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
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
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:; Ignacio Galindo, Arturo Gonzalez, J.C.
Gavilanes, Carlos Navarro, CUICT-Universidad de Colima, Mexico
(Email:; Hugo Delgado, Instituto de
Geofisica, UNAM, Mexico (Email:;
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.