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1.
The simultaneous quantitative determination of two-dimensional bromine monoxide (BrO) and sulphur dioxide (SO2) distributions in volcanic gas plumes is described. Measurements at the fumarolic field on the island Vulcano (autumn 2004) and in the plume of Mt. Etna volcano (spring 2005) were carried out with an Imaging DOAS instrument. The SO2 fluxes of several fumaroles were estimated from two-dimensional distributions of SO2. Additionally, the first two-dimensional distributions of BrO within a volcanic plume were successfully retrieved. Slant column densities of up to 2.6 × 1014 molecules per square centimetre were detected in the plume of Mt. Etna. The investigation of the BrO/SO2 ratio, calculated from the two-dimensional distributions of SO2 and BrO, shows an increase from the centre to the edge of the volcanic plume. These results have significance for the involvement of ozone during BrO formation processes in volcanic emissions.  相似文献   

2.
We describe analytical details and uncertainty evaluation of a simple technique for the measurement of the carbon isotopic composition of CO2 in volcanic plumes. Data collected at Solfatara and Vulcano, where plumes are fed by fumaroles which are accessible for direct sampling, were first used to validate the technique. For both volcanoes, the plume-derived carbon isotopic compositions are in good agreement with the fumarolic compositions, thus providing confidence on the method, and allowing its application at volcanoes where the volcanic component is inaccessible to direct sampling. As a notable example, we applied the same method to Mount Etna where we derived a δ13C of volcanic CO2 between −0.9 ± 0.27‰ and −1.41 ± 0.27‰ (Bocca Nuova and Voragine craters). The comparison of our measurements to data reported in previous work highlights a temporal trend of systematic increase of δ13C values of Etna CO2 from ~ −4‰, in the 1970’s and the 1980’s, to ~ −1‰ at the present time (2009). This shift toward more positive δ13C values matches a concurrent change in magma composition and an increase in the eruption frequency and energy. We discuss such variations in terms of two possible processes: magma carbonate assimilation and carbon isotopic fractionation due to magma degassing along the Etna plumbing system. Finally, our results highlight potential of systematic measurements of the carbon isotopic composition of the CO2 emitted by volcanic plumes for a better understanding of volcanic processes and for improved surveillance of volcanic activity.  相似文献   

3.
There is widespread use of passive remote sensing techniques to quantify trace gas column densities in volcanic plumes utilizing scattered sunlight as a light source. Examples include passive DOAS, COSPEC, and the SO2 camera. In order to calculate trace gas concentrations or volcanic emission fluxes, knowledge about the optical path through the plume is necessary. In the past, a straight photon path through the plume has always been assumed although it was known that this is not always true. Here we present the results of model studies conducted specifically to quantify the effects of realistic radiative transfer in and around volcanic plumes on ground-based remote sensing measurements of SO2. The results show that measurements conducted without additional information on average photon paths can be inaccurate under certain conditions, with possible errors spanning more than an order of magnitude. Both over and underestimation of the true column density can occur. Actual errors depend on parameters such as distance between instrument and plume, plume SO2 concentration, plume aerosol load, as well as aerosol conditions in the ambient atmosphere. As an example, a measurement conducted with an SO2 camera is discussed, the results of which can only be correctly interpreted if realistic radiative transfer is considered. Finally, a method is presented which for the first time allows the retrieval of actual average photon paths in spectroscopic (i.e. DOAS) measurements of adequate resolution. By allowing for a wavelength dependent column density during the evaluation of DOAS measurements, we show how radiative transfer effects can be corrected using information inherently available in the measured spectra, thus greatly enhancing the accuracy of DOAS measurements of volcanic emissions.  相似文献   

