"The approximately 3-year gas emission crisis from Santiago Crater continued in late 1982. Total SO₂ flux was apparently reduced from the very large levels reported before. Incandescence within the inner crater was dull red-orange, as compared to the brilliant orange observed in February, 1982. The 7 October, 1982 explosion threw out abundant, juvenile, highly vesiculated scoria, which was often flattened and oxidized against the ground surface. Numerous fragments of sublimate minerals torn from the lip of the inner crater were ejected with the juvenile scoria. No new explosions have thrown debris out of Santiago Crater but several gas bursts have been reported by Park guards."

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.

Information Contacts: S. Williams, R. Stoiber, Dartmouth College; G. Hodgson V., D. Fajardo B., INETER.