Volcanic Rock
Chapter 14 Earth Science Book
read pages 252-256
restate & answer Topic Questions 1-6
Essay # 4
Topic 1:
Page 253 Earth Textbook
Magma
Molten Rock Underground
Lava: Molten Rock on the Surface
Volcano: Where Magma erupts as Lava
Earth’s layers can be classified based on composition.
Crust
• 1% of Earth’s volume
• oceanic crust
• mostly basalt
• continental crust
• mostly granite
Mantle
• 83% of Earth’s volume
• mainly silicon and oxygen
Core
http://www.llnl.gov/str/JulAug04/gifs/Fried1.jpg
• 16% of Earth’s volume
• mainly iron (90%) and
nickel
Earth’s layers can also be classified by physical properties.
Lithosphere
• cool, rigid
Athenosphere
• hot, partially melted
Lower mantle
Core
• outer core
• liquid
• inner core
• solid
•
o
Topic 1:
Page 253 Earth Textbook
Magma
FELSIC: High concentrations of SILICA.
Light in color, Light in density. Can contain
trapped gasses. Associated with explosive
volcanic eruptions.
MAFIC: High concentrations of Iron &
Magnesium. Dark in color. Heavier in
density. Gasses are not usually present.
Associated with non-explosive eruptions
Felsic or Mafic?
Which is which? How do you know?
Felsic or Mafic?
Which is which? How do you know?
Felsic: Light
overall color
Mafic: Dark overall
color
FELSIC & MAFIC ROCKS
Igneous Rock Identification

Felsic Granite, Rhyolite, Obsidian,
Pummice





Mafic (Gabbro, Basalt, Scoria)





High in Si + O
Low in Fe + Mg
Mostly feldspar & quartz
Light-colored
“Low” in Si + O
High in Fe + Mg
no quartz, abundant ferromagnesian minerals
Dark colored
Intermediate (Diorite)
Volcanoes




Volcanoes are the result of hot spots within the
crust or mantle of the earth.
The hot, liquid rock will break through weak
spots in the surface and form volcanoes or flood
basalts.
Many volcanoes do not release lava, instead
they spit ash and small bits of lava called lapilli.
Some eruptions are quiet with very fluid (low
viscosity) lava flows while others are explosive
Pacific Ring of Fire
Volcanism is
mostly
focused at
plate
margins
Topic 6:
Page 256 Earth Textbook
Subduction Eruptions
*occur at subduction boundaries
*erupt violently with gasses
*usually contain felsic magma
Trench
Volcanoes
Mt. St. Helen before the explosive eruption
Volcanoes
Volcanoes
Mt. St. Helen after the eruption
Volcanoes
Volcanoes
Topic 5:
Page 256 Earth Textbook
Rift Eruptions
*occur at spreading centers
*erupt as slow flows with few gasses
*usually contain mafic magma
Ridge
Volcanoes are formed by:
- Subduction - Rifting - Hotspots
Volcanoes
Quiet
lava
flows
Flood basalts
Volcanoes
Flood basalts
Basalt is a type of rock that is
produced from the mantle
Volcano locations
What are Hotspot Volcanoes?

