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

Volcanic Hazards and Mitigation Figure 7-1

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

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

Lava Flows

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

Redoubt Volcano, Alaska April 1990

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

Pyroclastic flow: Will the hills protect the town?

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

Suspended Ash

3 months after eruption

Ash clogs lungs and air filters

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

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

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

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

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