Hawaii issued an aviation red alert Tuesday after the Kilauea volcano spewed a plume of ash into the air, with authorities warning the volcano could become more explosive.

Rising up to 12,000 feet, ash and volcanic smog drifted southwest over 18 miles from the Kilauea crater, Reuters reports.

“We’re observing more or less continuous emission of ash now with intermittent, more energetic ash bursts or plumes,” Hawaiian Volcano Observatory (HVO) Deputy Scientist-In-Charge Steve Brantley told reporters.

“At any time, activity may become more explosive, increasing the intensity of ash production and producing ballistic projectiles near the vent,” the HVO said in a later statement.