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11.
The sequence of large Vulcanian explosions occurring at the andesitic Popocatépetl volcano, Mexico during November 1998 to April 1999 was studied. The size of 26 largest explosions was estimated from broadband seismic records at the distance of 4 km from the crater. The sequence began with the largest explosion (E = 2.6 × 1012 J) occurring on 25 November at 08:05, and following largest daily explosions were characterized by gradual decrease in the energy. The energy of 20 large (E ≥ 1011 J) explosions was distributed as Student's t-distribution with a geometrical mean Log E = 11.81 (J). 相似文献
12.
Jiménez J. C. Raga G. B. Baumgardner D. Castro T. Rosas I. Báez A. Morton O. 《Natural Hazards》2004,31(1):21-37
A 17-day field campaign was carried out in April–May 1999 to determine thecontribution that gaseous volcanic emissions make to the compositionof solid particles,particularly to the presence and quantity of sulfates. Theexperimental site was located inTonantzintla (in the State of Puebla), only 30 km E from the volcanoPopocatépetl, whichhas been in an active phase since the end of 1993. An analysis ofthe carbon monoxide(CO) and sulfur dioxide (SO2) in the ambient air identifiedvolcanic influence in 6 out ofthe 17 days sampled. Particles collected in an 8-stage cascadeimpactor were analyzed for inorganic ions (by liquid chromatography).A non-parametric test indicates asignificant difference on the total particle mass and thesulfate fraction between days withand without volcanic influence. This difference was predominantlyobserved in the stages that collect the smaller particles. Windsat 500 mb (roughly corresponding to thesummit of the volcano) indicate a westerly transport from thevolcano to the experimentalsite, even though surface winds do not show a clear signal ofsuch a transport. Back trajectories from the experimental site werecalculated and clearly indicated that air parcels on the daysindependently identified as with volcanic influence had indeed passed over the volcano. 相似文献
13.
Servando De la Cruz-Reyna Gerardo Carrasco-Núez 《Journal of Volcanology and Geothermal Research》2002,113(1-2)
Citlaltépetl or Pico de Orizaba is the highest active volcano in the North American continent. Although Citlaltépetl is at present in repose, its eruptive history reveals repetitive explosive eruptions in the past. Its relatively low eruption rate has favored significant population growth in areas that may be affected by a potential eruptive activity. The need of some criteria for hazards assessment and land-use planning has motivated the use of statistical methods to estimate the time and space distribution of volcanic hazards around this volcano. The analysis of past activity, from late Pleistocene to historic times, and the extent of some well-identified deposits are used to calculate the recurrence probabilities of eruptions of various size during time periods useful for land-use planning. 相似文献
14.
M. A. Armienta S. De la Cruz-Reyna O. Morton O. Cruz N. Ceniceros 《Journal of Volcanology and Geothermal Research》2002,113(1-2)
Leachates from ash samples of the Popocatépetl eruptions of April 30, 1996, May 12, 1997, and October 17, 1998 settled at different distances from the crater were analyzed for anions (SO42−, Cl−, F−) and some metals. This study is aimed at determining the causes of the compositional variations of the leachates, to assist the assessment of water, soil and crop contamination due to ash deposits. Different behavior was observed in the ion concentrations with distance for the three eruptions. On April 30, 1996, SO42− and F− concentrations increased with distance, and Cl− remained almost constant. On May 12, 1997, concentrations of the three anions decreased with distance. On October 17, 1998, F−, Cl− and SO42− increased more than three-fold with distance. Tephra size distributions were also different for the three eruptions. The observed trends of the leachates’ anion concentrations may have different causes: the type and intensity of the eruptions, the distribution of the tephra sizes, the degree of interaction of the tephras with volcanic gases, humidity, static charge, the original characteristics of the solid material, the transport time from the crater to the site of settling, and the relative angle between the wind direction and the sampling line. Enrichment factors and concentration trends for metals with distance suggest that Co, Ni, Cu and Pb in the leachates resulted mostly from volcanic gas adsorption. 相似文献