Arenal Volcano, situated in the northern region of Costa Rica, is a major natural landmark. Its nearly symmetrical, conical form has made it one of the country’s most recognizable and photographed sights. Although the volcano has a reputation for being highly active, it is currently resting. This shift has moved the focus from eruption viewing to enjoying the surrounding geothermal features and rainforests. Answering how many times it has erupted requires understanding its complex history, as a simple count is insufficient.
Geological Context and Pre-Modern History
Arenal is classified as an andesitic stratovolcano, characterized by a steep profile and explosive eruption style. It is one of Costa Rica’s youngest volcanoes, with an eruptive history extending back approximately 7,000 years. During this time, Arenal experienced major explosive events, such as Plinian eruptions, interspersed with centuries-long periods of quiescence.
Prior to its modern awakening, the volcano was inactive for an estimated 400 to 530 years before the mid-20th century. The cone was covered in dense vegetation, and locals often referred to it simply as “Cerro Arenal,” or Arenal Mountain. This dormancy led many to mistakenly believe the volcano was extinct or permanently inactive.
The Cataclysmic 1968 Event
The modern eruptive period began abruptly on July 29, 1968. The initial explosion was a powerful lateral blast that devastated the western flank, burying over 15 square kilometers under rock, ash, and lava. This Pelean-type eruption involved pyroclastic density currents and ballistics, ejecting giant rocks at speeds up to 600 meters per second.
The eruption continued intensely for several days, completely destroying the nearby villages of Pueblo Nuevo and Tabacón. The disaster resulted in the death of 87 people and dramatically reshaped the volcano’s structure. The explosions opened three new craters, labeled A, B, and C, on the western flank, marking the start of its modern activity count. Crater C, the lowest and largest vent, became the primary source of activity for the following decades.
Decades of Continuous Activity (1968–2010)
Following 1968, Arenal entered a 42-year phase of nearly continuous activity, making a simple numerical count of “eruptions” impossible. The volcano exhibited sustained activity, characterized by a combination of effusive and explosive phenomena, including Strombolian and Vulcanian eruptions.
Activity was concentrated in Crater C, which constantly extruded basaltic andesite lava flows. These slow-moving flows mainly descended the west and northwest flanks, often creating incandescent avalanches and pyroclastic flows as the lava fronts collapsed. During this four-decade span, the volcano produced more than 100 lava flows and over 60 pyroclastic flow events, maintaining daily ash emissions and frequent explosions until its activity began to decline.
Current State of Dormancy
The long eruptive cycle that began in 1968 concluded, with the last significant lava flows and explosive activity ceasing around late 2010. Since then, Arenal has been classified as dormant or resting, retaining the potential to erupt again. The decline was marked by a decrease in volcanic earthquakes, tremors, and a reduction in the temperature of gas emissions.
Currently, activity is limited to weak gas emissions from fumaroles in the craters. The Observatorio Vulcanológico y Sismológico de Costa Rica (OVSICORI) continues to monitor the volcano, detecting only low concentrations of gases like carbon dioxide and hydrogen sulfide. Although the explosive risk is low, the remaining geothermal heat fuels the area’s famous hot springs, which draw visitors to the quiescent volcano.