Report on Masaya (Nicaragua) — 16 December-22 December 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 16 December-22 December 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Masaya (Nicaragua). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 16 December-22 December 2015. Smithsonian Institution and US Geological Survey.
11.984°N, 86.161°W; summit elev. 635 m
All times are local (unless otherwise noted)
INETER reported that rumbling and shock waves from small gas explosions at Masaya's Santiago Crater were reported during 15-17 December. Scientists conducting field work on 18 December observed that the crater hosting a lava lake had widened. Sounds from the volcano were louder and sulfur dioxide emissions had increased. During 19-20 December spatter from the lava lake was ejected from the vent and landed a few meters away on the crater floor. RSAM levels were stable at low-to-moderate levels.
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.