mt Vesuvius eruption
It was August, 79 AD, when the event that changed the lives of thousands took place. The cities of Pompeii and Herculaneum were situated along the Bay of Naples (shown on the map) and overshadowing both of them was the volcano, Mt Vesuvius. Pompeii was substantially larger than Herculaneum, in regards to population, with 15,000 people, compared to Herculaneum's 5,000. Both cities thrived with trade, as the soil around Mt Vesuvius was extremely fertile and therefore useful to the businessmen of the cities. Mt Vesuvius had been dormant since the 8th century BC, leaving the residents of Pompeii, Herculaneum and surrounding cities living with no fear of the volcano.
In 62 AD, violent earthquakes rocked the cities surrounding Mt Vesuvius, as the gases within the volcano began to build up. In 79 AD, the pressure built up once again. However, this time a thick layer of lava hardened and formed something similar to a plug in the crater of the volcano. This plug was not enough to restrain the gases, and for several days there were tremors that affected the places surrounding Mt Vesuvius. People took no notice of these tremors, as they were common in the area, and it came as a surprise to many when Mt Vesuvius had it's initial eruption after noon on that day in August. The eruption sent a cloud of heated rock and gas over 20 kilometres into the sky, and in Pompeii, the ash had blocked the sun by 1pm. It fell at a rate of 15 centimetres an hour, and people tried to clear heavy ash from their rooftops as it fell, but to no avail. The cloud continued to blow southwards, over Pompeii, and eventually everything was pitch black. Violent tremors continue to be emitted from the volcano, causing the roofs of houses to collapse in on themselves.
During the evening, ash and pumice stones fell down on Pompeii, effectively trapping people in their houses, blocking the doors. Since Pompeii was downwind from the volcano, it was rained upon with small volcanic stones. These were not found at Herculaneum, despite it being closer to Mt Vesuvius. The eruption then released an mass of heavy stones and pumice, causing buildings to collapse and triggering the first pyroclastic surge. Shortly after midnight, the cloud of ash reached it's peak of 30km into the sky, and then collapsed. A wall of volcanic mud surged towards Herculaneum, destroying the town as citizens ran towards Pompeii. The surge consisted of mud that reached temperatures so high it killed everyone it touched instantly.
Around 6:30 am the next day, the cloud of volcanic gas and debris headed towards Pompeii. Victims died instantly, like in Herculaneum, because their lungs were burned by the superheated air. This also contracted their muscles, leaving the bodies in a curled position. They were rapidly buried in ash, preserving their bodies for hundreds of years. The cloud collapsed one last time, enveloping Pompeii and Herculaneum in darkness.
This event has been incredibly significant to society today, and it is the letters from eye witness Pliny the Younger that has helped people understand what exactly happened that day. His letters (see 'Evidence' for more information) have also shaped how scientists understand volcanic activity today. Nowadays, volcanologists monitor changes in levels of seismic activity at Mt Vesuvius constantly, because they now have knowledge that the same earth tremors and volcanic eruptions can happen again. Through measuring this activity, they can be sure to predict an eruption months in advance. Scientists are also aware that the activity of Vesuvius is recurrent, and the explosions will be greater as the intervals between each eruption get longer. This is why the 79 AD eruption was so immensely disastrous; there was an extended period of time where Mt Vesuvius had been inactive prior to it.
The type of eruption that took place in 79 AD is what is now known as a Plinian (or Vesuvian) eruption, referring to the eye witness, Pliny the Younger. Plinian eruptions are historic eruptions that emit powerful clouds of ash that ascend up to 45 kilometres in the air. The duration of these explosive eruptions isn't specific, lasting from hours to days. Plinian eruptions produce eruption plumes, which are maintained for a period of time because the bubbles inside them rise at the same rate as the magma which is moving through them. These clouds exit the volcano at speeds of hundreds of metres per second, and the clouds cover larger areas with pumice and ash. All of this is extracted from studying the eruption of 79 AD, which has significantly shaped how volcanoes are studied today.
