Geologic Background:
Located 280 km south of Farallon de Pajaros and
nearly 2,000 km SSE of Tokyo. Pagan Island, the largest
and one of the most active of the Marianas Islands,
consists of two stratovolcanoes connected by a narrow
isthmus. Both North and South Pagan stratovolcanoes were
constructed within calderas, 7- and 4-km in diameter,
respectively. The 570-m-high Mount Pagan at the NE end of
the island rises above the flat floor of the caldera,
which probably formed during the early Holocene. South
Pagan is a 548-m-high stratovolcano with an elongated
summit containing four distinct craters.
Historic Activity:
- The pre-1981 Pagan record includes 11 eruptions
dating back to the early 1800's, and a tentative eruption
in 1669.
- Eruptions in 1669, 1825, 1864, 1873, 1909, 1917,
1923-1925, 1929-1930, and 1966.
- Most of the historical eruptions of Pagan have
originated from North Pagan volcano.
Recent Activity:
- Major eruption (largest of its 13 historical
eruptions) in May 1981. The 1981 eruption, which sent a
Plinian column to >13 km elevation, was the largest
eruption in Pagan's historical record. The island's 53
residents were evacuated at the start of the eruption,
and have made only temporary visits since then. Despite
infrequent observations by former residents, scientists,
aircraft overflights, and from nearby islands, several
small to moderate ash eruptions have been reported. Since
the May 1981 eruption, several small to moderate ash
eruptions have been observed, and plumes have
occasionally been visible on satellite imagery. Seismic
monitoring of Pagan ended in 1984.
- An ash cloud extended 110 km NW from Pagan on August
25, 1988. Another ash eruption occurred on Oct. 11 with a
ash cloud reaching 3 km high and extending roughly 40 km.
Small ash eruption occurred on April 13, 1992. Ground
surveys show inflation which began in Sept. 1990.
- A 168-km deep Benioff-zone earthquake (Mb 5.7)
occurred on January 18, 1993 with an epicentral location
approximately 40 km north of Pagan. It is speculated that
the earthquake affected the behavior of the volcano.
Columns rising to 2000 m above the summit were observed
in mid-January and on March 17. It is thought that other,
unobserved eruptive events have also occurred. A distinct
change in seismic activity took place on about Feb. 13,
1993. Intermittent ash ejections continued from North
Pagan, the larger of the two strato-volcanoes on the
island, into Nov. 1993. Eruptive pulses, 30 to 60 minutes
long, were occurring several times each day during this
period.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 6, No. 4 to V. 13,
No. 10)
- Global Volcanism Network (V. 15, No. 9 to V. 19, No.
2)
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