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Volcano Under the City

Classroom Activity


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:

  • compare and measure the relative flow rates of different liquids.

  • state that different kinds of lava differ in their viscosity.

  • understand that a lava's viscosity influences how quickly it flows.

Materials for each team
  • copy of the "Thick and Thin" student handout (PDF or HTML)
  • 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
  • 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

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

Silica Content


Approximate Flow Rate




30-60 km/hr


in between

in between

10 km/hr




1 km/hr

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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.)

  6. 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.

Activity Answer

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*

Corn syrup



Trial 1

30 sec

>1<2 sec

less than 1 sec

Trial 2

24 sec

2 seconds

less than 1 sec

Trial 3


2 seconds

less than 1 sec

Average Result

27 sec

about 1.8 sec

less than 1 sec

Viscosity Rating (1-3)




*test tube with 25 ml of liquid

Sample Rate of Flow Data*

Corn syrup



Trial 1

3 min. 10 sec

44 sec

3 sec

Trial 2

2 min. 56 sec

42 sec

2 sec

Trial 3

3 min. 4 sec.

43 sec.

2 sec

Average Result

3 min. 4 sec
(184 seconds)

43 sec

2.3 sec


25 cm

25 cm

25 cm

Flow Rate

25 cm/184 sec =
.1 cm/sec

25 cm/43 sec =
.6 cm/sec

25 cm/2.3 sec =
11 cm/sec

*ramp resting on end of wood block 3.8 cm high, flow distance = 25 cm

Student Handout Questions

  1. 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.

  2. 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.

  3. 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.

Links and Books

Web Sites

NOVA—Volcano Under the City
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
Describes the Nyiragongo volcanic eruption that occurred January 17, 2002.

Discusses volcanic eruptions and includes information on lava flow rate and viscosity.


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

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


Teacher's Guide
Volcano Under the City

Video is not required for this activity
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