Plinian eruptions, also known as 'Vesuvian eruptions', are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 (as described in a letter written by Pliny the Younger, and which killed his uncle Pliny the Elder).
Plinian eruptions are marked by columns of gas and volcanic ash extending high into the stratosphere, a high layer of the atmosphere. The key characteristics are ejection of large amount of pumice and very powerful continuous gas blast eruptions.
Short eruptions can end in less than a day, but longer events can take several days to months. The longer eruptions begin with production of clouds of volcanic ash, sometimes with pyroclastic flows. The amount of magma erupted can be so large that the top of the volcano may collapse, resulting in a caldera. Fine ash can deposit over large areas. Plinian eruptions are often accompanied by loud noises, such as those generated by Krakatoa.
Pliny's description 
Pliny described his uncle's involvement from the first observation of the eruption:
On the 24th of August, about one in the afternoon, my mother desired him to observe a cloud which appeared of a very unusual size and shape. He had just taken a turn in the sun and, after bathing himself in cold water, and making a light luncheon, gone back to his books: he immediately arose and went out upon a rising ground from whence he might get a better sight of this very uncommon appearance. A cloud, from which mountain was uncertain, at this distance (but it was found afterwards to come from Mount Vesuvius), was ascending, the appearance of which I cannot give you a more exact description of than by likening it to that of a pine tree, for it shot up to a great height in the form of a very tall trunk, which spread itself out at the top into a sort of branches; occasioned, I imagine, either by a sudden gust of air that impelled it, the force of which decreased as it advanced upwards, or the cloud itself being pressed back again by its own weight, expanded in the manner I have mentioned; it appeared sometimes bright and sometimes dark and spotted, according as it was either more or less impregnated with earth and cinders. This phenomenon seemed to a man of such learning and research as my uncle extraordinary and worth further looking into.
— Sixth Book of Letters, Letter 16, translation by William Melmoth
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 Vesuvius with no apparent injuries on 26 August, after the plume had dispersed, confirming asphyxiation or poisoning.
Ultra Plinian 
According to the Smithsonian Institution's Volcanic Explosivity Index, a VEI of 6 to 8 is classified as "Ultra Plinian." They are defined by ash plumes over 25 km (16 mi) high and a volume of erupted material 10 km3 (2 cu mi) to 1,000 km3 (200 cu mi) in size. Eruptions in the "Ultra Plinian" category include Lake Toba (approx 74000 years ago), Tambora (1815), and Krakatoa (1883).
- The 2010 eruptions of Eyjafjallajökull in Iceland
- The June 2009 eruption of Sarychev Peak in Russia
- The 1991 Mount Pinatubo eruption in Luzon in the Philippines;
- The 1980 eruption of Mount St. Helens in USA
- The 1883 eruption of Krakatoa in Indonesia
- The 1815 eruption of Mount Tambora in Indonesia
- The 1667 and 1739 eruptions of Mount Tarumae in Japan
- The 180 AD Lake Taupo eruption New Zealand
- The AD 79 eruption of Mount Vesuvius in Italy, which was the prototypical Plinian eruption.
- The 400s BC eruption of Mount Meager in British Columbia, Canada
- The 1645 BC eruption of Santorini in Greece
- The 4860 BC eruption forming Crater Lake in USA
- The Long Valley Caldera eruption in USA over 760,000 years ago.
See also 
- USGS Photo Glossary Entry for Plinian Eruptions
- Chakraborty P. et al. (2009). "Volcanic mesocyclones". Nature 458: 495–500.