The park can be reached along the Road Alajuela- San Isidro- Dulce Nombre- Fraijanes- Poasito-park-headquarters. Distance 47 kms. from Alajuela
Poás Volcano National Park, which extends over 5,600 hectares, is located on the continental divide of the volcanic Central Mountain Range, from 1,500 meters above sea level on the Caribbean side to 2,300 above sea level on the Pacific side.
Poás is a compound basaltic volano that towers 2,708 meters above sea level. It has a slow, effusive activity of the lake kind. Since 1989, it has geatly increased its emission of gases, causing acid rain that has damaged the strawberry and coffee plantations in the Central Western Valley. Depending on the direction and velocity of the wind, unpleasant odors can be detected at places as far away as Alajuela, Grecia, San Ramón, Sarchí and Naranjo.
At the rim there are two craters. The main crater measures 1,5 kms. in diameter and is 300 meters deep. It has a circular hot-water lake at the bottom, 350 meters in diameter, and a cinder cone 40 meters high with very active fumaroles.
The second crater is the seat of a cold-water lake, Botos, which clearly originates from rainfall and drains into the Caribbean by means of the River Angel, a tributary of the River Sarapiquí.
There are four main habitats in the park: areas with no o very scarce vegetation, an area of arrayans, a stunted forest and a cloud forest. In the latter which is very shady and humid, most of the trees, such as the oak, cedar and white Podocarpus, grow to heights of some 20 meters and are completly covered in moss, liverwort, and other plants. On the slopes of the Caribbean Sector, the forests are taller and more humid, with a wealth of palms, tree ferns and epiphytes. Identification has been made in both forest masses of 79 species of birds, including the sooty robin, resplendent quetzal, black guan and emerald toucanet. There are not many mammals in the highlands of the park, although coyotes, long-tailed weasels, amazon Skunks and some felines live on the Caribbean slopes.
Poás volcano has a long history of eruptions that range from emissions of hot vapors and muddy water to blowouts of ash and incandescent rocks. On 25th of January, 1910 an enourmous column of ash that was over 8000 meters high was visible from several different places around the county. The last period of violent eruptions with large clouds of ash and incandescent rocks took place between 1952-1954. Because of its geyserlike eruptions when columns of muddy water and steam shoot up into the air, Poás is known as the largest geyser in the world. This is a phenomenon that ca be repeated within a period of several minutes or not take place again for several years.