INETER reported that the lava lakes in three vents on the floor of Masaya's Santiago crater were active during 20 February-1 March. Volcanic tremor remained high and RSAM values were at high to very high levels. On 23 February small explosions ejected spatter onto the crater floor. During fieldwork volcanologists observed active lava lakes in all three vents on the crater floor, and noted that the inner walls of the crater were being eroded due to the lava lake. A new vent was forming on the SE part of the crater floor. During a second visit on 24 February INETER staff noted that the vents had become larger due to landslides on the crater walls. Small streams of lava sporadically originated from the NE vent. By 1 March the two vents in the SW part of the crater had almost merged.

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)