At the bottom of the ocean, around hot vents called black smokers, water gets unbelievably hot. Measurements have clocked it at over 400°C - well above the boiling point of water at the surface. But the water still flows out as liquid, not steam.
Why? Pressure. The deep ocean above pushes down with more than 250 atmospheres of force. At that pressure, water needs to be much hotter than 100°C before it can turn into a gas. Even 400°C isn’t enough. So the superheated water just keeps flowing, dissolving minerals out of the rocks it passes through, and shooting up out of the vents like dark smoke.
When that mineral-rich water hits the cold ocean, the minerals cool and crystallize into towering “chimneys” of black rock. Some vent chimneys grow 10 stories tall, built entirely by the cooling chemistry of black smoker water.
