Announcements

• Exam Weds. March 7, review March 5, here, 5 PM

• Pinatubo video worksheets on the table -- if you missed the video without an authorized excuse, you can try Cline library media services; I don’t know if they have it (In the Path of a Killer Volcano)

Today

• What are different kinds of volcanoes?

• What makes a volcano likely (or not) to pose a significant hazard?

A quick review question (more later)

(Level of one of the May, 1980, lahars on the Muddy River, WA)

(clickers please)

What is a difference between a cinder cone and a maar?

1. A cinder cone is rhyolite and a maar is basalt

2. A maar is pyroclastic and a cinder cone is effusive

3. A maar forms when basalt magma runs into groundwater

4. A cinder cone erupts for a few years; a maar erupts for hundreds of years

Things we want to keep track of about different kinds of volcanoes…

• Size (height and diameter)

• Lifespan (how long they are active)

• Composition of material they erupt

• Eruptive products

Basalt volcanoes

shield

Basalt, lava flows, long-lived (a million years or more), up to several hundred meters (several thousand feet) high, 35-40 km in diameter (e.g., most of the way from Flag to Williams, Flag to Meteor Crater: big)

SP Crater, AZ

Capulin Volcano,NM

cinder coneBasalt “popcorn”, often with one or more lava flows; short-lived (<10 years); 1-2 km diameter (~1 mile), <300 m high (1000’)

Ukinrek volcano, AK

maar

Basaltic, explosive, can have lava flows, active for days, 300 m wide (1000’) hole in the ground

Andesitic/dacitic volcanoes

Mt Jefferson, OR

stratovolcano

Fuji-san, Japan

Mount St. Helens, April-May, 1980

Spirit Lake

June, 1979

April, 1980

Debris avalanche

• Explosion or collapse of volcano’s side: a large part of MSH just fell off.

Mt. Shasta,CA

“Within a matter of seconds, perhaps 15 seconds, the whole north side of the summit crater began to move instantaneously. . . The nature of movement was eerie. . . The entire mass began to ripple and churn up, without moving laterally. Then the entire north side of the summit began sliding to the north along a deep-seated slide plane.”

Mt UnzenJapan

lava dome

Mount St. Helens

Soufriere Hills Volcano, Monserrat

Pyroclastic eruptions• What happens when you shake a can of soda and

pop the top?• Magma sits in the upper crust (5 km below the

surface) and the gas pressure builds hugely

• Can bust the top off by earthquake (MSH), too much pressure (Mayon,Philippines)

Dacitic/rhyolitic volcanoes

Crater Lake (Mt Mazama), OR

Taupo, New Zealand

Clickers, please

What kind of volcano is this?

1. Cinder cone2. Stratovolcano 3. Caldera4. Maar5. Dome

What kind of volcano is this?

1. Cinder cone2. Stratovolcano 3. Caldera4. Maar5. Dome

If your last name starts with A, B, C, D, E, or F, write your and your partner’s names and why you gave the answer you gave

What kind of volcano is this?

1. Cinder cone2. Stratovolcano 3. Caldera4. Maar5. Dome

What kind of volcano is this?

1. Cinder cone2. Stratovolcano 3. Caldera4. Maar5. Dome

Same group (A-F): why did you give the answer you did?

What kind of volcano is this?

1. Cinder cone2. Stratovolcano 3. Caldera4. Maar5. Dome

(notice 2-lane roadway)