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Volcano Under the City
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Classroom Activity
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Activity Summary
Students will experiment with three different liquids to determine
the relative viscosity and flow rate of each liquid.
Learning Objectives
Students will be able to:
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compare and measure the relative flow rates of different
liquids.
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state that different kinds of lava differ in their viscosity.
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understand that a lava's viscosity influences how quickly it
flows.
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copy of the "Thick and Thin" student handout (PDF
or
HTML)
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copy of the "Data Sheet" student handout (PDF
or
HTML)
- three 25 ml test tubes
- 25 ml each of water, cooking oil, and light corn syrup
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5 ml each of water, cooking oil, and light corn syrup in separate
paper cups
- masking tape
- small metal paper clips of identical size and mass
- stopwatch/timer
- small wood block about 4 cm in height
- non-stick cookie sheet or pan, at least 25 cm long
- ruler or measuring tape
- 3 plastic spoons
- paper towels
- graph paper
- calculator
Background
Magma is molten rock below Earth's surface. Magma rises in volcanic
vents; when it reaches the surface it is called lava. The three
common types of lava—basaltic, andesitic, and
rhyolitic—contain different amounts of silica
(SiO2) and dissolved gases. They have different
viscosities based on the amount of silica they contain. Low-silica
lavas are less viscous and travel faster than higher-silica lavas,
which are more viscous and travel slower. Viscous lavas sometimes
cool before they travel very far, which is why they are often less
hazardous. When magma or lava cools and solidifies, it forms igneous
rock. (Basalt, andesite, and rhyolite are all igneous rocks.) The
following chart lists common lava types and their flow rates. Note
that lava flows pass through a range of viscosities as they cool and
solidify; as lava loses heat, its viscosity increases.
Lava Type
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Silica Content
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Viscosity
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Approximate Flow Rate
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basaltic
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least
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least
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30-60 km/hr
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andesitic
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in between
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in between
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10 km/hr
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rhyolitic
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most |
most |
1 km/hr
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Mount Nyiragongo is a volcano in the Democratic Republic of the
Congo, 18 kilometers from Goma near the Rwandan border. The area
surrounding the mountain is highly populated. The volcano has very
fluid basaltic lava with an unusually low silica content, which
moves quickly. During the 1977 eruption, the initial speed of the
lava flow was estimated at 100 kilometers per hour. When Nyiragongo
erupted in January 2002, more than 250,000 people were temporarily
displaced when the lava, flowing at speeds of about 60 kilometers
per hour, overran the town of Goma.
Key Terms
flow rate: Determined by distance/time.
lava: Magma that has erupted from a volcano and flowed to the
Earth's surface or the ocean floor.
silica: A common mineral composed of silicon and oxygen.
Silica makes up almost 75 percent of Earth's crust.
tephra: Air fall material, such as ash, produced by a
volcanic eruption.
viscosity: The resistance of a fluid's (gas or liquid) flow
on a parallel plane.
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Prepare the test tubes and cups for each team prior to the
experiment. Pour 25 milliliters of each liquid into separate
test tubes. Make sure each tube contains the same amount of
liquid.
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Discuss the concept of viscosity with students. Point out that
viscosity is a fluid's resistance to flow. The viscosity of lava
differs depending on the amount of silica in each type of lava.
Discuss some possible reasons why scientists might want to study
lava viscosity.
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Organize students into teams and provide a set of materials to
each team. Explain to students that the different liquids model
different types of lava. Tell students that they will be
experimenting with how liquids differ in their viscosity and how
liquid viscosity and rate of flow are related.
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Before having students conduct the paper clip dropping
experiment, tell them that one way to test the viscosity of a
liquid is to drop an object into the liquid and find how long it
takes the object to sink. Discuss buoyancy and density and talk
about why the same object must be used for each liquid.
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Have students conduct the experiments according to the
instructions on their handouts. Try to have students set up
their ramps at about the same angles (if ramp angles are not the
same, results will be relative). When students have completed
the activity, record average results for each student team (for
both experiments) on the board. Discuss the experiments and
results. What did students observe about the three liquids? What
is the relationship between viscosity and flow rate? Can
students think of some examples of everyday items in which
viscosity plays an important role?
