Gas Eruption Research Articles

Weak mixing in Lake Kivu: New insights indicate increasing risk of uncontrolled gas eruption

The deep waters of the East African Rift Lake Kivu contain large amounts of dissolved carbon dioxide and methane. The release of a fraction of these gases, which could be triggered by a magma eruption within the lake, would have catastrophic consequences for the two million people living on its shore. Up to now the safety assessment of the lake was based on the assumption that the gas concentrations in the deep waters are in a steady state with a residence time of 400 years. Turbulent transport was regarded as the main pathway of vertical exchange. Recent measurements and the analysis of the vertical transport processes in the lake radically change this evaluation. The vertical turbulent exchange is negligible, as documented by a spectacular set of several hundred double‐diffusive layers. Gases are mainly transported out of the deep zones by a slow upwelling with a residence time of 800–1000 years. Our results indicate that the methane production within the sediment has recently increased, leading to a gas accumulation in the deep waters and consequently decreasing the heat input needed to trigger a devastating gas release. With the estimated current CH4 production, the gas concentrations could approach saturation within this century.

Very long period oscillations of Mount Erebus Volcano

The exposed top of the conduit system at Mount Erebus Volcano, Ross Island, Antarctica, is a convecting lava (magma) lake hosting Strombolian eruptions caused by the explosive decompression of large (up to 5 m radius) gas slugs. Short‐period (SP; f ≥1 Hz) seismoacoustic eruption seismograms are accompanied by oscillatory very long period (VLP) signals observed in the near field by broadband seismometers 0.7 to 2.5 km from the lava lake. A variable VLP onset, preceding eruptions by several seconds, is followed by a repeatable VLP coda that persists for several minutes until the lava lake recovers to its preeruptive level. VLP signals are dominated by distinct decaying nonharmonic modes, the largest at periods of 20.7, 11.3, and 7.8 s, with respective source Q values of approximately 11, 18, and 4. Particle motions indicate a temporally evolving source producing increasingly vertical posteruptive displacements as the signal decays. VLP scalar moments, up to ∼5×1011 N m, exceed SP moments by an order of magnitude or more, suggesting distinct, though genetically related, SP and VLP source mechanisms. We conclude that VLP signals arise from excitation of a quasi‐linear resonator that is intimately associated with the conduit system and is excited by gravity and inertial forces associated with gas slug ascent, eruption, and magma recharge. VLP signal stability across hundreds of eruptions spanning 5 years, the persistence of the lava lake, and the rapid posteruptive lava lake recovery indicate a stable near‐summit magma reservoir and VLP source process.

Massive emissions of toxic gas in the Atlantic.

Recurrent eruptions of toxic hydrogen sulphide gas in the waters along the Namibian coast off southwestern Africa have been considered to be local features with only limited ecosystem-scale consequences. But satellite remote sensing has revealed that these naturally occurring events are much more extensive and longer-lasting than previously suspected, and that the resultant hypoxia may last for much longer. The effects on the marine ecology and valuable coastal fisheries of this region are likely to be important.

Experiments on conduit flow and eruption behavior of basaltic volcanic eruptions

Multiphase flow in basaltic volcanic conduits is investigated using analog experiments and theoretical approaches. Depending on gas supply, large gas bubbles (gas slugs) may rise through basaltic magma in regimes of distinct fluid‐dynamical behavior: ascent of single slugs, supplied slugs fed from the gas source during ascent, and periodic slug flow. An annular flow regime commences at the highest gas supply rates. A first set of experiments demonstrates that the growth of gas slugs due to hydrostatic decompression does not affect their ascent velocity and that excess pressure in the slugs remain negligible. The applicability of theoretical formulae describing slug ascent velocity as a function of liquid and conduit properties is evaluated in a second set of experiments. A third set of experiments with continuous gas supply into a cylindrical conduit are scaled to basaltic conditions over Morton, Eotvös, Reynolds, and Froude numbers. Gas flow rate and liquid viscosity are varied over the whole range of flow regimes to observe flow dynamics and to measure gas and liquid eruption rates. Foam generation by slug bursting at the surface and partial slug disruption by wake turbulence can modify the bubble content and size distribution of the magma. At the transition from slug to annular flow, when the liquid bridges between the gas slugs disappear, pressure at the conduit entrance drops by ∼60% from the hydrostatic value to the dynamic‐flow resistance of the annular flow, which may trigger further degassing in a stored magma to maintain the annular flow regime until the gas supply is exhausted and the eruption ends abruptly. Magma discharge may also terminate when magma ascent is hindered by wall friction in long volcanic conduits and the annular gas flow erodes all magma from the conduit. Supplied slugs are found to reach much higher rise velocities than unsupplied slugs and to collapse to turbulent annular flow upon bursting at the surface. A fourth set of experiments uses a conduit partially blocked by built‐in obstacles providing traps for gas pockets. Once gas pockets are filled, rising gas slugs deform but remain intact as they move around obstacles without coalescence or significant velocity changes. Bursting of bubbles coalescing with trapped gas pockets causes pressure signals at least 3 orders of magnitude more powerful than gas pocket oscillation induced by passing liquid. Our experiments suggest a refined classification of Strombolian and Hawaiian eruptions according to time‐dependant behavior into sporadically pulsating lava fountains (driven by stochastic rise of single slugs), periodically pulsating lava fountains (resulting from slug flow), and quasi‐steady lava fountains (oscillating at the frequency of annular‐flow turbulence).

