Gas Burst Research Articles

A vacuum modification for the philips CM30 electron microscope

For the Philips CM30 (or earlier EM430), the large surface area in the gun, the relatively poor pumping speed at the base of the gun, and the use of the same 100 l/s ion getter pump (IGP) for the column and gun, all lead to a significant degradation of gun vacuum (and slow recovery) following the gas burst involved in specimen exchange, even with extended pumping in the airlock. Since the vacuum quality in the gun is important for LaB6 filament life and high voltage stability, we adopted a conservative approach to the maximum pressure Pc allowed for the application of high voltage or filament emission; we chose an IGP reading of 22 (5 × 10−5 Pa). Delays of ~15 min typically occurred following specimen insertion. To avoid these problems the vacuum system has been modified. The goals were threefold: (1) To increase the pumping speed at the gun. The conductance of the original 600-mm-long vacuum line with three 90° elbows and a valve (V5) results in a pumping speed of < 10 l/s at the base of the emission chamber and a routine pressure of 3 × 10−5 Pa (1.5 × 10−7 torr).

Geological control of shallow gas and pockmarks in the Norwegian Channel; high resolution shallow subbottom profiling of small scale features

High resolution bathymetric and fine-scale parametric subbottom profiling along a line to the SW of Stavanger, Norway near the NE flank of the Norwegian Channel, show pockmarks clustered over neotectonic shallow fold structures in Quaternary sediments. Detailed profiles of the pockmarks indicate that they are collapsed gas seeps, rather than being collapse structures that followed doming and breaching with a more dramatic gas burst. The gentle folding and weak structures along the margin of a Mesozoic through Cenozoic sedimentary basin are probably due to differential uplift generating light compressional strain.

Helium and carbon fluxes in Lake Nyos, Cameroon: constraint on next gas burst

On 21 August, 1986, a lethal gas burst issued from Lake Nyos in Cameroon, western Africa, killing at least 1700 people. Although the consensus is that the victims died of asphyxiation by CO 2 of magmatic origin, the frequency of such catastrophic degassing events is still unknown. The CO 2 flux at the bottom of Lake Nyos is estimated based on the measurement of 3He 4He and 4He 20Ne ratios and the chemical composition of gases exsolved from the lake water. The calculated CO 2 flux at the bottom of Lake Nyos is (4.4 ± 2.3) × 10 13cm 3STP/year . Combined with the estimated release in the August 1986 event of ( 8 ± 2) × 10 14 cm 3 STP, the CO 2 flux suggests that the gas burst may happen about once in 18 ± 10 years, although the significant uncertainty should be taken into account for the frequency resulting from assumptions such as steady-state fluxes in the lake and small fractionization of the C/He ratio during the degassing event. Several yearly measurements of hypolimnetic fluxes and seasonal measurements of epilimnetic fluxes are needed to constrain better the recurrence interval. In addition, the results of a regional 3He 4He survey of carbonated mineral springs in northwestern Cameroon are discussed in the context of the regional geotectonics.

Radiometric studies of Lake Nyos (Cameroon) sediments: evidence of strong mixing and excess 210Pb

Abstract A one-meter-long sediment core was extracted from the middle of Lake Nyos six months after the August 1986 gas burst disaster. Major and trace elements have been determined in twenty samples, including alpha and gamma spectrometry for the radioisotopes. Preliminary results show that: • - 137 Cs is present in uniform concentrations throughout the core. The measured activity (7.3 Bq kg −1 ) corresponds to a total deposit of approximately 1800 Bq m −2 in the one-meter-thick sediment layer, similar in magnitude to the average amounts deposited at these latitudes by atmospheric thermonuclear tests. • - 210 Pb, with a half-life of 22 years, is also uniformly distributed, showing a measured activity of 233 Bq kg −1 , three to four times higher than the values observed in other Cameroon lakes. The activity ratio of 210 Pb to 226 Ra is about 4. These data are interpreted as follows: • - The uniformly distributed 137 Cs and 210 Pb concentrations suggest complete mixing of the top of sediments at the sample location.; • - From the amount of deposited 137 Cs found in the core, this sediment mixing process does not appear to have involved significantly more than that top layer. • - The 210 Pb excess, not supported by 226 Ra, can be explained by an upwards release of radon gas ( 222 Rn) prior to the CO 2 burst.

