Rincon de la Vieja is an active volcano. The area is remote, making volcano monitoring difficult. Very few population centers are located within a distance of 10 Km from the volcano. Its last strong eruption period was between 1966 and 1970, when it produced earthquakes, ash clouds and underground noises. Other eruptions, of lower intensity, took place between 1983 and 1984 without causing much alarm among the scarce population located nearby.

According to the scientists of Costa Rican Volcanological and Seismological Observatory at Universidad Nacional, Heredia, Costa Rica (OVSICORI-UNA), the last important eruption occurred in November 1995. On the 6th of this month Rincon de la Vieja volcano started a period of increased activity, which had its highest peak on the 8th. After that, the volcano continued to have very strong fumarolic activity and small to moderate size vapor eruptions.

The climax of the eruption occurred in the morning of November 8, 1995 when the frequency and strength of eruptions was the largest and produced eruption columns up to 3 kilometers high above the active crater, with a rich content of water and wet ash. The speed, at which the ash descended to the main road on the north flank of the volcano near Buenos Aires de Upala, was estimated to range between 23-93 Km/h, with an average of 44 Km/h.

The shock wave of an eruption on November 9, 4:11, was felt in Liberia, located 25 Km southwest of the volcano. Glowing rocks on the northern flank of Rincon de la Vieja were reported seen by observers, during that same eruption.

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