OutlineHazards

Mt. St. Helens Case Study

Precursors

Pompeii Case Study

Volcanic Hazards and Mitigation

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, AlaskaApril 1990

Pyroclastic flow:

When plume cools, it falls toearth, 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

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

Volcanic Mudflows

• Icy to boiling temperatures (hot mudflow called lahar)

• Mudflows from Mount Rainier have buried valleys where many communities now sit

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”

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

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