(New Scientist) The Old Faithful geyser in Yellowstone national park is famed for its clockwork eruptions – every 90 minutes, on average. Now a secret chamber has been found in the rocks beneath the geyser, radically changing our understanding of how it erupts.

In the early 1990s, researchers lowered a camera into Old Faithful’s throat and, 7 metres down, saw a “choke-point” less than 10 centimetres wide. Below that was a cavern about the size of a small car. But the camera couldn’t go deeper than 14 metres because of the violent churn of boiling fluids.

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