In nearly five decades in politics, Ms. Bonino wielded outsize influence on Italian discourse, helping erode the political sway of the Catholic Church.

Rescuers found a 29-year-old man in serious condition on the volcano’s eastern slope on Sunday. He was later pronounced dead at a hospital in Catania.

Etna erupts often, but it usually doesn’t release this much ash, an expert said. Tens of thousands of travelers’ plans have been disrupted in the past week.