The geological term for an underwater mountain range is "mid-ocean ridge." These mountain ranges are formed by tectonic plate movements, often where tectonic plates are diverging or converging. They are characterized by volcanic activity and can create new oceanic crust as magma rises from the mantle. Mid-ocean ridges are crucial for understanding plate tectonics and ocean circulation. They also host unique ecosystems that thrive in the dark, under high pressure, showcasing remarkable species adapted to these extreme conditions.