A hydrothermal vent is a lot like an underwater geyser. Sea water seeps down into the cracks and fissures created by the spreading of the sea floor, sometimes as much as two or three miles into the earth’s crust. As the water comes into contact with the magma, the seawater is superheated. Then the hotter sea water rises to the surface back through the fissures, carrying with it minerals leached from the crustal rocks below. The superheated seawater then spews out of the holes in the crust, rising quickly above the colder, denser waters of the deep ocean.