1. Outline Hazards Mt. St. Helens Case Study Precursors
Pompeii Case Study

2. Volcanic Hazards and Mitigation
Figure 7-1

3. 1/2 billion people live within 60 miles of active volcanoes

5. Hazards Lava flows Pyroclastic flows Ash and Pumice
Lahars: Mud flows from volcano
Poisonous gases

6. Lava Flows

7. Pyroclastic ash plume: Interferes with airplane flight
(causes engine failure)

8. Redoubt Volcano, Alaska
April 1990

9. Pyroclastic flow:
When plume cools, it falls to
earth, creating a high-speed,
hot, gaseous cloud of death

10. Pyroclastic flow:
Will the hills protect the town?

11. Pyroclastic Flows and Surges
Pyroclastic flows can travel over surface of water
Figure 7-10

12. Suspended Ash

13. 3 months after eruption

14. Ash clogs lungs
and air filters

15. Volcanic Mudflows Ash + water = flowing wet concrete Triggers:
eruption of volcano covered in ice or snow
heavy rain
Figure 7-13

16. Volcanic Mudflows
Icy to boiling temperatures (hot mudflow called lahar)
Mudflows from Mount Rainier have buried valleys where many communities now sit
Figure 7-17

18. Poisonous Gases Pressure keeps gas dissolved in magma
At surface, gases exsolve
More escaping gas: impending eruption
Gas in atmosphere forms aerosols  volcanic smog, “vog”
Figure 7-19

19. Poisonous Gases
Carbon dioxide in high concentrations is colorless, odorless, denser than air (hugs ground) and deadly
1986 Cameroon: magmatic carbon dioxide bubbled out of Lake Nyos
Killed more than 1700 people, 3000 cattle
Figure 7-20

20. Poisonous Gases
Carbon dioxide from Long Valley Caldera in eastern California has killed huge areas of trees
Other volcanic gases include sulfur dioxide, hydrogen sulfide, chlorine compounds, fluorine
Figure 7-21