QCOSTARICA – An eruption occurred Wednesday (April 6) morning at 2:42 am local time from the volcano’s crater northern area. The event lasted about 3 minutes and generated a steam plume that rose 500 meters (1,640 feet) from the crater which is approximately at a 3,200 meters (10,500 feet) altitude.
There was apparently no warning for the eruption, which came without detectable precursors, such as increased seismic activity, an increase in temperature at the fumaroles or other geophysical changes.
During other eruptions of Poás, the temperature at the northern crater rim’s fumaroles often had been seen increasing from 100°C to 900°C.
Volcanologist Javier Pacheco from Costa Rica’s monitoring agency OVSICORI-UNA explained in an interview with La Nación this had not been the case yesterday, as the eruption seems to have not involved any new magma, but almost purely ejected steam, it was likely a phreatic (steam-driven) explosion.
It is actually rather typical that such phreatic explosions occur with little or no warning at an active volcano: Fluids, water and gasses, contained in the subsurface system of cracks and cavities normally form a circulating system that allows heat and excess gasses that can no longer be stored in solution to be transferred to the surface, where degassing takes place, often in the form of fumaroles or hot crater lakes.
Rincon de la Vieja also erupts
Some kilometers north, in the province of Guanacaste, on Thursday morning afternoon, at 11:42 am and 1:23 pm local time, the Rincon de la Vieja volcano recorded eruptions with a column of smoke rising 500 meters above the height of the crater and 2,416 meters (7924.48 ft) above sea level.