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. Plinian/Vesuvian eruptions are marked by columns of volcanic debris and hot gases ejected high into the stratosphere, the second layer of Earth's atmosphere. The key characteristics are the ejection of a large amount of pumice and very powerful continuous gas-driven eruptions. Short eruptions can end in less than a day, but longer events can continue for several days or months. The longer eruptions begin with production of clouds of volcanic ash, sometimes with pyroclastic surges. The amount of magma ejected can be so large that it depletes the magma chamber below, causing the top of the volcano to collapse, resulting in a caldera. Fine ash and pulverized pumice can be deposited over large areas. Plinian eruptions are often accompanied by loud sounds. The sudden discharge of electrical charges accumulated in the air around the ascending column of volcanic ashes also often causes lightning strikes, as depicted by the English geologist George Julius Poulett Scrope in his painting of 1822 or observed during 2022 Hunga Tonga–Hunga Ha'apai eruption and tsunami. The lava is usually dacitic or rhyolitic, rich in silica. Basaltic, low-silica lavas rarely produce Plinian eruptions unless specific conditions are met (low magma water content <2%, moderate temperature, and rapid crystallization); a recent basaltic example is the 1886 eruption of Mount Tarawera on New Zealand's North Island.

Pliny's description

Pliny the Younger described the initial observations of his uncle, Pliny the Elder, of the 79 AD eruption of Mount Vesuvius: Pliny the Elder set out to rescue the victims from their perilous position on the shore of the Bay of Naples, and launched his galleys, crossing the bay to Stabiae (near the modern town of Castellammare di Stabia). Pliny the Younger provided an account of his death, and suggested that he collapsed and died through inhaling poisonous gases emitted from the volcano. His body was found interred under the ashes of the eruption with no apparent injuries on 26 August, after the plume had dispersed, confirming asphyxiation or poisoning.

Examples

Ultra-Plinian

In 1980, volcanologist George P. L. Walker proposed Hatepe eruption as the representative of a new class called ultra-Plinian deposits, based on its exceptional dispersive power and eruptive column height. A dispersal index of 50,000 square kilometres (19,000 sq mi) has been proposed as a cutoff for an ultra-Plinian eruption. In the criteria of Volcanic Explosivity Index, recognizing an eruption as ultra-Plinian would make it at least VEI-5 or higher. The threshold for ultra-Plinian eruptions is defined by an eruptive column height of 45 km, or 41 km more recently. The few instances of eruptions that lie at the transition between Plinian and ultra-Plinian include the P3 phase of 1257 Samalas eruption, 1991 eruption of Mount Pinatubo, the Plinian phase of the Campanian Ignimbrite, Tsankawi Pumice Bed of Tshirege Member of Bandelier Tuff, and the 1902 eruption of Santa María. The once unequivocal ultra-Plinian classification of the Hatepe eruption has been called into question, with recent evidence showing that it is an artifact of an unrecognized shift in the wind field rather than extreme eruptive vigor.