Etna's history is long and complex. The oldest lavas, exposed on the lowermost flanks of the volcano, erupted 300,000 years ago. Some of these are pillow lavas, indicating Etna started as a submarine volcano and grew above sea level. Between 150,000-100,000 several volcanic centers coalesced and calderas formed and filled. Between 65,000-25,000 years ago a major vent grew to the southeast of the present summit. Phreatomagmatic eruptions were common during this period. Most of the summit of this volcano was removed by subsequent caldera collapse. Between 18,000-5,000 years ago four major volcanic centers continued to construct Etna and three calderas formed.
Etna has the longest record of historic eruptions. The first recorded eruption was in 1500 B.C. Since then Etna has erupted at least 190 times. Most of these eruptions have a volcanic explosivity index of 1 or 2 and activity consists of gently effusion of lava or Strombolian explosions. Large eruptions are rare.