4.
Volcanoes provide important contributions to atmospheric budgets of SO2 and reactive halogens, which play significant roles in atmospheric oxidative capacity and radiation. However, the global source strengths of volcanic emissions remain poorly constrained. These uncertainties are highlighted here by the first measurements of gas emission rates from Ambrym volcano, Vanuatu. Our initial airborne ultraviolet spectroscopic measurements made in January 2005 indicate fluxes of 18–270 kg s-1 of SO2, and 62–110 g s-1 of BrO, into the atmosphere, placing Ambrym amongst the largest known contemporary point sources of both these species on Earth. We also estimate high Cl and F fluxes of ~8–14 and ~27–50 kg s-1, respectively, for this period. Further observations using both airborne and spaceborne remote sensing reveal a fluctuating SO2 output between 2004 and 2008, with a surge in the first half of 2005, and underline the substantial contribution that a single passively degassing volcano can make to the atmospheric budget of sulfur and halogens.  相似文献   

5.
Imaging Differential Optical Absorption Spectroscopy (IDOAS) is an optical remote-sensing method using scattered sunlight as light source. It combines a “pushbroom” imaging spectrometer with the DOAS technique and thus allows imaging two-dimensional trace gas distributions, e.g., in volcanic plumes. The highly sensitive and specific detection of many trace gases simultaneously (specific molecules, not just elements, e.g. SO2, BrO, NO2, O3, HCHO, etc.) is possible, and the temporal and spatial variation of these gases can be measured. The IDOAS system presented here enables the taking of two-dimensional images of trace gas distributions in a volcanic plume with a spatial resolution of 100 pixels horizontally × 64 pixels vertically, each with a field of view of 0.087° in horizontal and 0.208° in vertical directions. Therefore, IDOAS provides useful information about the chemical composition and chemical variability in a volcanic plume and allows studying plume dispersal and chemical transformations. The technique was applied to map the SO2 distribution in the plume of Mt. Etna volcano for the first time in October 2003.  相似文献   

6.
 Two methods were used to quantify the flux of volcanic sulphur (as the equivalent mass of SO2) to the stratosphere over different timescales during the Holocene. A combination of satellite-based measurements of sulphur yields from recent explosive volcanic eruptions with an appropriate rate of explosive volcanism for the past 200 years constrains the medium-term (∼102 years) flux of volcanic sulphur to the stratosphere to be ∼1 Mt a–1, with lower and upper bounds of 0.3 and 3 Mt a–1. The short-term (∼10- to 20-year) flux due to small magnitude (1010–1012 kg) eruptions is of the order of 0.4 Mt a–1. At any time the instantaneous levels of sulphur in the stratosphere are dominated by the most recent (0–3 years) volcanic events. The flux calculations do not attempt to address this very short timescale variability. Although there are significant errors associated with the raw sulphur emission data on which this analysis is based, the approach presented is general and may be readily modified as the quantity and quality of the data improve. Data from a Greenland ice core support these conclusions. Integration of the sulphate signals from presumed volcanic sources recorded in the GISP2 core provides a minimum estimate of the 103–year volcanic SO2 flux to the stratosphere of 0.5–1 Mt a–1 over the past 9000 years. The short-term flux calculations do not account for the impact of rare, large events. The ice-core record does not fully account for the contribution from small, frequent events. Received: 27 September 1995 / Accepted: 13 December 1995  相似文献   

7.
Decompression experiments of a crystal-free rhyolitic liquid with ≈ 6.6 wt. % H2O were carried out at a pressure range from 250 MPa to 30–75 MPa in order to characterize effects of magma ascent rate and temperature on bubble nucleation kinetics, especially on the bubble number density (BND, the number of bubbles produced per unit volume of liquid). A first series of experiments at 800°C and fast decompression rates (10–90 MPa/s) produced huge BNDs (≈ 2 × 1014 m−3 at 10 MPa/s ; ≈ 2 × 1015 m−3 at 90 MPa/s), comparable to those in natural silicic pumices from Plinian eruptions (1015–1016 m−3). A second series of experiments at 700°C and 1 MPa/s produced BNDs (≈ 9×1012 m−3) close to those observed at 800°C and 1 MPa/s (≈ 6 × 1012 m−3), showing that temperature has an insignificant effect on BNDs at a given decompression rate. Our study strengthens the theory that the BNDs are good markers of the decompression rate of magmas in volcanic conduits, irrespective of temperature. Huge number densities of small bubbles in natural silicic pumices from Plinian eruptions imply that a major nucleation event occurs just below the fragmentation level, at which the decompression rate of ascending magmas is a maximum (≥ 1 MPa/s).  相似文献   