A seafloor crater in the German Bight and its effects on the benthos

In 1963 a deep crater was formed about 65 m below sea level in the western part of the German Bight, due to a gas eruption caused by drilling carried out from the platform ’Mr. Louie’. The study area is situated in a sandy to muddy bottom area inhabited by an Amphiura filiformis association (sensu Salzwedel et al. 1985). The crater, sometimes called ’Figge-Maar’, functions as a sediment trap, concentrating particles and organisms from the water column, thus leading to extreme sedimentation rates of about 50 cm, on average, per year. Crater stations, compared with stations situated in the vicinity, show enrichments of juveniles. Echinoderms, especially the subsurface-dwelling heart urchin Echinocardium cordatum and ophiuroids are responsive to enrichment. Other species that are typical of the Amphiura filiformis association are shown to be unable to cope with the special conditions in the crater.

Methane solubility in synthetic oil-based drilling muds

The development of new drilling technologies and the reinforcement of environmental legislations require improvements of drilling fluid formulations. In particular, mineral oil-based muds have been recently replaced by low toxic or substitution oil-based muds (SBM). The molecular composition of these oils is adapted to the fluid property requirements. Very little is known on methane solubility in these oils and in their invert emulsions under reservoir conditions, though this is of crucial importance for predicting gas eruption risks when drilling. This is particularly the case of offshore deep drilling areas for controlling gas hydrate formation. In this work, solubility measurements of methane in four base oils have been performed at 90°C and pressures from 150 to 350 bar. The solubility in the fluid mixtures was found to be proportional to the solubility in water and oil, respectively. In order to extrapolate the experimental results to other conditions, a Peng–Robinson equation has been used. The critical parameters of the unknown constituents have been determined either by correlations based on the normal boiling point and the density or by a group contribution model. A single binary interaction parameter has been fitted between methane and the other oil components. Such results can be pertinent for predicting the risks related to gas/mud interactions.

Explosive volcanic eruptions--X. The influence of pyroclast size distributions and released magma gas contents on the eruption velocities of pyroclasts and gas in Hawaiian and Plinian eruptions

Previous treatments of the relationship between the mass fraction of released magma volatiles and the eruption speeds of gas and pyroclasts in steady explosive eruptions have not taken detailed account of the dynamic effects associated with the finite size distribution of the pyroclasts. When this is done, it is found that previously published estimates of exsolved magma volatile contents obtained from the analysis of pyroclast size distributions in near-vent deposits overestimate the volatile content by approximately 20 per cent in the case of Plinian eruptions. The discrepancy is much worse for pyroclast size distributions skewed towards coarse clasts, as is common in basaltic lava fountains; in such cases pyroclast dispersal studies may overestimate the exsolved magma volatile content by at least 200 per cent. An analogous problem arises if released magma volatile amounts deduced from studies of fluid inclusions in pyroclasts are inserted into most current computer models of eruption dynamics, but the gas eruption speeds deduced have an even larger error, being underestimated by up to 300 per cent in the case of coarse-grained eruptions. The more sophisticated of the currently available numerical models of eruption dynamics can in principle avoid this problem, but practical implementation limitations have so far prevented such models being run with a sufficiently wide range of grain sizes for the importance of these effects to be fully appreciated.

