Download Volcanoes - Jefferson Township Public Schools

Volcanoes
and Plate Tectonics (part 1)
“an opening in the Earth’s crust
through which an eruption takes place”
Volcanoes (cont.)
 Nature
of a volcanic eruption depends on
the Magma
 Magma
– hot, liquid rock beneath the
Earth’s surface.
– hot, liquid rock that reaches (and
goes above) the Earth’s surface.
 Lava
Volcanoes (cont.)
Possible sources of heat below the surface:

Radioactive decay is a breaking apart of the
nucleus of an atom; as a nucleus breaks apart, it
releases energy which is changed into heat.

Original Heat inside the earth may have been
trapped when the earth first formed.

Friction – results from the movement of
lithospheric plates.

Fusion in the core – nuclear fusion, similar to
the sun, is occurring in the core
Volcanoes (cont.)
 Active
Volcano – 1300 volcanoes on land
around the world are thought to be active,
have erupted within the last few hundred
years.
 Dormant Volcano – ‘sleeping’ volcano, but
capable of being activated
 Extinct Volcano – has not erupted for the
last several thousand years.
Volcanoes (cont.)
Types of volcanoes
Types of volcanoes are determined by the
strength and explosiveness of the eruption

Eruption Depends on
– a) temperature,
– b) composition, and
– c) amount of dissolved gases these affect the
magma’s viscosity (ability to flow – more
viscous –greater resistance to flow)
Volcanoes (cont.)
Temperature –
the hotter-the
runnier (less
viscous)…
Volcanoes (cont.)
Composition – movement of magma
depends on the amount of silica
the more silica the greater the viscosity.
Felsic - High silica – granitic – 70% silica
Mafic - Low silica – basaltic – 30% silica;
(molecular silica links to make long chains,
even before crystallization begins)
Volcanoes (cont.)
Dissolved gases – this provides the force of an
eruption.
As magma moves closer to the surface (like in a
volcano) the pressure is reduced and the dissolved
gases are released – sometimes suddenly i.e. Soda
bottle
Gases are:
water vapor
Sulfur
Sulfur Dioxide, SO2
Carbon Dioxide (CO2)
Carbon Monoxide (CO)
Hydrogen Sulfide, H2S
Volcanoes (lava)

Felsic –
high silica
Flows slowly,
gas held
within; does
NOT allow
gasses to
escape
readily –
EXPLOSIVE
Volcanoes (cont.)

Mafic – low silica; more fluid, DOES allow
gasses to escape readily – NON-Explosive
Volcanoes (cont.)
…….. In short…
Lava (magma that reaches the surface)
 Felsic - flow slowly, gas is held within –
explosive
 Mafic - more fluid, gas easily escapes –
lava pours out slowly
Volcanoes (cont.)
Lava type
Felsic
Mafic
Silica %
High
Low
Viscosity
High (thick)
Low (thin)
Color
Light
Dark
Rate of movement
Slow
Quick
Dissolved gasses
Cannot easily escape Escapes easily
Nature of eruption
Explosive
Quiet
Eruptive Fragments
Pyroclastic

Tephra: lava that is blasted into the air
by violent volcanic eruptions and solidifies
as it falls to the ground as ash, lapilli,
cinders, blocks, and volcanic bombs
– Ash – less than 2mm diameter
– Lapilli (also cinders) – up to 64 mm
– Blocks more than 64 mm (solid)
– Bombs more than 64 mm (liquid)
Tephra
(Actual size of tephra)
Anatomy of a Volcano




Vent – in volcanic regions, an opening in the
Earth’s surface through which lava, ash and
steam flow
Crater – opening at the top of a volcano
Dike – igneous rock that forms when magma
is squeezed into a vertical crack and solidifies
(crosses layers)
Sill – small body of igneous rock that forms
when magma is squeezed into a horizontal
crack and then solidifies (parallel to layers)
Anatomy of a Volcano
Anatomy of a Volcano
Anatomy of a Volcano
Crater at the top of the vent
Evidence of Volcano
Volcanic neck: the core of a volcano’s
vent that remains after the outer layers of
lava and tephra have been eroded away
from an extinct volcano
 Caldera: the large opening formed at the
top of a volcano when the crater collapses
into the vent following an eruption

Volcanic Neck
Crater Lake
Crater Lake
The End
volcanoes AND additional features so make sure the
information is recorded in your OWN notebook
Types of Volcanoes - Group




Composite volcano
Shield volcano
Cinder Cone Volcano
Caldera and other interesting features of volcanoes
Each type of volcano the following information will be
recorded in your notebook and reported to the group.
For your type of volcano, you will find:





The structure / make up of the volcano
Type of magma / lava produced; type of tephra produced
How does this type of magma/lava relate to eruption the volcano produces
Examples of this kind of volcano and the places they are located.
Last eruption or most famous eruption and explain what happened.
Extra Credit
Find a news article regarding Volcanoes in a
newspaper or magazine or online
If online: print, read and highlight
Type two paragraphs: one paragraph
summary and a one paragraph response
Give it to me discreetly at the beginning of
class BEFORE the end of the unit on
volcanoes.