Why do some geysers erupt regularly?

Question from Davood Ahmed

Each geyser sits atop a unique network of cavities and fractures within a rock, and it is unclear what differentiates regularly erupting ones. Geysers require a rare combination of geothermal heat, abundant groundwater and interconnected chambers inside rock where water and steam can collect. 

Side chambers in the rock trap pockets of steam at depth, which bubble up, heating the water above. Although the water at depth reaches 100 degrees Celsius, the weight of the water above initially prevents it from boiling. Then the surface water starts to boil, relieving
the pressure and allowing the water below to boil abruptly, triggering a violent eruption.

Answered by Alexandra Franklin-Cheung  for Brain Dump in How It Works issue 109.

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