Case Study: Volcano - Mt Etna

• African (oceanic) plate


  • Subducted below the Eurasian (continental) plate
• Slab window


  Dense high temperature magma rises to the surface through this in the subducting African plate, accounting for the effusive nature
• More than 25% of Sicily's population live on Etna's slopes
• Main sources of income for the island

  • Tourism
  • Agriculture
• Mt Etna


  • Composite volcano, made up of layers of ash and solidified lava
• Etna has 4 summit cones with the most recently active being the south east crater
• Strombolian eruptions


  • Produce ash, tephra and lava fountains
  • Fairly common from these craters
• Eruptions are frequent and can be more or less continuous for many years
• From 1995-2001 there were 150 summit eruptions involving lava flows and fire fountains
• Eruption began


  5th April 1971
• Eruption


  • Two fissures, 80-100m long opened up where the snow had been melting
  • South east crater formed
• Mitigation


  1. Government planned disaster response in advance

  2. Aerial photographs taken to map geographical features

  3. Rumbling sounds closely monitored to help predict eruption

  4. Ground temperature measurements taken

  5. Orderly evacuations took place when necessary

  6. Mobile aid available

  7. Lava travelled very slowly - people could see the danger coming
• Eruption started


  14th December 1991
• 1991-1993 eruption


  • Lasted 473 days
  • Most voluminous eruption for over 300 years at 250 million m3
  • Lava flowed down the south east flank into the Valle del Bove
  • Low rate of lava emitted which posed little threat to human life
• Mitigation


  1991-1993
• Immediate responses

  1. During 1992 the Italian Authorities built an Earth barrier over 400m long and 20m high in order to stop the lava from reaching Zafferana

  2. It contained the lava for a month before overflowing

  3. 3 smaller embankments were built after this

  4. The US marines then became involved in 'Operation volcano buster'

  5. Here they used explosives to blast a hole in the lava tube and then used helicopters to drop concrete blocks in the main lava flow in order to slow it down

  6. Finally a diversion channel was dug and explosives used to divert the lava onto an adjacent flank of the volcano

  7. The lava flow stopped 850m from Zafferana (27th May)

  8. Some geologists argued the eruption was ending anyway
• Long term responses


  1. The institute of volcanology in Sicily has continued to improve methods of monitoring by:

  2. Measuring radon gas to detect lava movements in the volcano

  3. Using GPS to examine changes to the slope angle of the volcano and use highly sensitive seismometers to measure minute tremors that may indicate lava being forced into the volcano
• Infrasound


  Volcanic noises that can enable early warnings to be issued quickly and dependably
• Infrasound-Mitigation


  1. From 2008-2016 the infrasound sensors detected 57/59 eruptions and sent alerts to researchers about 1 hour before an eruption

  2. Using the system, the Italian government were able to activate an emergency plan about 1hr prior to an eruption for the first time in 2015

  3. Infrasound sensors are placed 6km from the volcano