From a physics standpoint, how can a volcanic eruption shift the earth?

I read that the Krakatoa eruption did so. How can an eruption shift the earth and what kinds of shifts are possible (i.e. shift in path around sun, shift in rotation speed/angle, etc.)? I want a physics-based explanation that accounts for conservation of momentum. I.E., in general, if you were deep in space at rest with respect to a refrigerator and you pushed it away from you at less than escape velocity, then both you and the refrigerator would eventually return to your exact, original positions... or would you? Feel free to use your own ogies if you wish.