Arenal is the most active volcano in Costa Rica and one of the most active in the world. The area where it is located remained virtually unexplored until way into the XX century. The first documented expedition to its summit was accomplished in 1937.
The earliest known eruptions of Arenal occurred about 7,000 years ago. Since then, periodic explosive eruptions at several-hundred-year intervals alternated with periods of lava effusion, have built the 1,657 mts high perfectly cone shaped mountain.
Its huge explosive eruption of July 1968 marked the beginning of the actual eruptive period. That day the explosion blew a huge hole out the west side of the mountain. The Volcano killed 87 people and buried the villages of Tabacon and Pueblo Nuevo. Eruptions continued for several days and completely covered over 15 square kilometers with rocks, lava and ash.
After the 68 eruption, La Fortuna gained international fame and soon became the main site for studying volcanoes in Costa Rica. Thanks to the research carried on during the last 30 years we know that Arenal has had at least 22 important eruptions (some similar in magnitude to those of Mount Vesuvius in the year 79 DC or Mount Saint Hellens in 1980) and dozens of other smaller ones like the one in 1968.
Continuous daily activity with slow lava effusion and occasional pyroclastic flows (avalanche of hot gases, ashes and small rocks) and explosive eruptions persist to this day and visitors can enjoy the amazing sight of one of the most active volcanoes in the world.
These are a couple of links to learn more about volcanoes:
• How volcanoes work? Excellent educational link describing the science behind volcanoes:
• Volcano Info: