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THE ELECTRONIC VOLCANO

This volcano model is more appropriate for a high school physics class or a home hobbyist. Read on. You might be amazed how much some wires, resistors, a bulb, a battery, and a condenser are like a volcano.

Volcanologists in Hawaii have noted two extremes in eruption behavior:



Some eruptions proceed at slow rates, about the same rate magma is supplied from greater depths, and continue for months, years or decades. Photo of the Kupaianaha lava pond by Steve Mattox, December 1988.


Other eruptions proceed at faster rates, far exceeding the rate magma is supplied from greater depths, and produce short duration, often spectacular eruptions. Photograph of Puu Oo lava fountain by R.W. Decker, U.S. Geological Survey, October 5, 1983.

Back in 1968, Bob Decker, a volcanologist, noted the similarities between the behavior of volcanoes and the storage and discharge of electricity in a resistance-capacitance circuit. The model for the behavior of Hawaiian volcanoes is based on work by Eaton and Murata.

In this simple comparison, the pressure exerted by the rising magma is similar to the battery. The resistance to the rising magma, caused by the overlying rocks, is similar to a network of electrical resistors between the battery, the condenser, and the bulb. The shallow magma reservoir is much like the condenser. An eruption is signified by the lighting of the neon bulb.


The electrical circuit (left side of diagram) is made by a battery (B), a condenser (C), a resistor (R), and a neon bulb (N). The current from the battery charges the condenser through the resistor. The bulb comes on when the voltage across the condenser reaches the firing voltage of the bulb. The bulb turns off when the voltage drops below the sustaining level. In a Hawaiian volcano (right side of diagram), the force of the rising magma (B) represents the battery, conduits from the deep source to the shallow magma chamber (R) are like a resistor, and the shallow magma chamber (C) is the condenser. When a dike reaches the surface (N) or magma moves into a rift zone the pressure in the magma chamber (voltage) is reduced. An eruption is equivalent to the bulb lighting.


The electrical circuit. The battery is on the left. Wires lead to a resistor, condenser, and a bulb. A voltmeter monitors changes in the system. Photo by Steve Mattox.

This system allows the roles of the following factors to be evaluated either separately or in combination:

  1. changes in pressure of the rising magma
  2. resistance to flow
  3. volume of the shallow magma chamber.

A few examples show how these factors are related. If the pressure of the rising magma were doubled, the time between eruptions would be cut in half and the long-term volume of lava produced would double. The volume of individual eruptions would stay the same.

If the capacity of the shallow magma chamber was increased, the time between eruptions would also increase. The volume of eruptions would be proportionally greater.

If the strength of the rocks was changed, so they broke with less or more pressure exerted on them by the magma, both the time between eruptions and the volume off the eruptions could change. This would be analogous to using a different neon bulb.



Bob Decker demonstrating the electronic volcano to earth science teachers. Photo by Steve Mattox.

Can you make your electric volcano behave in the two styles described at the beginning of this page?


Sources of Information:

Decker, R.W., 1987, 1. The Hawaiian-Emperor volcanic chain Part II: in Decker, R.W., Wright, T.L., and Stauffer, P.H., (eds.), Volcanism in Hawaii, U.S. Geological Survey Professional Paper 1350, v. 2, p. 997-1018.

Decker, R.W., 1968, Kilauea volcanic activity: an electrical analog model [abstract]: Eos, Transactions American Geophysical Union, v. 49, p. 352-353.

Eaton, J.P., and Murata, K.J., 1960, How volcanoes grow: Science, v. 132, p. 925-938.

Shimozuru, D., 1981, Magma reservoir systems inferred from tilt patterns: Bulletin Volcanologique, v. 44-3, p. 499-504.