Report on Masaya (Nicaragua) — April 1996
Bulletin of the Global Volcanism Network, vol. 21, no. 4 (April 1996)
Managing Editor: Richard Wunderman.
Masaya (Nicaragua) Incandescent vent in Santiago crater emitting large amounts of gas
Please cite this report as:
Global Volcanism Program, 1996. Report on Masaya (Nicaragua). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 21:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199604-344100.
11.984°N, 86.161°W; summit elev. 635 m
All times are local (unless otherwise noted)
Masaya was visited on 15-16 March by a joint team from the Open University, the Universite de Montreal, Reading University, and INETER. Large amounts of gas exiting a 5-m-wide vent at the bottom of Santiago crater formed a distinct plume clearly visible from the Managua airport. The vent was intensely incandescent, even during mid-day. Eight correlation spectrometer (COSPEC) traverses beneath the gas column on 16 March measured an SO2 flux of 600 ± 290 metric tons/day (t/d). These fluxes are similar to those measured during the degassing crisis of the early to mid-1980's (Stoiber and others, 1986). Microgravity measurements revealed a continued decline of the gravity field in the summit region since re-activation of the volcano in 1993 (BGVN 18:06). Systematic decreases of up to 160 microgals have been recorded during this time near the active crater.
Reference. Stoiber, R.E., Williams, S.N., and Huebert, B.J., 1986, Sulfur and halogen gases at Masaya caldera complex, Nicaragua: Total flux and variations with time: Journal of Geophysical Research, v. 91, p. 12,215-12,231.
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: Hazel Rymer and Mark Davies, Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom; John Stix, Dora Knez, Glyn Williams-Jones, and Alexandre Beaulieu, Departement de Geologie, Universite de Montreal, Montreal, Quebec H3C 3J7, Canada; Nicki Stevens, Department of Geography, University of Reading, Reading RG2 2AB, United Kingdom; Martha Navarro and Pedro Perez, INETER, Apartado Postal 2110, Managua, Nicaragua.