VOLCANOES

I. Parts of a volcano

rim

cratervent

pipeParasitic

cone

II. Locations of volcanoes

A. Along subduction zones (convergent boundaries)

B. Along mid-ocean ridges (divergent boundaries)

C. Hot spots (not along plate boundaries)

The magma chamber is well below the lithosphereand does not move. The lithospheric plate moveswhich creates a chain of volcanic islands.

V. Volcanic cones (three basic shapes)

A. Shield cones- have broad bases and gently slopingsides (15 º)because they are made of mafic lava.These cones are typically large and have quiet lava eruptions.

Example: Hawaii

V. Volcanic cones (three basic shapes)

A. Shield cones-

Geometric Structure

Silica Low

Gases Low

Eruptive Style Quiet

Where in the World? Hawaii

Igneous Rx created Basalt – Pahoehoe, aa

B. Cinder cones- have steep slopes (up to 40 º) and arenot more than 100 meters high because they are madeof felsic lava. These cones create explosive eruptions.

Example: SP crater in Arizona

V. Volcanic cones (three basic shapes)

Cinder Cones

Geometric Structure

Silica High

Gases High

Eruptive Style Explosive

Where in the World? Arizona

Igneous Rx created Pumice/Scoria

C. Composite cones (stratovolcanoes)- these cones are created by alternating quiet and explosive eruptions

Examples: Mt. Fuji- Japan Mt. Hood- U.S. Mt. Rainier- U.S. Mt. Shasta- U.S. Mt. St. Helens- U.S.

V. Volcanic cones (three basic shapes)

Composite Cone

Geometric Structure

Silica Very High

Gases Very High

Eruptive Style Very Explosive

Where in the World? Mt. St. Helen’s

Igneous Rx created Pumice/Scoria

D. Fissure: fracture or crack in rock along which there is a

distinct separation from which lava erupts.

Example: Hawaii

V. Volcanic cones (three basic shapes)

Fissure Eruption

Geometric Structure

Silica Low

Gases Low

Eruptive Style Quiet – Medium

Where in the World? Hawaii - Iceland

Igneous Rx created Basalt

ERUPTION UPDATES

• http://hvo.wr.usgs.gov/kilauea/update/maps.html

• http://www.nps.gov/havo/planyourvisit/halemaumau_newgasvent.htm

III. There are three types of lava: (mafic, felsic, intermediate)

A. Mafic- dark in color and contains high amounts ofiron and magnesium.

1. Has a low viscocity- (flows easily)

2. Volcanoes with mafic lava are not explosive.

a. Types of mafic lava:

-pahoehoe- has a wrinkled surface. Formed when lava is still hot.

-aa- has a jagged appearance. Formed when lava cools down some.

B. Felsic- lavas with a lot of silica. Are light incolor and less dense than mafic lava.

1. Are viscous lavas (thick)

2. Often contain high amounts of dissolved gases.

3. Volcanoes with felsic lavas are explosive.

B. Intermediate lava- composition is between felsicand mafic lava.

IV. Types of pyroclastics (tephra)- material that explodes out of a volcano.

Volcanic ash- between 0.25 and 2mm in diameter

Lava Flow – Magma that erupts onto Earths Surface.

Lahar- Pyroclastic mudflow/landslide.

Pyroclastic Flow - flows are fast-moving currents of hot gas and rock

Volcanic bombs- aerodynamic tephra

Volcanic blocks- can be as large as a house

Volcanic Gases

• The principal components of volcanic gases are water vapor (H2O), carbon dioxide (CO2), sulfur – either as sulfur dioxide (SO2) (high-temperature

volcanic gases) or hydrogen sulfide (H2S) (low-temperature volcanic gases), nitrogen, argon, helium, neon, methane, carbon monoxide and hydrogen.

VI. Caldera- a large basin-shaped depression caused from a volcano that collapses.

Examples: Krakatoa- Indonesia Crater Lake- Oregon

VII. Volcanic rock

A. Extrusive igneous rock- Molten rock that cools above ground. The rock cools fairly quickly andthe crystals are not large enough to be visible.

B. Intrusive igneous rock- molten rock that cools below ground. This takes a long time and largecrystals form.

Pikes Peak is made of intrusive igneous rocks (granite).It was molten rock deep within the Earth and it cooledoff slowly over time.

Pikes Peak is a batholith