INETER reported that during 20-22 January the lava lake in Masaya's Santiago crater continued to be active. Abundant gas emissions rose 350 m above the crater rim on 20 January, and an increase in sound waves from the lava-lake activity was reported. During a field visit that same day, volcanologists noted that the lava lake in the vent on the S part of the crater floor had risen, and that a vent on the NE part of the floor was incandescent. During 21-22 January small gas explosions sounded like gunshots.

Geological Summary. Masaya volcano in Nicaragua has erupted frequently since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold" until it was found to be basalt rock upon cooling. It lies within the massive Pleistocene Las Sierras caldera and is itself 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 Nindirí and Masaya cones, the source of observed 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 6,500 years ago. Recent lava flows cover much of the caldera floor and there is a lake at the far eastern end. A lava flow from the 1670 eruption overtopped the north caldera rim. Periods of long-term vigorous gas emission at roughly quarter-century intervals have caused health hazards and crop damage.

Source: Instituto Nicaragüense de Estudios Territoriales (INETER)