Hot mantle plumes breaching the
surface in the middle of a tectonic
plate
The Hawaiian island chain are
examples of hotspot volcanoes.
Photo: Tom Pfeiffer / www.volcanodiscovery.com
Pacific Ring of Fire
Hotspot
volcanoes
The tectonic plate moves over a fixed hotspot
forming a chain of volcanoes.
The volcanoes get younger from one end to the other.
Mid-Plate Hotspots
Hotspot
Mid-Plate Hotspots
Mid-Plate Hotspots
Volcanoes
Shield
Earthquakes
Chapter 15 Earth Science Book
read pages 270-273
restate & answer Topic Questions 1-4
Essay # 5
Topic 1:
Page 271 Earth Textbook
What is an Earthquake?
shaking of the Earth’s crust caused by a release
of energy. Movement of lithospheric plates
* over a million a year on Earth
* one every 30 seconds
Topic 2:
Page 271 Earth Textbook
Causes of Earthquakes
*eruption on a volcano
*collapse of a cavern
*impact of a meteor
*Major Cause is the release of stress
between two lithospheric plates.
Topic 2:
Page 271 Earth Textbook
Causes of Earthquakes
*Major Cause is the release of stress
between two lithospheric plates.
* Elastic Rebound Theory - Overtime
plates move, friction holds plates until they
release and suddenly snap back into place
Topic 3:
Page 272 Earth Textbook
Depth of Earthquakes
depends on the type of plate boundary
* Spreading centers/sliding boundaries
tend to be shallow – less than 30 km
* Subduction boundaries however
plunge to depths of 700km down
Topic 3:
Page 272 Earth Textbook
Earthquake Terms
* Focus – the point on the fault plane where
movement occurs
* Epicenter – the point on the surface
directly above the focus
Diagram on page 272
Earthquakes
Topic 4:
Page 273 Earth Textbook
Earthquake Waves
The speed of a wave depends on the material
they are passing through
The more dense the material the faster the wave
travels (dominoes closer together – faster)
P waves, S waves, L waves
Topic 4:
Page 273 Earth Textbook
Earthquake Waves
P waves
* primary wave, fastest wave
* compressional wave, like sound
* material moves back and forth
* travels through solid liquid & gas
Topic 4:
Page 273 Earth Textbook
Earthquake Waves
S waves
* secondary wave, slower than P
* shear wave
* material moves side to side
* travels through solids only
Topic 4:
Page 273 Earth Textbook
Earthquake Waves
L waves
* Love wave, slowest wave
* surface wave
* material moves like ripples on pond
* travels through solid liquid & gas
Earthquakes generate seismic waves.
Seismic waves travel through Earth and along its surface.
Seismic waves form in two types:
1) surface waves
• sometimes seen as an
wavelike motion in the
ground
• cause most of the property
damage in an earthquake
2) body waves (P and S waves)
• useful for analyzing Earth’s
interior structure
http://ja.wikipedia.org/wiki/%E7%94%BB%E5%83%8F:Pswaves.jpg
Body waves
1) P (primary) wave
• a compressional wave
• similar to a sound wave
• pass through liquids and solids
http://www.met.gov.pk/Subpage4/waves_files/pwave_web.jpg
2) S (secondary) wave
• a shear wave
• like a rope shaken side to side
• pass through solids only
• about 1/2 the speed of P waves
http://www.geo.uib.no/jordskjelv/img/s-wave.jpg
seismograph
P waves are faster than S waves
About 3.5 km/sec
About 6 km/sec
Sumatra-Andaman earthquake (26 December 2004)
http://zog.typepad.com/malaysia/epicenter.jpg
How do we locate the epicenter of an earthquake?
http://www.theimage.com/geology/notes15/index.html
http://ja.wikibooks.org/wiki/%E9%98%B2%E7%81%BD_%E5%9C%B0%E9%9C%87
http://www.calstatela.edu/faculty/acolvil/earthquakes.html
If the Earth were homogenous, the paths of seismic waves
would be straight lines
Richard Oldham
• British geologist
http://cires.colorado.edu/~bilham/oldham.gif
If the Earth were homogenous, the paths of seismic waves
would be straight lines
Richard Oldham
• British geologist
http://cires.colorado.edu/~bilham/oldham.gif
Found that seismic waves
arrived earlier than
expected at seismographs
far from the quake
waves traveled faster as
they went into Earth
Earthquake wave shadow zones confirmed the presence of Earth’s core.
refraction
Data from an earthquake confirmed the model of Earth layering.
Anchorage, Alaska
27 March 1964
9.2 on Richter scale
P and S waves were very large
and easily detected at great
distances
• helped confirm the models of
Earth layering.
http://www.greatdreams.com/alaska/alaska-collapse-1964.jpg

As with volcanoes, earthquakes are not
randomly distributed over the globe
Figure showing
the distribution of
earthquakes
around the globe

At the boundaries between plates, friction
causes them to stick together. When built up
energy causes them to break, earthquakes
occur.
Where do earthquakes form?
Figure showing the tectonic setting of earthquakes
Earthquakes
Earthquakes
Earthquakes
Earthquakes
Tidal waves or Tsunamis result when a large section of the sea floor
suddenly moves and therefore displaces a massive amount of water.
Earthquakes
Location of worldwide earthquakes
Earthquakes
Chapter 15 Earth Science Book
read pages 270-273
restate & answer Topic Questions 1-4
Essay # 5