Smithsonian Institution, Bulletin of the Global Volcanism Network
Volume 21, Number 1, January 1996
Popocatepetl (Mexico)  High steam column and variable fumarolic

Several months of explosive activity began at Popocatepetl on 21
December 1994. The eruption followed over a year of increased
seismicity, SO2 flux, and fumarolic activity (Bulletin v. 18, no.
11; v. 19, nos. 1-4, 6, 8, 10, 12).

Beginning at 1140 on 6 January 1996, observers in Puebla saw a
steam column reaching ~6.1 km (20,000 ft). Meteorologists at the
Synoptic Analysis Branch of NOAA were unable to see this steam
column in either the GOES visible or infrared satellite imagery.
On 7 January, as viewed from towns at the volcano=FEs base (such as
Amecameca and Atlautla), strong fumarolic activity continued from
the crater.

Three days later, on 10 January, a helicopter from the
Procuraduria General de la Republica flew L. Cardenas, H.
Delgado, C. Siebe, and others over the volcano. They noted that
fumaroles in the crater appeared rather weak, including those in
the field on the volcano=FEs NW side first noticed in April 1995.
New fumaroles had sprung up on the N crater rim. No emanations
were seen coming from the E-flank fumarolic field.

Later, when observed in conditions of good visibility from
surrounding towns on 13-14 and 17-18 January, fumarolic activity
was absent. Around this time a climb to the crater rim by
Cardenas and Delgado enabled them to look inside; they again saw
fumarolic activity that was weaker compared to that seen during
most of 1994 and 1995. Despite this weak activity, two boccas on
the rim of the old inner lava dome each contained an intensely
hissing fumarole. The rocks cradling the fumarole glowed a
reddish color visible in daylight, attesting to very high
temperatures. In addition, fresh rockslide rubble that had
probably sloughed off the crater=FEs N walls lay on the crater
floor. The crater=FEs inner E wall looked extremely altered,
suggesting that it may be susceptible to additional mass wasting
in the near future.

They saw more intense fumarolic activity from the crater rim than
they had ever seen before, possibly indicating that the main
conduit below the crater floor was in the process of sealing. In
this context they advised against mountaineers climbing to the
summit area, because small Vulcanian explosions could occur at
any time without warning.

C. Valdes-Gonzalez, G. Gonzalez-Pomposo, and A. Arciniega-
Ceballos (UNAM) reported on seismic activity from November 1995
through early January 1996. Activity was monitored using seismic
station PPM, a part of the Mexican National Seismic Network,
located on the north flank at 3,900 m elevation. Seismic events
were classified as type-A, -B, and -AB (Bulletin v. 19, no. 1).

Type-B events dominated during 1 November-8 January, an interval
when 617 were recorded. Where data are available in the interval
1 November-8 January (figure 1), the number of type-B events
ranged between 3 and 18 events/day. During this same interval,
type-A and -AB events registered only 7 and 6 times,
respectively. Fewer than 13 type-B events/day registered during
late November through early January, ending on 5 and 6 January 17
and 18 events/day were recorded, respectively.

Galindo and others (1995) summarized the available SO2 flux
estimates for 2 January 1994-28 January 1995. Other reports in
the same volume described different facets of the volcano=FEs
behavior, including those relevant to public health (e.g. ash-
aerosol dispersion).

Reference: Galindo, I., Gonzalez, and Ayala, R., 1995, Emisiones
de Bioxido de Azurfre del Volcan Popocatepetl, Mexico durante la
erupcion de Diciembre 1994-Enero 1995; Comite Cientifico Asesor
CENAPRED-UNAM, 1995, Volcan Popocatepetl Estudios Realizados
Durante la crisis de 1994-1995; Capitulo VI, Aspectos GeoQuimicos
y de Impacto Atmosferico, p. 245-256.

Information Contacts: Claus Siebe and Hugo Delgado, Instituto de
Geofisica, UNAM, Cuidad Univ., 04510 D.F., Mexico (Email: (Siebe) or (Delgado)); Guillermo Gonzalez-
Pomposo, Carlos Valdes Gonzalez, and Ana Lillian Martin del
Pozzo, Departamento de Sismologia y Volcanologia, Instituto de
Geofisica, UNAM, Cd. Universitaria, 04510, D.F., Mexico (Email:; NOAA/NESDIS Synoptic Analysis Branch,
Room 401, 5200 Auth Road, Camp Springs, MD 20746 USA.

Figure 1. Type-B events (1.0-1.6 Hz) at Popocatepetl, 1 November
1995 to 8 January 1996. Blank where data were unavailable.
Courtesy of UNAM.