Arenal (Costa Rica): Recorded Eruptions and Historical Activity

Arenal is a stratovolcano located in Costa Rica, standing at an elevation of 1,670 meters within a subduction zone and continental crust tectonic setting. Official records from the Smithsonian Global Volcanism Program document a total of 27 confirmed eruptions spanning thousands of years, with activity characterized by methods ranging from radiocarbon dating and tephrochronology to direct historical observations.

Overview of Recorded Activity

The confirmed eruption record for Arenal extends from prehistoric times into the 20th and 21st centuries. Across the 27 confirmed eruptions, the largest recorded Volcanic Explosivity Index (VEI) reaches 4.0. The earliest recorded eruption in the dataset dates back to 5060 BCE with an uncertainty of 150 years, while subsequent activity is distributed across multiple centuries BCE and CE.

Representative records from the Smithsonian Global Volcanism Program illustrate the diverse documentation methods used across Arenal's timeline:

• 5060 BCE (±150 years): Recorded with a VEI of 4.0, evaluated via calibrated 14C isotopic evidence.
• 2250 BCE: Recorded with a VEI of 4.0, determined through tephrochronology correlation.
• 270 BCE: Recorded with a VEI of 4.0, also using tephrochronology correlation.
• 1400 CE: Recorded with a VEI of 4.0, identified using uncalibrated 14C isotopic evidence.
• 1968–2010: An eruption beginning on July 29, 1968, with a VEI of 3.0 affecting the west flank and summit, concluding on December 16, 2010, based on reported observations.

Eruption Chronology and Methods

The historical record combines absolute dating techniques with direct observations. Prehistoric events rely heavily on isotopic and tephrochronological correlations, providing a framework for understanding the volcano's long-term behavior. Later events, such as the activity starting in July 1968, are documented through direct reporting. The profile notes a last-known eruption year of 2010, marking the conclusion of the activity period that began in 1968.