The weight, in turn, increases the pressure on the base of the column, and increases the boiling point of the water. When the water boils, it expands pushing some of the water out into the air. When the weight of the column reduces the pressure drops causing the water to drop. Geysers are formed by rivers, and lakes, where water drains through the Earth deep under the surface. A deep channel reaches from the surface far into the Earth.
Cold water seeps down the channel on to very hot rocks.
Then it fills the channel. The water at the bottom gets hot from the rocks. Gradually the heat at the bottom of the column rises far above the boiling point for water. Steam starts to form. The rising bubbles lift the water column a little, pushing some of the water in the channel over the opening onto the surface of the Earth.