1. A fissure in the sea bottom through which hot aqueous solutions rise from the magma beneath the crust; a hot spring: Hydrothermal vents are located on the seabed mainly along the central axes of the ridges in mid-ocean.
2. A geyser on the sea bottom through which super-hot aqueous solutions rise from the magma beneath the earth's crust: The hydrothermal vents create a surrounding system of mineral-rich water which helps to support a distinctive type of ecosystem not found in typical cold-water environments at the same ocean depth.