The volcanic eruption of Mount Vesuvius occurred in Plinian form due to its viscosity. Because plinian eruptions include ntermediate/felsic magma, its vesicles rise independently and create a high amount of gas pressure. This exsolution emerges at the vent of the volcano and shoots out magma several hundred meters per second. This type of eruption usually lasts from hours to days; in the case of Mount Vesuvius, the main phases of the eruption lasted about 24 hours. Although there was no technology at the time to record such a volcanic eruption, we know that Mount Vesuvius erupted in plinian because eyewitness accounts saw a grey column of ash, or an eruption column, rise from the mountain above the volcano.
Plinian eruptions can be distinguished by three sections of the volcano: a jet phase, convective phase, and umbrella region.
Plinian eruptions can be distinguished by three sections of the volcano: a jet phase, convective phase, and umbrella region.
The first phase, the jet phase, is marked by a gas region that thrusts fragments up by the force of expanding gas in the conduit of the inner volcano.
The second phase, the convective phase, occurs when the air expands and mixes with the hot volcanic gasses.
The third phase, the ubrella cloud, is when the gasses reach a height where they become naturally buoyant, spread, and create ash deposit.
The second phase, the convective phase, occurs when the air expands and mixes with the hot volcanic gasses.
The third phase, the ubrella cloud, is when the gasses reach a height where they become naturally buoyant, spread, and create ash deposit.
The Ejecta of the Volcano
Mount Vesuvius had many different stages of destruction that caused people to die during the eruption. The first was from the pumice lapilli ash deposit layer that resulted from column fallout. After this layer was a basal ash layer followed by a pyroclastic flow. Tephrachronology is the study of the widespread airfall deposits that are radiometrically dated as stratigraphic marker horizons. These are the ranges of airfall material size and tephra that occured during the Mount Vesuvius eruption:
< 1/16th of a mm = coarse blocks and large particles
1/16th to 2 mm = fine blocks and smaller particles
2 to 64 mm = lapilli
64 to 256 mm = coarse ash
> than 256 mm = fine ash
Because around 2,000 people in Pompeii would not abandon the city, they died from the ash, basal, and pyroclastic flow that engulfed the city. Below is a map of the red-zone areas that were affected by this eruption.
< 1/16th of a mm = coarse blocks and large particles
1/16th to 2 mm = fine blocks and smaller particles
2 to 64 mm = lapilli
64 to 256 mm = coarse ash
> than 256 mm = fine ash
Because around 2,000 people in Pompeii would not abandon the city, they died from the ash, basal, and pyroclastic flow that engulfed the city. Below is a map of the red-zone areas that were affected by this eruption.