8.
Use of eddy covariance (EC) techniques to map the spatial distribution of diffuse volcanic CO2 fluxes and quantify CO2 emission rate was tested at the Horseshoe Lake tree-kill area on Mammoth Mountain, California, USA. EC measurements of CO2 flux were made during September–October 2010 and ranged from 85 to 1,766 g m−2 day−1. Comparative maps of soil CO2 flux were simulated and CO2 emission rates estimated from three accumulation chamber (AC) CO2 flux surveys. Least-squares inversion of measured eddy covariance CO2 fluxes and corresponding modeled source weight functions recovered 58–77% of the CO2 emission rates estimated based on simulated AC soil CO2 fluxes. Spatial distributions of modeled surface CO2 fluxes based on EC and AC observations showed moderate to good correspondence (R 2 = 0.36 to 0.70). Results provide a framework for automated monitoring of volcanic CO2 emissions over relatively large areas.  相似文献   

9.
During 2007–2008, three CO2 flux surveys were performed on El Chichón volcanic lake, Chiapas, Mexico, with an additional survey in April 2008 covering the entire crater floor (including the lake). The mean CO2 flux calculated by sequential Gaussian simulation from the lake was 1,190 (March 2007), 730 (December 2007) and 1,134 g m−2 day−1 (April 2008) with total emission rates of 164 ± 9.5 (March 2007), 59 ± 2.5 (December 2007) and 109 ± 6.6 t day−1 (April 2008). The mean CO2 flux estimated from the entire crater floor area was 1,102 g m−2 day−1 for April 2008 with a total emission rate of 144 ± 5.9 t day−1. Significant change in CO2 flux was not detected during the period of survey, and the mapping of the CO2 flux highlighted lineaments reflecting the main local and regional tectonic patterns. The 3He/4He ratio (as high as 8.1 R A) for gases in the El Chichón crater is generally higher than those observed at the neighbouring Transmexican Volcanic Belt and the Central American Volcanic Arc. The CO2/3He ratios for the high 3He/4He gases tend to have the MORB-like values (1.41 × 109), and the CO2/3He ratios for the lower 3He/4He gases fall within the range for the arc-type gases. The high 3He/4He ratios, the MORB-like CO2/3He ratios for the high 3He/4He gases and high proportion of MORB-CO2 (M = 25 ±15%) at El Chichón indicate a greater depth for the generation of magma when compared to typical arc volcanoes.  相似文献   

10.
 The Soufrière Hills Volcano, Montserrat, erupting since 18 July 1995, intensified its degassing in early 1996 with the continuing growth of the lava dome inside the summit crater. During this period of increased activity, between 11 and 18 March 1996, we measured gases and particles within the visible plume to determine whether at that time it posed a health risk to the population of Plymouth, the capital town, which is 5 km southwest (downwind) and was then still occupied. Gravimetric measurements were made of total suspended particles (TSP) and particles having an aerodynamic diameter of less than 10 μm (PM10). Measurements were made of sulphur dioxide (SO2), hydrochloric acid (HCl), hydrofluoric acid (HF), nitric acid (HNO3), acetic acid (CH3COOH), formic acid (HCOOH), and particulate sulphate (SO4 2–), chloride (Cl–), nitrate (NO3 –), fluoride (F–), methanesulphonate (CH3SO3 –), acetate (CH3COO–), formate (HCOO–), ammonium (NH4 +), sodium (Na+) and acidity (H+). Trace metals having human health implications [chromium (Cr), nickel (Ni), cobalt (Co), copper (Cu), zinc (Zn), arsenic (As), selenium (Se), cadmium (Cd), tin (Sn), mercury (Hg) and lead (Pb)] were also determined. Mean concentrations of HCl, SO2 and HF obtained in the town of Plymouth were 14.0, 5.9 and 0.8 ppbv, respectively. Corresponding concentrations in the mixed plume on the crater edge were 533, 168 and 22 ppbv. There were no direct emissions of HNO3, although nitrate was detected in coarse particles at the source. Higher concentrations of CH3COOH and HCOOH were measured close to the crater. Mean TSP and PM10 were 64 and 15 μg m–3 in Plymouth, and 455 and 47 μg m–3 on the upper volcano slope. Aerosols were highly acidic at the source but rapidly neutralised during transport. Trace metals were enriched in the aerosol relative to crater surface material. The concentrations of the acid gases, sulphur dioxide in particular, and particles were found to be too small to pose a health hazard at the time of these measurements, when relatively modest volcanic activity was occurring. Received: 9 September 1998 / Accepted: 29 August 1999  相似文献   

