After several small eruptions on Friday, Turrialba Volcano - located 50 kilometers east of Costa Rica's capital - erupted at 5:10 a.m. on Saturday.
According to the Volcanological and Seismological Observatory of Costa Rica (OVSICORI), the volcano spewed gas and vapor and launched ash 800 meters into the air.
The eruption lasted for 30 minutes.
OVSICORI geologists report that the ash is being carried south and will fall primarily in areas immediately surrounding Turrialba.
There have been no reports of ash in San Jose or the surrounding suburbs.
OVSICORI officials reported increased seismic activity at the volcano earlier this week and warned that an eruption could be imminent.
After a series of major eruptions in 2014, Turrialba Volcano had been inactive for the past several months.
With this explosion and another last Friday, volcanologists say that the volcano is reawakening.
"We are seeing a reactivation in the volcano, but it isn't anything like the large eruptions we had last year," OVSICORI official Javier Pacheco told daily La Nacion.
"This is a slow reactivation that has been underway since Oct. 10."