Physical volcanology and eruption dynamics of peralkaline agglutinates from Pantelleria

Peralkaline rhyolitic lava-like lobes showing direct evidence for a spatter-fed origin are associated with eruptive centres that document a transition from explosive to effusive fountain-fed activity. Owing to the preservation of spatter clasts, clast dimensions can be used to model the eruptive dynamics of these deposits. We conducted an integrated field, experimental and theoretical study of the Cala di Tramontana centre, Pantelleria, Italy, with the aim to better understand its eruptive behaviour. This centre is composed of four units and a close association of fall lapilli, tack-welded agglutinate, and spatter-fed lava-like lobes. These units were fed initially from a fissure vent, and later, from a circular vent. For the last-erupted lobe, field evidence indicates that fall-out accumulated rapidly, coalescing into a 10 m thick deposit that flowed downslope and became lava-like. High eruption rates and high heat flows are interpreted to promote welding of spatter proximal to the vent. Overburden pressures and thermal insulation from the accumulating spatter caused complete homogenisation of spatter within the interior of the flow. Laboratory vesiculation experiments show that peralkaline obsidian can vesiculate at temperatures as low as 620 °C (over a 4 hour period), and indicate that airborne agglutinate can deform and weld rapidly within minutes of landing. We measured viscosity on a natural Pantellerian sample using the parallel-plate method over a temperature range of 560–600 °C. Viscosities of 10 10–10 11 Pa s, and an activation energy of 311 kJ mol were obtained. Based on undeformed clast sizes and densities, eruption dynamics modelling indicates that gas eruption velocities ranged from ~ 90 to ~ 130 m s −1. Erupted mass fluxes were ~ 200 kg s −1 m −1 and ~ 2 × 10 4 kg s −1 from the fissure and localised circular vents, respectively. Magmatic viscosities of between 10 5 and 10 7 Pa s (for T = 750–850 °C) precluded intermittent Strombolian activity due to gas bubble coalescence. In addition, the amount of magmatic water available to drive the eruption fountains ranged from 0.4 to 0.6 wt.%—significantly less than the estimated ~ 1.5 wt.% of exsolved volatiles—implying that significant passive degassing occurred.

Thermodynamics of gas and steam-blast eruptions

Thermodynamics of gas and steam-blast eruptions

A large methane plume east of Bear Island (Barents Sea): implications for the marine methane cycle

A pockmark field extending over 35 km2 at 74°54′N, 27°3′E, described by Solheim and Elverhoi (1993), was re-surveyed and found to be covered with more than 30 steep-sided craters between 300 and 700 m in diameter and up to 28 m deep. The craters are thought to have been formed by an explosive gas eruption. Anomalously high concentrations of methane in the shelf waters around the craters suggest that a strong methane source near this area is still active today. Methane enrichment more than 10 km away from the crater field indicates the large dimensions of a plume and the amount of gas released from sources below the seafloor of the Barents Sea shelf. From the characteristic vertical decrease of methane towards the sea surface, it is concluded that biota are extensively using this energy pool and reducing the methane concentration within the water column by about 98% between 300 m depth and the sea surface. Degassing to the atmosphere is minimal based on the shape of the methane concentration gradient. Nevertheless, the net flux of methane from this area of the Barents Sea is about 2.9 × 104 g CH4 km−2 yr−1 and thus in the upper range of the presently estimated global marine methane release. This flux is a minimum estimate and is likely to increase seasonally when rough weather leads to more effective vertical mixing during autumn and winter. The amount of methane consumed in the water column, however, is about 50 times greater and hence should significantly contribute to the marine carbon inventory.

Thermodynamics of gas and steam-blast eruptions

Eruptions of gas or steam and non-juvenile debris are common in volcanic and hydrothermal areas. From reports of non-juvenile eruptions or eruptive sequences world-wide, at least three types (or end-members) can be identified: (1) those involving rock and liquid water initially at boiling-point temperatures (‘boiling-point eruptions’); (2) those powered by gas (primarily water vapor) at initial temperatures approaching magmatic (‘gas eruptions’); and (3) those caused by rapid mixing of hot rock and ground- or surface water (‘mixing eruptions’). For these eruption types, the mechanical energy released, final temperatures, liquid water contents and maximum theoretical velocities are compared by assuming that the erupting mixtures of rock and fluid thermally equilibrate, then decompress isentropically from initial, near-surface pressure (≤10 MPa) to atmospheric pressure. Maximum mechanical energy release is by far greatest for gas eruptions (≤∼1.3 MJ/kg of fluid-rock mixture)-about one-half that of an equivalent mass of gunpowder and one-fourth that of TNT. It is somewhat less for mixing eruptions (≤∼0.4 MJ/kg), and least for boiling-point eruptions (≤∼0.25 MJ/kg). The final water contents of crupted boiling-point mixtures are usually high, producing wet, sloppy deposits. Final erupted mixtures from gas eruptions are nearly always dry, whereas those from mixing eruptions vary from wet to dry. If all the enthalpy released in the eruptions were converted to kinetic energy, the final velocity (v max) of these mixtures could range up to 670 m/s for boiling-point eruptions and 1820 m/s for gas eruptions (highest for high initial pressure and mass fractions of rock (m r) near zero). For mixing eruptions, v max ranges up to 1150 m/s. All observed eruption velocities are less than 400 m/s, largely because (1) most solid material is expelled when m r is high, hence v max is low; (2) observations are made of large blocks the velocities of which may be less than the average for the mixture; (3) heat from solid particles is not efficiently transferred to the fluid during the eruptions; and (4) maximum velocities are reduced by choked flow or friction in the conduit.

