Activity—Modeling lava viscosity
(demonstration)
This activity was developed by Bonnie Magura, Jackson Middle School, Portland, OR.
[Note from editor: This activity requires an overhead projector (the very expensive “accelerometer” given to her by a wealthy
donor to the sciences) and a grand sense of theater to emphasize the drama of the heat. Sense of theater is good.]
Purpose
To illustrate the concept that mineral
composition helps determine viscosity of lava,
type of eruption, and resulting profile and type
of volcano.
Background
As students complete the Table of Volcanic
Eruption Styles (next pages of this document;
answer sheet follows), the last section on Flow
Rate is left for students to hypothesize. A fun
and imaginative demonstration helps connect
viscosity, mineral content, and topographic
profile of the resulting volcano with
chemistry of lava. After the demonstration,
students complete the chart and a closure
discussion helps tie concepts together. Your
imagination and showmanship can shine in this
demonstration!
Materials:
• Overhead projector (or similar
“accelerometer”)
• Rock samples (hand size or larger) of Rhyolite,
Dacite, Andesite, and Basalt
• Handful of gravel or other small rocks
• Sheet of acetate or transparency
• Tongs
• Heat resistant gloves
• Safety Goggles or Face Shield
• Caution sign: “CAUTION! EXTREME HEAT!
1300°C (>2000°F)”
• Lab coat and anything you can think of to help
create the illusion of heat.
• 8 small black or gray camera film containers
4 of the containers hold a few small pieces
of rock (gravel) Label the containers:
Rhyolite, Dacite, Andesite, and Basalt
4 of the containers hold one of the
following:
Chocolate syrup— label “Basalt”
Honey— label “Andesite”
Ketchup*— label “Dacite”
Marshmallow cream*— label “Rhyolite”
* add a drop of black food coloring to provide a
more uniform color among samples.
Student worksheet and answer sheets follow.
Science Standards
• Systems
• Inquiry
• Evidence of Change
• Forces and Motion
• Energy & Matter: Transformation
& Conservation
• Cycles in Earth Science
• Predictability & Feedback
Activity —Modeling Lava Viscosity
1
Procedures
1. Before the demonstration, assemble 4 film
containers with rock fragments so that it
appears that each rock type has been broken
up to facilitate melting. Fill the remaining
4 film containers with materials of different
viscosity. Assemble pairs of containers with their
representative rock samples near your overhead or
data projector. Set the stage with caution sign and
have your heat accessories ready.
2. Begin to tell your fabricated story of your amazing
heat accelerator that can reach temperatures high
enough to melt rock! This accelerator (give it
a name) has been added to your projector etc. –
perhaps a gift or grant for use in your classroom…
3. Dramatically, suit up for the demonstration.
Turn on your “heat accelerator” and pick up the
basalt rock sample. Ask the students to predict
how fast the basalt will flow when it is melted.
Repeat with each rock type. Pick up one of the
film containers with rock fragments and shake
the container. Explain that you pulverized the
rock so that you could melt it on the accelerator.
Remove the lids from the containers of flow
materials and carefully place each one on the
overhead transparency. Continue talking giving
the containers time to “melt”.
4. Pick up the basalt container with the tongs –
(lots of drama here to show extreme heat!) and
carefully pour out a small amount of the chocolate
sauce onto the acetate or transparency sheet.
Repeat with the andesite, dacite, and rhyolite
materials. You may need to use a metal spatula to
help remove the material from the container.
5. Carefully pick up the acetate sheet at an angle so
that each material begins to flow down the sheet.
Ask for observations and discuss. Dramatically
turn off the “accelerator”.
2
TOTLE workshop
Suggestions
Students will want to crowd around and look into
the containers, SAFETY requires that they
stay back! They may say they smell chocolate,
etc, but be prepared for with a good story. It is
important to quickly remove all liquid materials
into a tub or nearby sink to hide the evidence!
6. Return now to the “Table of Volcanic Eruption
Styles” and complete the flow rate section.
Congratulations!
You deserve an Oscar for your performance!
Activity —Modeling Lava Viscosity
3
Lava Flow Rate
Examples
Style of Eruption
Profile Shape
Type of Volcano
Iron
(Fe)
Silica
(Silicon Dioxide; SiO2 )
Color (most common)
Type of Igneous Rock
TABLE OF VOLCANIC ERUPTION STYLES
Name _______________________________________
4
TOTLE workshop
Cinder Cone
Dome
Domes
Viscous flows
Sometimes explosive
(e.g. Caldera forming)
Explosive or
pasty flows
Black Butte
Cerro Negro, Paricutin
Explosive or
Very sticky flows
Newberry Caldera “Big
Obsidian Flow”
Mt. Mazama
Slowest
Examples
Lava Flow Rate
Style of Eruption
Profile Shape
Type of Volcano
~ 4%
~ 2%
Iron
(Fe)
63 – 68%
68 – 77%
Silica
(Silicon Dioxide; SiO2 )
Light gray
Dacite
Light gray
(Obsidian – black)
Rhyolite
Color (most common)
Type of Igneous Rock
TABLE OF VOLCANIC ERUPTION STYLES
Cascade Mts.
Andes
Combines
Explosive and “Quiet”
Large Composite
Strato-Volcano
Small Cinder Cone
~ 6%
52 – 63%
Medium gray
(can vary widely)
Andesite
Fastest
Hawaiian, Mt. Etna
Columbia River Basalt
“Quiet”
Shield
Flood basalts
~ 10 – 12%
48 – 52%
Dark gray
Basalt
Teacher answer page