Transcript Ch_18_Volcanoes

Chapter 18
Volcanic Activity
Lesson 5
Volcanoes: The Basics
Think About It…
What happens when you shake
a can of soda and then open it?
Focus Question…
How does the composition of
magma affect its
explosiveness?
http://www.pbs.org/wgbh/nova/volcanocity/anat-08.html
1.
What is magma?

A mixture of molten rock, suspended
mineral grains, and dissolved gases
deep beneath Earth’s surface
Nyiragongo
Volcano
East
African Rift
Valley
http://www.ncgeology.com/Eno_interactive_webs/Geologic_Principles_igneous%20rocks.html
2. Types of Magma: Basaltic…
Gas Content
1.

1–2%
Silica Content
2.

50%
Viscosity
3.

low
Explosiveness
4.

least
Origin/Location of
Magma/Lava
5.

oceanic/continental
crust
Example
6.

Mt. Kilauea in Hawaii
Mt. Kilauea
A Hot Spot
Volcano
Types of Magma: Andesitic…
Gas Content
1.

3-4%
Silica Content
2.

60%
Viscosity
3.

intermediate
Explosiveness
4.

intermediate
Origin/Location of
Magma/Lava
5.

continental
margins
Examples…
6.

Mt. St. Helens
and Mt. Rainier
(Washington)
http://vulcan.wr.usgs.gov/Volcanoes/MSH/Images/july_22_images.html
Mt. St. Helens – From the
Summit of Mt. Rainier
Types of Magma: Rhyolitic (Granitic)
Gas Content
1.

4-6%
Yellowstone Volcano
Silica Content
2.

70%
Viscosity
3.

high
Explosiveness
4.

greatest
Origin or Location of
Magma/Lava
5.

continental crust
Example
6.

Yellowstone
Supervolcano in Wyoming
Yellowstone…
http://www.hbci.com/~wenonah/history/img/krakatoa.jpg
Types of Magma…
3. The higher the silica content…

the higher the viscosity (resistance to flowing)…

the greater the explosiveness!
Krakatoa – Highly viscous and explosive!
http://romanmythology.wikia.com/wiki/Pluto
Intrusive Activity…
What is a pluton?
1.

An intrusive igneous rock body
Pluto –
god of the
underworld
http://earthsci.org/mineral/rockmin/chart/iroccur.gif
http://www.yosemiteriversideinn.com/
Batholiths
2. A batholith is the largest of plutons common
in the interiors of major mountain chains.
Yosemite – Part of the Sierra Nevada Batholith
El Capitan and Half-Dome, Yosemite National
Park – Examples of Batholiths
Intrusive Activity…
Where did all the magma
come from?
 Scientists hypothesize
that…



At subduction zones,
a plate subducts,
melts,
cools into a pluton.
http://herramientaslinker.com.ar/convergent-boundary-subduction&page=7
Melting at an ocean/continental boundary
formed the batholiths of Yosemite National
Park, CA.
:
http://www.smate.wwu.edu/teched/geology/vo-eruption2.html
Volcanoes…
1. What is lava?
 molten rock that has
reached Earth’s
surface
2. What is a volcano?
 A mountain or
opening in Earth’s
crust from which
lava erupts
Paricutin in Mexico, 1943
3. The Anatomy of a
Volcano…
Vent – the opening in the crust through
which lava erupts
b. Crater – bowl-shaped depression around
the vent
c. Caldera – larger depressions around a vent
where the volcano has collapsed into the
magma chamber
d. Magma chamber – area under the volcano
which holds the magma
a.
Slides of Crater, Caldera…


Crater Lake
Yellowstone Caldera
4. Label the Volcano…
http://rbaadvisors.com/what-are-the-main-features-of-a-volcano&page=3
Types of Volcanoes…

Type of Volcano


How It Forms


Basaltic lava builds
up (Quiet eruptions)
Description


Shield
http://www.cnn.com/2014/10/28/us/hawaiivolcano/index.html
IN THE NEWS…
Wide with gentlysloping sides
Example


Kilauea in Hawaii
(hot spot)
Iceland (divergent)
http://www.discoverhawaiitours.com/blog/tag/kilauea/
Types of Volcanoes…
• Type of Volcano
Cinder cone
• How It Forms
Ejected tephra falls
back to earth and
piles up (Explosive)
• Description
Small but steep
• Example
Paricutin in Mexico
Convergent boundary
Paricutin, Mexico
http://volcano.oregonstate.edu/vwdocs/volc_images/img_paricutin.html
Types of Volcanoes…




Type of Volcano
 Composite
How It Forms
 Tephra eruptions
alternate with lava
flows
Description
 Large & steep
Example
 Krakatoa
 Mt. St. Helens
 Convergent
http://pubs.usgs.gov/fs/2005/3045/images/fig1.jpg
Mt. St. Helens Before and After!
Mt. St. Helens… as seen from
the crater of Mt. Rainier!
Mt. Rainier: Cascade Range
Hiking in the crater!
July 12, 2013
A Composite Volcano…

http://www.pbs.org/wgbh/nova/volcanocity/an
at-flash.html
Lesson 6
Volcanoes: Effects on the
Lithosphere
Tephra…
1. What is tephra?