Ring-like craters in single-crystal Si, Ge, and GaAs by deuterium-ion implantation

By detecting protons from the deuteron fusion reaction and partial pressure of mass number 4, we have made for the first time a real-time observation of an intermittent eruption of deuterium gas from surfaces of single-crystal Si, Ge, and GaAs irradiated with 90 keV deuterium ions. As a result, ring-like craters are formed on the implanted surfaces.

Three generations of mud volcanoes on the Louisiana continental slope

Three mud volcanoes were identified in a small area of the upper continental slope of the Gulf of Mexico. One is actively accreting by small, intermittent eruptions of gas and fluid mud. Eruptions occur from a pool of gas- and oil-saturated muds that upwell and spill over the central crater edge and down the flanks of the coneshaped buildup. A second structure, a possible sand volcano, is in the last stages of activity, with only slight evidence of gas-saturated sediments. The third structure is a dormant mud volcano with furrowed sides and scattered authigenic carbonate plates and rubble but no venting of gas or fluids.

Gas seepages, gas eruptions and degassing structures in the seafloor along the Strömma tectonic lineament in the crystalline Stockholm Archipelago, east Sweden

The crystalline Stockholm Archipelago contains several deep seated tectonic lineaments of mainly Svecofennian age. Along parts of these lineaments, gas with a thermogenic signature rises to the surface creating pockmarks in the seabed. Ground water is known also to leak from intersecting submarine eskers in the area, but this phenomenon has so far not been proved to develop distinct pockmarks. The east-west direction is regarded to be the youngest out of four main lineament directions in the Archipelago. Investigations have been carried out along the eastwest Strömma lineament at Stavsnäs with respect to pockmark structures, location of main fractures within the lineament, and the gas content in clay samples along a line perpendicular to the lineament. Chemical analyses show that anomalous amounts of gas with thermogenic signature are contained in samples collected from within the lineament as compared to samples collected in the adjacent areas to the north and south. Gas eruptions are reported to occur frequently nearshore along the islands within the lineament at Stavsnäs.

Pockmarks and gas-charged sediments in the eastern Skagerrak

Extensive patches of shallow gas-charged sediments have previously been documented in the Eastern Skagerrak (the strait between Norway and Denmark). Recently obtained high-resolution side scan sonar and sub-bottom profiler data presented here document several surface and sub-surface features at the border and inside zones of such gas-charged shallow sediments. Three examples are presented and discussed: a low-profile, 3 m-deep pockmark and gas-charged sediments; a low profile, 6 m-deep pockmark associated with a rugged sub-surface reflector; large, up to 25 m deep and 500 m wide pockmarks. From similarities with previously described features it is concluded that the pockmarks are formed by gas eruption and seepage and that the rugged subsurface reflector could possibly represent the upper surface of a diapirically deformed unit of gas-charged plastic clays. Therefore, pockmarks occur preferentially when this rugged surface is close to the seabottom, thus allowing gas-emanation.

Solar sources of geomagnetic storms

Because geomagnetic storms can have important effects on communications and electrical power distribution, an ability to predict these storms has considerable value. We have recently come to understand that coronal mass ejections (CMEs) cause most large geomagnetic storms during the most active part of the solar cycle [Gosling et al., 1991]. CMEs are huge eruptions of hydrogen gas that originate low in the corona; they are often associated with eruptive prominences and solar flares. CMEs can travel as much as three or four times faster than the slower solar wind plasma ahead of them. As a fast CME travels outward through the solar wind toward Earth, both the material ahead of the CME and the leading portion of the CME itself are compressed, shocks are formed, and magnetic field lines from the ambient solar wind are draped across the front of the CME. When this disturbance reaches the Earth, the Earth's magnetic field is affected.

