2706 m.a.s.l It has three craters, only one active. It measures 1500 metres lengh (the second widest crater of the world), and 300 metres of depth. On its bottom there is the most active bubling lake in the world. Its geiser eruptions shooted at 40 metres above. To the north from the main crater, Von Frantzius crater (the oldest one) is situated (it`s named after german doctor who searched it in 1860). The third crater Botos is filled with blue water lake and ringed by thick forests. On the west side of volcano winds the Toro Amarillo river.
According to some people, its name comes from an indigenous Indian group who lives in the areas around. The other hipothesis says that it comes fromthe word "Poas" meaning "thorny".
The first person to visit the volcano was Miquel Alforo in 1828. The first mention of Poas volcanic activity dates back to 1834. The first naturalist to visit Poas was the Dane Andres Sandoe Oersted in 1863. Its eruption from 1889 made an earthquake, due to which, a piece of volcanic wall was torn off and a deep hole filled with water was made. (Fraijanes Lake). During the eruption from 1910, the ash cloud was shot 8.000 metres into the air. In 1952-1954 there were similar clouds ashes substituted by deep tremors. Since 1989 the increase of gas emissions has been observed. It`s in charge of acid rains, that destroyed the strawberry plantations on the western side of volcanoe.
On June 2001, after seven years in which the level of the lake in the crater of Botos had remained unchanged, the scientists have noticed that there is ever less and less water. If the trend continues the geyser-like activity that characterized the volcano in the past is likely to return.