9.4

Volcanic collapses can produce many hazards

Among all volcanic hazards, the collapse of volcanoes is one of the most catastrophic scenarios threatening nearby populations and infrastructure worldwide. Although relatively rare events in a human lifetime, volcanic collapses can be extremely deadly due to  their size, travel distance, and secondary events.

  • Debris avalanches: They represent the most catastrophic and hazardous event associated with an edifice collapse, due to the magnitude of the event involving several or even tens or more km3 of rock material(1 km³ of material would fill ~400,000 Olympic-sized swimming pools) that moves downstream with great mobility and threaten populations and infrastructure. These can travel up to 100 km away from the source.

Map showing the extent of the 16 ± 5 km3 debris-avalanche deposit (dashed and solid lines) from Santa Ana volcano in El Salvador.The avalanche traveled about 50 km and extended the shoreline (Siebert et al., 2004).

  • Lateral blasts: These events can travel up to 30 km away from the source and have been clocked at over 220 mph– the fastest person in the world can run ~16 mph.

  • Magmatic eruptions: When slope failure is completed, normal open-vent explosions may occur.because collapses “un-cap” volcanoes. This allows the pressure inside of magma chambers to escape and cause magmatic eruptions.
  • Lahars: Lahars have been reported a few hours after the emplacement of a debris avalanche due to a dewatering process or as a secondary event due to important topographic changes such as drainage obstruction and formation of temporary lakes. In these cases, lahars generally flow farther that the associated debris avalanche with devastating effect. These events can travel >100 km away from the source– the length of 910 football fields. (Carrasco-Núñez, G., Siebert, L., and Capra, L., 2011)
  • Tsunamis: Large waves can be caused by volcanic activity as the volcano sheds large volumes of rock material into the sea during a collapse. Although tsunamis are not a volcanic phenomena, they represent in fact the most catastrophic event indirectly related to edifice failure. Nearly 20,000 casualties are related to tsunamis, nearly three-fourths of all those originating from volcanic landslides.can travel up to 1,000 km away from the source (Carrasco-Núñez, G., Siebert, L., and Capra, L., 2011). Therefore, volcanoes near coastline have the potential to produce significant damage, even if they are dormant. Here is a list of volcano-generated tsunamis on volcanolive.com.

The diagram below illustrates a sequences of events with multiple hazardous events associated with a volcanic collapse:

Hazards associated with volcanic collapses (Geological Survey of Canada)

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