Geysers and volcanic activity

In areas of volcanic activity, where hot magma is close to the Earth’s surface, geysers are often found.

Geysers are mostly little air pockets in the Earth’s surface which are associated with one or more narrow chutes that lead down into a large underground pool of water. Water gradually seeps down through the ground until it reaches the hot floor. This then heats up the water.

The water rises back up to the surface by convection (meaning that the warmest water rises to the top). After a while, as the geyser fills up, the water at the top cools down, but because the chute is so narrow, the cooler water cannot sink to the bottom again. The cold water at the top presses down on the hot water below – a bit like the lid on a pressure cooker.

As a result, the water in the pool becomes ‘overheated’, meaning that it remains liquid at a temperature well over 100°C.

How does the geyser erupt?

Finally the water gets so hot that it begins to boil anyway, and bubbles of steam rise in the chute. When the steam bubbles come out of the geyser’s air hole and explode, the pressure falls inside the geyser and the overheated water becomes steam that boils in the whole of the chute.

The hot water and expanding steam become foam that sprays out of the geyser.

The water that is left in the geyser cools to below the boiling point and the explosion ends; warm ground water begins to collect in the pool, and the whole process begins again.