Although the national emergency commission has lifted a mid-level alert at the mountain, a report Tuesday by the Observatorio Vulcanológico y Sismológico de Costa Rica said that the creation of new vents also was reported before the 1864 and 1868 eruption of Turrialba:
“The stories on the 1864-68 eruption of Turrialba volcano mention the formation of numerous similar fumarolic vents prior to the phreatic and phreatomagmatic eruptions. More recently, Irazú volcano started its activity by the opening of tens of high-pressure fumarolic vents before erupting in 1963.”
A phreatic eruption is when the hot magma makes contact with surface water and produces a steam explosion. Phreatomagmatic eruptions are the result of explosive thermal contraction, many scientists believe.
The scientists said that the vents are the product of the rock weathering and collapsing as a result of rainfall. There are now three high-pressure and high-temperature vents on the peak of the volcano, and the scientists said they expect more vents to be formed because of the weakening of the crater wall rock and the high rainfall.
The observatory put out a report in English Tuesday as well as one in Spanish. The reports said that the volcano is not yet showing signs of imminent eruption within a short time.
“It is important to keep in mind that it remains highly active with the potential of endangerment related to its volcanic activity,” said the English version. The creation of new vents probably will generate ash emissions and throw more volcanic rocks, it added.
The Thursday ash plume traveled mainly to the north northwest, but some was reported in Tres Ríos some 27 kilometers (17 miles) southwest of the volcano, said the report. A plume emitted Friday did not contain ash but was a vigorous output of bluish gas at high temperature that generated a jet-like noise sound audible from the visitor outlook, said the more detailed English report. Scientists estimated the temperature of the Friday plume at 592 degrees C or about 1100 F.
The observatory report was prepared by Geoffroy Avard, Jorge Brenes Marín, Erick Fernández Soto, María Martínez Cruz, Efraín Menjívar P., Javier Pacheco Alvarado, Wendy Sáenz Vargas and Rodolfo Van der Laat Valverde. Many of the scientists visited the mountain peak.
The Comisión Nacional de Prevención de Riesgos y Atención de Emergencias said Tuesday that because the volcano seems to have returned to normality, it was lowering the alert level from yellow to green in the area around the volcano and the adjacent Parque Nacional Volcán Turrialba. The agency said it was maintaining a green preventative alert for the cantons of Turrialba, Alvarado, Jiménez and Oreamuno. The mountain remains a potential risk to humans and animals, it said. The park remains closed to visitors.
The commission also said it asked the Consejo Nacional de Vialidad and the Municipalidad de Turrialba to improve roadways in anticipation of a possible evacuation.