Underwater volcanoes erupt quite often, and the flowing lava creates impressive formations on the seabed. The most prolific volcanic systems on Earth are hidden beneath the ocean depths. Scientists have estimated that there could be more than a million underwater volcanoes around the world. Volcanic eruptions result in a remarkable variety of formations as molten lava hardens at various rates in cold seawater, to form spectacular features such as bulbous cushions, hollow domes and canals, jagged pillars and folding leaves.