Download Volcanoes PPT notes

I. Parts of a volcano
rim
crater
pipe
vent
Parasitic
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 lithosphere
and does not move. The lithospheric plate moves
which creates a chain of volcanic islands.
V. Volcanic cones (three basic shapes)
A. Shield cones- have broad bases and gently sloping
sides (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 conesGeometric 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 are
not more than 100 meters high because they are made
of 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. Rainier- U.S.
Mt. St. Helens- U.S.
Mt. Hood- U.S.
Mt. Shasta- 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/hale
maumau_newgasvent.htm
III. There are three types of lava: (mafic, felsic,
intermediate)
A. Mafic- dark in color and
contains high amounts of
iron 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 in
color 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 felsic
and 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) (lowtemperature 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 and
the crystals are not large enough to be visible.
B. Intrusive igneous rock- molten rock that cools
below ground. This takes a long time and large
crystals form.
Pikes Peak is made of intrusive igneous rocks (granite).
It was molten rock deep within the Earth and it cooled
off slowly over time.
Pikes Peak is a batholith