Download Learning session 3: Volcanoes

Learning session 3: Volcanoes
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We have learnt so far that very hot magma is beneath Earth’s crust which is broken up into tectonic plates.
These plates can converge and diverge-what could be the result of the combination of these factors on the
formation of earth’s landscape? Co-construct some possible outcomes to share with the class. You may wish
to develop models to support your theories.
Students may be encouraged to explore the emergence of volcanoes, as the tectonic plate boundaries
enable the magma to escape.
Have a close look at this map. The yellow dots are active volcanoes. Do you notice any pattern in their
locations?
Discussion
Encourage the students to see that the volcanoes are often found in lines. This is because they are on
tectonic plate boundaries. Bring to their attention the Pacific Ring of Fire. This name is given to the
volcanoes circle the fringe of the Pacific Ocean and includes New Zealand.
Did you notice that the volcanoes are located on the tectonic plate boundaries? I wonder why that is?
Encourage the discussion towards the realisation that magma can escape from the Earth at the tectonic
plate boundaries. The escaped magma builds volcanoes. Show students images of NZ volcanoes:
http://www.sciencelearn.org.nz/Contexts/Volcanoes/Sci-Media/Animations-and-Interactives/Volcano-map-ofNew-Zealand
So what are volcanoes? Here are some images of volcanoes. Do you notice anything different with their
shape? Why do you think they look different?
They have all been created by magma escaping from the Earth and gradually building a mountain. When
magma comes out of the Earth we call it lava. Maybe it’s something to do with the lava. Let’s experiment
with how magma/lava may be able to form into different types of volcanoes.
Experiment: Making lava fudge
Check out this link.
Viscosity is important in volcanology. The more fluid a magma, the more likely it is to erupt. On the other
hand, when thicker lavas do erupt, they usually do so explosively. This viscosity also affects the shapes of
lava flows and the mountains they erupt from. The more viscous the magma, the fatter the lava also the
steeper the volcano's sides.
On Earth today there are 550 active volcanoes. Some volcanoes last for hundreds of thousands of years,
while others may only last a few decades. In 1943 a farmer in Mexico had a volcano form in one of his
paddocks. In nine years the volcano had built a large mountain.
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Another volcano erupted in the sea off the coast of Iceland, and over the years it created a large island. The
Islands of Hawaii are actually a string of volcanoes that grew from the ocean floor. The largest volcano on
Earth is Mauna Loa it is about 10 km) tall. The largest known volcano in our solar system used to be
Olympus Mons on Mars. It is 27km tall and over 520 km across! What factors do you think could cause this
volcano to be so large?
Cinder cones are the simplest type of volcano. They are built from particles and blobs of congealed lava
ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small
fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Most cinder cones
have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their
surroundings.
Composite volcanoes are sometimes called strato volcanoes. They are typically steep-sided, symmetrical
cones of large dimension built of alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs
and may rise as much as 8,000 feet above their bases. Most composite volcanoes have a crater at the
summit which contains a central vent or a clustered group of vents. Lavas either flow through breaks in the
crater wall or issue from fissures on the flanks of the cone. Lava, solidified within the fissures, forms dikes
that act as ribs which greatly strengthen the cone.
Shield volcanoes are built mostly of fluid lava flows. Lava pours out in all directions from a central summit
vent, or group of vents, building a broad, gently sloping cone of flat, domical shape. They are built up slowly
by the accretion of thousands of highly fluid lava flows called basalt lava that spread widely over great
distances, and then cool as thin, gently dipping sheets. Lavas also commonly erupt from vents along
fractures (rift zones) that develop on the flanks of the cone. Some of the largest volcanoes in the world are
shield volcanoes.
Video presentation: The Life of a Volcanologist
Activity
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Comparison of volcano types. Create a Venn diagram for the three main types of volcanoes: shield,
composite and cinder cones. Write into the correct areas what makes each distinct and what is common.
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Label parts of the volcano by clicking here.
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Further activities
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Label the volcano diagram
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Volcano quiz
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Interpret the data on this New Zealand website to find out which are our most active volcanoes in New
Zealand’s. Share with the class. You may wish to include maps and data.
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Create a model showing the impact of lava’s viscosity on mountain formation.
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Create a series of volcano models or drawings showing the comparison the cinder, shield and composite
cones.
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Research what to do if you live near a volcano, how could you prepare for an eruption.
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Geonet in New Zealand have a website where you can monitor the latest volcanic data. Explain how they
decide on the level of alert for volcanoes in NZ.
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Cryovolcanoes do not form on earth but they are in our solar system .What are they and where can they
be found?
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Investigate which planets and moons in our solar system that have volcanoes. How is this significant
and why would scientists be interested in this?
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Create a demonstration that illustrates how volcanic activity could create an island.
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