Those volcanoes are called seamounts. Seamounts arise in ocean seafloor. They rise at least 1000 meters, so seamounts can be found in deep sea. Most of them are made during volcanic processes.
Submerged basaltic volcanoes that rise above 1 km are called seamounts, which are formed from volcanic activity either at oceanic spreading centers or over hot spots. They can support rich marine ecosystems and influence ocean currents. When they rise above sea level, they become volcanic islands.
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