Italy's Mount Etna erupts, closing Sicily's Catania Airport

Smoke rises over the city of Catania during an eruption of Mount Etna on Monday.

(CNN)Mount Etna -- Europe's highest and most active volcano -- erupted on Monday, causing a magnitude 3.3 earthquake and the closure of Sicily's Catania Airport.

"Due to the eruption of #Etna from today 2pm (December 24th) #Catania airspace is closed," the airport tweeted.
The airport said that while it would be closed, some airspace would be reopened to allow four flights an hour to arrive.
    It advised passengers to contact their airline before heading to the airport and confirmed that a "crisis unit" was expected to meet.
      Etna's eruptions are relatively frequent and, according to Italy's National institute of Geophysics and Volcanology, there has been a gradual increase in activity on the volcano over the last month.