Yellowstone Caldera Chain: The current caldera at Yellowstone is the most recent in a series of eruptions that span millions of years. The North American Plate is moving west over a stationary hot spot. As the plate moves, the hotspot produces an enormous eruption (and a large caldera) every few million years.
Composite volcanoes (also called stratovolcanoes) are much more explosive than shield volcanoes, the other important type of volcano. The large and generally cone-shaped volcanoes form along plate boundaries called subduction zones where one of the Earth's plates moves below another.
Yellowstone's volcanic and hydrothermal history suggests the potential for various kinds of eruptions in the future. The likelihood of a certain type of eruption occurring in the future can be judged by how often eruptions have occurred in the past. The most likely type of eruption would not be volcanic but, rather, hydrothermal.
Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed.
Phreatomagmatic eruptions, which are typically underwater, are the result of tectonic plates plunging downwards into Earth's mantle. This type of eruption is the opposite of a magmatic eruption in that it involves the addition of pressure to magma, rather than the release of pressure.
Eruptions at the shield volcano are generally centered within the large summit caldera or on the numerous fissures and cinder cones on the volcano's flanks. Lava flows from the most recent century extend down the flanks more than 30 km (19 mi) from the summit, reaching as far as Lake Kivu.
Hawaiian eruptions get their names from the Kilauea Volcano on the Big Island of Hawaii, which is famous for producing spectacular fire fountains. Two excellent examples of these are the 1969-1974 Mauna Ulu eruption on the volcano's flank, and the 1959 eruption of the Kilauea Iki Crater at the summit of Kilauea.
Plinian eruptions or Vesuvian eruptions are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in 79 AD, which destroyed the ancient Roman cities of Herculaneum and Pompeii. The eruption was described in a letter written by Pliny the Younger, after the death of his uncle Pliny the Elder.
Vulcanian Eruption. A Vulcanian eruption is a short, violent, relatively small explosion of viscous magma (usually andesite, dacite, or rhyolite). This type of eruption results from the fragmentation and explosion of a plug of lava in a volcanic conduit, or from the rupture of a lava dome (viscous lava that piles up over a vent).