Hydrothermal, broken down means water (hydro) and heat (thermal). That is exactly what it is! Hydrothermal systems are the movement of water underground and above ground due to heat. Hydrothermal systems consist of a heat source, reservoir, recharge region, and connecting pathways that allow water to move underground. The water can be heated by magma, hot rocks, and the Earth’s mantle. As this happens, water starts to circulate underground and heats up and cools down through the cycle. These systems cause geysers, hot springs, hydrothermal vents in the ocean, and more! A great example of this is Yellowstone National Park, with its natural hot springs and geysers.
Old Faithful eruption in front of the sun