Like the other volcanoes in the Central Volcanic Cordillera, the silhouette of Poás Volcano as seen from the Central Valley gives no hint of the power and pent-up fury below the surface. But once at the summit and standing on the crater's rim, it becomes easier to understand the forces that have shaped this towering massif.

With a diameter of 1.5 km., the active crater is reportedly the widest of any volcano in the world. If it is clear enough to see to the bottom of the 300-meter deep crater, you will surely observe some type of activity ranging from fumaroles to bubbling emissions on the surface of the small rain-filled lake to actual geyser-type eruptions, but it is constantly changing. During the early 1990s, there was enough geyser activity to cause the lake to lose its water by the end of the dry season (April/May); this resulted in increased gaseous emanations that forced the park to close on a few occasions.

Looking to the left of the crater you can see the deleterious effects of the volcanic gases that cause a localized form of acid rain. For several kilometers downwind from the crater the vegetation is brown and dying. On exceptionally clear days you can see the top of Arenal Volcano (60 km. distant) by looking in this direction. If you keep your eye on it long enough, you may be able to see the cloud of ash that accompanies an eruption.

A few meters back down the trail from the active crater overlook, a 1.5 km. trail leads off to Lake Botos, a densely forested dormant crater filled with rain water. A portion of this trail goes through an eerie-looking section of stunted forest. The trunks and branches of the small trees here are gnarled and twisted from the harsh climatic conditions in exposed areas at high elevations. At the Lake Botos overlook you'll be near the highest point in the park which is 2,704 meters.

At this elevation wildlife is not particularly abundant, but there is usually a fair amount of bird activity. Some of the more common species are the Fiery-throated Hummingbird, Sooty-capped Bush-Tanager, Slaty Flowerpiercer, Mountain Eleania, Black-billed Nightingale-Thrush, and Black-and-yellow Silky-Flycatcher.

Given its high visitation, the National Park Service has chosen Poás as a model park. One of the benefits of this is the Visitors' Center which presents a thorough explanation of volcanism and the natural history of Poás using a variety of entertaining and informative displays.

To get there: From San José, drive to the town of Alajuela. Coming in town from the airport will put you on Calle 2, take this street all the way through town and follow it up the mountain (Rt. 130) to Itiquis and Fraijanes, following the signs for the volcano.

As it only takes 90 minutes to drive the paved road to the volcano's summit, this national park receives more visitors than any other. On weekends and holidays it is very popular with local citizens as a picnic spot.

Climate: It can get cool at this 2,500+ meter elevation, so layers are advised. If it is sunny, use plenty of sunscreen because the thinner air lets the UV rays through even more intensely than if you were at the beach. Mornings tend to be clear, but the clouds can build up quickly. The driest months are from January to April.

History: Written accounts of Poás only date back to 1828, and the first mention of volcanic activity is from 1834. Between then and the present there have been four other periods of eruptive activity, the most recent one lasting from 1952-54. The largest of any of these relatively recent eruptions was in 1910 when an immense column of smoke and ash issued from the crater. The fallout from this eruption has been estimated to have been nearly three-quarters of a million tons of ash.

In a way, we have Poás Volcano and the Great Smoky Mountains in Tennessee to thank for Costa Rica's extraordinary National Park system. On a visit he made to the U.S. in the 1960's, Park Service founder, Mario Boza, was so impressed with the Great Smokies that upon returning to Costa Rica he drew up a management plan for Poás Volcano as if it were a national park. This, his masters thesis, was the start of what would become perhaps the most ambitious system of national parks and refuges anywhere in the world.