Report on Masaya (Nicaragua) — April 1992
Bulletin of the Global Volcanism Network, vol. 17, no. 4 (April 1992)
Managing Editor: Lindsay McClelland.
Masaya (Nicaragua) Weak gas emission; acid gas and rain effects diminish
Please cite this report as:
Global Volcanism Program, 1992. Report on Masaya (Nicaragua). In: McClelland, L. (ed.), Bulletin of the Global Volcanism Network, 17:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199204-344100.
11.984°N, 86.161°W; summit elev. 635 m
All times are local (unless otherwise noted)
During a 26 April visit to Santiago Crater, extremely weak emissions were observed from two or 3 small, quiet fumaroles at the base of the talus in the inner crater and up the W wall (toward Nindirí Crater). COSPEC measurements indicated an SO2 flux of <10 metric tons/day (t/d), compared to 1500-2000 t/d during lava lake activity in 1980 (SEAN 05:12). Simultaneous use of SO2 and HCl INTERSCAN instruments at the crater indicated HCl concentrations several times greater than SO2. A drive on the WSW (downwind) ridge, the site of extensive acid gas deposition and acid rain during the early 1980's (SEAN 05:12, 06:12, and 07:08), showed that vegetation had recovered somewhat; the same stark deforested appearance was still evident, but low shrubs were healthier and larger.
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 Nindirí 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: S. Williams, Arizona State Univ; Martha Navarro C. and Silvia Arguello G., INETER.