Is this vent in a car or house??
They are an undersea thermal vent or hydrothermal vent.
It is a geyser in the sea floor
is it possible that the vent hose are disconected?
Leaking heater core
A chimney like vent on the ocean floor. It is a hydrothermal vent.
Replacing floor vents is a fairly easy process. Each are usually held to the floor by two screws, so remove those. Then pull out the vent from the cavity. If you measure this cavity you will know what size you need to replace the vent taken out.
Floor registers are not the registers you find checking out at a grocery store. Floor registers are the cover from the heating vent in a home or business.
four inch
Yes you can. They are easily found online and come in many patterns - do a search for 'wooden floor registers'.
Seawater seeps into the ocean floor through cracks in the crust
Heat is coming from the engine.