The nation of Italy has dozens of beautiful scenic islands. Many of these islands are volcanic in
origin, such as Stromboli, Lipari, or Ischia. However, one of these islands stands apart, as it
contains the only active shield volcano in Italy. The island in question is called Pantelleria,
which is located halfway between the island of Sicily and Tunisia. This island contains several
fascinating volcanic features, and last produced an eruption in 1891. This video will discuss this
volcano, and mention what its future hazards are. The reason why this volcanic island exists is due
to a rift zone. This rift zone has caused the crust in the area to slowly spread apart to the
north and south, allowing magma to travel upwards and erupt onto the surface. (pause 2 seconds)
It is not known when this volcano began forming, but it started as a submarine volcano about 1000
meters beneath the Mediterranean Sea. Over time, this volcano built a large profile,
which continued to creep towards the surface. Then, 220,000 years ago,
an eruption broke the surface. This eruption constructed a rounded lava dome, as this lava
was built out of a rock type called trachyte, which contained a high viscosity as lava.
Over the next several thousand years, dozens of other vents reached the surface,
thus expanding the island. Then, volcanic activity moved towards the modern south of the island.
Over time, numerous explosive eruptions deposited a thick layer of volcanic ash
which in some locations measured 300 meters thick. The reason why Pantelleria subsequently formed
into a shield volcano instead of a stratovolcano was due to the wide variety of lavas it erupted.
Although it produced explosive eruptions from siliceous lavas such as dacite and rhyolite,
it also produced large volume fluid eruptions out of basalt which formed the shield profile.
For example, 120,000 years ago, a fluid basaltic eruptions occurred on the eastern edge of the
aforementioned cliffs. It is not known what the exact relation was to subsequent events, but soon
after this low silica eruption a massive eruption occurred on the surface. As many cubic kilometers
of ash were ejected high into the atmosphere, pyroclastic flows raced across the entire island.
Then, due to the large volume of magma erupted, the volcano collapsed downwards
to form a 6.5 kilometer wide caldera. The remnants of this caldera can today be seen
on the southeast of the island, where it formed a 100 meter tall caldera rim.
After another series of eruptions, a second caldera forming eruption occurred 45,000
years ago. This eruption formed a 6 kilometer wide caldera rim in the center of Pentelleria.
In the aftermath of this eruption, a large lava dome called Monte Grande began growing in the
most recent caldera's center. By 35,000 years ago, this lava dome became so large that it suffered a
partial collapse to the east. Afterwards, a second lava dome called Monte Gibele erupted out of the
remnants of this collapse. After this dome stopped erupting, it was slowly uplifted several hundred
meters by rising magma. This uplift caused the older volcanic dome to have a notable tilt to it.
22,000 years ago, a rare highly siliceous volcanic rock called rhyolite erupted onto
the surface on the northwest of the island. Eventually, this dome also collapsed,
causing flows of rhyolite lava to reach the ocean. Within the last 10,000 years, 6 lava dome forming
eruptions occurred on the island. The majority of these occurred adjacent to Monte Grande,
and resulted in deposits of ash around Pantelleria. The most recent of these
eruptions occurred in 1080 BC. However, in both 1831 and 1891, there were credible reports of
submarine volcanic eruptions just off the island's coast. Scientists are now certain
of the source of the latter eruption which is located just off the coast of Punta Fram.
Since then, no additional eruptions have occurred. In all likelihood, the next eruption from
this volcanic complex will occur at the same site of the 1891 eruption.
Such an eruption would only require a small evacuation within a 5 kilometer radius of this
vent due to the potential threat of ejected bombs of volcanic rock falling in a close radius. In the
rare event of an unusual rhyolite lava eruption in the center of the island, it would require
the entire island's populace to be evacuated for months to years. Rhyolitic eruptions would be two
orders of magnitude larger than those typically witnessed at Mount Stromboli. Overall, the
odds of this volcano erupting on land or in the Mediterranean sea are about 1 in 1100 each year.
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