Popocatepetl Volcano - Update 003

Date: Fri, 23 Dec 1994 16:47:45 MST
From: Rick Wunderman-Global Volcanism Network 
Subject: Popocatepetl

        central Mexico (19.02xN, 98.62xW)
           (summit elevation 5,465 m)
        All times local (= GMT - 6 hours)

     An E-mail message sent by Servando De la
Cruz near midnight on 22 December contained the
following report:
  "The fumarolic activity that had been developing
during the last two years or so culminated on early
December 21, 1994, when a series of volcanic
earthquakes, probably associated with phreatic
explosions, marked the beginning of a new stage of
eruptive activity.  The seismic events, detected at
01:31, 01:32, 01:38, 01:40 and 01:48, were very
impulsive, high frequency, short duration signals, and
were followed by a major, lower frequency event at
01:53.  The events were recorded by 4 telemetric
stations operated jointly by CENAPRED (National
Disaster Prevention Center) and the Institutes of
Geophysics and Engineering of the National
University of Mexico (UNAM).  As the day cleared an
ash plume was observed for the first time in decades
emerging from the volcano crater.  The ash emission
was moderate and produced an almost horizontal
plume causing a light ashfall over the city of Puebla,
about 45 km ENE of the volcano's summit.  A
helicopter flight at 10:30 showed that most of the ash
was issued near the lower rim of the inclined crater at
the NE sector.  A radial fissure could be observed on
the NE flank of the cone.  Some steam-producing
vents could also be observed along the fissure, though
the cloudy conditions makes this interpretation
doubtful.  Old cracks in the glacier appeared to have
extended a significant amount towards the W.  A
second flight the same day at 14:30, revealed a
substantial increase in the ash production (about 3 to
4 times the amount observed in the morning).  The
light-gray ash appeared to be emitted in episodes, with
"puffs" every few minutes.  The seismic levels of
activity (mostly low amplitude B-type earthquakes,
concurrent with high-frequency A-type events)
increased during the day, though maintaining lower
levels than those observed during the previous night.
At this stage and after several consultations between
the scientific group and the Civil Protection
authorities, an evacuation of the most vulnerable
towns and villages of the East sector of the volcano
was started around 21:00 of December 21, and about
31,000 persons were moved during the night to
shelters in safer areas.  19 towns were evacuated.
Since then the situation has remained fairly stationary,
though long duration, low amplitude tremors appeared
in the night between Wednesday and Thursday, and
continue.  More information is expected to be sent
     As of Friday, 23 December, an Associated Press
report stated that the Puebla state government said
75,000 people would be evacuated from the
countryside around the volcano.  One of the evacuated
towns, Santiago Xalitzintla, is located about 13 km NE
of the summit and sits along the road over the pass
between Popocatepetl and the adjacent stratovolcano
to the N, Iztaccihuatl.
     Popocatepetl's Holocene activity has consisted
of alternating effusive and pyroclastic periods, ranging
from mild steam-and-ash emissions to plinian
eruptions accompanied by pyroclastic flows and surges.
Boudal and Robin (1989) identify three periods of
vigorous explosive activity during the Holocene:
10,000-8000 BP, 5000-3800 BP, and 1200 BP-present.
The last cycle ended an effusive period from
3800-1200 BP with a vigorous explosive eruption that
both enlarged the summit crater and generated St.
Vincent-type pyroclastic flows.  Another large
explosive eruption occurred about 1000 yrs BP and
produced pyroclastic flows that descended the
northern flank.
     Historical eruptions depicted on Aztec codices
date back to 1345 AD.  About 30 eruptions have been
reported in historical time, although documentation is
poor.  Most historical eruptions were apparently
restricted to mild-to-moderate Vulcanian steam and
ash emission.  Lava flows restricted to the summit area
may also have occurred in historical time, but cannot
be attributed to specific eruptions.  Larger explosive
eruptions, possibly Plinian in character, were recorded
in 1519 and possibly 1663.  The last significant activity
took place from 1920-22.  Then, intermittent explosive
eruptions produced 6.6-km-high columns and a small
lava plug was intruded into the summit crater.  
Minor ash clouds were also reported in 1923-24, 1933,
1942-43 and 1947.

Boudal, C., and C. Robin, 1989, Volcan Popocatepetl:
Recent eruptive history, and potential hazards and
risks in future eruptions, IAVCEI Proceedings in
Volcanology 1; J.H. Latter (Ed.), Volcanic Hazards,
Springer-Verlag Berlin Heidelberg, pp. 110-128.
     Information Contacts: S. De la Cruz-Reyna
(Instituto de Geofisica-CENAPRED; e-mail:
sdelacrr@tonatiuh.igeofcu.unam.mx), Roberto Quaas
(Instituto de Ingenieria-CENAPRED), Esteban
Ramos, EnriqueGuevara Ricardo Gonzalez, Bertha
Lopez, Salvador Medina (CENAPRED).