Plate Tectonics- Vulcanicity Case Study

Mt Etna, Sicily, Italy, 1991-1993

Location

• Mt Etna is located on the island of Sicily in Italy. Italy is an MEDC and had a GDP per capita of over $20,000 in 1991.
• More than 25% of the population of Sicily live on the flanks of Mt Etna.
• The lava from previous eruptions provide fertile soil for growing citrus fruit and vines, Mt Etna itself is a tourist attraction and has ski slopes. 
• Mt Etna is the largest volcano in Europe – it is a stratovolcano which has formed on top of an ancient shield volcano which creates a wide variety of eruption types.

Causes

• Mt Etna is located on a destructive plate margin between the African and Eurasian plates. 
• The northern edge of the African plate is being subducted.
• The eruption in 1991 started on 14th December and lasted for 473 days which was the most voluminous eruption from Etna in over 300 years (250 million m³)
• The lava flowed down the SE flank of the volcano into the Valle del Bove.
• The acidic lava had a low effusion rate (rate and volume of lava emitted in m³/sec) which posed very little threat to human life.

Impacts

Social:

• There were NO deaths as a result of the eruption.
• The lava destroyed the springs which provided the water supply to the town of Zafferana with a population of 8,000 people.
• Several people who lost homes and farm land in the Val del Bove blamed the government for not acting soon enough.
• In interviews made during the late 1990s with people from the Zafferana area,when asked about their fear of a future eruption, many of them expressed that they had no fear because "when there will be a lava flow it will be diverted anyway".

Economic:

• The total cost of the management and responses as well as insurance claims for damage to property ran into millions of Lira.

Environmental:

• Vineyards and Chestnut orchards were destroyed

Management & Response

Immediate/short term:

• During 1992 the Italian authorities built an earth barrier over 400 metres long and 20 metres high in order to stop the lava reaching the town of Zafferana – this contained the lava for about a month before overflowing. 3 smaller embankments were then built.
• The US marines then became involved in ‘Operation volcano buster’ in which they used explosives to blast a hole in the lava tube and then used helicopters to drop concrete blocks into the main lava flow in order to slow down the lava. 
• Finally, a diversion channel was dug and explosives were used to divert the lava onto an adjacent flank of the volcano. 
• The overall outcome of these interventions resulted in the lava flow stopping 850 metres from Zafferana but some geologist argued that the eruption was ending anyway.

Long term:

The Institute of volcanology in Sicily (INGV) has continued to improve methods of monitoring since the 1992 eruption by:

• Measuring radon gas to detect lava movements within the volcano
• Using GPS to examine changes in slope angle of the volcano 
• Using highly sensitive seismometers to measure minute tremors which might indicate lava being forced into the volcano
• The responses involved many different organisations including the police, fire brigade, the civil defence department, the local council, geologists, volcanologists, the Italian army, Italian Red Cross and the US army.