Popocatepetl update, May 3, 1996 by Claus Siebe On March 29 juvenile lava that started forming a viscous, presumably dacitic dome was first observed by Hugo Delgado during a COSPEC flight. Since then the dome did grow at a rapid rate. Emissions of ash along a NE-SW running fracture located at the SE inner wall of the main crater have also continued intermittently. Apparently, the emission center of the new domes is located between this fracture and the center of the small inner crater formed during the eruption in the 1920s. I did attend helicopter overflights on April 10, 12, 24 and 29. On all these occasions the gases emanating from the dome did not allow a clear view. The height of the dome was difficult to estimate but was at least 50 m. The dome was in addition growing horizontally from the SE towards the NW with a steep terminal flow front in the NW. On the SE it was leaning in part directly against the inner crater wall of the main crater. The old inner small crater is by now totally covered by the new dome. By comparing pictures of the dome formed in the 1920 s with the present dome it is absolutely clear that the present dome is by now already much larger than the dome in the 1920 s. On April 30 at 13.19 PM local time a major explosion occurred at the new dome. A shower of ejecta was dispersed towards the NE. Maximum clast diameter was 0.5 cm in the village of Xalitzintla, ca. 12 km NE of the crater, sandsized ash fell in the City of Tlaxcala at a distance of 60 km. Because of bad weather conditions the explosion and accompanying phenomena were not recorded by the video camera aimed at Popo. Yesterday, May 2nd, five mountain climbers were found dead a few hundred meters below the NE crater rim on Popos slopes. Their corpses were recovered by Civil Protection authorities and the first information regarding the possible cause of their death was due to lightning, because of severe burns. Latest information indicates that the climbers ascended the mountain in the early morning of April 30 and were reported missing the following day. In addition to the severe 3rd degree burnings, the corpses do also show severe injuries by contusions. It appears that the climbers could also have been killed by the explosion on April 30. Autopsies of the corpses should soon reveal the cause of death. During a helicopter flight this morning (May 3) I could clearly observe a depression at the surface of the new dome, near the SE inner wall of the main crater. In addition streaks of gravel and boulders were running down the NE outer slopes of the cone. These streaks of coarse material were 10 to 20 m wide and a few hundred meters long and very close to the route of ascent to the mountain which is usually taken by most climbers. It is absolutely possible that similar explosions will occur again in the near future for which reason montain climbers should take the signs posted at Paso de Cortes seriously and not attempt (by no means $) to get around the official prohibition to climb Popo. The possibility of ejecta with clast diameters larger than just 0.5 cm falling on nearby villages without major warning and detection of the monitoring system should also be considered seriously and discussed. P.S.: Apparently, the ejecta produced by April 30 was warm at the time of falling in Xalitzintla. The shower on Xalitzintla lasted for ca. 2 minutes. Preliminary inspection of the material delivered in my office points towards mostly juvenile material, light grey dacite, very glassy and with incipient vesiculation.