Small mud and sulfur cones up to 3 m high were formed during 1989 on the floor of the active crater. A period of eruptive activity from June 1987 to June 1990 included geyser-like crater lake eruptions, the ejection of mud and pyroclastic sulfur, the formation of temporary small pools of liquid sulfur, and the emission of sulfur lava flows up to 30 m long. Acidic gas plumes caused extensive damage to plantations on the volcano's flanks.

Photo by Jorge Barquero, 1989 (Universidad Nacional Costa Rica).

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