Volcanoes V: Volcanic Explosivity Index and Hazards

## Volcanic Explosivity Index (VEI)

* logarithmic scale from 0-8
* describes the size of an explosive volcanic eruption
* key characteristics:
* volume of ash produced
* height of eruption cloud above vent
* duration of eruption
* mainly depends on total volume of material erupted explosively
* increase by 1 unit = 10x more volume erupted

## Mt. Pinatubo, Phillipines

* VEI = 6
* second largest (terrestrial) eruption in the 20th century
* 28 mile high ash cloud
* valleys filled with up to 660 ft of volcanic deposits
* 20 million tonnes of SO2
* 0.9 degrees F in global temperatures in 1991-1993

## What Would A VEI 8 Eruption Look Like?

* imagine 100 pinatubos erupting at the same time
* toba caldera (supervolcano) eruption:
* 75,000 years ago
* 2800km^3 (675 miles^3) of material erupted
* global temperature decreased by 5.4-6.3 degrees F (as much as 27 degrees F at high latitudes)

## Volcanic Hazards


1. lava
2. pyroclastic material


1. pyroclastic (ash) fall
2. pyroclastic fall
3. gases
4. lahars
5. lateral blast

## Lava

* slow
* easy to predict its path
* usually not dangerous
* hazardous only to buildings and other infrastructure
* lava flows have low viscosity
* usually mafic lava
* two general types:


1. A’a
2. Pahoehoe

## Lava Flow- A’a

* mafic lava flow
* blocky and more vicious

## Lava Flow- Pahoehoe

* mafic lava flow
* forms ropes and less vicious

## Pyroclastic Material

* rock fragments ejected from a volcano
* different types distinguished based on particle size
* ash (