Ecology And Environment

The Difference between the Mount Vesuvius Eruptions of 79 Ad and 1944



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Vesuvius, the only active volcano on mainland, has experienced a number of eruptions over the years. The volcano overlooking the Bay of Naples in Italy is part of the Campanian volcanic arc formed over the subduction zone between the African and Eurasian tectonic plates. The other volcanoes forming this arc, such as Etna and Stromboli, occur on islands within the Mediterranean Sea. The volcano formed about 17,000 years ago and one of its early periods of volcanic activity occurred during the ice age. The earliest recorded eruption occurred about 900 BCE.

After an eruption in 320 BCE, Vesuvius entered a period of dormancy. It remained in this dormant state until the famous eruption of 79 AD, which destroyed a number of towns including Pompeii, Herculaneum and Stabiae. This eruption followed major earthquakes in the region in 62 AD and 64 AD. Starting on 24 August 79 AD the first part of the eruption involved a large cloud of volcanic ash erupting to an estimated 33 km high. The ash and pumice from this column fell on the nearby towns. During the day, the volcanic activity increased blocking out the sun by 1 pm. The following day a series of pyroclastic flows buried the doomed towns. On the 26 August the eruption started to wane, leaving 300 sq km of the surrounding area buried under approximately 8 cubic km of pumice and ash. The observation of this eruption by Pliny the younger has led to volcanologists calling similar eruptions "Plinian".  Many thousands were killed in this eruption.

The most recent eruption occurred towards the end of the Second World War. This longer eruption occurred at the end of a period of about 300 years during which the volcano erupted approximately every 20 years.  While the 79 AD eruption lasted only three days the 1944 eruption lasted two-weeks starting on 18 March 1944 when a lava flow started from the central crater. The 79 AD eruption exhibited no lava flows. The lava flow phase was followed by the appearance of a series of eight lava fountains starting on 21 March. The final fountain, the most explosive reached a height of 1000 m on 22 March. Pyroclastic flows characterized the final phase of the eruption, which finished on 29 March.  While still a powerful and impressive sight, the 1944 eruption was far less destructive than its famous predecessor. Coming towards the end of the war the volcano did cause some problems for the invading allies by the ash damage to airplanes a problem not experienced by the earlier Roman Empire in 79 AD!

Since 1944, Vesuvius has not erupted. However, there have been numerous earthquakes and some fumarole activity.  The area surrounding Vesuvius is densely populated and scientists maintain observations for any changes indicative of an eruption to allow evacuation of the populace. History has shown that an explosive eruption frequently follows a long quiet period from Vesuvius.

Reference Sources:

Geology.com

European Research on Understanding Processes and Timescales in magma systems

Volcano live



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