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. 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. 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.