Iraz˙, or "Nature's power keg" as it has been called, is an irregularly sub conical active stratovolcano. At 3,432 m high, it is the highest in the country, and has a long history of eruptions and eruption cycles. They typically consist of powerful emissions of large clouds of steam, ashes and scoria, often accompanied by local or regional seismic tremors; by subterranean rumblings, which can sometimes be heard in the Central Valley and by showers of rocks, which are occasionally incandescent.
The first historic account of an eruption dates from 1723; the last period of strong activity took place between 1963 and 1965. At present, there is continuous fumaroles activity and it is believed that it could become violently active at any time. On clear days, it is possible to see the oceans and most of Costa Rica from the top of Iraz˙.
At the top there are three main craters. El Principal is almost circular, 1,050 m in diameter and 250 to 300 m deep. At its base there is a temporary lagoon with greenish yellow water. Another crater is called Diego de la Haya, which is circular, 690 m in diameter and 80 m deep. It is blocked and rainwater frequently collects in the flat bottom, forming a small lagoon. These two structures are partially surrounded on the southern side by the remains of the giant crater of a caldera. Two other small craters are located to the southeast of the first one. On the flanks of the volcano two parasitic cones can be seen.
The flora has been greatly altered due to the eruptions. Most of the park presents stunted vegetation, mainly made up of arrayan (Vaccinium consanguineum), a small bush with leathery leaves. In some small patches of primary and secondary forest, the most abundant trees are the miconia (Miconia spp.), the black oak (Quercus costaricensis), the growing stick (Oreopanax xalapensis) and the mountain mangrove (Clusia odorata).
Iraz˙ is very poor as regards animal life. The most frequent mammals are the eastern cottontail (Sylvilagus brasilensis) and the coyote (Canis latrans), Little spotted cat (Leopardus tigrinus) has also been seen. Among the birds, there are many humming birds and volcano juncos (Junco vulcani).
Iraz˙ Volcano National Park is situated in the Central Volcanic Cordillera. A road runs the 32 km from Cartago almost to the edge of El Principal and Diego de la Haya. There is a look-out point for views of El Pricipßl crater. Visitors are not allowed to walk through areas marked as high risk or go down into the craters. Two kilometres before arriving at the craters, there is an information stand and a picnic area with tables, toilets and drinking water. There is a bus service on Saturdays and Sundays from San JosÚ and Cartago. Along the access road to the park there are hotels, restaurants and grocery stores.