That is why geysers and volcanoes are found in the same area. When the magma reaches the surface, a volcano is formed. On the surface the liquid rock is called lava. Geysers, though rare, are found in the same geologic settings where volcanic heat sources are available. All volcanic areas do not have geysers, however.
Geysers require a specific set of conditions in order to form.
Other thermal features such as fumaroles and hot springs are common in volcanic areas and can also be heated by near surface magma bodies. The magma is the source of much of the volcanic rocks in Yellowstone. The major eruption which formed the Yellowstone caldera was about 600,000 years ago and spread wind born ash as far away as Louisiana. The area is considered by some geologists to have potential for additional eruptions, though, there have been none during recorded time. Hold your Nose.