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Volcanoes
Liquid Hot Magma.
Tungerahua Volcano, Ecuador
Picture by Alcinoe Calahorrano
Volcano Stats
• Definition of Volcano
– Mountain that forms when molten rock
(magma) is forced to the Earth’s surface
• Number of active volcanos = ?
– 20 erupting right now
(50-60/year) (155/decade)
• Number of volcanologists = 1,500
Lava flow
Volcanic Eruptions
• Nonexplosive Eruptions
Lava fountain
• Explosive Eruptions
What is Lava?
-magma that flows onto
the Earth’s surface
1. What did you learn?
Write/draw this in your
science journal.
Volcanoes
form around
Vents
Lava
vents that
release magma
onto the Earth’s
surface.
Magma chamber
The Composition of Magma Determines
whether it is explosive or not!
• High
content
– More likely to be
• High
!!!
content
– More likely to be
– Why?
!!!
• Silica has a thick, stiff consistency
– Flows slowly
– Tends to Harden in the volcano’s vent
d.Blocky lava
What Erupts from a
Volcano?
Lava can be
thick or thin.
a.Pahoehoe
b.Aa
Lava flows slowly,
like wax-glassy surface
with wrinkles
Is cool, stiff lava that does not travel
Far from the volcano
Lava pours out quickly,
forms a brittle crust with
jagged edges
c.Pillow lava
Forms when lava erupts
under water, round lumps
What Erupts from a Volcano?
Pyroclastic material
• Rock fragments created by
eruptions
•magma explodes from volcano and solidifies in the air
•existing rock is shattered by powerful eruptions
Volcanic ash
Forms
when gas
bubbles
explode
Volcanic bombsVolcanic blocksLargest pieces of
solid rock erupted
from volcano
Large blobs of
magma that harden in
the air, shape is
created by magma
spinning in the air
LapilliLittle rock- pebbel-like
Bits of magma that
harden before they hit
the ground
How do volcanoes affect the Earth?
Flows and Fallouts
• hot ash can flow really
quickly
•Knock down buildings
•Dam rivers (flooding/drought)
•Kill crops and livestock
Climatic Changes
•Ash & Gases can block sunlight
•Drop average global temperature
noticeably
Types of Volcanoes
Cinder cone volcanomade of pyroclastic material usually
explosive, small and have short eruption
times.
Shield volcanobuilt by layers of flowing lava, with
gently sloping sides
Composite volcano
also called stratovolcanoes are the
most common type of volcanoes.
They have Explosive eruptions
that are a combinations of lava
and pyroclastic material. Steep
bases and sides.
Shield Volcano
• Is wide and
somewhat flat.
• It forms from a
quiet eruption.
• Lava flows out
quietly and for
great distances.
Cinder Cone Volcano
Has tall, very
steep sides.
Has explosive
eruptions.
This eruption
produces a lot of
cinder and ash.
Composite Volcano
Form from
explosive
eruptions.
Produce a lot of
lava and ash.
Is small, with
steep sides.
Craters, Calderas, and Lava
Plateau
Crater
• From explosions of material out of
the vent and the collapse of material
back into vent
Caldera
• Much larger depression that
forms when magma chamber
empties and its roof collapses
Lava Plateau
• Forms when lava erupts from long cracks, or fissures,
and spreads out evenly (thousands of km)
What causes volcanoes?
The Formation of Magma
• Mantle rock melts when the
temperature increases
or the pressure decreases.
What causes volcanoes?
Where Volcanoes Form
• Tectonic Plate Boundaries!!!
~75% world’s active volcanoes in Ring of Fire
What causes volcanoes?
What causes volcanoes?
Hot Spots
How do volcanologists predict
eruptions?
• Measuring Small Quakes
– Before eruption, increase in number & intensity
• Measuring Slope
– Bulges may form with magma (tiltmeter)
• Measuring Volcanic Gases
– Outflow of volcanic gases
• Sulfur dioxide, carbon dioxide
• Measuring Temperature from Orbit
– Measure changes in temperature over time
You should not be a
Volcanologist if….
Robert
McGimsey
USGS
A. Ozerov
• You don’t like
hiking,
backbacking,
rockclimbing, etc.
• You are not
interested in
experiencing
extreme
temperatures
and heights.
• If you don’t like
to travel to
incredible places
and see
breathtaking
views of the
world.