Arenal Volcano, Active stratovolcano in northern lowlands, Costa Rica.

Arenal is a volcano in northern Costa Rica that rises to 1657 meters above sea level with steep flanks of dark andesite rock. The conical summit stands at the center of a national park covering more than 12,000 hectares of tropical rainforest and secondary forest.

Arenal was treated as an extinct "Cerro" before 29 July 1968, when at 7:30 a.m. magma broke the surface and three new craters opened on the western flank. Blocks travelling at up to 1,350 km/h killed 87 people and destroyed Tabacón, Pueblo Nuevo and San Luís. Strombolian activity continued until October 2010, when the last incandescent material was ejected.

The name Arenal was recorded from 1922 because the volcano's lavas break down into lithic and crystalline sands that settle on the cone's flanks, giving it the look of a sand mound. Earlier names include Los Ahogados (1852) and Cerro Pan de Azúcar (1896). Maleku legends tell of a fire god living inside the mountain.

Several walking routes lead through the park to viewpoints where you can watch the cone and sometimes rising steam plumes. The surrounding region offers thermal baths fed by the mountain's geothermal system and they provide relief after longer walks.

Before 1968 the volcano was widely considered extinct and was known simply as Cerro Arenal; hikers had camped in its crater sheltered by fumaroles, which numbered 8 in 1937, 15 in 1951 and 30 by 1959. The 1968 blast threw blocks at 1,350 km/h, gouging impact craters up to 25 m wide and 4 m deep.