11.
 Measurements of CO2 fluxes from open-vent volcanos are rare, yet may offer special capabilities for monitoring volcanos and forecasting activity. The measured fluxes of CO2 and SO2 from Mount St. Helens decreased from July through November 1980, but the record includes variations of CO2/SO2 in the emitted gas and episodes of greatly increased fluxes of CO2. We propose that the CO2 flux variations reflect two gas components: (a) a component whose flux decreased in proportion to 1/ √t with a CO2/SO2 mass ratio of 1.7, and (b) a residual flux of CO2 consisting of short-lived, large peaks with a CO2/SO2 mass ratio of 15. We propose two hypotheses: (a) the 1/ √t dependence was generated by crystallization in a deep magma body at rates governed by diffusion-limited heat transfer, and (b) the gas component with the higher CO2/SO2 was released from ascending magma, which replenished the same magma body. The separation of the total CO2 flux into contributions from known processes permits quantitative inferences about the replenishment and crystallization rates of open-system magma bodies beneath volcanos. The flux separations obtained by using two gas sources with distinct CO2/SO2 ratios and a peak minus background approach to obtain the CO2 contributions from an intermittent source and a continuously emitting source are similar. The flux separation results support the hypothesis that the second component was generated by episodic magma ascent and replenishment of the magma body. The diffusion-limited crystallization hypothesis is supported by the decay of minimum CO2 and SO2 fluxes with 1/ √t after 1 July 1980. We infer that the magma body at Mount St. Helens was replenished at an average rate (2.8×106 m3 d–1) which varied by less than 5% during July, August, and September 1980. The magma body volume (2.4–3.0 km3) in early 1982 was estimated by integrating a crystallization rate function inferred from CO2 fluxes to maximum times (20±4 years) estimated from the increase of sample crystallinity with time. These new volcanic gas flux separation methods and the existence of relations among the CO2 flux, crystallization rates, and magma body replenishment rates yield new information about the dynamics of an open-vent, replenished magma body. Received: 15 February 1995 / Accepted: 30 March 1996  相似文献   

12.
Forward Looking Infrared Radiometer (FLIR) cameras offer a unique view of explosive volcanism by providing an image of calibrated temperatures. In this study, 344 eruptive events at Stromboli volcano, Italy, were imaged in 2001–2004 with a FLIR camera operating at up to 30 Hz. The FLIR was effective at revealing both ash plumes and coarse ballistic scoria, and a wide range of eruption styles was recorded. Eruptions at Stromboli can generally be classified into two groups: Type 1 eruptions, which are dominated by coarse ballistic particles, and Type 2 eruptions, which consist of an optically-thick, ash-rich plume, with (Type 2a) or without (Type 2b) large numbers of ballistic particles. Furthermore, Type 2a plumes exhibited gas thrust velocities (>15 m s−1) while Type 2b plumes were limited to buoyant velocities (<15 m s−1) above the crater rim. A given vent would normally maintain a particular gross eruption style (Type 1 vs. 2) for days to weeks, indicating stability of the uppermost conduit on these timescales. Velocities at the crater rim had a range of 3–101 m s−1, with an overall mean value of 24 m s−1. Mean crater rim velocities by eruption style were: Type 1 = 34 m s−1, Type 2a = 31 m s−1, Type 2b = 7 m s−1. Eruption durations had a range of 6–41 s, with a mean of 15 s, similar among eruption styles. The ash in Type 2 eruptions originates from either backfilled material (crater wall slumping or ejecta rollback) or rheological changes in the uppermost magma column. Type 2a and 2b behaviors are shown to be a function of the overpressure of the bursting slug. In general, our imaging data support a broadening of the current paradigm for strombolian behavior, incorporating an uppermost conduit that can be more variable than is commonly considered.  相似文献   

