Geology
Volcanoes Lecture
Name_______________
Standards
• Describe the composition, structure and formation of igneous rocks
• Describe the geological manifestations of plate tectonics (e.g., volcanoes) that occur at
plate boundaries
• Describe the impact of plate motions on societies and the environment (e.g., volcanoes)
I. Where are Volcanoes Formed?
 Plate boundaries
 Hot spots
A. Plate _______________________
 Two types of plate boundaries where volcanoes are formed:
 Subduction zones
 Divergent boundaries
1. _______________________ zones
a. Friction is caused by plates rubbing together, and
b. Fluids get released from sediments on oceanic crust
i. These cause rock above downgoing plate to melt and form magma
c. Associated with explosive eruptions because the lava contains lots of
silica and is therefore viscous (sticky)
Examples:
 Ring of Fire – ____% of world’s active volcanoes. Located around
_________________
Plate
 _____________ arc volcanoes - volcanoes formed at oceanic-___________
subduction zones, such as Japan (Mt. _________), Indonesia, West Indies
 ______________ Volcanoes – form at oceanic-_________________
subduction zones, such as Mt. St. Helens
2. ___________________ boundaries
a. Upwelling magma fills space and forms volcanoes where plates are pulling
apart from each other.
Examples:
 Mid-ocean ridges, such as ______________, on the Mid-Atlantic Ridge
 __________ valleys, such as the _____________________ Volcanoes, in
the Rio Grande Rift
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B. ______ Spots
1. ___% of world’s active volcanoes.
2. Formed by _____________ of heated material in _______________ that originates
near core.
3. Single ______________________ cell that is stationary (plate moves over hot
spot).
a. Ex: Hawaii, Yellowstone, Iceland (also a divergent boundary), ______________
Islands
II. Structures Formed by Magma
 Plutonic Structures
 Volcanic Structures
A. __________________ Structures
1. Formed by magma ______________________
a. Classified as concordant or discordant
2. _______________________ Plutonic Structures
a. Magma body is ________________ to surrounding ____________ of rock
i. __________ – horizontal sheet of magma
ii. _______________ – _________ shaped with a flat bottom
3. _____________________ Plutonic Structures
a. Magma cuts at an ______________ through surrounding rock layers
i. _______ – _______________ magma body. Formed when magma fills a
crack in the rock.
ii. _____________________ – large chamber of solidified magma.
Examples: Sandia Mountains, Sierra Nevada Mountains
iii. ____________ – mini batholith
B. __________________ Structures
1. Are formed by _____________ that cools and solidifies on Earth’s _____________.
a. Classified as
 Volcanic cones
 Lava domes
 Lava plateaus
2. Volcanic _________ (_________________)
a. Form where lava reaches the surface through ___________.
b. Volcanic debris forms cones
c. There are 3 types of cones/volcanoes:
 Composite cones
 Shield cones
 Cinder cones
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a. _______________________ cones/volcanoes
i. Also called ____________________________
ii. The classic volcano shape that we usually think of.
iii. Made of alternating layers of _______ and ___________________ material.
iv. Typically ________________ eruptions because the lava contains lots of
______________, which makes it viscous (sticky).
 Examples: Mt. St. Helens (U.S.), Mt. Pinatubo (Philippines), Mt. Fuji
(Japan)
b. _________________ cones/volcanoes
i. ________________ slopes made up of several layers of ____________
(non-viscous), _________________ lava flows.
ii. Shape of a flattened dome.
iii. Typically ____________ eruptions (i.e., not explosive).
 Examples: Kilauea & Mauna Loa (Hawaii), Piton de la Fournaise
(Reunion Island)
c. ________________ cones/volcanoes
i. ___________ slopes made up of fragments of lava called _____________ or
____________
 Examples: Albuquerque Volcanoes, Parícutin (Mexico)
3. Lava ____________
a. Blobs of ______________ (sticky) lava that are squeezed out of a volcanic vent.
b. Lava domes typically build up inside the craters of ____________________
volcanoes.
c. ______________ of lava domes triggers explosive eruptions and
_________________ flows.
4. Lava _________________
a. Created by ____________ amounts of fluid lava that erupts from
________________ (cracks).
b. Lava flows can be up to 2000’ thick.
c. Often called ____________ ________________.
 Example: Columbia River Plateau (Oregon, Washington & Idaho)
III. Features in Volcanic Rocks
A. _____________-scale features:
1. Lava – magma (liquid rock) that reaches the surface. Two types:
a. ________________ – smooth, ________ surface
b. ____ – crumbly, ______________, jagged, vesicular surface. _____________
means it contains holes left by _______ ______________.
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c. ___________ lava – forms under ____________. Rapid cooling causes outside
to solidify quickly. Shapes look like pillows.
2. __________________ material – ________________ of volcanic _______ ejected
from vent.
Ex: ash, rocks
B. ___________-scale features:
1. Lava __________ – ______________ formed when ______________ of lava flow
solidifies and the still-molten lava inside flows out
Ex: El Malpais, NM, and Kilauea, Hawaii
2. _____________ joints – 4-6 sided columns of _______________
Ex: Devil’s Tower (Wyoming), Giant’s Causeway (Ireland), El Cabezon (NM)
IV. Volcanic Products (Solids, Gases & Liquids)
A. __________________
1. ________________ material
2. __________ (solidifies into rock)
B. ____________ – trapped gases cause ______________ eruptions
1. ___________ ____________ – most abundant volcanic gas. 70% by weight.
2. ____________ ____________ – 14%
3. _________________ gases – sulfur dioxide & hydrogen sulfide (rotten egg smell)
4. Trace amounts of other gases.
C. ________________
1. Lava – up to 1100 C (2000 F), speeds up to 40 km/hr
a. _________ – ___________, gases usually escape
Ex: basalt
b. _________ – ___________, gases usually trapped = explosive
Ex: rhyolite
V. _________ Cycle of Volcanoes
A. Stages of acivity:
1. ___________ – recent activity, within recorded history
2. ___________ – no recent activity but area still active. Could erupt again.
3. ___________ – not presently erupting and not likely to do so for a long time in the
future.
VI. New Mexican Volcanoes
A. __________ _______________ has the most volcanoes of the western states
B. There are _________ volcanoes within ____ miles of _____________________
1. Albuquerque Volcanoes
a. ______________ Black, and JA are the 3 largest.
b. 18 total along fissure.
c. Erupted __________________ years ago.
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2. Jemez Caldera (____________ ____________)
a. 55 miles north in Jemez Mountains.
b. ____________ is ____ miles across.
c. Eruptive activity started 15 Ma.
d. Large eruptions 1.4 – 1.2 Ma (75 times the force of Mt. St. Helens).
e. Last eruptions 40 – 60 thousand years ago.
3. Valley of _____________
a. Carrizozo
b. Large lava flows (one of longest young flows in world)
4. Zuni-Bandera Volcanic Field, El _______________
a. Grants
b. ___________ years old
c. Most _____________ in NM
5. _______________ Magma Body
a. Most __________ area in NM currently.
b. Socorro _____________ _____________ – earthquakes caused by magma body
located about ____ miles underground
c. Based on current data, most likely area to erupt in future

L.
Brown
Updated January 2013
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