Etna has four primary craters at its summit from which eruptions occur: the Northeast Crater, the Southeast Crater, the Bocca Nuova and the Voragine. However, eruptions also occur in the vents on its flanks; these eruptions are often more dangerous than those at the summit, as they happen at lower altitudes and close to populated areas. Of the estimated 60 eruptions that have occurred on Etna's flanks, close to half have happened since the beginning of the 20th century, and five already in the 21st.
Etna's most destructive eruption happened in 1669. An earthquake destroyed the village of Nicolosi, and was followed by lava that branched into three streams, one of which reached Catania. The lava traveled 15 miles over the course of about four weeks, creeping over the 60-foot walls of Catania to destroy a large part of the city. Twenty thousand people died in the eruption, largely because they stayed behind to defend their homes. One such effort was led by Diego de Pappalardo, who took 50 men to the slopes to divert the lava. Unfortunately, their successful diversion sent lava toward the town of Paterno. The citizens from both towns then began to fight with one another, while the lava continued to flow and regained its course toward Catania. A national decree enacted after the eruption made it illegal to interrupt the natural flow of lava from Italy's volcanoes.
The most devastating eruption in the 20th century was the eruption of 1928. This eruption was the only one besides the 1669 eruption that completely destroyed a population center, in this case the town of Mascali. As the eruption happened during the height of Italy's Fascist era, rebuilding Mascali so that it was even better than it was before became one of Mussolini's propagandist objectives. The Fascist reconstruction left its stamp on the city's new main church with a statue of the Fascist torch resting above the statue of Jesus.
The 1983 eruption is significant because it was the first time that man-made diversions were successfully used to protect important areas from lava flow. In this eruption, lava flowed out of a fissure on the south flank and headed immediately toward a tourist area, destroying or damaging most of the buildings: a restaurant, two hotels and a ski lift. In spite of controversy about building the barriers (which cost about $3 million and saved the country an estimated $5 to $25 million in repairs), lateral diversions of the lava saved the Grand Hotel of Etna and the Astrophysics Observatory.
Etna has been extremely active since the beginning of the 21st century. In 2001 and 2002, eruptions came not just from the summit, but from both the north and southeast flanks as well. In 2001, the fissures related to the craters (or the lateral fissures) emitted magma similar to the kind that had been seen over the last 300 years, but the eruption was unique in that it produced a second kind of magma from the eccentric fissures that no one had seen for 15,000 years. The 2002 eruption was much larger and could be seen as far away as Libya. Lava flowed out of the mountain in 2004 and 2005, and eruptions occurred again from 2006 through 2008. As of October 2009, the 2008 eruption, which began on May 10th, was the longest so far in the 21st century, lasting just over six months.
