Most schools in the U.S. are far from active volcanoes, and few students
have the opportunity to witness eruptions. Simulations of eruptive
processes, or analog models, provide ways for students to visualize
eruptive processes and apply basic physical principles when field
observations are not feasible. In this paper, we describe a safe
simulation of violent volcanic explosions, one that can be carried out
simply and easily as a demonstration for specialized volcanology classes,
introductory classes, and science outreach programs.
Volcanic eruptions are fundamentally gas-driven phenomena.
Depressurization of volatiles dissolved in magma during ascent is the
driving force behind most explosive eruptions. Furthermore,
phreatomagmatic eruptions result from the conversion of water to steam
during magma-water interaction. During an eruption, the exsolution and
expansion of gas causes ascent velocity of the magma to increase. When the
volume fraction of bubbles exceeds about 80%, the magma fragments
explosively and is carried by a gas stream (e.g. Sparks,
We have developed a demonstration whereby the instructor can initiate a
gas-driven eruption, which produces a dramatic but safe explosion and
eruptive column. First, one pours liquid nitrogen into a weighted, plastic
soda bottle, which is then sealed and placed into a trashcan filled with
water. As the liquid nitrogen boils, the pressure inside the bottle
increases until it fails, resulting in an explosion. The expansive force
propels a column of water vertically, to 10 or more meters. Because liquid
nitrogen is thermodynamically unstable at room temperature (boiling point
at 1 atmosphere: -195.8°C), its
boiling provides the pressure necessary to cause an explosion,
illustrating an important process that drives real volcanic eruptions
with most simulations, this one is imperfect. Unlike magma, the gas does
not exsolve from the liquid, and consequently it is not dispersed
throughout the water prior to explosive expansion. Also, there is no real
transfer of heat during the eruption. Nevertheless, it is an
exceedingly effective demonstration of gas-driven liquid explosions and
one that is safe if done properly.
Most of the supplies necessary for this demonstration are common items;
liquid nitrogen is the only material that may be difficult to obtain, but
it is frequently used in science demonstrations (e.g., Nolan and Gish,
1996; McRae et al., 2002) and can be obtained on most college campuses or
from gas supply companies at relatively low cost. Here we describe the
details of the procedure (Table 1 includes further equipment details):
- Be sure to
inform all participants of the potential dangers of contact with
liquid nitrogen (e.g., Young, 2003) and the risks of sealing liquid
nitrogen in closed containers. The Material Safety Data Sheet on
liquid nitrogen is available at http://msds.ehs.cornell.edu/msds/msdsdod/a97/m48467.htm;
- Metal garbage
cans are inappropriate for this demonstration, because they simply
rupture along the welded seams. In most cases, we use a high-grade,
plastic contractor’s trashcan (Table 1).
- Only two
people should carry out the demonstration. They must have clothing
covering their legs, arms, and feet and they must wear safety glasses
and gloves throughout the process.
- Prior to
handling any liquid nitrogen, the demonstrators should do a practice
run of the entire procedure. We recommend that the two participants
rehearse their roles several times until everyone is confident of
their part in the demonstration process, without hesitation.
- Make sure the
audience members remain at least 5 meters from the trashcan at all
- Fill the
trashcan about 80% full of water. This is about 95 L (25 gallons),
nearly 100 kg, thus the trashcan should be filled at the exact site
where the explosion is to take place. The demonstration is more
impressive if the trashcan is located on a horizontal paved surface, not
grass, and never on a cart.
- Secure a 0.5 to
1 L plastic soda bottle to 1-2 bricks using duct tape around the middle
of the bottle. Align the bottom of the brick(s) with the bottom of the
soda bottle, so that the brick-bottle apparatus stands freely. Ensure
that the weight of the brick(s) is sufficient to keep the bottle
submerged by performing a practice run with an empty bottle. The sealed
bottle and brick must submerge completely.
- Set the open
bottle and attached brick upright on the ground with the funnel in
it. Have one individual hold the cap, so that it can be placed on
the bottle quickly.
- One person
holds the funnel far enough out of the bottle opening to make an air
outlet for the gas, otherwise boiling liquid nitrogen splashes out, and
the bottle will not fill efficiently.