The Lake Nyos gas disaster: chemical and isotopic evidence in waters and dissolved gases from three Cameroonian crater lakes, Nyos, Monoun and Wum

Abstract To better understand the cause of the Nyos gas disaster of August 21, 1986, we conducted geochemical and limnological surveys in October 1986, of three lakes (Nyos, Monoun and Wum) which are located in the Cameroon volcanic zone that is characterized by a prevalence of young alkaline basalts and basanitoids. Lake Wum was studied as a non-active control: CO2 is dissolved in significant concentrations (about 1 5 of saturation) in gas-active lakes (Nyos and Monoun), but is virtually absent in Lake Wum. Stable isotopic ratios of total dissolved carbon (δ13C= −3% for Nyos and −5.5% for Monoun) and of helium (5.7 Ratm for Nyos and 3.6 Ratm for Monoun) indicate a mantle origin of these gases. However, SO42− and Cl concentrations are found to be very low. Concentrations of dissolved chemical species like Fe2+, Mg2+, Ca2+, and HCO3− are high in the two gas-active lakes, whereas they are very low in the gas-inactive lake. High salinities in the gas-active lakes are probably due to dissolution of indigenous mafic rocks and transported lateritic soil in acidic CO2-rich, warm water. The gas-active lakes are characterized by increasing temperature and salinity with increasing depth, indicating an active influx of heat and dissolved materials at the bottom. Density estimates show that the lake water is stably stratified in spite of the inverse temperature profile of the lakes, on account of dissolved chemical species. The concentrations of dissolved carbonate species (CO2(aq) and HCO3−) are positively correlated with those of ionic dissolved species, indicating their common occurrence in the bottom water. The August 1986 gas bursts from Lake Nyos were most likely caused by rapid exsolution of dissolved CO2 within the lake; an explosive process such as a phreatic eruption or a CO2 gas-jetting from beneath the bottom is unlikely because of low concentrations of Cl− and SO42−, no oxygen isotopic shift, low turbidity, and no reported perturbation of the bottom sediments. Exsolution of CO2 bubbles could occur if CO2-saturated bottom water was displaced upwards by an increased influx of high salinity water from the bottom during the rainy season. Exsolution of CO2 at the upper layers was possibly accelerated by upwelling of a two-phase fluid (CO2 bubbles and solution), a mechanism known as a pneumatic lift pump, resulting in discharge of a large amount of CO2 gas. The H2S concentration in the gas cloud must have been kept far below the lethal level because of a high Fe2+ concentration of the lake water.

The significance of siderite in the sediments from Lake Nyos, Cameroon

Small amounts (1–3 wt.%) of endogenic siderite (FeCO3) and traces of pyrite (FeS2) are present in a 1 m-long sediment core from Lake Nyos. Thermodynamic modeling shows that the deep waters are supersaturated with respect to siderite and pyrite. No other carbonates were found to be stable. This rare occurrence of siderite is symptomatic of the build-up of large concentrations of CO2 and Fe2+ in the Lake Nyos waters. A search for siderite in the deeper sediments could reveal the existence of previous gas burst events that have occurred at Lake Nyos or in other Cameroon lakes.

Ways of preventing rock and gas bursts: Hess, H GluckaufV124, N4/5, 3 March 1988, P230–235 (german), P126–131 (english)

Ways of preventing rock and gas bursts: Hess, H GluckaufV124, N4/5, 3 March 1988, P230–235 (german), P126–131 (english)

Another gas burst in a Cameroon lake?

Another gas burst in a Cameroon lake?

