On 18 April INETER reported that there continued to be no signs of lava-lake activity at the bottom of Masaya’s Santiago Crater after material from a landslide had covered the lake on 2 March. Small landslides continued to occur periodically, and one was shown in a webcam photo from 17 April. Continuous diffuse gas emissions rose from a vent on the crater floor and from a new vent located on the inner SW wall.

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)