A new hydrogeochemical and geotectonical interpretation of the Lake Nyos disaster in Cameroon

The gas eruption in Lake Nyos allows solely a deep inorganic origin of the CO2, and CO2 ascent along intersecting ruptures to be considered. Enormous gas volumes can be liberated from ascension paths with voids in the deep sections of the Earth's crust rather than from the water-dissolved phase (a lake) on the Earth's surface. In this case, rupture activity rather than volcanic activity should be involved. Similarly to volcanic activity, other events are also associated with open ruptures in the Earth's crust. No interrelations exist between the single phenomena. One of them consists in the ascent of CO2 with no relation to magma. Earthquakes, too, are associated with ruptures. Even a very slight tremor of the Earth's crust can contribute to the liberation of deepseated compressed CO2. However, disturbing the equilibrium of the water-column pressure and the compressed gas can result in an eruption even with no external impetus, e. g. an earthquake.

Large pockmarks, gas-charged sediments and possible clay diapirs in the Skagerrak

Extensive patches of shallow gas-charged sediments have previously been documented in the eastern Skagerrak (the strait between Norway and Denmark). Recently obtained high resolution side-scan sonar and sub-bottom profiler data presented here document several surface and sub-surface features at the border and inside zones of such gas-charged shallow sediments. Four examples are presented and discussed: (1) a low profile, 3 m deep pockmark and gas-charged sediments; (2) a low profile, 6 m deep pockmark associated with a rugged sub-surface reflector; (3) large, up to 24 m deep and 500 m wide pockmarks; and (4) patches of exposed material from the rugged sub-surface reflector. From similarities with previously described features and also with features found in the Kattegat, further south, it is concluded that the pockmarks are formed by gas eruption and seepage and that the rugged sub-surface reflector could possibly represent the upper surface of a diapirically deformed unit of gas-charged plastic clays.

Gas content, eruption rate and instabilities of eruption regime in silicic volcanoes

In silicic volcanoes, eruptions commonly begin with violent explosive phases and evolve towards a regime of dome formation. This transition is characterized by a decrease of gas volume fraction, which has usually been attributed to chemical gradients in the volcano chamber. Petrological and geochemical studies suggest that this interpretation may be oversimplified. A critical observation is that the eruption rate decreases with time and is markedly smaller during dome growth than during explosive activity. Following Eichelberger et al. [1], we suggest that the transition from explosive activity to dome formation is due to gas loss through permeable conduit walls. Further, in some cases, the same process may be responsible for the transition from the ash fall regime to pyroclastic flows. Both transitions are a direct consequence of a decrease of eruption rate at constant conduit radius. The gas content of lava rising towards the Earth's surface is determined by two competing processes: pressure release leading to gas exsolution and expansion, and gas loss to the country rock. The amount of gas lost is inversely proportional to the eruption rate and proportional to the pressure difference between conduit and country rock. The critical variable is the pressure in the volcano chamber. This pressure steadily decreases with time as the chamber empties, implying a decrease of eruption rate. In turn, this decrease acts to increase the fraction of gas lost to the country rock and hence to reduce the gas content of the erupted material. The model therefore predicts that, with time, the eruption undergoes a transition from explosive to non-explosive conditions. These transitions occur as bifurcations in the evolution of gas volume fraction with height in the conduit. We find that very small pressure fluctuations of the order of one bar in the chamber lead to large changes of gas content at the vent. This suggests that the transitions of eruptive regime are unstable, and provides an explanation for observed alternations between explosive phases and dome formation. With time, such pressure fluctuations occur when the average vesicularity is smaller and may manifest themselves by extrusion events through an existing dome. In Appendix B, we use data on the height of the Montagne Pelée spine in 1902 and 1903 to show that the pressure driving this eruption decreased by about 2 MPa in a year.

Lithostratigraphy, volcanism, paleomagnetism and palynology of Quaternary lacustrine deposits from Barombi Mbo (West Cameroon): Preliminary results

We present preliminary results from the study of 23.50-m core from Lake Barombi Mbo, representing the last 25,000 years. The lake is in an explosion crater formed during Quaternary time. The very laminated sediment is composed mostly of clay containing 5–10% organic carbon. Each couplet is commonly composed of a basal lamina rich in quartz, plant debris, muscovite and sponge spicules, and of a more clayey upper lamina often with siderite. A perturbed section near the base of the core, before ca. 21,000 yr B.P., could be the result of a violent release of gas, such CO 2 , comparable to the recent Nyos gas eruption. The paleomagnetic studies exhibit high-frequency oscillations interpreted as paleosecular variations of the local geomagnetic field. This first record obtained on the African continent can be closely compared to the type record obtained in Western Europe. The pollen results demonstrate the presence of a forest refuge in West Cameroon during the last great arid period, ca. 18,000 yr B.P. When equatorial forest was broken up, elements of montane vegetation spread to the lowlands. These phenomena resulted from a drying and cooling climate.