- The second
person pours the liquid nitrogen through the funnel into the bottle
until the bottle contains approximately 20-30 mL of liquid nitrogen
(i.e., 2-5 cm depth from the bottom). The amount need not be precise,
and much of the nitrogen boils away as it is poured.
- Time is of the
essence at this point. The person holding the funnel should toss it
aside and cap the bottle tightly. Be sure not to cross-thread the
cap. It is critical that the cap be finger tight, so the bottle is
- Within no more
than 5 seconds, one of the demonstrators should pick up the bottle/brick
apparatus and drop it gently in the garbage can. Try to put the bottle
in the center of the can and not against a side, where it is more likely
to rupture the plastic walls.
- After immersion
of the N2(l)-filled bottle and brick, the two people
performing the demonstration should walk away quickly and wait, at least
5 meters from the can. There is a delay of approximately 10-30 seconds
before the explosion, so they do not need to run. The liquid nitrogen
undergoes a phase change into gas. In the absence of the confining
bottle, the small amount of liquid in the soda bottle would expand (at
standard temperature and pressure) to well over 20 L. Because they are
built to sustain overpressures from carbonated drinks, the bottle
resists the expansion while pressure builds. Eventually, the bottle
ruptures, and the force of the gas expansion passes into the water,
resulting in an eruption column of water several meters high. The
garbage can often makes an impressive jump as well.
- If the bottle
does not explode within the anticipated 10-30 seconds, do not approach
it; we have seen the rare event where the bottle is particularly strong
and resists for close to a minute. If you see vapor bubbling out of the
can (which is just escaping nitrogen), then there is a leak in the cap
or bottle, and it may or may not explode. There is a tendency for
impatience at this point, but under no circumstance should anyone
approach the trashcan until they are positive that the bottle has failed
and all of the N2(l) has boiled away, and then only the
demonstrators (with covered shoes and safety glasses) should go to the
trash can. In our experience, the most common mistake is that the cap is
not put on properly, which is not a dangerous situation.
Pedagogical Uses of the Eruption
Level and Community Groups
At the simplest level, the eruption column demonstration illustrates
gas-driven eruptions, dispelling the common misconception that there is
some kind of fire or hot explosive involved in volcanic eruptions. Because
the blast is short-lived, it is best to explain the procedure and its
significance first, then carry out two detonations, so people can watch
the second more carefully after the surprise of the first explosion. We
have performed this experiment for groups as large as 500 people, provided
there is an outdoor amphitheater of some kind. We routinely carry out the
demonstration for students of all ages.
modification of the demonstration simulates the famous lateral blast at
Mt. St. Helens on May 18, 1980. An inexpensive trashcan will
usually fail along one of the molded seams, propelling some of the water
At both Colgate and
the University of Idaho, we have expanded this demonstration into a series
of guided inquiry investigations (e.g., Smith et al., 1995; Beiersdorfer
and Beiersdorfer, 1995) with a small class (20-35 students) of advanced
students. Each group of 3-5 students has a trashcan full of water,
a selection of bottles, material to simulate tephra (Table 1), and a
measuring tape. They go through a detailed safety orientation covering
liquid nitrogen safety prior to embarking on the exercise. The groups then
design their own experiments to address the following problems, or others
they generate in the investigative process:
By measuring the height of the eruption column, students can use
basic physics to calculate the ejection velocity of the water
propelled from the trashcan and compare the results to the
velocities observed at actual volcanic eruptions.
Using their calculated ejection velocities, students can
then determine the pressure needed to propel the water column using the
modified Bernoulli equation: ½ U2 = (Pi –
Ps) / S, where U is the ejection velocity in m/s, Pi
is the reservoir pressure (in Pascals, Pa), Ps is atmospheric
pressure (Pa), and S is the magma density (the density of water in
kg/m3). The students can once again compare their results to
observations from real volcanic eruptions.
Students can use the estimated volume of gaseous nitrogen in
the soda bottle (via the ideal gas law) and the volume of water in
the trashcan to calculate the average vesicularity prior to eruption,
which they can then compare to theoretical estimates of fragmentation
(Sparks, 1978). The density of N2(l) is ~0.807 g/cm3
under standard conditions.
