Geologic Background:
Popocatepetl, whose name is the Aztec word for
smoking mountain, towers above Mexico City and is North
America's 2nd highest volcano (5,420 m). Popocatepetl
looms over the Mexico and Puebla valleys, potentially
threatening over 20 million people.
The glacier-clad stratovolcano contains a
steep-walled, 250- to 450-m-deep crater. The generally
symmetrical volcano is modified by the sharp-peaked
Ventorrillo on the northwest, 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
south of the volcano resulting in a 6.5 x 11 km caldera.
The modern cone was constructed in two stages. El Fraile
volcano was formed prior to 10,000 years before present
(BP) and was partly destroyed by three episodes of
explosive activity, the last from about 5,000 to 3,800
years BP. The current summit of Popocatépetl was
formed to the south of El Fraile cone by repeated lava
effusions until about 1,200 years BP, after which the
current, dominantly explosive phase began. Frequent
historical eruptions have been recorded since the
beginning of the Spanish era.
In the Holocene Popocatepetl has produced both
effusive and pyroclastic activity. The latter has ranged
from mild steam-and-ash emissions to Plinian eruptions
accompanied by pyroclastic flows and surges. Vigorous
Holocene explosive activity took place in three periods
(in years before present, ybp): a) 10,000 to 8,000,
b)5,000 to 3,800, and c) 1,200 to present. An effusive
period from 3,800 to 1,200 ybp ended with a vigorous
explosive eruption that both enlarged the summit crater
and generated St. Vincent-type pyroclastic flows. Another
large explosive eruption, about 1,000 ybp, produced
pyroclastic flows that decended the north flank.
Historic Activity:
- About 30 eruptions have occurred since 1347 (early
records are Aztec codices, mostly mild-to-moderate
Vulcanian steam and ash emissions. 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 to
1922. Then, intermittent explosive eruptions produced
6.6-km-tall columns and a small lava plug extruded onto
the floor of the summit crater.
- Ash clouds were also reported in 1923-24, 1933,
1942-43, and 1947.
Recent Activity:
- Continuous fumarolic activity began in August
1988.
- Substantial output from steam vents during Oct.-Nov.
1993. The fumarolic activity that had been developing
during the last two years or so culminated on early Dec.
21, 1994, when a series of volcanic earthquakes marked
the beginning of a new stage of eruptive activity. Ash
plumes were observed on satellite imagery to extend upto
250 km to the NE at hieghts of upto 7 km.
- Activity then quieted down with periodic ash
emissions through March 1996. On March 29 a new lava dome
was observed on the east side of the craterfloor and a
lava flow was also observed in the crater. On April 30 a
major explosion from the dome dispersed ejecta to the NE.
Maximum clast diameter was 0.5 cm in the village of
Aalitzintla, ~12 km northeast, and sand-sized ash fell in
Tlaxcala, 60 km away.
- Minor activity January through April, 1997 with a
large explosion on April 29. Large ash emissions occurred
on May 11,14,15, 24, 27, June 3, 11, 14, 19, 21, and 30.
The June 30th eruption was the largest recorded since
current eruptive episode began in 1994. After July 30
activity decreased except for a moderately large emission
on Aug. 12. Gas and steam emmisions continued through
October. Lava extrusion and explosions in December.
- Explosion on Jan. 1, 1998 produced fires and
ashfalls. Minor ash ejections in Jan. thru Oct. Moderate
eruption on Oct. 17 produced ashfall in Mexico
City. Dome grows in crater resulting in moderate to
large explosions in November and December.
- Intermittent explosions from January to July 1999,
low-level activity for remainder of year.
- Growth of small dome in summit crater in February
2000. Small ash eruptions through August. Increase in
activity during Sept. and Oct. Continued dome growth
through Dec.
- Steam-and-ash emissions and periods of dome growth
during 2001.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 11, No. 1 and V. 14,
No. 4)
- Global Volcanism Network (V. 15, No. 8 to V. 25, No.
12).
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