September 30, 2011 – Mount Etna Erupts in a Spectacular Display of Fire: On the evening of September 29, 2011; the new southeast crater of Mount Etna produced another spectacular eruption. This episode was more violent than those of the preceding blow-offs.
The activity started slowly during the afternoon, with exponentially rising levels of volcanic tremor, ash emissions and increasing “strombolian” activity originating from several vents inside the new crater.
“Strombolian” eruptions are named after the Italian volcano Stromboli, where such eruptions consist of ejection of incandescent cinder and lava bombs. They are small to medium in volume, with sporadic violence. They typically glow red when leaving the vent. However, the ejected magma cools and assumes a dark to black color and may significantly solidify before impact. The lava flows are viscous (having a thick, sticky consistency between solid and liquid) and are, therefore, shorter and thicker than the typical Hawaiian eruptions. Instead, the gas coalesces into bubbles, called gas slugs that grow large enough to rise through the magma column, bursting near the top due to the decrease in pressure and throwing magma into the air. Each episode thus releases volcanic gases, sometimes as frequently as a few minutes apart. Gas slugs can form as deep as 3 kilometers (2 miles), making them difficult to predict.
Strombolian eruptive activity can be very long-lasting because the conduit system is not strongly affected by the eruptive activity, so that the eruptive system can repeatedly reset itself. For example, the Parícutin volcano (a cinder cone volcano in the Mexican state of Michoacán) erupted continuously from 1943 to 1952. Mount Erebus, in Antarctica, has produced Strombolian eruptions for at least 25 years. Mount Stromboli itself (located in the Tyrrhenian Sea, north of the island of Sicily and west of Italy) has been producing Strombolian eruptions for several thousand years.
Mount Etna is on the east coast of the Island of Sicily. Both Mount Stromboli and Etna are associated with the subduction of the African tectonic plate under the Eurasian plate.
Mount Etna, towering above Catania, Sicily’s second largest city, has one of the world’s longest documented records of historical volcanism, dating back to 1500 BC. Historical lava flows cover much of the surface of this massive volcano, the highest and most voluminous in Italy. Two styles of eruptive activity typically occur at Etna. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more of the three prominent summit craters; the Central Crater, northeast Crater, and southeast Crater. Flank eruptions (the sides of the volcano), occur less frequently and originate from fissures that open progressively downward from near the summit. A period of more intense intermittent explosive eruptions from Etna’s summit craters began in 1995.
The Master of Disaster