Summit visits in March and April 1989 revealed large sulfur deposits in the main and inner craters, and more than 20 fumaroles on the upper S flank that had not been present 2 years earlier (14:04). The following is a report from Servando de la Cruz-Reyna.

"On 15 November 1989, the first telemetering seismic monitoring station at Popocatépetl began operation near Tlamacas, on the NW flank at 3,980 m above sea level. The station consists of a 3-component, 1-second seismometer, continuously transmitting analog signals to the Instituto de Geofísica, UNAM, in México City. The vertical component is registered on a drum analog recorder, and all three components are digitally recorded on a hard disc, then on an optical disc, when signal amplitudes exceed a preset level. The transducer and recording devices are property of the National Seismological Service, UNAM; the transmitter/receiver set was donated by the Japan International Cooperation Agency. A basic 6-point deformation network was also set up in November 1989 on the NW flank between 3,980 and 4,525 m altitude.

"So far, the 9-month seismic record indicates that background seismicity is dominated by small regional earthquakes occurring within a radius of 40 km, mainly W and SW of the volcano. However, a number of very small local B-type earthquakes have been persistently recorded. The activity has not shown any significant changes. Though minor, the B-type activity and the persistent condensation of sulfur in the inner parts of the crater call for more intensive monitoring."

Geological Summary. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Information Contacts: S. de la Cruz-Reyna, UNAM, México D.F.