Seamounts, or underwater mountains, are defined in Oceanography as independent structures that rise at least 1,000 metres above the seabed.
Their summit can often stand out from the seabed for several thousand metres, without ever reaching sea level. It is estimated that there are around 30,000 underwater mountains on our planet, but only a few have been studied.
Seamounts are almost always formed by underwater volcanoes, either extinct or still active.
They can then reach above sea level and become volcanic islands, or stay below and remain underwater volcanoes.