupt and reversible shifts in eruption style, e.g., from ‘wet’ to ‘dry’ eruption conditions, and transitions from fall to flow activity. The main eruption began with a ‘dry’ subplinian phase (B), followed by a shift to a very powerful phreatoplinian ‘wet’ eruptive phase (C1). A shift from sustained ‘wet’ activity to the formation of ‘wet’ pyroclastic density currents followed with the C2 pyroclastic density currents, which became dryer with time. Severe ground shaking accompanied a migration in vent position and the onset of the intense ‘dry’ Plinian phase (D). Each of the fall units can be modeled using the segmented exponential thinning method (Bonadonna et al. 1998), and three to five segments have been recognized on a semilog plot of thickness vs. area1/2. The availability of very proximal and far-distal thickness data in addition to detailed observations taken during this eruption has enabled calculations of eruption parameters such as volumes, intensities and eruption column heights. This comprehensive dataset has been used here to assess the bias of volume calculations when proximal and distal data are missing, and to evaluate power-law and segmented exponential thinning methods using limited datasets.

The nature of erupting kimberlite melts

The compositions of kimberlite magma and associated melts during eruption and hypabyssal intrusion are elusive due to contamination by xenolithic material and strong alteration, notably by serpentinisation. Textures and mineralogical attributes of kimberlite dykes and sills indicate that some groundmass minerals, including igneous calcite, are replaced in the process of serpentinisation. Large volume changes during serpentinisation occur in chemically open systems, producing an increase in SiO 2 and MgO and decrease in CaO and CO 2 in bulk rock chemistry. Reconstructed compositions of kimberlite melt components, taking into account alteration, are shifted towards compositions transitional to carbonatite, indicating overestimation of SiO 2 and MgO contents in previous published estimates of kimberlite melt compositions. Further evidence that these compositions are problematic come from experimental investigations of three putative kimberlite melt compositions. Experiments at 100 and 200 MPa at temperatures of 1100 °C to 1275 °C with excess CO 2, H 2O and CO 2–H 2O mixtures show that previously proposed compositions cannot be pure melts under eruptive conditions. Their SiO 2 and MgO-rich characteristics lead to high liquidus temperatures (> 1350 °C) inconsistent with estimated kimberlite magma temperatures (< 1200 °C). The experimental residual melts are depleted in MgO and have high CaO and SiO 2 contents, characteristics that are not consistent with kimberlite groundmass mineralogy that indicate significantly lower SiO 2 in the natural systems. Serpentinisation, causing changes in the relative proportions of CaO, MgO and SiO 2, can explain these results. Recognising the effects of serpentinisation, combined with petrographic observations, suggest that kimberlite melts have low SiO 2, SiO 2/MgO < 1 and evolve by crystallization towards increasingly silica-poor carbonate-rich residual melts during eruption of intrusion.

Explosive volcanic eruptions on Mercury: Eruption conditions, magma volatile content, and implications for interior volatile abundances

Images obtained by the MESSENGER spacecraft have revealed evidence for pyroclastic volcanism on Mercury. Because of the importance of this inference for understanding the interior volatile inventory of Mercury, we focus on one of the best examples determined to date: a shield-volcano-like feature just inside the southwestern rim of the Caloris impact basin characterized by a near-central, irregularly shaped depression surrounded by a bright deposit interpreted to have a pyroclastic origin. This candidate pyroclastic deposit has a mean radius of ~ 24 km, greater in size than the third largest lunar pyroclastic deposit when scaled to lunar gravity conditions. From the extent of the candidate pyroclastic deposit, we characterize the eruption parameters of the event that emplaced it, including vent speed and candidate volatile content. The minimum vent speed is ~ 300 m/s, and the volatile content required to emplace the pyroclasts to this distance is hundreds to several thousands of parts per million (ppm) of the volatiles typically associated with pyroclastic eruptions on other bodies (e.g., CO, CO 2, H 2O, SO 2, H 2S). For comparison, measurements of the exsolution of volatiles (H 2O, CO 2, S) from basaltic eruptive episodes at Kilauea volcano, Hawaii, indicate values of ~ 1300–6500 ppm for the terrestrial mantle source. Evidence for the presence of significant amounts of volatiles in partial melts derived from the interior of Mercury is an unexpected result and provides a new constraint on models for the planet's formation and early evolution.

Upper-mantle volatile chemistry at Oldoinyo Lengai volcano and the origin of carbonatites

Carbonatite lavas are highly unusual in that they contain almost no SiO(2) and are >50 per cent carbonate minerals. Although carbonatite magmatism has occurred throughout Earth's history, Oldoinyo Lengai, in Tanzania, is the only currently active volcano producing these exotic rocks. Here we show that volcanic gases captured during an eruptive episode at Oldoinyo Lengai are indistinguishable from those emitted along mid-ocean ridges, despite the fact that Oldoinyo Lengai carbonatites occur in a setting far removed from oceanic spreading centres. In contrast to lithophile trace elements, which are highly fractionated by the immiscible phase separation that produces these carbonatites, volatiles (CO(2), He, N(2) and Ar) are little affected by this process. Our results demonstrate that a globally homogenous reservoir exists in the upper mantle and supplies volatiles to both mid-ocean ridges and continental rifts. This argues against an unusually C-rich mantle being responsible for the genesis of Na-rich carbonatite and its nephelinite source magma at Oldoinyo Lengai. Rather, these carbonatites are formed in the shallow crust by immiscibility from silicate magmas (nephelinite), and are stable under eruption conditions as a result of their high Na contents.

