Sulfur and halogen gases at Masaya Caldera Complex, Nicaragua: Total flux and variations with time
Sulfur and halogen gases at Masaya Caldera Complex, Nicaragua: Total flux and variations with time
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尼加拉瓜马萨亚火山口综合体的硫和卤素气体：总通量和随时间的变化
DOI：
10.1029/jb091ib12p12215
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发表时间：
1986
影响因子：
--
通讯作者：
B. Huebert
中科院分区：
文献类型：
--
作者：
R. Stoiber;S. Williams;B. Huebert
尼加拉瓜马那瓜附近马萨亚火山口复合体的圣地亚哥火山口在1979年末进入了强烈的岩浆脱气阶段。1980年2月，SO2通量从以前的平均380 t d−1迅速增加到大约1200 t d−1。我们报告了气体通量和地球化学研究的结果，这些研究是火山及其对邻近环境影响的更广泛的跨学科研究的一部分。Masaya火山是一个不寻常的火山，因为它的低盾状结构，一致的拉斑玄武岩成分，频繁的活动，特别是因为大约25年周期的主要非喷发脱气危机。我们使用了包括遥感（使用相关光谱仪）的SO2通量和直接过滤采样的硫和卤素气体和气溶胶的比例的技术组合，以量化所有这些物种的通量。三级过滤器依次捕获气溶胶、卤素酸气体和二氧化硫，并通过离子色谱法进行分析。利用COSPEC对SO2通量的测量，我们计算出SO2的平均通量为1275 t d−1，HCl为830 t d−1，HF约为16 t d−1，HBr最多为1 t d−1。H2S和SO4 =只是较小的硫种。
Santiago Crater, of Masaya Caldera Complex near Managua, Nicaragua, entered a phase of intense magmatic degassing in late 1979. The flux of SO2 increased rapidly from a previous average of 380 t d−1 to approximately 1200 t d−1 in February 1980. We report on results of a study of the gas flux and geochemistry conducted as part of a broader interdisciplinary study of the volcano and its impact on the adjacent environment. Masaya is an unusual volcano because of its low shield like form, consistent tholeiitic basaltic composition, frequent activity, and especially because of the approximately 25 year cycle of major non-eruptive degassing crises. We have used a combination of techniques involving remote sensing (using a correlation spectrometer (COSPEC)) of the flux of SO2 and direct filter sampling of the ratios of the sulfur and halogen gases and aerosols to quantify the flux of all of these species. The three-stage filters successively trap aerosols, halogen acid gases, and sulfur dioxide and are analyzed by ion chromatography. We have used the ratios of various species, with the COSPEC measurements of the flux of SO2, to calculate that the average flux of SO2 is 1275 t d−1, HCl is 830 t d−1, HF is about 16 t d−1, and HBr is at most 1 t d−1. H2S and SO4 = are only minor sulfur species.
The flux of SO2 and HCl represents the largest reported noneruptive sustained volcanic release of these species in the world. Masaya contributed 7% of the total SO2 estimated to have been released by volcanoes worldwide in 1981. The flux of SO2 has declined by about 9% each year since 1979 and can be modeled as a first-order kinetic rate law with a decay constant of approximately 0.04 yr−1. Approximately 2.2 × 106 tons of SO2 has been released between September 1979 and September 1985. The ratio S/Cl has declined more rapidly than the flux of SO2, reflecting the greater solubility of HCl than SO2 in the magma. The SO2 flux at Santiago varies more widely within a single day than observed at other degassing volcanoes and may be controlled at least in part by effects of the solid earth tide. An area larger than 500 km2 has been severely impacted downwind of the volcano. Downwind ground-level concentrations of SO2 of 0.25 ppm are frequently encountered. Acid rain, unusually chloride rich, has a pH as low as 2.63. S/Cl ratios in the gas plume increase downwind, probably as a result of the high solubility and dry-deposition velocity of HCl. Preliminary analyses of primary concentrations of sulfur and chlorine in the magma of the present lava lake are used to calculate that at least 1.2 km3 has been completely degassed, with respect to sulfur, to provide the observed flux. This implies that 10 km3 have been degassed by previous crises in the past century and further suggests a magma supply rate of approximately 0.1 km3/yr (comparable with Kilauea or Etna volcanoes). During historic time, only two lava flows have been extruded, implying an unusually low ratio of extrusion/intrusion of only 0.0007