All volcanoes erupt, but not always in the same way. There are seven types of volcanic eruptions: Strombolian, Vulcanian, Peléan, Hawaiian, Phreatic, Plinian, and subglacial.
A Strombolian eruption, named after Stromboli in Sicily, consists of large blobs of magma thrown tens to hundreds of meters in the air, until they fall to the ground and produce short, viscous streams of lava. Strombolian volcanic eruptions are caused by the buildup of bubbles, called gas slugs, which rapidly rise to the surface, emerging with such force that they eject many tons of magma into the air. Strombolian eruptions are of low or medium intensity.
Vulcanian eruptions, named after Vulcano, a volcanic island in the Mediterranean, are characterized by large amounts of gas released in an explosive fashion. Vulcanian eruptions are often accompanied by Phreatic, or steam-blast eruptions, caused when red-hot magma comes into constant with ground water and turns it instantly to steam. In Vulcanian eruptions, a large cloud of volcanic ash forms in the sky above the volcano, with white steaming ash making up the highest part of the smoke pillar. Vulcanian volcanic eruptions usually do not eject much magma into the air.
Peléan eruptions, also called "glowing cloud" eruptions, are named after Mt. Pelée in the Caribbean. Peléan eruptions are characterized by sudden explosions of gas, dust, ash, and lava fragments which rain down on kilometer-wide areas in a pyroclastic avalanche. When a Peléan eruption occurs in a populated area it can cause many deaths. Peléan volcanic eruptions are often accompanied by the creation of a lava dome.
Hawaiian eruptions are named after the eruptions of the volcano Mauna Loa in the Hawaiian islands. These are among the most peaceful eruptions, and may last for many years. They consist of large amounts of low-viscosity lava pouring down the volcano's slope, and produce very little volcanic ash or gas. A Hawaiian eruption is safe enough to view up close, and many helicopter tours in Hawaii offer tours of the actively volcanic Mauna Loa. Over geologic time, Hawaiian eruptions produce very large mountains, as is the case with the island of Hawaii itself — if measured from the ocean floor, Mauna Loa can be considered the tallest mountain on Earth.
Phreatic eruptions, also known as steam-blast eruptions, are named after a word meaning "well" or "spring" in Greek, and refers to the contact of superheated magma with a subterranean water table. Phreatic eruptions result in explosions of steam, water, ash, rock, and volcanic bombs, and have been known to kill hundreds of people, mostly due to the release of poisonous gases such as carbon dioxide or hydrogen sulfide. The former merely causes asphyxiation, while the latter is actually an active poison, killing plants and animals alike.
Plinian eruptions, named after Pliny the Younger, whose uncle was killed in the Plinian eruption of Mt. Vesuvius in 79 CE, are the most severe and extreme of the volcanic eruptions. They consist of an extremely tall column of ash and magma being ejected all the way into the stratosphere (>11 km, 6.8 mi). This column spreads out at its top, resembling a stone pine tree. Plinian volcanic eruptions are known to distribute dust over areas hundreds of miles wide, and are often accompanied by very loud explosive noises which can be heard from thousands of miles away. Sometimes, Plinian eruptions eject so much magma that the volcano's summit collapses, forming a caldera.
Subglacial volcanic eruptions occur when a volcano erupts from beneath an ice sheet, which is usually more than a kilometer deep. Only five subglacial eruptions have been recorded in modern history, and only the most severe are capable of actually melting through the entire ice cap above.