What causes geysers to erupt?

Geysers erupt when underground water is heated by magma and trapped in a confined space. As the water temperature rises, it expands into steam, building pressure until it bursts through the surface. This creates a dramatic eruption of water and steam. Geysers often occur in areas with volcanic activity, such as Yellowstone National Park, and are rare natural phenomena due to the unique combination of heat, water, and geology required.