Volcano experts are keeping a close eye on Poás volcano, northwest of San José, after plumes of steam and rock sediment soared out from its crater Friday.

Park guards who witnessed the eruption said gases and particles sailed up to 300 meters in the air, which is approximately the height of the crater wall.

The phreatic eruption indicates significant changes to the volcano's behavior and physical makeup. It occurs when hot magma within the volcano comes into contact with surface water and causes an explosion of gas and ground particles.

The temperature of the volcano, which is normally between 100 and 135 degrees Celsius, rose to 369 degrees Celsius last week and caused the volcanoes sulfur to burn – an infrequent phenomenon that hasn't been seen at Poás since July of 1994. According to the National Seismology System (RSN), based at the University of Costa Rica, sulfur begins to burn when volcano temperatures hit 248 degrees Celsius and causes frequent phreatic eruptions.

The extreme heat combined with this year's drought has also caused a loss of 400,000 cubic meters of water inside the volcano's acid crater.

The recent activity has not prompted park closures, but scientists said the gases and particles could cause nominal eye damage to those standing on the crater wall's edge.

Volcanologists expect more phreatic eruptions and said they will continue to monitor the volcano.