Report on Masaya (Nicaragua) — July 1993
Bulletin of the Global Volcanism Network, vol. 18, no. 7 (July 1993)
Managing Editor: Edward Venzke.
Masaya (Nicaragua) Small ash eruption precedes formation of lava lake; fumarole temperatures rise
Please cite this report as:
Global Volcanism Program, 1993. Report on Masaya (Nicaragua). In: Venzke, E (ed.), Bulletin of the Global Volcanism Network, 18:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199307-344100.
11.984°N, 86.161°W; summit elev. 635 m
All times are local (unless otherwise noted)
In the last week of March 1993 a fissure was observed to open in the bottom of Santiago crater, with no associated seismic activity. Enlargement of the fissure to 10 m in diameter was accompanied by high-pressure gas emissions. In the first week of April, an earthquake swarm occurred approximately 3 km E of Masaya City; the largest event was M 2.7. At the same time, minor microearthquake activity was registered beneath Santiago crater (1-2 events/day). On 16 June a small ash eruption in the late afternoon lasted for about 13 minutes. That same night incandescence was observed in the bottom of the Santiago crater (BGVN 18:06).
A 7-8 m diameter vent with liquid lava splashing at a depth of about 30-40 m was present on 20 June according to a report by Alain Creusot (BGVN 18:06). An additional report from Creusot indicates that an incandescent hole that had opened above the lava lake was 1-2 m larger in late July. A significant increase in gas emission has maintained a plume rising from the crater. As of 28 June, the temperature of gas emissions from the crater had increased. INETER reported that fumarole temperatures have generally been around 50°C since the beginning of the year, but have now increased to almost 250°C. Seismicity has generally remained low, with a slight increase on 4 July.
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: Oscar Leonel Urbina, Departamento de Volcanes, INETER; Alain Creusot, Instituto Nicaraguense de Energía, Managua, Nicaragua.