Sunday, May 15, 2011

Apple #524: Mount Etna

I check frequently.  It's a wellspring of information.  Today, I learned from that uber-useful site that Mount Etna erupted recently.  So I thought I'd find out more about the volcano.

  • As of this writing, Etna's most recent eruption happened on Thursday, May 12, 2011.
  • Etna is one of the most active volcanoes in the world.

Etna is a volcano on the island of Sicily, which is south of Italy.  It's about ten miles from a town called Catania, whose citizens have been dodging Etna's lava for centuries.
(Map from

  • Eruptions have been documented as far back as 1500 B.C. and it has erupted more than 200 times since then.  
  • Scientists think it originated underwater.  It has erupted so many times, it's now above sea level.
  • Notable eruptions include one in 1669 that marked people's first efforts to try to control the flow of lava, but the lava made it all the way to the town of Catania and the sea as well.  It killed somewhere between 60,000 and 100,000 people.  After that disaster, artificial attempts to stop the flow of lava were outlawed until the 1980s.

From a fresco in the cathedral at Catania depicting the eruption of Mount Etna in 1669. There are two vents shown here, the smaller of the two with a 9 kilometer-long fissure extending from it.
(Image from U.C. Davis)

  • Another notable eruption happened in 1852 when the volcano spewed forth more than 2 billion cubic feet of lava that covered more than three square miles of land nearby.
  • In 1979, Etna began an eruption that would continue for 13 years.
  • In 1992, people tried to control the lava flow again, this time by using explosives to make a hole beneath the lava tunnel and then dropping huge concrete blocks into the hole to try to stop it up.  Like the effort in 1669, this was unsuccessful.
  • Etna's most recent series of eruptions started in 2007 and is considered to be "ongoing."

Etna's eruptions are so common that this recent outburst was described in the media mainly in terms of whether it might affect this year's Giro d'Italia.  Cycling fans were assured that the race would go on as usual, with the eruption acting as a picturesque backdrop.  Officials did have to close the airport in Catania for a while, though.
(Photo from the AP via the Daily Telegraph)

  • Scientists aren't exactly sure why Etna erupts as often as it does and where it does.  They have proposed lots of theories but none quite fit the data.  But Etna's behavior is probably related to the fact that it's located right where the African tectonic plate meets with the Eurasian tectonic plate.
  • Its unusual behavior may also be related to the fact that Etna is actually two volcanoes, one on top of the other.  The bottom volcano is a shield volcano.  The one on top is a more recent stratovolcano.
  • Shield volcanoes are usually huge in diameter, not that tall, and with broad long sloping sides that are built of many layers of lava flows.  Mauna Loa in Hawaii is the world's largest shield volcano.  Typically, the lava flows that come from these are relatively slow-moving.  The lava may also escape from fissures along the flank of the volcano, rather than exclusively from the central vent.

Lava that flowed down from Mount Etna to the town of Nicolisi in July 2001.
(Photo from Getty Images via National Geographic News)

  • Stratovolcanoes, on the other hand, are more cone-shaped, rise higher into the air, and are made up of layers of lava flows, mud flows, and pyroclastic material (I'll define that word in a minute). Mt. Fuji is the most notable type of stratovolcano.  
  • Stratovolcanoes are often the most deadly variety of volcano.  They are usually located at the convergence of two tectonic plates.  In most cases, stratovolcanoes are dormant for long periods of time, as the energy from the movement of the plates beneath builds up.  When stratovolcanoes do erupt, their eruptions are usually very explosive, powerful, and deadly.
  • One of the things that makes stratovolcanoes so dangerous is their creation of pyroclastic materials.  These are huge chunks of magma and rock that get blown to bits when a lava explodes.  The pyroclastic materials may range in size from rocks the size of a fist, to pebbles smaller than a dime, to ash. 
  • "Some of them are bigger than cars, and some might be as big as trucks," said one volcano watcher of the boulders coming out of Etna this week.
  • In spite of Etna's dual-volcano personality and its potential to cause a lot of damage, the fact that it erupts so frequently probably keeps it from being that much of a threat.  More dangerous stratovolcanoes hold in their energy for decades until it explodes and it's all released at once.  Etna's regular release of energy and gases are probably why it's not considered a pressing danger to people living in nearby Catania.
  • 2010 was a relatively quiet year for the volcano. When it erupted in January 2011, vulcanologists expected that it would continue erupting this year pretty much continually, maybe for weeks or months at a time. This eruption is confirming that expectation.

Lava flows from Mount Etna's eruption in January 2011
(Photo from National Geographic News)

An eruption on the flank of Mount Etna in 2007.
(Photo from Earthweek)

An especially pyrotechnic eruption from Mount Etna.  I don't know what year this was taken.
(Photo by Luke and Alyssa Meyr, sourced from MIS Blue Team Science)

  •  "Etna" is Greek for "I burn."  Seems aptly named, doesn't it?
The Sofia Echo, Mt Etna in Sicily erupts, international airport closed, May 12, 2011
The Daily Telegraph, Volcanic threat erupts as Francisco Ventoso wins sixth stage of the Giro d'Italia, May 13, 2011
Brett Israel, Mount Etna blasts lava, ash into the sky, OurAmazingPlanet via MSNBC News
ABCNews, Volcano Chasers at Mt. Etna
Mt. Etna erupts "like cannon" 6 tourists killed, 23 injured, The Montreal Gazette, September 13, 1979
Jessica Ball,, Mount Etna - Italy 
San Diego State University, Department of Geological Sciences, Shield Volcanoes, Stratovolcanoes
USGS, Shield Volcanoes
Solcomhouse, Mount Etna


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