Underwater Volcanoes account for 75% of annual magma output. Usually when people hear of volcanic eruptions they automatically think of volcanoes such as Mt. St Helens, etc. However there are numerous underwater volcanoes that erupt and it is estimated that there are many we still have not discovered. Underwater volcanoes vary in size just like volcanoes found on land but there are some very massive ones that reach the surface. An example is Mauna Loa, in Hawaii. It rises off of the seafloor to 13,000 feet above sea level or about 29,000 feet above the seafloor. The Hawaiian Islands were all formed by underwater volcanoes that built up over time and reached the surface. An recent example of a huge underwater volcano that was found is off the coast of Indonesia. It was discovered by a group of US and Indonesian researchers exploring marine ecosystems off Sulawesi island. The volcano towers about 3,000 meters above the ocean floor which is about two miles. They believed that they are many more underwater volcanoes even greater in size that have not been discovered yet. There is an estimate that about 5,000 active volcanoes exist underwater.