 Subject
Science
Objectives
The student will:
- Participate in demonstration of a caldera-forming
volcanic eruption through use of a model.
- Measure crustal deformation through use of
a model.
- Locate areas of earthquake activity through
use of a model.
Materials
Large, plastic dishwashing tub
Sand (enough to fill the bottom half of the tub)
Spray bottle filled with water
3-foot-long clear, flexible tubing with a diameter
large enough to be snug inside the lip of the balloon
Bicycle pump
Rubber bands or duct tape
Balloons—large and round
Felt tip marker
Cloth or plastic measuring tape
Plastic measuring cup—any size.
Background
Three caldera-forming eruptions have occurred in
the Yellowstone region in the last two million years.
Molten rock, charged with gases, accumulated at
shallow levels below the ground’s surface.
The overlying surface of the land domed upwards,
triggering earthquakes. Finally catastrophic eruptions
occurred, spewing out enormous amounts of magma
and ash. The last immense eruption occurred in Yellowstone
approximately 640,000 years ago, leaving a caldera
measuring 30 by 45 miles (56 by 64 kilometers).
Until 70,000 years ago, lava continued to ooze into
the caldera, partially refilling it. The lava gradually
hardened into rhyolite. Rhyolitic soil supports
much of the present Yellowstone ecosystem.
An area of partially molten rock still underlies
the Yellowstone region, heating the water of the
park’s geysers and hot springs. Scientists
think regional uplift and magmatic earthquakes
in Yellowstone are caused by movement of magma,
hydrothermal fluids, or gases below the ground’s
surface.
Procedure
The instructor will:
- Prepare the demonstration prior to class
by attaching a balloon to the plastic tubing
with tape or a rubber band. Lay the balloon
on the bottom of the dish tub, with the tubing
running out of the tub. Fill the tub with sand
until the balloon is completed covered and the
tub is at least 1/3 to ½ full. Attach
the other end of the plastic tubing to a bicycle
pump.
- Review information in the Background section
with the students and ascertain that students
understand that Yellowstone is a volcanic system.
- Explain that when the magma and gases begin
to accumulate below the ground, the ground domes
upwards, triggering earthquakes. Tell the students
that during the demonstration, they should be
observant of areas where the sand is doming
or cracking, which are simulations of crustal
deformation and earthquake activity.
- Select one student to use the bicycle pump
to gradually inflate the balloon. The student
should stop when the balloon barely breaks the
surface of the sand.
- Direct a student to place two marks on the
balloon, at least 1/2 inch apart, with a felt
tip marker, and to measure the distance between
the two marks with the measuring tape.
- Instruct the student using the bicycle pump
to continue pumping until the balloon is largely
visible and the upper portion of it is above
the sand.
- Select another student to measure the distance
between the two dots again and verbally note
the difference. Tell students that this is a
simulation of crustal deformation, and inform
them that there are areas of uplift in Yellowstone
that can also be measured. Ask students to point
out places in the model where the sand has cracked
and tell them that these cracks indicate areas
of earthquake activity.
- Direct the student to continue using the bicycle
pump for a couple more strokes. Once again select
a student to measure the distance between the
dots and verbally note the difference.
- Select a student to pop the balloon with a
pin, if necessary, simulating the volcanic eruption
and resulting caldera.
- Select a student to measure the width of the
caldera.
- Ask students to speculate on what would happen
if lava continued to ooze into the caldera,
and eventually hardened into rock.
- Select a student to demonstrate by gradually
pouring sand into the “caldera”
with the measuring cup. Explain that this is
what has happened in Yellowstone in the past,
and that areas of partially molten rock still
underlie the Yellowstone region.
Assessment
Caldera
Demonstration Rubric (pdf) |
