Some of the most stunning landscapes on Earth lie deep beneath the ocean’s surface. Volcanic activity on the seafloor creates scattered oases known as hydrothermal vents. These underwater geysers spew superheated water rich in dissolved minerals. When that scalding-hot water comes in contact with frigid deep-ocean water, the minerals crystallize, raining tiny flecks of “ash” to the seafloor. Those mineral deposits build up over time, creating breathtaking spires and “chimneys” that can grow to hundreds of feet tall.