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Plinian Eruption
Composite volcanoes commonly exhibit Plinian eruption style. These are the largest and most violent style of explosive eruption, creating a vast eruption column of gas, magma and debris. The name of the eruption style derives from Pliny the Younger, a Roman historian, who compared the shape of eruption to an Italian pine tree. Composite volcanoes contain more SiO2 and silica than shield volcanoes, which means the lava they transport is often stickier. This means they have a greater propensity to be blocked by a sticky plug of lava, and this can cause pressure to build up and lead to a Plinian eruption. Plinian eruptions are also associated with the production of very viscous magmas, containing dactite and rhyolite minerals. Eruption columns can reach over 45 km in height, and the ash can be blown for hundreds of thousands of miles.
Example of Plinian Eruptions
Although their eruptions are spectacular when they occur, composite volcanoes generally erupt far less frequently than shield volcanoes. Mount Vesuveus in Sicily is a famous volcano known to have experienced numerous Plinian eruptions during its history. Indeed, the first was observed and recorded by Pliny himself in 79 AD, in letters to the historian Tacitus. In fact, although his account goes into much detail, the primary purpose of the letters was to record the death of his uncle, Pliny the Elder, as a result of the eruption. The city of Pompeii was also destroyed and evacuated as a result of the eruption. Other famous examples of composite volcanoes which have experienced Plinean eruptions include Krakatoa in Indonesia in 1883, Mount St. Helens in 1980 and Eyjafjallajökull in Iceland in 2010.
Vulcanian Eruption
Composite volcanoes can also exhibit vulcanian eruptions, which are smaller and less catastrophic compared to Plinian eruptions, but still violent. Vulcanian eruptions result from the rupture of a lava dome or the explosion of a volcanic plug blocking the volcanic conduit, and they create powerful explosions, in which the material can travel over 800 miles per hour. They produce pyroclastic density currents, which are clouds of hot ash, gas, and rock debris, which flow almost like a fluid.
Example of Vulcananian Eruption
Vulcanian eruptions were named after Vulcano in Italy, a small volcano which derived its name from Vulcan, the Roman god of fire. Vulcanian eruptions can last for days, months, and even years. In 1930, the volcano in Stramboli, Italy experienced a violent vulcanian eruption, which occurred with very little warning beforehand. It was preceded only by an increase in ash emission some two hours prior to the eruption, and the eruption lasted for less than a day, but caused extensive damage and several deaths.