Flights passing over the island of Sicily are being disrupted after the Toulouse Volcanic Ash Advisory Centre issued a warning for aviation to avoid the area around Mount Etna, following an eruption on Friday 11 October 2019. Volcanic ash is extremely hazardous to aircraft in a number of ways. At
its most obvious it is opaque, both visually and to radar. Then it is
abrasive, ash particles physically scour aircraft, damaging components
and frosting windows. However the ash is most dangerous when it is
sucked into jet engines, here the high temperatures can melt the tiny
silica particles, forming volcanic glass which then clogs engine. When
this happens the only hope the aircraft has is to dive sharply, in the
hope that cold air passing through the engine during the descent will
cause the glass to shatter, allowing the engine to be restarted.
Obviously this is a procedure that pilots try to avoid having to
perform.
An ash cloud over Mount Etna on 11 October 2019. l’Osservatorio Etneo dell’Istituto Nazionale di Geofisica e Vulcanologia.
Etna first erupted about half a million years ago, beneath the sea off
the east coast of Sicily, and has been going strong ever since. It now
stands 3330 m above sea level, and covers 1200 km³. It is responsible
for fertile soils across eastern Sicily. Records of eruptions on Etna go
back to 1500 BC. It is Europe's second largest volcano, after Teide in
the Canary Islands, and is one of the most active volcanoes in the
world.
Despite all this Etna has only ever
caused 77 recorded deaths (the most recent being two tourists caught in a
summit explosion in 1987) and relatively little destruction. In 1928 it
destroyed the village of Mascali on its northeastern flank, though
there were no reported casualties, the village being slowly overrun by a
lava flow. In 1669 a much larger lava flow destroyed at least 10
villages, reaching the walls of the city of Catania, 40 km to the south,
but again without loss of life. In 122 BC a heavy ash fall covered much
of the region, causing several buildings to collapse in Catania. The
destruction was deemed so severe by the Roman authorities that they
granted the city a 10 year tax holiday. In about 6000 BC a landslide on
the eastern flank of the volcano is thought to have caused a tsunami
that caused destruction around much of the eastern Mediterranean.
Etna
is located on the border of the African and European Plates,
specifically where Africa is being subducted beneath the European Plate.
As it is drawn into the Earth's interior material from the African
Plate melts, and the lighter portions rise up through the overlying
European Plate, causing a number of volcanoes including Etna and
Vesuvius.
Map showing the tectonic plates underlying Italy and southern Europe, and the location of the l'Aquila Earthquake. Napoli Unplugged.
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