Smithsonian Institution, Bulletin of the Global Volcanism Network Volume 21, Number 1, January 1996 Popocatepetl (Mexico) High steam column and variable fumarolic activity 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: email@example.com (Siebe) or firstname.lastname@example.org (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: email@example.com); 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.