By definition, a volcano is a hole in the Earth’s …show more content…
Volcanoes are formed on land near coastal areas when a continental plate and an oceanic plate converge. The oceanic plate submerges, due to its higher density, and is pushed deeper and deeper beneath the surface. The high temperature and pressures below melt the rock which creates hot, buoyant magma. Ultimately this magma rises towards the surface and accumulates in a reservoir, known as the magma chamber. The eruption occurs when the pressure within in the chamber surpasses the pressure of the upper rock, magma forces its way through the cracks in Earth’s crust. Magma that is low in gas and silicon dioxide produces thin quickly spreading lava which has a low viscosity, while a magma that is heavily composed of gas and silicon dioxide will yield a thick, viscose magma. The thicker magma builds up and because of this pressure, will cause a large …show more content…
The first was a Plinian phase, in which material was ejected in a tall column, spread into the atmosphere and finally fell to the earth like rain. The name Plinian came from the name of Pliny the Younger, a young man whose recorded observations of the eruption became one of the most important pieces of history. The material being shot into the air is called tephra, and it creates a form similar to the mushroom cloud of a nuclear explosion. Pliny had described this effect as a “pine tree” because of its vertical height; scientists now call it the Plinian column. It began at midday on the 24th of August 79 AD and was approximately 20 kilometers (66,000 feet) high. From this, a shower of ash and pumice rained over the city and lasted approximately eighteen hours. The full weight of the pumice and ash amounted to an estimated 2330 kg/m squared. The second phase was the Pelean phase in which pyroclastic flow, avalanches of gas and dust, streamed down the sides of the volcano. This is an intensely damaging reality of a volcanic eruption. The high velocity of pyroclastic flows and surges hit the city unexpectedly on the morning of August 25th 79 AD. Traveling at 100 km per hour, the first surge left a deposit of 10-20 cm, followed by a surge which left 70 cm of air fall ash along with 10-20 cm of limestone and volcanic rocks. Bodies were found buried under 75 feet of solidified ash. They had been there