Plinian eruption
From Wikipedia, the free encyclopedia
Plinian eruptions are volcanic eruptions marked by their similarity to the eruption of Mt. Vesuvius in AD 79 (as described in a letter written by Pliny the Younger) that killed Pliny the Elder.
Plinian eruptions are marked by columns of smoke and ash extending high into the stratosphere. 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. Longer events can take several days to months. The longer eruptions begin with production of clouds of volcanic ash, optionally 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 heard at Krakatoa.
The examples of large Plinian eruptions resulting in formation of a caldera are the 1883 Krakatoa eruption in Indonesia, the 1980 eruption of Mount St. Helens, the 1815 eruption of Mount Tambora, also in Indonesia, the 1667 & 1739 eruptions of Mount Tarumae in Japan [1], the 1600 BC Thera eruption, and the 4860 BC eruption that formed the Crater Lake, and of course Vesuvius in AD 79, which was the prototypical Plinian Eruption. The lava is usually rhyolitic and rich on silicates; basaltic lavas are unusual for Plinian eruptions, the example is the 1886 eruption of Mount Tarawera.
Contents |
[edit] Pliny's description
He 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.)
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.
[edit] References
- ^ Enlightenment activities for improvement on disasters from Tarumae Volcano, Japan, Cities on Volcanoes 4, 23-27 January 2006