Fissure eruptions in Tharsis, Mars: Implications for eruption conditions and magma sources

The Tharsis region has been the focus of many studies of volcanism on Mars. Not only are the largest volcanoes on the planet located here, but also many of the youngest volcanic features are found within Tharsis. Comparatively little attention has been given to understanding the origin of the smaller volcanoes within Tharsis, and these smaller structures may provide important information on both the regional tectonics of the area, and the availability of magma from the shallow or deep crust. We have identified six separate, but physically close, vent systems in eastern Tharsis just to the east of the volcano Jovis Tholus. These vents are typically linear fissures a few to ~ 20 km in length that have built small shields rising to ~ 50–85 m above the level of the surrounding topography. The maximum length of individual lava flows from these fissures is ~ 30 km, but more typical lengths are 15–20 km. Mapping of the vent complexes reveals that smooth material, interpreted to be spatter from fire fountaining, is located on the rims of some of the fissures. This spatter then formed either short (< 5 km) flows or merged close to the fissure to form the longer flows. There appears to have been some temporal evolution of the flow field, as the oldest parts of the basement at each center are built from a series of compound flows that cannot be subdivided into individual flows. We find evidence of frozen lava ponds and channelized flows from central vents. Photoclinometric profiles are constructed across one of the longer flows to confirm an unusual attribute, originally identified by Mouginis-Mark and Christensen [Mouginis-Mark, P.J., Christensen, P.R., 2005. New observations of volcanic features on Mars from the THEMIS instrument. J. Geophys. Res. 110: E8, doi: 10.1029/2005JE002421], of the flows from the central vent complex: they are all < 5 m thick, which is a factor of ~ 8–15 thinner than flows elsewhere on Mars. To investigate the unusual eruption conditions (limited total volume of the construct and of individual flows) we model the lava rheology, the duration of emplacement, the subsurface conditions that may have led to these eruptions, and the volatile content of the magma. We find lava viscosities and yield strengths to be ~ 100 Pa s and ~ 100 Pa, respectively, eruption rates to be ~ 5000 m 3 s − 1, flow speeds to be 1–2 m s − 1, durations of emplacement of individual flow units to be ~ 5 h, and the equivalent magma water content to be 0.1–0.2 mass%. These eruption conditions are consistent with a wide range of possible depths of the magma reservoirs feeding the eruptions. Small vents such as the ones studied here have also been identified in other parts of eastern Tharsis, so that the eruptions described here may characterize a common style of volcanism on Mars that can only be identified now that image spatial resolution in the range 1–20 m/pixel is available. It is therefore possible that additional searches of other volcanic areas (Syrtis Planum, Elysium Planitia, and Hesperia Planum) may also show greater diversity of activity than is currently accepted.

Safety research in the gasification process of novel multi-thermal-source coal gasifier

In order to collect the gas safely produced in the gasification process of the novel multi-thermal-source coal gasifier, based on its gasification skill and the characteristics of the products, this paper analyzes the possible dangers in the gasification process, devises the gasifier eruption and explosion experiments, explores the conditions of gasifier eruption and gas explosion, studies their effects on the gasification process and establishes safe operation measures. Gasifier eruption hazard occurs easily in the gasification process of one-thermal-source coal gasifier when M SiO2 is far higher than that in the normal adjuvant. The gas permeability in the gasifier is not the same and the power supply is too large. However, similar conditions in the gasification of multi-thermal-source coal gasifier do not produce a gasifier eruption accident so easily. When it erupts, the gasifier should be stopped and then cooled down naturally or inert gas can be sprayed on the gasifier to cool it off, and thus gas explosion can be avoided. There is a possibility of direct gas explosion, but it can be avoided when the gas in the gas collecting space is replaced slowly by supplying a small amount of power or the inert gas fills the space in the previous gasification. The time a fire is lit is strictly controlled, the gas is drawn in by using the aspirator pump, and the gasifier pressure is kept in the state of micro-positive pressure in the middle and later gasification process. The conclusion is that the gasification process of the novel multi-thermal-source coal gasifier is safe according to normal operation rules.

Dynamics of magma flow near the vent: Implications for dome eruptions

Magma erupting out of a volcanic vent into a flow or a dome is subjected to a marked change of boundary conditions which strongly affects the distribution of gas pressure and stress within the flow. A numerical code is implemented to study the role of degassing-induced crystallization. The 2-D governing equations for a compressible viscous liquid are solved with a fully axially symmetric Finite Element Model for different crystal contents and vent geometrical shapes. The potential effects of gas pressure, deformation rates and elongational stresses on the stability of endogenous dome growth are studied for two shallow vent structures. For common eruption conditions, values of the internal gas pressure at the vent may be as large as 2 MPa. The magnitude of gas pressure at the vent is sensitive to the amount of crystallization and to the shape of the shallow conduit beneath the vent. High tensile stresses of ≈ 2 MPa are generated at the vent, which may account for ring fracturing of the dome and gas escape through shallow fissures. Such failure conditions may also lead to a change of exit conditions, from lateral spreading to the vertical protrusion of a lava spine.