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Volcanoes
What is Magma?
Magma
Magma
• Magma: Liquid rock under Earth’s surface
• Most rock stays solid even at high
temperatures because of the high pressures
within Earth
Magma forms when…
1. The temperature rises above the rock’s melting
point
2. Pressure gets lower, which lowers the melting point
3. Addition of fluids (water) lowers the melting point
of rock
On Earth’s surface all rock
will melt at 1200 C
Volcano 101 video
• https://www.youtube.com/watch?v=uZp1dNybgfc
• The video says that volcanoes are “both creators
and destroys”.
• What does this mean? What are examples of this?
Volcanism
• Volcanism: the movement of magma onto Earth’s
surface
Volcanism
• Magma rises through cracks in the Earth’s crust,
because it is less dense than solid rock
Volcanism
• As bodies of magma rise, they grow larger,
Melting the surrounding rock
Volcanism
• Lava: magma that has reached Earth’s surface
Explain the difference between
magma and lava.
Volcanism
• Volcano: an opening in Earth’s surface through
which magma and gases are expelled
• Lava flows out, solidifies, and forms a mound
Major Volcanic Zones
• Most volcanoes form along convergent or
divergent plate boundaries
The Ring of Fire
• The Ring of fire: an area surrounding the Pacific
Ocean where a large number of volcanoes and
earthquakes occur.
Subduction Zones
• Review:
• Subduction occurs when a dense oceanic plate
meets another plate and sinks beneath it
• Water from the subducting plate combines
with rock, lowering the melting point of the
rock
• Magma forms, rises, and a line of volcanic
mountains or a volcanic island arc forms
Divergent Boundaries: Mid-Ocean Ridges
• The largest amount of lava rises at divergent
boundaries
• Most are unnoticed by humans because the
eruptions happen underwater
Mid-Ocean Ridge
Iceland
• Iceland is the only place on Earth where a
divergent boundary is above sea level
• It is the Most volcanic spot on Earth because of
its 130 volcanoes, 22 of which erupt everyday
What about Hawaii?
Hot Spots
• Not all volcanoes form along plate boundaries
• Hot spots: areas on Earth’s crust located above
a mantle plume.
Hot Spots
• Mantle plume: places where heat rising
through the mantle melts the lithosphere
above it
Hot Spots
http://education.sdsc.edu/optiputer/flash/hotSpots.htm
• Volcanos form where melted lithosphere rises
to surface
• The mantle plume remains stationary and the
plate moves past it, forming a chain of
volcanoes
• Hawaii and Yellowstone are examples of hot
spots
Types of Magma
• Mafic magma: rich in iron and magnesium and
forms dark colored rock
• Example: Oceanic crust
• Produces: runny, quiet eruptions
Types of Eruptions
• Felsic magma: rich in silicate materials and
forms light colored rock
• Example: continental crust
• Produces: thick, explosive eruptions
• Magma with more dissolved gases is more explosive
Types of Eruptions
• The flow of magma or lava depends on the
viscosity of the magma
• Viscosity: how much a fluid resists flowing
• High Viscosity= slow moving lava
• Low Viscosity= Fast moving lava
High Viscosity
Low Viscosity
Viscosity demo
Viscosity Lab
https://www.youtube.com/watch?v=488BkTUsMa4
Quiet Eruptions
• Quiet eruptions: mafic magma flows our
slowly and has a high viscosity
• Oceanic volcanoes with mafic magma
Explosive Eruptions
• Explosive Eruptions: Felsic magma that is thicker and
cooler
• More explosive because it has more dissolved gases
in it
• Explosive eruptions are like a soda can that has been
shaken
http://www.youtube.co
m/watch?v=3XTVZmAt
u0s
Types of Lava
1. Pahoehoe lava: mafic lava that flows slowly
and cool forming a wrinkled crust
• lava flows
https://www.youtube.com/watch?v=Z9iW_oXMBB8
Lava Flows
2. Aa lava: mafic lava that flows faster and has a
more chunky texture
• Aa lava flow
Lava Flows
3. Blocky Lava: cooled lava at surface breaks into
large chunks
Video quiz
• https://www.youtube.com/watch?v=GaSjwAu3yrI
• What type of lava is shown in the video?
Types of pyroclastic materials
• Pyroclastic Material: Escaping gases send molten
and solid particles shooting into the air
Types of Pyroclastic Material
• Classified by particle size
• Ash: less than 2mm diameter
Cont. Types of Pyroclastic Material
• Volcanic bombs: molten rock larger than 64
mm in diameter
• Volcanic blocks: solid rock blasted from
vent, can be as big as a house
BOOM!
• Volcanic eruptions can be more powerful than
atomic bombs!!
How Volcanoes Form
• When eruptions occur, volcanic material
builds up around the vent
• Each new eruption adds a new layer
Volcano model activity
• Make two volcanoes out of the descriptions
provided and the clay.
1. This volcano is large, has broad at base,
and gently sloping sides.
2. This volcano is large, tall cone-shaped and
has steep sides.
3. This volcano is smaller than the other
types, has very steep slopes and a large
crater.