SOURCES:
http://www.britishmuseum.org/whats_on/past_exhibitions/2013/pompeii_and_herculaneum/pompeii_live/eruption_timeline.aspx
http://www.history.com/this-day-in-history/eruption-of-mount-vesuvius-begins
http://www.livescience.com/27871-mount-vesuvius-pompeii.html
http://www.bbc.co.uk/history/ancient/romans/pompeii_portents_01.shtml
http://www.geology.sdsu.edu/how_volcanoes_work/Plinian.html
In 62 AD, violent earthquakes rocked the cities surrounding Mt Vesuvius, as the gases within the volcano began to build up. In 79 AD, the pressure built up once again. However, this time a thick layer of lava hardened and formed something similar to a plug in the crater of the volcano. This plug was not enough to restrain the gases, and for several days there were tremors that affected the places surrounding Mt Vesuvius. People took no notice of these tremors, as they were common in the area, and it came as a surprise to many when Mt Vesuvius had it's initial eruption after noon on that day in August. The eruption sent a cloud of heated rock and gas over 20 kilometres into the sky, and in Pompeii, the ash had blocked the sun by 1pm. It fell at a rate of 15 centimetres an hour, and people tried to clear heavy ash from their rooftops as it fell, but to no avail. The cloud continued to blow southwards, over Pompeii, and eventually everything was pitch black. Violent tremors continue to be emitted from the volcano, causing the roofs of houses to collapse in on themselves.
During the evening, ash and pumice stones fell down on Pompeii, effectively trapping people in their houses, blocking the doors. Since Pompeii was downwind from the volcano, it was rained upon with small volcanic stones. These were not found at Herculaneum, despite it being closer to Mt Vesuvius. The eruption then released an mass of heavy stones and pumice, causing buildings to collapse and triggering the first pyroclastic surge. Shortly after midnight, the cloud of ash reached it's peak of 30km into the sky, and then collapsed. A wall of volcanic mud surged towards Herculaneum, destroying the town as citizens ran towards Pompeii. The surge consisted of mud that reached temperatures so high it killed everyone it touched instantly.
Around 6:30 am the next day, the cloud of volcanic gas and debris headed towards Pompeii. Victims died instantly, like in Herculaneum, because their lungs were burned by the superheated air. This also contracted their muscles, leaving the bodies in a curled position. They were rapidly buried in ash, preserving their bodies for hundreds of years. The cloud collapsed one last time, enveloping Pompeii and Herculaneum in darkness.
This event has been incredibly significant to society today, and it is the letters from eye witness Pliny the Younger that has helped people understand what exactly happened that day. His letters (see 'Evidence' for more information) have also shaped how scientists understand volcanic activity today. Nowadays, volcanologists monitor changes in levels of seismic activity at Mt Vesuvius constantly, because they now have knowledge that the same earth tremors and volcanic eruptions can happen again. Through measuring this activity, they can be sure to predict an eruption months in advance. Scientists are also aware that the activity of Vesuvius is recurrent, and the explosions will be greater as the intervals between each eruption get longer. This is why the 79 AD eruption was so immensely disastrous; there was an extended period of time where Mt Vesuvius had been inactive prior to it.
The type of eruption that took place in 79 AD is what is now known as a Plinian (or Vesuvian) eruption, referring to the eye witness, Pliny the Younger. Plinian eruptions are historic eruptions that emit powerful clouds of ash that ascend up to 45 kilometres in the air. The duration of these explosive eruptions isn't specific, lasting from hours to days. Plinian eruptions produce eruption plumes, which are maintained for a period of time because the bubbles inside them rise at the same rate as the magma which is moving through them. These clouds exit the volcano at speeds of hundreds of metres per second, and the clouds cover larger areas with pumice and ash. All of this is extracted from studying the eruption of 79 AD, which has significantly shaped how volcanoes are studied today.
SOURCES:
http://www.britishmuseum.org/whats_on/past_exhibitions/2013/pompeii_and_herculaneum/pompeii_live/eruption_timeline.aspx
http://www.history.com/this-day-in-history/eruption-of-mount-vesuvius-begins
http://www.livescience.com/27871-mount-vesuvius-pompeii.html
http://www.bbc.co.uk/history/ancient/romans/pompeii_portents_01.shtml
http://www.geology.sdsu.edu/how_volcanoes_work/Plinian.html