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Report on Masaya (Nicaragua) — May 1985

Scientific Event Alert Network Bulletin, vol. 10, no. 5 (May 1985)
Managing Editor: Lindsay McClelland.

Masaya (Nicaragua) Small ash eruptions

Please cite this report as:

Global Volcanism Program, 1985. Report on Masaya (Nicaragua). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 10:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198505-344100.

Volcano Profile |  Complete Bulletin



11.984°N, 86.161°W; summit elev. 635 m

All times are local (unless otherwise noted)

In December 1983, 4,993 microearthquakes were recorded at Masaya. Early that month, a very large gas column was continuing to emerge from Santiago Crater. A series of small ash eruptions occurred in April 1984. There was a small gas explosion on 23 January 1985, and another ash eruption occurred in April 1985.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras pyroclastic shield volcano and is a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The twin volcanoes of NindirĂ­ and Masaya, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra 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 north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals cause health hazards and crop damage.

Information Contacts: D. Fajardo B., INETER.