The region of lakes, volcanoes mountains and hot-water rivers can be reached from the Central Valley by the road between San Ramón and La Fortuna (67 kms).
The almost perfect cone of Arenal Volcano soars 1,633 meters above sea level, has a crater 140 mts. deep formed over an ancient caldera. It dates back to 2-3 million years ago. On July 29th 1968, it ceased to be dormant and began a new stage of eruptions that has lasted to the present day. At the time it destroyed 1,500 hectares, affected 32,000 hectares and covered over 700 hectares with lava, as a result of its emissions of pyroclasts, ash steam and burning clouds. There is no record of any eruptions that took place during the Spanish Conquest and subsequent colonisation, but some carbon-dated potsherds and samples of coal suggest there was volcanic activity between 1200-1500. By 1937 records were being kept of the activity in the crater.
The episode of 1968 began with an eruption on 29th-30th July, killing 87 people and causing some damage. A quiet phase followed from 31st July-9th August, during which time the volcano emitted hot vapours and large amounts of ash. On 9th August, fumarolic activity began in the new craters, on the 14th explosions were heard, and on the 19th there was a lava flow 25 meters thick that advanced towards the Tabacón River Valley at a rate of 10-30 meters a day. Today, part of the altered slopes have been carpeted by vegetation, and others are just beginning a stage of natural colonisation in an excessivly humid and cloudy habitat. The constant small emissions of lava can be observed better at night.