13.
We present thermal measurements made by high spatial resolution ground-based (a hand-held thermal camera) and low spatial resolution space-based (MODIS) instruments for a lava flow field active during the last phase of the May–July 2003 eruption at Piton de la Fournaise (La Réunion). Multiple oblique ground-based thermal images were merged to provide full coverage of the flow-field. These were then corrected for path length attenuation and orthorectified, allowing the at-surface radiance emitted by the flow-field to be estimated. Comparison with the radiance recorded by the MODIS sensors during the eruption reveals that, for clear-sky conditions and moderate-to-low viewing angles (satellite zenith <40°), the satellite measurements represent ∼90% of the at-surface radiance, and thus represent valuable data for quantifying volcanic thermal anomalies. Nevertheless, extreme viewing geometries and the presence of clouds strongly affect the radiance reaching the sensor and affected data from 94% of the overpasses. Ground-based thermal data were used to investigate an empirical relationship between the radiant heat flux and lava discharge rate during the emplacement of pahoehoe flows. While the average radiation temperature for flow surface that were 6–24 h old ranged between 500 K and 625 K, the ratio between radiative heat flux and Time-Averaged lava Discharge Rate (TADR) ranged between 1.5 × 108 J m−3 and 3.5 × 108 J m−3. This relationship was used to estimate TADR values from optimal MODIS data and produced results in line with those obtained from GPS surveys (Coppola et al. 2005). Our results underscore the importance of ground-based thermal analysis for the interpretation of satellite measurements, particularly in terms of calculating discharge rate trends.  相似文献   

14.
A simple system was designed using7LiOH-impregnated filters to collect acidic gases from ambient air and from highly concentrated volcanic plumes or gas streams. These filters were developed for analysis using instrumental neutron activation analysis, but other analytical techniques could be used as well. The sampling system was designed to use a series of 1–3 M7LiOH-impregnated filters to collect high concentrations of acidic gases found in gas plumes of active volcanoes. The filters are quantitative for SO2 and the halide acids when sufficient base is present to neutralize the acidic species. Extremely high concentrations of SO2 may not be collected quantitatively since SO2 is a relatively weak Lewis acid compared to the halide acids. The acidic oxides of Sb, As, and Se were also collected quantitatively. A particle filter preceded the impregnated filters in order to remove particles from the fumes. This system has proven effective under difficult sampling conditions and, since it is portable and light weight, it could be used for many volcanological applications where high levels of acidic gaseous phase species need to be collected.  相似文献   

15.
 The 1963 eruption of Gunung Agung produced 0.95 km3 dense rock equivalent (DRE) of olivine±hornblende-bearing, weakly phyric, basaltic andesite tephra and lava. Evidence for magma mixing in the eruptive products includes whole-rock compatible and incompatible trace element trends, reverse and complex compositional zoning of mineral phases, disequilibrium mineral assemblages, sieve-textured plagioclase phenocrysts, and augite rims on reversely zoned orthopyroxene. Basalt magma mixed with pre-existing andesite magma shortly before eruption to yield basaltic andesite with a temperature of 1040–1100  °C at an assumed pressure of 2 kb, f O2>NNO, and an average melt volatile content (H2O±CO2) of 4.3 wt.%. Magma-mixing end members may have provided some of the S and Cl emitted in the eruption. Glass inclusions in phenocrysts contain an average of 650 ppm S and 3130 ppm Cl as compared with 70 ppm and 2220 ppm, respectively, in the matrix glass. Maximum S and Cl contents of glass inclusions approach 1800 and 5000 ppm, respectively. Application of the petrologic method to products of the 1963 eruption for estimating volatile release yields of 2.5×1012 g (Mt) of SO2 and 3.4 Mt of Cl released from the 0.65 km3 of juvenile tephra which contributed to stratospheric injection of H2SO4 aerosols on 17 March and 16 May, when eruption column heights exceeded 20 km above sea level. An independent estimate of SO2 release from atmospheric aerosol loading (11–12 Mt) suggests that approximately 7 Mt of SO2 was injected into the stratosphere. The difference between the two estimates can be most readily accounted for by the partitioning of S, as well as some Cl, from the magma into a water-rich vapor phase which was released upon eruption. For other recent high-S-release eruptions of more evolved and oxidized magmas (El Chichón, Pinatubo), the petrologic method gives values two orders of magnitude less than independent estimates of SO2 emissions. Results from this study of the Agung 1963 magma and its volatile emissions, and from related studies on eruptions of more mafic magmas, suggest that SO2 emissions from eruptions of higher-S-solubility magma may be more reliably estimated by the petrologic method than may those from more-evolved magma eruptions. Received: 29 June 1994 / Accepted: 25 April 1996  相似文献   