Gas Bursts from Cameroon Crater Lakes: A New Natural Hazard

Gas bursts from tropical crater lakes constitute a hitherto unrecognized natural hazard, which claimed 37 lives around Lake Monoun in 1984 and 1,746 lives in 1986 around Lake Nyos in Cameroon, west Africa. Studies of these events indicate that the lethal gas clouds were dominantly CO(2) which exsolved catastrophically from deep waters of the lakes, producing in the case of Lake Nyos a gas cloud of 1.94 times 10(6) tons CO(2) . Carbon-isotope data indicate a magmatic source of the carbon dioxide, but the geochemistry of deep water and gases does not support a sudden injection of volcanic gas from a deep source into the lakes. Rather, it is proposed that the gas bursts were preceded by gradual build-up of dissolved bicarbonate in deep waters, where anoxic conditions in enclosed and stagnant basins led to low pH and pCO(2) close to saturation. Steady input from the Earth's mantle to submerged mofettes or CO(2) -rich soda springs within the lakes is most likely the primary source of carbon dioxide. Lethal effects of the gas bursts are almost entirely due to CO(2) -induced asphyxia. A small percentage of victims awoke from coma one or two days after the event, but most died. Unusual skin lesions on about 5% of victims arose from the comatose state. It is shown that the mass of gas required to account for the lethal effects and observed gas clouds is an order of magnitude less than the potential gas yield from the lakes. In view of the lethal gas bursts from the small Cameroon lakes, the potential hazard of future gas bursts from other much larger density-stratified equatorial lakes must be seriously considered, particularly in Lake Kivu in east Africa, where methane and carbon dioxide gas content is higher by two to four orders of magnitude than that of the Cameroon lakes. A gas burst from Lake Kivu would form a carbon dioxide cloud up to 340 km(3) in volume and expansion of the exsolving gas from deep water to atmospheric pressure would correspond to an energy release equivalent to 8 megatons of explosive.

Re-emission of He from a-Sic irradiated with 200 keV He ions

Sintered α-SiC samples were irradiated with 200 keV He ions in the fluence range from 1 × 10 15 to 1 × 10 20 ions/cm 2 at room temperature. Re-emission rates of injected He atoms were measured in the subsequent annealing process from 50 to 1500 °C. The re-emission started around 350 ° C for the samples irradiated with various fluences and a peak due to gas burst was observed around 1000 ° C for the irradiation at fluences above 1 × 10 18 ions/cm 2. High retention states of He atoms above 1500 ° C were observed and the retention fraction increased with irradiation fluence.

Steady advance of coal and gas bursts

This paper establishes a one-dimensional model to analyse the mechanism of coal and gas bursts. It is found that the intrinsic factor governing bursts is the coupling of the initiation of the moving of coal fragments with the gas seepage. A typical (strong) burst can be treated as a steady advance process. The significant dimensionless parameters concerning bursts and an approximate burst criterion are given, and they are in good agreement with the statistics of field data.

Lethal gas bursts from Cameroon Crater Lakes

On August 15, 1984, a cloud of gas burst out of Lake Monoun in Cameroon, killing 37 people by asphyxiation. A study of the lake revealed that it occupies a 96‐m‐deep crater and that very high levels of dissolved carbon dioxide prevail in the anoxic deep waters [Sigurdsson et al., 1987]. The carbon isotope characteristics of Lake Monoun indicate derivation of the CO2 from mantle source (high 14C age of lake; ∂13C of −7) , but the chemistry of the lake showed no indication of input of hot magmatic gases, such as elevated levels of sulfur or evidence of halogen compounds or gases in the water. We therefore proposed that the Lake Monoun event was not related to a volcanic explosion but was rather the consequence of long‐term buildup of mantlederived CO2, which was dissolved in the anoxic lake waters and was derived from soda springs or other carbon dioxide‐rich groundwater flow into the submerged crater. Sudden degassing of the CO2‐rich waters was attributed to an upset of the density stratification of the lake by a landslide from the crater's eastern rim.

