1. Volcanoes
Key Question: How are volcanoes hazardous to human populations and what controls risk?
Key Words
Risk and Hazard
Primary and Secondary Effects

2. What is the difference between a hazard and risk?
Anything that poses a threat to humans or property
Hazard =
Risk =
Probability or likelihood of being affected by the hazard

3. Why do volcanoes erupt in different styles
Red (Shield)
One control on risk of eruptions in volcano type.
Task: Decide what type of plate boundary each forms at and think of some of the hazards associated with each
Grey (Cone)

4. Why do volcanoes erupt in different styles
Grey (Cone)
Red (Shield)
Volcano
Type
Hazards
Task: Decide what type of plate boundary each forms at and think of some of the hazards associated with each

5. Grey (Cone)
Hazards:
Ash / tephra (roof collapse and breathing difficulties)
Lava flows (High Viscosity Andesite and Rhyolite )
Pyroclastic Flows
Famine
Tsunami
Volcanic Gases
Lateral Blasts
Climate Change
Mudflows (lahar)

6. For these highlighted explain how they occur
Grey (Cone)
Hazards:
Ash / tephra (roof collapse and breathing difficulties)
Lava flows (High Viscosity Andesite and Rhyolite )
Pyroclastic Flows
Famine
For these highlighted explain how they occur
Volcanic Gases
Lateral Blasts
Climate Change
Mudflows (lahar)

7. Red (Shield) Hazards: Lava (low viscosity basalt –effusive) Ash Gas
Climate change

8. Why do volcanoes erupt in different styles
Grey (Cone)
Red (Shield)
Volcano
Type
Mudflows (lahar)
Lava (low viscosity basalt –effusive)
Climate Change
Hazards
Lateral Blasts
Ash
Task: Now decide which are primary and secondary
Volcanic Gases
Pyroclastic Flows
Gas
Famine
Lava flows
Climate change
Ash / tephra
tsunami

9. Primary Hazards

10. How can their explosivity be measured?
VEI 0
The Volcanic Explosivity Index (VEI) is used for classifying explosive eruptions.
VEI 1 & 2
open-ended
VEI 5
10 times larger than the previous value (logarithmic)
VEI 6
VEI 7
VEI 8

11. Measuring Volcanic Eruptions
Non-explosive eruptions. gentle effusion of low-viscosity basaltic magma e.g. Hawaiian and Icelandic volcanoes. EFFUSIVE ERUPTION.
VEI 0
Small explosive eruptions that eject enough debris (100,000m³) to cover London with a thin dusting of ash!
VEI 1 & 2
More violent explosive eruption of the more viscous andesitic magmas such as the 1980 Mount St Helens eruption in the USA
VEI 5
Mt. Pinatubo in the Philippines in This was the largest eruption in the 20th Century and blasted out sufficient material to bury the City of London to a depth twice that of the height of the former World Trade Centre towers in New York!
VEI 6
1815 eruption of Tambora in Indonesia, the largest eruption since the end of the last Ice Age - 10,000 years ago. The Tambora eruption blasted out over 100km³ of debris - enough to bury the City of London to a depth of 1km!
VEI 7
Toba, in Sumatra in Indonesia over 70,000 years ago. This blast ejected sufficient gas and debris into the atmosphere to bury the whole of Greater London to a depth of 1km, as well cause a rapid and dramatic change to the global climate. SUPERVOLCANIC ERUPTION.
VEI 8

12. Explosivity of Volcanic Eruptions
Red volcano
Explosiveness
Effusive
Grey volcano
Low gas pressure
Gas pressure
Viscosity
Fluid
Silica content in magma
52-45% SiO2
Magma type
Basaltic
Plate tectonic setting
Constructive Plate Margin

13. Volcanic risk? What controls your overall risk? Eruption Style
Level of Development
Volcanic risk?
Population Density
Technology
Finally Is living in Indonesia or Iceland is more dangerous and why (for volcanoes).
Task: Explain how each changes the risk