Smithsonian Institution Global Volcanism Network Bulletin v. 19, no. 10, October 1994 Popocatepetl (Mexico) SO2 flux increases since May; increase in number of seismic events Popocatepetl central Mexico (19.02N, 98.62W) During late-October, Carlos Valdez-Gonzalez and co-workers identified a sudden, prominent (roughly 1.6- to 10-fold) increase in daily earthquakes compared to previous months (figure 5). Station locations and the terms "A-", "B-", and "AB-type" were previously defined (Bulletin v. 19, nos. 1 and 2). Although Figure 5 shows only B-type events, the other two types remained at 0-1 events/day during September and October. Prior to mid-October, the daily count of B-type events generally remained below 10, but by 28 October they climbed to 26. The B-type events for the first half of 1994 were previously published (Bulletin v. 19, no. 6). Carlos Valdes-Gonzalez noted that this was the fastest rate of increase in the last 23 months. Ignacio Galindo contributed the following report. "A new series of ultraviolet absorption correlation spectrometry (COSPEC) measurements was made by scientists from Universidad de Colima (A. Gonzalez, J.C. Gavilanes and C. Navarro), UNAM (H. Hidalgo) and USGS (T. Casadevall) on 5 November from a rented Cessna 310 airplane. The measurements were requested by the Secretaria de Gobernacion through the Centro Nacional para la Prevencion de Desastres (CENAPRED). Between 1024 and 1148 on 5 November, the plume was traversed 12 times at an altitude between 3,539 and 4,545 m a.s.l. [above sea level] in partially cloudy conditions. The aircraft's global positioning system (GPS) computed the wind speed independently for each traverse. These measurements were each used to make individual SO2 flux calculations, removing the need to use average wind speed (Bulletin, v. 19, no. 8). This procedure is advantageous when the wind speed varies significantly. SO2 data were sent to a datalogger, besides the typical COSPEC strip chart. All the recorded data were transferred into a personal computer where evaluation software produced the final SO2 results together with a statistical analysis of the time series. A manual SO2 determination using data from strip chart records (as reported in Bulletin v. 19, no. 8) was also made by C. Navarro; it reproduced the average values within 2.4% on average. "The SO2 flux on 5 November ranged from 924 to 1,877 metric tons/day (t/d), with a standard deviation of 285 t/d and an average value of 1,261 t/d. Table 1 compares our recent measurements with those of 4 May, which were determined with the same methodology (Bulletin, v. 19, no. 4). The SO2 flux increased substantially between 4 May and 5 November. Although our determinations show absolute values less than those reported by other authors (see Bulletin v. 19, nos. 1 and 8), both data sets show increased SO2 flux." Information Contacts: Guillermo Gonzalez-Pomposo^1, Carlos Valdes-Gonzalez, and A. Arciniega-Ceballos, Departamento de Sismologia y Volcanologia, Instituto de Geofisica, UNAM, Ciudad Universitaria 04510 D.F., Mexico (Email: firstname.lastname@example.org); Ignacio Galindo, Arturo Gonzalez, J.C. Gavilanes, Carlos Navarro, CUICT-Universidad de Colima, Mexico (Email: email@example.com); Hugo Delgado, Instituto de Geofisica, UNAM, Mexico (Email: firstname.lastname@example.org); Thomas J. Casadevall, USGS, Denver Federal Center MS 903, Denver, CO 80225, USA; ^1Also at Benmerita Universidad Autonoma de Puebla. Figure 5. Daily number of B-type seismic events at Popocatepetl, May-October, 1994. Courtesy of Carlos Valdes-Gonzalez, UNAM. Date Average Maximum Minimum STD (t/d) (t/d) (t/d) 4 May 900 1,462 485 232 5 November 1,261 1,877 924 285 Difference: 361 415 439 Percentage: 40 28 91 Table 1. Popocatepetl SO2 flux measurements on 4 May and 5 November 1994. Courtesy of Ignacio Galindo, Universidad de Colima.