Geologic Background:
The 7-km-wide, lake-filled Apoyo caldera is a
large silicic volcanic center immediately SE of Masaya
caldera. An early shield volcano contructed of
basaltic-to-andesitic lava flows and small rhydocitic
lava domes collapsed following two major dacitic
explosive eruptions. The caldera-forming eruptions have
been radiocarbon dated at about 23,000 years before
present. Post-caldera ring-fracture eruptions produced
lava flows below the scallaped caldera rim. Eruptions
along a slightly arcuate N-S fracture system 2 km E of
the caldera rim formed the Granada cinder cones and La
Joya collapse craters. The age of the latest eruptive
activity is not known. The surface of Laguna de Apoyo
lies only 78 m above sea level; the steep caldera walls
rise about 100 m to the eastern rim and up to 500 m to
the western rim. The younger slightly arcuate,
N-S-trending La Joya fracture system that cuts the
eastern flank of the caldera only 2 km east of the
caldera rim is a regional fissure system structurally
unrelated to Apoyo caldera.
Historic Activity:
Recent Activity:
- No fumarolic or seismic activity was detected in
1990.
- A swarm of seismic events was observed in June 1997,
centered on the east flank of the Laguna de Apoyo. The
strongest event was a M 3.7 on June 8. The events were of
tectonic character.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 13, No. 1)
- Global Volcanism Network (V. 16, No. 2 and V. 22, No.
6).
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