Volcanoes are openings in the Earth's crust where magma and gases escape. They are found at boundaries where tectonic plates are diverging or converging. When magma reaches the surface it is called lava, and eruptions produce lava, rock fragments, ashes, dust, and gases. There are over 550 active volcanoes distributed around plate boundaries on land and undersea. The type of eruption depends on factors like the crust's strength, pressure, and magma composition. Volcanoes are classified based on their shape, eruptive behavior, and deposits. Major hazards include lava flows, eruption columns, pyroclastic flows, and volcanic mudflows.

1. Volcanoes
Katelyn Kilgore

2. What volcanoes are…
• An opening in the
planet’s crust
• Causes volcanic
ashes and gases to
escape
• Found where plates
are diverging or
converging

3. Vulcanism
• Magma is expelled
onto the surface (still
molten)
• Magma solidifies on
the surface
• Magma solidifies far
below the surface

4. Volcanism
• Lava- magma that has
departed and has
contacted with the
surface
• Rock fragments
• Solidified lava blobs
• Ashes
• Dust
• Gas
• steam

5. Distribution
• About 550 active
volcanoes
• Surface and
underwater eruptions
• Associated with plate
boundaries

6. Factors of an eruption
• Surface crust strength
• Pressure
• Chemicals
– Silica (SiO2) is believed
to be the main source of
very explosive eruptions
– Low silica content
usually produces more of
a fluid explosion

7. Classifications
• Broad
• Sloping gently
• Layers of lava flow
• “quiet” eruptions
• Examples: Hawaiian
Islands and Tahiti

8. Classifications
• Large and steep
• Lava flows,
pyroclastics, hardened
mud flow deposits
• Both “quiet” and
explosive eruptions
• Examples: Mt. Fuji, Mt.
Rainier, Mt. Shasta, Mt.
Vesuvius, Mt. St.
Helens

9. Classifications
• Small and sometimes an
irregular shape
• Plug of lava that is
covered by pyroclastics
(frequently occurs in the
crater of Composite
Volcano)
• Examples: Lassen Peak,
Mono Craters

10. Classifications
• Small and steep sided
• May be composed of
ash or cinder-sized
pieces
• Produces “quiet” and
explosive eruptions
• Examples: Paricutin,
Sunset Crater

11. Other Classifications
• Caldera- produced
when volcano
explodes and/or
collapses
• Volcanic Neck-
small, sharp spire
that rises abruptly
above the
surrounding land

12. Hazards
• Lava Flows
– Rarely cause loss of life
– Does damage to the area
around it
– Either moves fast or
slow
– Flow on predictable
paths

13. Hazards
• Eruption Column and
Clouds
– Consists of pyroclastic
material and gases
– Volcanic ash and dust
form a cloud
– Volcanic bombs
– Can damage crops and
collapse buildings

14. Hazards
• Pyroclastic Flows
– Avalanche of hot gases,
ash, and rock fragments
– Also called nuée ardente
– Burns and buries
anything in its path

15. Hazards
• Volcanic Mudflows
– Caused by heavy rain or
melting of snow and
glaciers
– Water combined with ash
and pyroclastic flow
– Fast-moving slurry of
mud and boulders
– Buries the valley floor
– Also known as Lahars

16. Can it be prevented?
• Unfortunately no,
because it is a natural
occurrence all we
can do is be prepared
for when a volcano
blows its top.

17. Works Cited
Fisher, Richard V. "The Volcano Information Center." Volcano Information
Center (VIC). Web. 07 Dec. 2011. <http://volcanology.geol.ucsb.edu/>.
McKnight, Tom L., and Darrel Hess. "Chapter 14 The Internal Processes.“
Physical Geography: a Landscape Appreciation. Eighth ed. Upper
Saddle River, NJ: Prentice Hall, 2005. Print.
Topinka, Lyn. "CVO Menu - Volcanic Hazards, Features, and Phenomena.“
USGS Cascades Volcano Observatory (CVO). 30 Jan. 2003. Web. 07
Dec. 2011. <http://vulcan.wr.usgs.gov/Glossary/framework.html>.
"Volcano - Credo Reference Topic." Credo Reference Home. Web. 07 Dec. 2011.
<http://www.credoreference.com/topic/volcano>.
"Volcano | Define Volcano at Dictionary.com." Dictionary.com | Find the Meanings
and Definitions of Words at Dictionary.com. Web. 07 Dec. 2011.
<http://dictionary.reference.com/browse/volcano>.
"Volcano." Wikipedia, the Free Encyclopedia. Web. 07 Dec. 2011.
<http://en.wikipedia.org/wiki/Volcano>.