(Some items include car engines that need oil to run well and
food items like syrup that need to pour readily.)
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As an extension, have students determine how temperature affects
the viscosity of a liquid. Cool the liquids by placing a jar
containing the liquid in a refrigerator. Then ask students to
repeat the activity to determine whether cooling the liquid
affects viscosity and how quickly the liquid moves.
The experiment reveals a relationship between viscosity and flow
rate. Students' bar graphs should reflect the fact that water is the
least viscous of the three liquids and flows the fastest, while corn
syrup is the most viscous and flows the slowest.
Sample Paper Clip Dropping Data*
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Corn syrup
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Oil
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Water
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Trial 1
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30 sec
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>1<2 sec
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less than 1 sec
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Trial 2
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24 sec
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2 seconds
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less than 1 sec
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Trial 3
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27 |
2 seconds
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less than 1 sec
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Average Result
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27 sec
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about 1.8 sec
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less than 1 sec
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Viscosity Rating (1-3)
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3 |
2 |
1 |
*test tube with 25 ml of liquid
Sample Rate of Flow Data*
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Corn syrup
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Oil
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Water
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Trial 1
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3 min. 10 sec
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44 sec
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3 sec
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Trial 2
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2 min. 56 sec
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42 sec
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2 sec
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Trial 3
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3 min. 4 sec.
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43 sec.
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2 sec
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Average Result
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3 min. 4 sec
(184 seconds)
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43 sec
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2.3 sec
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Distance
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25 cm
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25 cm
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25 cm
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Flow Rate
(distance/time)
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25 cm/184 sec =
.1 cm/sec
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25 cm/43 sec =
.6 cm/sec
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25 cm/2.3 sec =
11 cm/sec
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*ramp resting on end of wood block 3.8 cm high, flow distance = 25
cm
Student Handout Questions
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Compare the relative viscosities of the liquids to the speeds
with which the liquids moved during your ramp tests. Based on
your data, how does the viscosity of the liquid influence the
rate at which the liquid flows?
More viscous liquids flow slower than less viscous
liquids.
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Nyiragongo is said to have lava that flows "like water." Based
on your investigation, describe the viscosity of the lava
produced by Nyiragongo.
Nyiragongo volcano lava is not very viscous and flows
quickly.
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How might the viscosity of lava from a volcanic eruption affect
the outcome of an evacuation?
More people and animals might be at risk if the lava is less
viscous and flows more quickly.
Web Sites
NOVA—Volcano Under the City
www.pbs.org/nova/volcanocity
Learn whether volcanic eruptions can be predicted, discover what it
was like to film in a volcanic crater, explore Nyiragongo's main
features, and read historic accounts of the some of the worst
volcanic disasters of the past 400 years.
Natural Hazards
earthobservatory.nasa.gov/NaturalHazards/natural_hazards_v2.php3?img_id=1608
Describes the Nyiragongo volcanic eruption that occurred January 17,
2002.
Volcanoes
www.learner.org/exhibits/volcanoes/entry.html
Discusses volcanic eruptions and includes information on lava flow
rate and viscosity.
Books
A Glorious Way to Die: The Kamikaze Mission of the Battleship
Yamato, April 1945
by Russell Spur. Newmarket Press, 1981.
Analyzes theYamato's last days from Japanese and American
perspectives.
Earthquakes and Volcanoes
by Fiona Watt. Usborne Ltd., 1994.
Provides diagrams, illustrations, and photographs to explain
earthquakes and volcanoes.
The Visual Dictionary of the Earth
by Charles Wills, editor. Dorling Kindersley, 1993.
Includes a section on different types of volcanoes and how they
erupt.
Volcanoes and Earthquakes
by Susanna Van Rose. Dorling Kindersley, 1993.
Presents a visual display of volcanoes and how they occur.
The "Thick and Thin" activity aligns with the following National
Science Education Standards (see
books.nap.edu/html/nses).
Grades K-4
Science Standard D
Earth and Space Science
Changes in Earth and sky
Grades 5-8
Science Standard D
Earth and Space Science
Structure of the Earth system
Classroom Activity Author
Margy Kuntz has written and edited educational materials for 20
years. She has authored numerous educational supplements, basal text
materials, and trade books on science, math, and computers.
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