Streams of volcanic rock that spewed from Arenal Volcano, in north-central Costa Rica, caused a lava avalanche that producing 700-meter craters in the volcano’s north side and isolated forest fires yesterday, according to volcanic monitoring specialist Eliecer Duarte from the Volcanological and Seismological Observatory of Costa Rica (OVSICORI), based at Universidad Nacional (UNA) in Heredia, north of San José.

According to witnesses, the lava flow ignited vegetated areas of the volcano, and the eruption produced a thick cloud of gases and ash, but the fires blew out on their own and no danger was posed to the surrounding community.

This type of activity is normal for Arenal, which has shown almost 40 years of sustained activity, Duarte said. “Eruptions occur every day, but not all of them cause an avalanche that produces craters of this size,” he added.

Scientists are studying Arenal to determine whether the eruption was caused by pressure inside the volcano or gravitational activity. Lava flow of this kind is beneficial, Duarte said, because it releases tension and prevents larger, potentially dangerous eruptions.

“As long as small rock slides occur, we can avoid larger ones,” he said. “It lets the weight and accumulation of material get stabilized.” Similar rock slides occurred in November, January and April of this year.

Residents in the Arenal area who have received informal training from OVSICORI monitor the volcano’s activity, Duarte said, and notified authorities of yesterday’s eruption.

By Amanda Roberson - Tico Times Staff