Rock fragments thrown into the air during a
volcanic eruption
Tephra classified by size…

dust  ash  lapilli  bombs  blocks
2. A pyroclastic flow is…


an eruption of gas, ash, and other tephra
These types of eruptions can be extremely
violent and deadly because… the PC flow
moves very fast and is very hot.
3. Ash and dust from a pyroclastic flow
blocks sunlight and lowers global
temperatures.
Effects of a Volcanic
Eruption… Lahars
1.
A lahar is a mixture
of mud & debris
created when…


heat from an
eruption melts
snow OR
rain forms around
dust or ash in the
atmosphere.
http://volcanoes.usgs.gov/hazards/lahar/index.php
Earthquakes, Landslides and
Tsunamis…
2.
Earthquakes are caused when…
Magma breaks rocks as it makes its way to
the surface.
3.
Landslides are caused in two ways…
… a volcanic earthquake (EQ) or the eruption
itself causes land to slide
4.
Tsunamis are caused when…
… the volcanic landslide “bulldozes” water
ahead of it
Earthquakes, Landslides and
Tsunamis…
http://volcanoes.usgs.gov/hazards/landslide/index.php
http://volcanoes.usgs.gov/Imgs/Jpg/Unzen/MayuyamaSlide_large.jpg
Earthquakes, Landslides and
Tsunamis…
5. Hawaii and Yellowstone…
… are formed at hot spots (very hot places in
the mantle/crust)
 … away from plate boundaries

6. Kilauea: Effects on Land…
Basaltic lava…

burns vegetation and buildings

creates new land (16 acres a year!)
http://www.ncgeology.com/Eno_interactive_webs/Geologic_Principles_igneous%20rocks.html
7. Krakatoa: Effects on Land…
The eruption of Krakatoa…

Created a caldera when it blew the island apart

Caused a pyroclastic flow and tsunami (1883)
http://www.ncgeology.com/Eno_interactive_webs/Geologic_Principles_igneous%20rocks.html
8. Iceland: Effects on Land…
Iceland’s volcanoes in the rift valley are causing it
to grow bigger – with older rocks on the east
and west sides of the island.
Convergent Boundary Volcanoes


Ocean plates subduct under other plates and
melt to form magma
Location – the Pacific Ring of Fire, the
Mediterranean Belt
Mt. Vesuvius and
Pompeii Victims
http://mrbpielglobal.edublogs.org/files/2010/12/vesuvius_24417-1qnp5rt.jpg
The Ring of Fire…
http://pubs.usgs.gov/gip/dynamic/graphics/Fig22.gif
Divergent Boundary Volcanoes


As plates move apart, magma is forced
upward into fractures and faults
Location – East Africa Rift Valley, mid-ocean
ridges, Iceland
http://rajeshsivananth.files.wordpress.com/2010/07/surtsey.jpg
Divergent Boundary
Volcanoes… Iceland
Surtsey Volcano
Pluton Slides…

The following slides depict different types of
plutons. I cut these slides from the notes but
left the slides on the ppt for future reference!
A Plethora of Plutons… Stocks

Stocks are
irregularlyshaped plutons
similar to
batholiths but
smaller.
http://belmont.sd62.bc.ca/teacher/geology12/photos/volcanoes/plutons.jpg
http://facweb.bhc.edu/academics/science/harwoodr/geol101/study/Plutons.htm
A Plethora of Plutons… Laccoliths

Laccoliths are mushroom-shaped plutons
with a round top and a flat bottom.
http://facstaff.gpc.edu/~pgore/geology/geo101/plutons.php
A Plethora of Plutons… Sills

A sill is a pluton that forms when magma
intrudes parallel to layers of rock.
The Palisades Sill, NY
http://www.exstrom.com/hbaromega/irondike.html
A Plethora of Plutons… Dikes

A dike is a pluton that cuts across preexisting
rocks.
Iron Dike Intrusion, Ironclads, Colorado
The Great Dike of Zimbabwe…