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VOLCANOES 101:
The word volcano comes from Vulcan, the Roman god Vulcan who “lived” under the
volcano, Mt. Etna. The study of volcanoes is referred to as Volcanology. Volcanoes are landforms that
develop where stratovolcanoes, cone, and shield volcanoes erupt molten magma from the earth’s mantle.
Stratovolcanoes most often erupt with explosions, cone volcanoes erupt less violently and shield or rift
volcanoes just ooze lava or have lava fountains. The two
major ways volcanoes form are the collision of tectonic
plates (subduction) and hotspots where magma plumes
burn through a crustal plate. Most volcanoes form on the
edges of tectonic plates and most volcanoes are found
under the sea. In convergence of plates, there is sinking
of a more dense plate (basalt) into the asthenosphere as
the plate begins sink the temperature increases and as the
rock melts, it forms magma and mixes with the mantle.
The hot, low density magma is less dense and floats
toward Earth’s surface forming Granite as it crystalizes.
Eventually, magma pushing up forms a plume. Magma
turns into the lava when it spills onto Earth’s surface.
After several eruptions, layers of ash and lava build up
into a landform called a volcano. Volcanoes are
important because when they erupt they can change the
composition of air, weather and disrupt or even end life.
HOT SPOTS
A hotspot is a plate area that is melted by a mantle
plume. Hot magma rises because it is less dense.
Pressure is put onto the surface of the Earth, forming a
bulge, and may form a volcano if it finds a weak spot
in the crust. A chain of volcanoes may form over a
series of many eruptions. Examples of a hot spot
leaving a trial of volcanoes in a plate would be
Yellowstone or the Hawaiian islands. Hawaii sits on
the Pacific Plate which is moving to the northwest.
There is a hot spot on the earth’s core causing magma
to rise. The plume is located in the mantle, and is
rising. The plate moves over the hot spot, forming a
line of volcanic islands.
The northern most Hawaiian Islands are the oldest
islands as they were formed first and we know this
because they are some of the coldest and least radioactive rocks found in the Hawaiian chain.
Magma and Viscosity
While volcanoes form in similar ways, not all volcanoes are alike. Some are tall, steep, and violent while
shield volcanoes are gentle as they erupt… Why so different? To understand what makes one volcano
different from another we need to look into the heart of the volcano, its viscosity (resistance to flow-i.e.Maple syrup has more viscosity than water) and the silica content of its liquid rock. The type of volcano and
how it erupts depends on magma’s viscosity:
The more silicon in the magma, the thicker and more viscous it is. The thicker it is, the more likely the gasses
(Carbon Dioxide and water vapor) trapped inside it will explode violently when the pressure is finally
released. Silica links together in long chains that stop magma from flowing easily and acts like a cork in a
bottle. The longer the silica chains, the more gasses are trapped in the magma and the more explosive the
volcano.
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The characteristics of the Stratovolcano, Cone and Shield volcanoes:
High Silica= Stratovolcano= High viscosity= High pressure/Violent explosive eruptions = Granite rock
Medium Silica= Cone Volcano= Medium viscosity= Medium pressure/explosive eruptions = Andesite rock
Low Silica=low viscosity= low pressure/gentle eruptions = Basalt rock
Answer these questions in complete sentences on this paper. Be detailed in your answers.
1. What is a volcano?
2. What are the two major ways in which volcanoes most often form?
3. Describe, in several sentences how a hot spot forms a volcano, like in Hawaii?
4. What does viscosity mean? How does silica content affect viscosity?
5. Why is viscosity so important?
6. Volcanoes can form on the ocean floor. [True or False.]
7. There is no relationship between plate tectonics and volcanoes.[ True or False.]
8. Cinder cone volcanoes produce gentle, quite eruptions. [True or False.]
9. A __________ often forms a mountain when layers of lava and volcanic ash erupt and build up.
10. One factor that determines whether a volcanic eruption will be quiet or explosive is ____________.
12. Silica-rich magma produces __________________ eruptions.
13. Two important factors that control whether an eruption will be explosive or quiet are ________ and
______________.
14. How are a soft-drink container and magma alike?
15. Why do volcanoes form at plate boundaries and hot spots?
16. What are the three major types of volcanoes?
17. How did Hawaii form?
18. Describe and identify some of the major volcanic hazards and effects from volcanic eruptions.
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Open the following link and answer the questions that follow.
http://news.bbc.co.uk/2/hi/science/nature/7533964.stm
http://www.glencoe.com/sites/common_assets/science/virtual_labs/ES10/ES10.html
http://www.cosmeo.com/braingames/virutal_volcano/index.cfm?title=Virtual%20Volcano
http://www.primarygames.com/arcade/skill/volcanicairways/
http://www.dartmouth.edu/~renshaw/eruption/eruption.html
http://www.swisseduc.ch/stromboli/volcano/simulation/vulcanosimulation-en.html
http://www.glencoe.com/sites/common_assets/science/virtual_labs/ES10/ES10.html
SODA BOTTLE VOLCANO
MATERIALS:
roll of mint Mentos (type of candy)
clear 2-liter bottle of Coke (diet works better)
PROCESS:
Go outside to an area where you have a lot of room. This experiment is messy!
Open the bottle of soda carefully. Position the bottle on the ground, so that it will not tip over.
*Diet soda works better than regular soda. Plus, diet doesn't leave a sticky mess.
Unwrap the roll of Mentos. The goal is to drop the Mentos into the bottle at the same time, which is very
tricky. One method is to roll a piece of paper into a tube just big enough to hold the loose Mentos. Put a card
under the roll and on top of the bottle top, so you can pull the card and the candies will just drop in at once.
Drop all of the Mentos into the bottle at the same time and then move out of the way just as quick as you can.
Watch the eruption!
EXPLANATION:
Why does this happen? Water molecules attract to other, linking together to form a tight mesh around each
bubble of carbon dioxide gas in the soda. When you drop the Mentos in the soda, the gelatin and gum arabic
from the dissolving candy break the surface tension. Each Mentos candy has thousands of pits on the surface.
These tiny pits are called nucleation sites, perfect places for the carbon dioxide bubbles to form. As soon as
you drop the Mentos in the soda, bubbles form all over the surface of the candy. Couple this with the fact that
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the candies are heavy and sink to the bottom of the bottle and you're just asking for an explosion. When all
this gas is released, it literally pushes all the liquid up and out of the bottle in an amazing blast.
http://www.geo.arizona.edu/~andyf/LaPalma/doomsday.html
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