Name: KEY
Earth & Environmental Systems Science
Unit III: The Lithosphere – Section 2 Volcanic Processes
Volcanic Processes Study Guide
Background Knowledge – Layers of the Earth
1. List the layers of the Earth starting and the surface and describe if they are solid or
liquid in state.
Continental Crust/Lithosphere - solid
Oceanic Crust/Lithosphere - solid
Mantle/Asthenosphere - liquid
Outer Core - liquid
Inner Core - solid
2. What data do we measure in order to determine the thickness of the layers? We use
seismic data and can measure the speed and timing of the earthquakes in order to
calculate the distance or thickness of the layers.
3. The plates of solid lithosphere ride on top of the asthenosphere.
4. Fill out the following chart:
Type of
Density:
Thick Type of Landform created when
Lithosphere: High/Low
/Thin Rock
meets other oceanic crust
Continental Low density due Thick
Granite
Trench
to high volume
Crust
High density due Thin
Oceanic
Basalt
Volcanic Island Arc
to low volume
Crust
Thermal Process – Convection
1. The movement of tectonic plates is driven by what thermal process in the mantle?
Tectonic plates including continental and oceanic crust move due to convection currents in
the mantle that transfer heat from the outer core to the mantle and then to the crust.
2. Define the term convection: Convection is a mixing due to unevening heating that causes a
difference in the temperature and density of the material that makes a rising or sinking
motion of the fluid.
3. True or False: Changes in the mantle material’s heat and density is
causes convection currents.
4. How does a lava lamp represent convection currents in the mantle? The
light bulb heats the material unevenly just like the outer core heats the
mantle unevenly. As the temperature rises, the volume expends, creating a
material that has a low density and a rising effect. As the material moves
away from the heat source, it cools, condenses, and sinks.
5. This picture shows a section of the
oceanic crust where a rift has split
the continents apart and separated
them with an ocean basin. Label
the convection currents with the
changes in temperature and
density.
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Cold
High Density
Hot
Low Density
Name: KEY
Earth & Environmental Systems Science
Unit III: The Lithosphere – Section 2 Volcanic Processes
Volcanic Processes Study Guide
Location of Volcanic Activity
1. At a divergent plate boundary, volcanoes form along which feature on the ocean floor?
Mid-Ocean Ridge (Rise)
2. What is an underwater mountain chain called? Ocean Ridge
3. At a mid-ocean ridge, where would the hottest crust temperature be located? At the
center of the mid-ocean ridge where mantle material is cooling to form new crust.
4. Describe the trends of the ocean floor age, sediment thickness, and heat flow as you
move away from the center of the mid-ocean ridge. As you move away from the center of a
mid-ocean ridge, the ocean floor gets older, the sediment on top of the floor gets thicker,
and the heat flow decreases or gets colder proving that the center of the Mid-Ocean Ridge
is the location of newly formed oceanic crust due to mantle convection currents.
5. What is one similarity and one difference between a rift valley and a mid-ocean ridge? Rift
Valleys and Mid-Ocean Ridges are locations where the crust is spreading apart due to
mantle convection currents and new crust is being formed. Rift Valleys are tearing
continents apart and may be covered by a small inlet and a sea. Mid-Ocean Ridges are
tearing oceanic crust apart to make new oceanic crust and are covered by vast oceans.
6. Why does oceanic crust sink beneath the continental crust at subduction zones? Oceanic
crust is more dense than continental crust and will sink or be over-ridden by the
continental crust. The oceanic crust is melted and recycled back into the mantle.
7. Compare the plate motion at a trench to the plate motion at a mid-ocean ridge. At a mid
ocean ridge, oceanic crust is moving outward to make new oceanic crust. At a trench a
collision occurs where oceanic crust is being subducted by continental crust, and the
oceanic crust is melted an recycled back into the mantle.
8. The picture to the left shows a top-view of the Peru-Chile trench. Draw a side view of the
plates (label: Pacific Ocean and South America), convection currents in the mantle, and
plate’s motion.
South America
Pacific Ocean
Subduction
Side View
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Name: KEY
Earth & Environmental Systems Science
Unit III: The Lithosphere – Section 2 Volcanic Processes
Volcanic Processes Study Guide
9. Draw in the convection currents based on the features of the mid-ocean ridge and
trench:
10. What feature is formed when a piece of continental crust and a piece of oceanic crust
collide?
The oceanic crust will be subducted because it is more dense. When the plates collide,
friction creates a pulling effect on both pieces of crust and a deep oceanic trench is formed.
11.What feature is formed when two pieces of oceanic crust collide? One piece of oceanic
crust will be subducted. When the plates collide, friction causes the subducting plate to
melt quickly, becoming less dense and sending magma upward. This magma cools and
solidifies as a volcanic island arc.
12.Use the picture below to label and define each of the features listed:
A: Island Arc – formed when oceanic crust converges (collides) with other oceanic crust,
subducts, melts due to friction, and rises to form a chain of islands.
B: Oceanic Trench – formed when oceanic crust converges (collides) with other crust and is
subducted and catches pulling downward due to friction.
C: Lithosphere – the rocky outer shell of the earth and is made up of continental/oceanic crust
and the upper-most portion of the mantle.
D: Continental Crust – crust that is low density, thick, and made of mostly granite.
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Name: KEY
Earth & Environmental Systems Science
Unit III: The Lithosphere – Section 2 Volcanic Processes
Volcanic Processes Study Guide
E: Oceanic Crust – crust that is made a MORs, has a high density, think, and made of basalt.
F: Asthenosphere – the upper part of the mantle that allow the plates to move and surf on top.
H: Subducting Plate – (explain why it is subducting): always an oceanic crust type will be
pushed and recycled back into the mantle because it is very dense.
13.Describe how hot spot volcanoes create and chain of islands on how that can predict
plate movement. The small hot spot stays stationary (at the same latitude and longitude)
and creates a shield volcano as the magma breaks through the thin oceanic crust. This
process continues to create a larger and larger volcano. The plate moves and will take the
volcano with it, eventually moving it.
14. Describe how the Hawaiian Islands were formed
based on the picture shown here.
Diagram 1 is a top view and shows that the Big Island
of Hawaii is the youngest and over the hotspot and extends
to the Northwest (the direction of plate movement) and the
islands get older and older meaning that
those islands were where the current Big
Island is located millions of years ago.
Islands not on the hotspot are considered to
be inactive or extinct. In a few million years
a new island will be formed to the Southeast
of the current Big Island.
Diagram 2 is a side view showing that the
hotspot stays in the same location with the crust moves to form a chain of islands with only one
active volcano.
15. Explain how the Caribbean Islands were formed and how their formation process is different
than the Hawaiian Island shown above?
The Carribean Islands are a chain of volcanic island arcs. They are formed at the boundaries
or edges of the tectonic plates where a plate is subducted to form the islands. All islands in the
chain have very dangerous eruptions that are frequent but unpredictable.
Hawaii is formed in the center of a tectonic plate and is made from a stationary hotspot in the
mantle that forms a chain as the oceanic crust continues to move over millions of years. Only
one island (on hotspot) erupts daily with very predictable flows.
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