At 1426 on 23 April a small explosion at Masaya's Santiago crater lasted for ~2 minutes and occurred in three phases. During the first phase volcanic gas under high pressure was explosively released and created a new vent in the bottom of Santiago crater. The eruption sent rock fragments up to 60 cm in diameter as far as 500 m from the crater. Several vehicles parked at a visitors platform near the crater were damaged by the ejecta and one person suffered minor injuries. During the second and third phases a mixture of hot volcanic gas, pieces of lava, and ash ignited dry vegetation near the crater. INETER personnel who monitored the seismic activity before the eruption and scientists from Cambridge University who were working in the crater one hour before the eruption did not notice any unusual activity at the volcano. INETER personnel monitored the volcano after the eruption and found that several small explosions, gas outbreaks, and minor collapses of the crater wall occurred. They warned that further explosions may occur that could affect areas near the crater (within ~500 m).

Geological Summary. Masaya is one of Nicaragua's most unusual and most active volcanoes. 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 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 6,500 years ago. Historical 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. 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 have caused health hazards and crop damage.

Sources: Instituto Nicaragüense de Estudios Territoriales (INETER), Associated Press