The combined analysis of imaging, mass spectrometry, and magnetospheric data suggests that the observed south polar plume emanates from pressurized subsurface chambers, similar to Earth's geysers or fumaroles. Fumaroles are probably the closer analogy, since periodic or episodic emission is an inherent property of geysers. The plumes of Enceladus were observed to be continuous to within a factor of a few. The mechanism that drives and sustains the eruptions is thought to be tidal heating. The intensity of the eruption of the south polar jets varies significantly as a function of the position of Enceladus in its orbit. The plumes are about four times brighter when Enceladus is at apoapsis (the point in its orbit most distant from Saturn) than when it is at periapsis. This is consistent with geophysical calculations which predict the south polar fissures are under compression near periapsis, pushing them shut, and under tension near apoapsis, pulling them open.