Mount Vesuvius

Mount Vesuvius is a somma-stratovolcano located on the Gulf of Naples in Campania, Italy, about 9 km east of Naples and a short distance from the shore. It is one of several volcanoes which form the Campanian volcanic arc.  Estimated to be about 17,000 years old, Mount Vesuvius measures approximately 30 miles around its base and rises to 4,203 feet above sea level.  


What is commonly called Mount Vesuvius is in fact an amalgam of two mountains: Monte Somma and Vesuvius.  The two peaks are easily distinguishable.  The active cone of Vesuvius was constructed within a large caldera of the ancestral Monte Somma volcano.  It  is a complex stratovolcano, built by layers of hardened lava, pumice, and volcanic ash.  Such composite volcanos have a conical shape with gentle lower slopes that rise steeply.  The crater is at the summit.  Eight major explosive eruptions have taken place in the last 17 000 years.  Major eruptions were often accompanied by surges and large pyroclastic flows, which is an avalanche of hot toxic gasses and fluidized rock that rushes down the side of a volcano at up to 100 km perhour. 

The eruption on the 24th, August 79 AD was said to have lasted more than 24 hours.  The first rain of ash and pumice was not necessarily lethal.  People who fled immediately stood a chance of survival.  But most tried to weather the storm and were caught by the pyroclastic flows.  The eruption released a hundred thousand times the thermal energy released by the Hiroshima bombing, spewing ash, mud and rocks, burying people under thick laters of ash.  Most people died instantly of extreme heat, when temperatures rose to up to 300°C [570°F] and more.  The remains of  1,500 people have been found, but the exact number of casualties is unknown.  The casts of hot ash and pumice covering the victims helped to preserve their clothes and faces.  When the eruption was at its height, Mount Vesuvius spewed 1.5 million tons lava per second.  Like shooting out 250, 000 fully grown elephants each second and letting them fall through the air!

Volcanologists have adopted the term “Plinian” from Vesuvius to describe large volcanic eruption clouds.  This is due to Pliny the Younger, who described the 79 AD eruption as a tall, “umbrella pine” shaped cloud that rose above the volcano.  Most of the rocks that erupted from Vesuvius are andesite.  Andesite lava creates explosive eruptions, which makes Vesuvius especially dangerous and unpredictable.  Vesuvius has erupted many times since then.  The eruption in 472 was said to spew ash that ended up as far away as present day Istanbul.  The eruptions of 512 were so severe, that people living on the the fertile slopes of Vesuvius were granted tax exemption.  A major eruption in December 1631 killed around 3 000 people and buried many villages under lava flows.  On April 7, 1906 Mount Vesuvius ejected more lava than ever and killed 100 people.  The last major eruption took place in March 1944. It lasted two weeks and destroyed almost 80 allied planes stationed at the Pompeii Airfield.  The were no people among the casualties.

None of the later eruptions were as large or destructive as the Pompeian one, but Vesuvius is still considered one the the world’s most dangerous volcanoes.  Ongoing efforts are being made to reduce the number of people living within the red zone, where there is a high risk of pyroclastic flows.  Today  600 000 people are living within the red zone and the authorities have a plan for their emergency evacuation.  Depending on the direction of the wind, an eruption may affect the inhabitants of large cities such as Naples, Avellino and Salerno.