Tuesday, April 2, 2013


Costa Rica’s Arenal volcano is the nation’s most active volcano. It is considered to be a stratovolcano, which is a large, steep-sided and symmetrical volcano made of rock, ash, and lava deposits. This particular stratovolcano was formed at a convergent plate boundary at the meeting place of oceanic and continental crust; the more dense oceanic crust sank beneath the less dense continental crust in this region. The subsiding crust was heated due to the increased temperatures beneath the Earth’s surface and eventually melted to produce magma. The magma then rose to the Earth’s surface to form the volcano. Arenal is 1,657 meters high, and is located to the northwest of the dormant Chato volcano, which has not erupted in 3,500 years.

Arenal is part of a volcanic chain that has moved northwest of its original location. By itself, Arenal has eruptions dating back 7,000 years, and continues to grow because of periodic eruptions that have occurred since 1968. Prior to this time, farmers and ranchers who lived in the area referred to the volcano as a mountain because it was dormant for 400 to 500 years. When it did eventually erupt on July 29, 1968, Arenal buried 15 square kilometers with rocks, ash, and lava over 232 square kilometers of land. The explosion also buried three villages and left 87 people dead. Rocks weighing several tons were thrown more than a kilometer away from the volcano at a rate of 600 meters per second at the height of the eruption. The explosion burst from three craters. The primary source of rocks and debris was “Crater A” in 1968, which is on the western flank of the volcano. “Crater C” is now the region capable of having the most activity. A fourth crater, “Crater D,” existed before this most recent explosive period. As a result of these craters, Arenal now appears to have a double summit.

Its activity has decreased since 2010, but from 1968 to 2010, the volcano erupted almost every single day. It is now an active tourist site in Costa Rica. There are currently six active volcanoes in Costa Rica and 61 dormant or extinct volcanoes.

Photo of Arenal eruption courtesy of Gregory G. and Mary Beth Dimijian at http://www.dimijianimages.com/.









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