Most people think they know all about the most famous volcanic disaster ever, but the
factual story is even more incredible than the fiction.
This August 24th is the 1936th anniversary of the violent erasure of Pompeii from the
shores of the Tyrrhenian Sea.
I've been to Pompeii, it's beautiful, but it's also amazingly expansive.
The city of Pompeii is three square kilometers, and excavation has been ongoing since it was
rediscovered in 1748.
As archaeology continues, modern scientific techniques are teaching us more and more about
that infamous day.
Around lunchtime on August 24, 79 CE, Mount Vesuvius exploded.
Eyewitness Pliny the Younger (whose grandfather, Pliny the Elder was a military officer stationed
in the region) wrote, "a cloud of unusual size and appearance," shot into the air from
Vesuvius, reminding him of an umbrella pine tree.
At its' height on that day, Vesuvius' column reached 27 miles (43km) into the sky before
branching out, and raining ash and pumice stones on the 2,000 Pompeians who hadn't already
fled the city.
The eruption caught people by surprise, many fleeing the city after that initial explosion
but before the city was completely buried by ash.
But from surviving records, we know there were signs something bad was coming.
Fish were floating dead in the rivers, wells were drying up, and the vines on the slopes
of the volcano inexplicably dried up; not to mention increasingly violent and regular
earthquakes were hitting the region.
Today we know, before volcanoes erupt, they swell slightly as the pressurized magma bulb
rises through the earth, like a massive zit…
Eventually, the mountain can begin to leak noxious gases, which might have contributed
to the death of the plants.
Measurements before the eruption of Pu'u O'o on Kilauea in 1983 found 150 tons of Sulfur
dioxide was released from the mountain per day!
People who fled Pompeii on August 24th would have escaped the coming disaster, but after
midnight on August 25th, between three and six massive superheated pyroclastic surges
-- like an avalanche, but of rock, dust and volcanic gas travelling 100 kph (62mph) -- slammed
into the city… burying Pompeii (and the people who remained) in volcanic dust for
many hundreds of years.
Looking at the distribution and type of debris in the ash layers, scientists estimated the
velocity and power of the 79 CE explosion of Vesuvius at 165,000 tons of debris per
second, with 84 rocks per square yard per minute raining down on the cities and temperatures
reaching 482 F (250C).
A 2013 study in Nature Communications found a mass extinction event in the lower Cretaceous
caused by a volcano resulted in exceptional fossil preservation, and Pompeii plays out
something similar.
If volcanic ash gets wet, it hardens like cement, preserving anything trapped inside.
Over time, the clothing and soft tissues of the Pompeians decayed, and today, their dry,
fragile bones and jewelry are all that survives.
Some of the most famous artifacts from Pompeii aren't the superb frescoes, houses, and even
bread in the ovens of the bakeries… but casts of the Pompeians themselves.
In 1777 excavators discovered an air pocket in the shape of a body, and in 1864 (almost
100 years later!) the director of excavations found a special mix of plaster of Paris which
could be poured INTO the cavities to mold out a body, revealing the heartbreaking detail
of the last moments of these people.
The wrong mixture of plaster can damage the delicate remains, so of the 1150 bodies found,
only 100 have been cast.
Today Pompeii is a UNESCO world heritage site, and now feeling the pains of exposure to pollution,
light, weathering, and water damage.
After heavy rains in some buildings in the city collapsed.
Even after preservation in volcanic ash for over 1600 years, we're losing Pompeii to the
elements.
Today, Vesuvius is the only active volcano on the European continent and 700,000 people
live in "death zones" immediately surrounding the mountain, ironically, they were drawn
there because the ash and lava flows emitted by volcanoes create some of the most fertile
soil on earth.
After a volcano erupts, the rock fragment particles ejected are called tephra, and over
time tephra breaks down thanks to chemical interaction from the atmosphere, resulting
in that super-rich soil.
And it's only a matter of time until Vesuvius hits it again.