16.
 Four co-ignimbrite plumes were generated along the flow path of the pyroclastic flow of 7 August 1980 at Mount St. Helens. Three of the plumes were generated in discrete pulses which can be linked to changes in slope along the channel. One plume was generated at the mouth of the channel where the flow decelerated markedly as it moved onto the lower slopes of the pumice plain. Plume generation here may be triggered by enhanced mixing due to a hydraulic jump associated with an abrupt slope change. Measurements of plume ascent velocity and width show that the co-ignimbrite plumes increased in velocity with height. The plumes have initial velocities of 1–2 m/s. Two of the plumes reached a velocity maximum (4.6 and 8.8 m/s, respectively, at heights of 270 and 315 m above the flow) and thereafter decelerated. The other plumes reached velocities of 6.2 and 13 m/s. The four plumes become systematically less energetic downstream as measured by their ascent rates, which can be interpreted as a consequence of decreasing interaction of the pyroclastic flow front with the atmosphere. Theoretical models of both co-ignimbrite plumes and discrete co-ignimbrite clouds assume that there is no initial momentum, and both are able to predict the observed acceleration stage. The rising plumes mix with and heat air and sediment out particles causing their buoyancy to increase. Theoretical models agree well with observations and suggest that the initial motion of the ascending material is best described as a discrete thermal cloud which expands as it entrains air, whereas the subsequent motion of the head may become influenced by material supplied from the following plume. The models agree well with observations for an initial temperature of the ash and air mixture in the range of 500–600 K, which is in turn consistent with the measured initial ash temperature of around 920 K. Ash masses of 3.4×105 to 1.8×106 kg are estimated. Received: 11 January 1996 / Accepted: 7 October 1996  相似文献   

17.
Bulk atmospheric deposition of major cations (Na, K, Ca, Mg) and anions (Cl, F, SO4) were measured at 15 sites around an active volcano, Mount Etna, from 2001 to 2003. Their composition indicates several natural sources, among which deposition of plume-derived volcanogenic gas compounds is prevalent for F, Cl and S. Plume-derived acidic compounds are also responsible for the prevailing acidic composition of the samples collected on the summit of the volcano (pH in the 2.45–5.57 range). Cation species have complex origin, including deposition of plume volcanogenic ash and aerosols and soil-dust wind re-suspension of either volcanic or carbonate sedimentary rocks. Variation of the deposition rates during the March 2001–March 2003 period, coupled with previous measurements from 1997 to 2000 (Appl Geochem 16:985–1000, 2001), were compared with the variation of SO2 flux, volcanic activity and rainfall. The deposition rate was mainly controlled by rainfall. Commonly, about 0.1–0.9% of HF, HCl and SO2 emitted by the summit crater's plume were deposited around the volcano. We estimate that ∼2 Gg of volcanogenic sulphur were deposited over the Etnean area during the 2002–2003 flank eruption, at an average rate of ∼24 Mg day−1 which is two orders of magnitude higher than that typical of quiescent degassing phases.  相似文献   

