Laguna de Arenal (Arenal Lake) is the largest lake in Costa Rica and it is man-made. In 1974 the Tronadera Dam was built to flood a basin. The dam now supplies the country with 40-75% of its electricity. The area is windy and wind turbines also generate electricity. Windsurfing and para-surfboarding are popular sports, along with fishing for the rainbow trout stocked in the lake.
Several towns, including the original town of Arenal, are covered by the lake. In the past few years the water level has dropped 18 feet as a result of El Niño, exposing a church steeple and a hillside cemetery.
Volcan Arenal (Arenal Volcano) is the most active volcano in the western hemisphere and one of ten of the most active in the world. It is a classical wide cone shape with clouds of steam escaping from the vents. It ejects car-sized boulders, spits lava, and shoots columns of ash into the air. Its location borders the region between cloud and rain forests, and it is often fogged in by clouds. It apparently sits directly over a magma chamber in a fault 3-13 miles below the surface of the earth.
It is the youngest strato-volcano in Costa Rica, being 2900 years old. Eruptions build up the volcano layer by layer, and it is now about 5372 feet in height. Eruptions were reported before the Spanish Conquest, but the volcano was quiet until fumaroles were seen in 1938, 1958, and 1960. In 1967, the water temperature of Rio Tabacon suddenly rose - in hindsight a warning of eruption. On July 28, 1968 there was a series of earthquakes and then at 7:30 AM on July 29th the volcano erupted, damaging areas up to three miles to the west, and killing 80 people and 45,000 cattle.
The area has many hot springs and several commercial spas have opened to allow people to bathe in pools of varying temperatures.
Parque Nacional Volcan Arenal (Arenal Volcano National Park) has been protected since 1995, covering 29,902 acres. Half of Costa Rica's land-dwelling invertebrates can be found here. There are several trails around the volcano, some crossing old lava flows, but one cannot climb the volcano because it is still active. The park is sometimes closed when the fumes are too strong, and steam and sulfur create sulfuric acid.
Next: 8. Arenal Volcano Excursion