Origin of the lethal gas burst from Lake Monoun, Cameroun

Abstract On 15 August, 1984, a lethal gas burst issued from a submerged 96-m-deep crater in Lake Monoun in Cameroun, western Africa, killing 37 people. The event was associated with a landslide from the eastern crater rim, which slumped into deep water. Waters below 50 m are anoxic, dominated by high Fe 2+ (∼600 mg/l) and HCO 3 − (≥ 1900 mg/l), anoxic and supersaturated with siderite, which is a major component of the crater floor sediments. The unusually high Fe 2+ levels are attributed to reduction of laterite-derived ferric iron gradually brought into the lake as loess and in river input. Sulfur compounds are below detection limits in both water and gas. Gases effervescing from depressurized deep waters are dominantly CO 2 with minor CH 4 , having δ 13 C of −7.18 and −54.8 per mil, respectively. Bacterial decomposition of organic matter may account for the methane, but 14 C of lake water indicates that only 10% of the carbon is modern, giving an apparent age of 18,000 years. The dominant source of carbon is therefore attributed to long-term emission of CO 2 as volcanic exhalation from vents within the crater, which led to gradual build-up of HCO 3 − in the lake. The density stratification of the lake may have been upset by an earthquake and underwater landslide on 15 August, which triggered overturn of the lake and caused nucleation of CO 2 in the deep water. The resultant ebullition of CO 2 from deep lake waters led to a gas burst at the surface and locally generated a water wave up to 5 m high. People travelling through the gas cloud were asphyxiated, presumably from CO 2 , and suffered skin discoloration from unidentified components.

Liquid carbon dioxide of magmatic origin and its role in volcanic eruptions

Natural liquid carbon dioxide is produced commercially from a 2.5-km-deep well near the 4,500-yr-old maar volcano, Mount Gambier, South Australia. The carbon dioxide has accumulated in a dome that is located on the extension of a linear chain of volcanic activity. A magmatic origin for the fluid is suggested by the geological setting, δ13CPDB of –4.0‰, for the CO2 (where PDB represents the carbon-isotope standard), and a relatively high 3He component of the contained helium and high 3He/C ratio (6.4 x 10−10). The 3He/4He and He/Ne ratios are 3.0 and > 1,370 times those of air, respectively. The CO2, as collected at the Earth's surface at 29.5 °C and 75 bar, expands more than 300-fold to form a gas at 1 atm and 22 °C. We suggest that liquid CO2 or high-density CO2 fluid (the critical point is 31.1 °C, 73.9 bar) of volcanic origin that expands explosively from shallow levels in the Earth's crust may be a major contributor to 'phreatic' volcanic eruptions and maar formation. Less violent release of magmatic CO2 into crater lakes may cause gas bursts with equally disastrous consequences such as occurred at Lake Nyos, Cameroon, in August 1986.

Origin of the lethal gas burst from Lake Monoun, Cameroun : Sigurdsson, H., J.D. Devine, F.M. Tchoua, T.S. Presser, M.K.W. Pringle and W.C. Evans, 1987. J. Volcanol. geotherm. Res., 31(1–2):1–16

Origin of the lethal gas burst from Lake Monoun, Cameroun : Sigurdsson, H., J.D. Devine, F.M. Tchoua, T.S. Presser, M.K.W. Pringle and W.C. Evans, 1987. J. Volcanol. geotherm. Res., 31(1–2):1–16

14B. Carbon dioxide gas bursts from Lake Nyos, Cameroon.

14B. Carbon dioxide gas bursts from Lake Nyos, Cameroon.

Geological Background of the Lethal Gas Bursts from Lake Nyos, Cameroon, August 1986

Geological Background of the Lethal Gas Bursts from Lake Nyos, Cameroon, August 1986

Calibration of gauges and mass spectrometers by defined gas bursts

Calibration of gauges and mass spectrometers by defined gas bursts

Lethal Gas Bursts from Lake Nyos, Cameroon, August 1986

Lethal Gas Bursts from Lake Nyos, Cameroon, August 1986

Calibration of a gas-analytical MS by defined gas bursts: R Dobrozemsky, Osterreichisches Forschungszentrum Seibersdorf, A-2444 Seibersdorf, Austria

Calibration of a gas-analytical MS by defined gas bursts: R Dobrozemsky, Osterreichisches Forschungszentrum Seibersdorf, A-2444 Seibersdorf, Austria