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.