Geologic Background:
Masaya lies 20 km southeast of Managua and
became Nicaragua's first national park in 1979. Masaya is
one of Nicaragua's most unusual and most active
volcanoes. It is a broad, 6 x 11 km basaltic caldera with
steep-sided walls up to 300 m high that is filled on its
NW end by more than a dozen vents erupted along a
circular, 4-km-wide fracture system. Masaya lies within
the massive Pleistocene Las Sierras pyroclastic shield
volcano. The twin volcanoes of Nindiri and Masaya, the
source of historical eruptions, were constructed at the
southern end of the fracture system and contain multiple
summit craters. A major basaltic plinian tephra was
erupted from Masaya about 6500 years ago. Historical lava
flows cover much of the caldera floor and have confined a
lake to the far eastern end of the caldera. A lava flow
from the 1670 eruption overtopped the N caldera rim.
Historic Activity:
- At least 16 eruptions from 1524 to 1972. Masaya has
been frequently active since the 16th century, with
intermittent lava lakes and minor explosive
activity.
- Masaya has been frequently active since the time of
the Spanish Conquistadors, when an active lava lake
prompted several attempts to extract the volcano's molten
"gold."
- The 1965 lava lake covered the entire floor of
Santiago Crater, before beginning to subside in 1979. An
inner crater gradually developed in the cooling lava
lake, reaching 80 m in diameter by 1982.
Recent Activity:
- A vigorous degassing episode, the 4th in this
century, has continued since 1979. Small tephra eruptions
have accompanied the degassing, and glowing lava has
frequently been evident at the bottom of a vent in the
frozen lava lake.
- In February 1989, collapse of portion of crater floor
was followed by a lava lake filling collapse crater and
intense lava fountaining in the center of the lava lake.
In April 1989 the lava lake drained.
- A lava lake reappeared in the bottom of Santiago
crater in late June 1993 for the first time in three
years. Reports of incandescence in May 1997. Small
explosions on Nov. 17, 1997
- Small explosions on Sept 14, 1998.
- Continued degassing and seismic activity in 1999.
Several reports of ash eruptions between Nov. 1999 and
Jan. 2000.
- Seismic activity in July 2000.
- Bomb charged explosion on April 23, 2001
Data Sources:
- Smithsonian's SEAN Bulletin (V. 3, No. 4 to V. 14,
No. 6)
- Global Volcanism Network (V. 15, No. 4 to V. 26, No.
4).
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