Geology
Geology |
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Environmental Geosciences |
Ms. Beth Johnson, a Ph.D. student in our department and pictured on the right, brought this idea
with her to use as a teaching aid in her introductory geology course. Its purpose is to demonstrate
an explosive volcanic eruption, safely and in miniature, and to generate no little excitement in
the class besides. A passer-by who observed one of our test runs was heard to say that he had
clearly majored in the wrong subject because we got to do such interesting things. Beth is ably
assisted in carrying out the demonstration by Ms. Jessica Olney, her fellow Ph.D. student, whose
picture is below on the left.
Briefly, the thing is done by placing a small amount of liquid nitrogen in a weighted plastic soft-drink bottle, which is then submerged in a plastic 55-gallon industrial-strength garbage can that has been filled about two-thirds to three-quarters full of water. The liquid nitrogen rapidly absorbs heat from its surroundings, changes phase from liquid to gas, and within a minute or so explosively ruptures the soft-drink bottle. The rapidly expanding gas permeates the water in the garbage can and violently expels the eruption column from the can. The process is accompanied by a most satisfying THA-WHOOMPH, there may be an identifiable base-surge, pyroclastic flow, or the like, and water goes everywhere.
Once is never quite enough. We usually have to do it a couple of times.
There are dangers inherent in this procedure, having to do with the handling of super-cold liquid nitrogen and in dealing with things that are intended to explode in the normal course of events. This procedure should not be undertaken by fools, nor by those who are otherwise either not capable of following, or who are disinclined to observe, the warnings, safety items, and simple instructions, provided in the reference listed immediately below. Never forget that Darwin's axiom applies to you as well as to all the other critters on the planet!
There is a webpage at Colgate University which offers a PDF copy of the article for download, along with extensive pictures and text. The page is a large one, and may take a while to load depending on your connection speed, so be patient because it's well worth a look. Read and heed all warnings and safety information provided.
Harpp, K.S., Koleszar, A.M., Geist, D.J., 2005, Volcanoes in the Classroom: A Simulation of an Eruption Column; Journal of Geoscience Education, v. 53, no. 2, p. 173-175.
What follows are links to slideshows of the simulated eruption in different formats and another to a movie in ".mov", that is, QuickTime® format. The slideshows consist of still pictures extracted from the movie, and offer the advantage that one can get a better look at the various stages of the eruption. Below these is a gallery of still pictures with discussion of the eruption phenomena illustrated.
Eruption, the movie, in QuickTime® format. ( 1.5 megs )
Eruption, the slideshow-1, in mpeg format. ( 9 megs )
Eruption, the slideshow-2, in Windows Media format. ( 3 megs )
The stage is set, and the tension is palpable. Beth has introduced the weighted soft-drink bottle into the water-filled trash can, approximately 0.9 meters tall, and we await developments. Note the position of the top of the trash can with respect to the concrete slab on which the students are located, for later reference. |
The column has begun to emerge from the top of the trash can, and the can itself is rising with it. The side of the can is slightly collapsed, indicating that it is being drawn upward by negative pressure. This is in part why plastic trash cans are recommended for use in these demonstrations, because they are sufficiently resilient to be able to withstand the stresses involved. Metal trash cans are too rigid, and come apart at the seams. |
The eruption column continues to develop, and it can be seen that it is uncommonly well-formed. Pictures from the reference article and our own experience show that a ragged column about the diameter of the trash can is much more common. A base-surge is just beginning to appear at the rim of the can, and a collapsed segment is visible on the left side of the can just below the top band. |
The base-surge is now well developed, and the base of the can has reached its maximum height. Comparison with the concrete slab shows that the can has risen approximately its own height above the ground. Do a little physics: Estimate the energy necessary to elevate about 40 gallons of water and three lead diving weights as high as you see in a fraction of a second, and you'll understand why it's important to perform these demonstrations with due care. |
The eruption column has reached its maximum extent, and the trash can is well on its way back to the ground. Note that the can is bulging a little on its left side near the bottom. |
The eruption column is beginning to collapse; the trash can is back on the ground, and wisps of pyroclastic flows are beginning to appear moving down the sides of the can. |
Collapse is well under way, and the pyroclastic flows have become well developed. |
Collapse and flows continue to evolve. |
The pyroclastic flows have become extensive. |
The eruption column is all but gone, and the pyroclastic flows have reached their maximum extent. |
The eruption column is gone, and the pyroclastic flows are dissipating. That's all, folks! |
The icon on the main page is a picture of Augustine Volcano, Cook Inlet, Alaska, which underwent a steam eruption, pictured here, on and about January 24, 2006. The photograph was taken by Cyrus Read, and is used courtesy of the Alaskan Volcano Observatory/U.S.G.S.