18.
Forward-Looking Infrared (FLIR) nighttime thermal images were used to extract the thermal and morphological properties for the surface of a blocky-to-rubbley lava mass active within the summit crater of the Caliente vent at Santiaguito lava dome (Guatemala). Thermally the crater was characterized by three concentric regions: a hot outer annulus of loose fine material at 150–400°C, an inner cold annulus of blocky lava at 40–80°C, and a warm central core at 100–200°C comprising younger, hotter lava. Intermittent explosions resulted in thermal renewal of some surfaces, mostly across the outer annulus where loose, fine, fill material was ejected to expose hotter, underlying, material. Surface heat flux densities (radiative + free convection) were dominated by losses from the outer annulus (0.3–1.5 × 104  s−1m−2), followed by the hot central core (0.1–0.4 × 104 J s−1m−2) and cold annulus (0.04–0.1 × 104 J s−1m−2). Overall surface power output was also dominated by the outer annulus region (31–176 MJ s−1), but the cold annulus contributed equal power (2.41–7.07 MJ s−1) as the hot central core (2.68–6.92 MJ s−1) due to its greater area. Cooled surfaces (i.e. the upper thermal boundary layer separating surface temperatures from underlying material at magmatic temperatures) across the central core and cold annulus had estimated thicknesses, based on simple conductive model, of 0.3–2.2 and 1.5–4.3 m. The stability of the thermal structure through time and between explosions indicates that it is linked to a deeper structural control likely comprising a central massive plug, feeding lava flow from the SW rim of the crater, surrounded by an arcuate, marginal fracture zone through which heat and mass can preferentially flow.  相似文献   

19.
2 and approximately 85% SO2 of the total sulfur gas. Relative amounts of He, Ar, and N2 show a distinct hot-spot signature ( ). The δ13C–CO2 is approximately −3.6‰ and δ34ST is approximately +3.3‰. The δD/δ18O of fumarole H2O indicates steam separation from local meteoric waters whose estimated minimum mean residence time from 3H analyses is ≤40 years. Fumarolic activity at Alcedo is controlled by a caldera-margin fault containing at least seven hydrothermal explosion craters, and by an intracaldera rhyolite vent. Two explosion craters which formed in 1993–1994 produce approximately 15 m3/s of steam, yet discharge temperatures are ≤97°C. Water content of the total gas is 95–97 mol.%, noncondensible gas is 92–98 mol.% CO2, and sulfur gas is dominated by H2S. Relative amounts of He, Ar, and N2 show extensive mixing between hot spot and air or air-saturated meteoric water components but the average . The δ13C–CO2 is approximately −3.5‰ and δ34ST is approximately −0.8‰. The δD/δ18O of fumarole steam indicates separation from a homogeneous reservoir that is enriched 3–5‰ in 18O compared with local meteoric water. 3H indicates that this reservoir water has a maximum mean residence time of approximately 400 years and empirical gas geothermometry indicates a reservoir temperature of 260–320°C. The intracaldera hydrothermal reservoir in Alcedo is probably capable of producing up to 150 MW; however, environmental concerns as well as lack of infrastructure and power users will limit the development of this resource. Received: 19 April 1999 / Accepted: 23 October 1999  相似文献   

20.
The correlation spectrometer (COSPEC), the principal tool for remote measurements of volcanic SO2, is rapidly being replaced by low-cost, miniature, ultraviolet (UV) spectrometers. We compared two of these new systems with a COSPEC by measuring SO2 column amounts at Kīlauea Volcano, Hawaii. The two systems, one calibrated using in-situ SO2 cells, and the other using a calibrated laboratory reference spectrum, employ similar spectrometer hardware, but different foreoptics and spectral retrieval algorithms. Accuracy, signal-to-noise, retrieval parameters, and precision were investigated for the two configurations of new miniature spectrometer. Measurements included traverses beneath the plumes from the summit and east rift zone of Kīlauea, and testing with calibration cells of known SO2 concentration. The results obtained from the different methods were consistent with each other, with <8% difference in estimated SO2 column amounts up to 800 ppm m. A further comparison between the COSPEC and one of the miniature spectrometer configurations, the ‘FLYSPEC’, spans an eight month period and showed agreement of measured emission rates to within 10% for SO2 column amounts up to 1,600 ppm m. The topic of measuring high SO2 burdens accurately is addressed for the Kīlauea measurements. In comparing the foreoptics, retrieval methods, and resultant implications for data quality, we aim to consolidate the various experiences to date, and improve the application and development of miniature spectrometer systems.  相似文献   

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