Styrofoam peanuts or spheres of different sizes, such as tennis
balls and apples can be used to simulate ballistic pyroclasts. After the
eruption, students can construct isopleth maps of the clasts. The
different densities and aerodynamic shapes of the “clasts” reproduce the
distributions of volcanic bombs, blocks, and cinders.
Different vessels for the demonstration affect eruption
style as well. For instance, a small rigid-sided wading pool generates a
base surge and a shorter eruption column. As mentioned above, a cheap
soft-sided trashcan is likely to fail along its seams, yielding a lateral
This simulation operates on physics similar to that which
drives volcanic eruptions, but on a scale accessible to students.
Furthermore, the simulation permits interaction and experimentation with
the driving forces behind eruptions, more so than can be accomplished by
narrative or video footage. This demonstration has repeatedly proven to
impress students of volcanology ranging from first-graders to professors
(including a group of high school and college physics instructors at a
national physics conference). In addition to being visually impressive, it
provides a safe means to illustrate and explore explosive volcanic
Table 1. Supplies for Eruption Column
Basic Version of Demonstration
plastic garbage can (a “contractor’s” trashcan, usually ~$35-40 at most
home supply stores); these are generally re-usable. Avoid small buckets or
other light plastic containers, as well as metal cans; all of these will
be destroyed in the blast and the metal cans will split along their seams
and possibly send out shrapnel.
Soda bottles (16-20
ounce size is most convenient, but the 2 L bottles are equally effective)
with their caps. Water bottles generally do not yield the same magnitude
eruption, because they are not as strong as soda bottles and fail before
pressure builds up significantly. One bottle is needed per demonstration,
and several back ups should be on hand.
2 bricks or a large
cinder block (must prevent the soda bottle from floating)
Hose from faucet to
site of detonation (a full trashcan is difficult to move to a new
Safety glasses for all
participating individuals (usually 2)
Insulated gloves for
liquid nitrogen protection (two pair per demonstration set-up)
The people performing
the demonstration must wear closed-toe shoes, long pants, and long-sleeved
Liquid nitrogen (~20 mL
per explosion) in a Dewar
Funnel for pouring the
nitrogen, preferably plastic
(e.g., Mount St. Helens)
Use an inexpensive
plastic, residential curbside trashcan with indentations in the side
($8-12; e.g., Falcon 32-gallon molded black plastic “heavy duty” can);
these generally fail in the explosion, resulting in a lateral blast, but
the can is obviously not reusable. Stronger cans that have been damaged or
have cracks in them also work for this version of the demonstration.
objects that are neither sharp nor hard (apples, half-filled water
balloons, Styrofoam packing peanuts or other non-water soluble packing
material, tennis balls, etc.), placed in the can prior to
Beiersdorfer, R.E. and
Beiersdorfer, S.I., 1995, Collaborative learning in an advanced
environmental-geology course, Journal of Geoscience Education, v. 43, p.
Francis, P., Volcanoes:
A Planetary Perspective (1993), Hong Kong, Oxford University Press, 443
Liquid Nitrogen Haiku,
McRae, R., Rahn, J.A.,
Beamer, T.W., and LeBret, N., 2002, The Liquid Nitrogen Fountain, Journal
of Chemical Education, v. 79, no. 10, p. 1220-1221.
Nolan, W.T. and Gish,
T.J., 1996, The Joys of Liquid Nitrogen, Journal of Chemical Education, v.
73, no. 7, p. 651-653.
Smith, D.L, Hoersch,
A.L., Gordon, P.R., 1995, Problem-based learning in the undergraduate
geology classroom, Journal of Geoscience Education, v. 43, p. 385-390.
Sparks, R.S.J., 1978,
The dynamics of bubble formation and growth in magmas: A review and
analysis, Journal of Volcanology and Geothermal Research, v. 3, p. 1-37.
Young, J.A., 2003,
Liquid Nitrogen, Journal of Chemical Education, v. 80, no. 10, p.
We would like to thank the
Colgate University “Volcano Cowboys” for their unerring dedication to
refining the demonstration method, including (but not entirely limited
to): David Kolodney, Adam Skarke, Jay Barr, Evan LeBon, Scott Annan,
Nathan Rollins, Ashley Nagle, and Vanessa Simpson. DJG would like to thank
the forgiving Secret Service agent who visited him when he performed the
demonstration on the same day a supreme court justice visited campus.