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1) The answer is that there is a huge amount of water available relative to the amount that can escape through a hole that size under whatever amount of pressure there is in the system. It could be groundwater from a wide area flowing down fractures until it gets deep enough to reach high temperatures and then flowing back up a fracture to where the well found it, or it could be water that was trapped in a sedimentary rock unit that’s now being forced out by pressure because it’s now buried under a whole bunch of younger sediments, or it could be from dehydration reactions as deeply-buried rocks undergo metamorphism. It could also be some combination of those things. In any case, there is a large volume of hot water rising through (relatively) small fractures then trying to escape through an even smaller hole.
2) It does actually flood its immediate surroundings, which is why you see pools of water in the picture. However, the sediments in the area are porous and very dry, so much of the water probably goes underground fairly quickly. Evaporation probably also removes quite a bit of water, since Nevada is hot, dry, and sunny.