79AD The Eruption

Italy Has Three Active Volcanoes Including: Etna, Stromboli and… Mt. Vesuvius http://volcano.und.nodak.edu/vwdocs/volc_images/img_vesuvius.html

Eruptive History The pattern of eruptions have followed from a period of quiescence to , explosive ash fall to eruptive lava flows. The Plinian type ash falls occurred in 1698,1779,1794,1822, 1834

Pyroclastic Surge Pyroclastic surges are turbulent, low-density clouds of rock debris and air or other gases that move over the ground surface at high speeds. They typically hug the ground and depending on their density and speed, may or may not be controlled by the underlying topography. Pyroclastic surges are of two types: "hot" pyroclastic surges that consist of "dry" clouds of rock debris and gases that have temperatures appreciably above 100 degrees C, and "cold" pyroclastic surges, also called base surges, that consist of rock debris and steam or water at or below a temperature of 100 degrees C. Both hot and cold pyroclastic surges damage or destroy structures and vegetation by impact of rock fragments moving at high speeds and may bury the ground surface with a layer of ash and coarser debris tens of centimeters or more thick. Because of their high temperatures, hot pyroclastic surges may start fires and kill or burn people and animals. Both types of surges can extend as far as 10 km from their source vents and devastate life and property within their paths

Pyroclastic Flow A pyroclastic flow is a ground-hugging avalanche of hot ash, pumice, rock fragments, and volcanic gas that rushes down the side of a volcano as fast as 100 km/hour or more. The temperature within a pyroclastic flow may be greater than 500° C, sufficient to burn and carbonize wood. Once deposited, the ash, pumice, and rock fragments may deform (flatten) and weld together because of the intense heat and the weight of the overlying material.

Pyroclastic flow from the Mayon Volcano in the Phillipines

Pompeii and Herculaneum- a varied experience

Tephra Tephra is a general term for fragments of volcanic rock and lava regardless of size that are blasted into the air by explosions or carried upward by hot gases in eruption columns or lava fountains. Tephra includes large dense blocks and bombs, and small light rock debris such as scoria, pumice, reticulite, and ash. As tephra falls to the ground with increasing distance from a volcano, the average size of the individual rock particles becomes smaller and thickness of the resulting deposit becomes thinner

Ash Tephra less than 2 millimeters in diameter. Terms Based on Size Ash Tephra less than 2 millimeters in diameter. Lapilli Tephra between 2 and 64 millimeters in diameter. Blocks Tephra greater than 64 millimeters in diameter

The basal pumice units found at Pompeii are missing at Herculaneum

In the last 25,000 years there have been at least 8 volcanic cycles *Quiescence- a period of rest *Cone building begins *The funnel of the volcano becomes blocked *Pressure builds up *Earthquakes and lava flows THE ERUPTION! Mt. Vesuvius

Mt St Helen’s in 1980

Mt Pelee eruption of 1902

Professor Haraldur Sigurdsson

20th century theories After the Mt Pelee eruption, archaeologists who had previously accepted Amedeo Maiuri’s explanation of the destruction by pumice and ash fall, suggested the more important impact of deadly pyroclastic surges and flows. At the request of National Geographic, Haraldur Sigurdsson was asked to examine the volcanic deposits at Herculaneum and Pompeii and compare them to Pliny’s account. Sigurdsson also obtained further evidence from Mt St Helen’s and El Chichon in New Mexico in 1982 Assess the reliability of a scientific study, funded by National Geographic and designed to draw comparisons with a 2,000 year old document

Knowledge gained from 20th century eruptions Scientists, due to the similarities in deposits from Pompeii and Mt St Helens, now understand the various stages of the eruption The scientific measurements of heat and the speed of particle movement now gives historians , understanding of how the people of Pompeii and Herculaneum died.

Dobran Simulation

Limitation of Scientific analyses No two eruptions are identical, and therefore no definitive statement can be made about the timing and duration of the stages of the Vesuvius eruption.