Volcanoes

7.1 Volcanoes and Plate Tectonics

• Magma – hot liquid rock• Volcanism – movement of magma toward suface• Lava – magma on the surface• Vent – structure which magma flows to surface• Volcano – material built up around the vent• Fissures – cracks, Iceland• Hot spots – volcanism in plate

http://www.nationalgeographic.com/forcesofnature/interactive/index.html?section=v

Where are Volcanoes? P.11

• Subduction zones

• Mid-ocean ridges

• Hot spots

- found within a plate not at a plate boundary

Magma p.12

• Magma is a complex high-temperature fluid substance. Temperatures of most magmas are in the range 700°C to 1300°C

• May reach as hot as 1600°C.

• Called magma when in the earth and lava when it is on the surface of the earth.

Felsic Magma p.13

– SiO2 >70%

– Fe-Mg: ~ 2% – Temp: < 900°C – Viscosity: High – Eruptive behavior: explosive – Distribution: hot spots in continental crust (

Yellowstone National Park), continental rifts, island arcs

Yellowstone

• The Yellowstone Caldera is the largest volcanic system in North America. It has been termed a "supervolcano" because the caldera was formed by exceptionally large explosive eruptions.

• The amount of ash and gases released into the atmosphere probably caused significant impacts to world weather patterns and led to the extinction of many species, primarily in North America.

Gases from Volcanoes p.14

• Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide.

• Sulfur dioxide kills vegetation and can cause acid rain.

Homework

After viewing the video, write a paragraph that states what fact you found the most interesting (disturbing) and why?

Eruptions

7.2 Volcanic Eruptions

• A. Kinds of Eruptions

• B. Volcanic Rock Fragments

• C. Volcanic Features

• 1. Types of volcanoes

• 2. Craters and Calderas

• D. Predicting Volcanic Eruptions

Volcanic Eruptions• 2 types of lava chemically, effects eruptions intensity

• 1. mafic lava – dark, rich in Mg and Fe• From ocean crust• Less explosive, quiet

• 2. felsic lava – lighter color, lots of silica, much less Mg and Fe• Found in continental crust• More explosive, contains dissolved gases

• Other types are in between• Pahoehoe – mafic lava cooling rapidly will wrinkle• Aa – when the lava breaks into chunks• Pillow lava – midocean ridge cools so rapidly forms round blobs

Pahoehoe

Aa

A. Kinds of Eruptions

• If magma has a lot of gases more explosive

• Ocean islands usually quiet

• Continental volcanoes with felsic lava have cooler and thicker lava so traps gases (H2O and CO2) big explosions

B. Volcanic Rock Fragments

• Felsic lava explodes so throws materials• Pyroclastic material – rock fragments (some still

molten, others cooled)• Volcanic ash - <2 mm• Volcanic dust - <.25 mm• Lapilli - < .64 mm• Volcanic bombs – red-hot lava cools in the air in

shape of spiral or round bomb• Volcanic blocks – big solid rocks as big as a

house

bombs

Volcanoes Can Cause Climate Change!

• Ash from a large volcano can shut out the sunlight for hundreds of miles.

C. Volcanic Features

• What it looks like

• 1. Types of volcanoes

• 2. Craters and Calderas

1. Types of volcanoes

• 1. Shield volcanoes – cones with broad base and gentle slope, made up of lava layers

• Hawaii• 2. Cinder cones – cone is made up of fragments

ejected • 3. Composite volcanoes (stratovolcanoes)• Combination of layers of lava and fragments

from some quiet and expolsive eruptions• Ex. Mt. Fuji, Rainier, Hood, Shasta• St. Helens

Types

2. Craters and Calderas

• Crater – funnel-shaped on the top vent

• Explosion forms

• Caldera – depression from collapsed crater

• Crater Lake National Park

Caldera

Crater Lake - Oregon

D. Predicting Volcanic Eruptions

• Not where we need to be yet• Saves lives• Seismographs• Temp• Pressure• Bulging surface• Gases given off• History/past• Dormant for long periods can be active

7.3 Extraterrestrial volcanism

• Moon

• Mars

• Lo

Moon

Surface covered with craters – meteorites

Lava flow evidence does show volcanic activity long ago

Nothing active

No plates for movement or convection current evidence

? Not sure how

Mars

• See pictures of

• None prove active

• They are much larger than earths because no continental drift

Lo

• Moon of Jupiter

• Pictures of active volcanoe

• Think the material is sulfur and sulfur dioxide from color

• Constantly erupting