Nearly 50 years ago, Dr. John Wright came to Mexico to study pyroclastic flows: great “rivers” of incandescent volcanic ash that flowed across the landscape some 95,000 years ago when a huge, explosive volcanic eruption occurred not far from what is now Guadalajara.
Among the curiosities that Wright encountered during two field trips to the woods around Tala, 30 kilometers west of Guadalajara, were rock formations that less scientific nature lovers have dubbed “fairy footstools.”
Typically, they look like rounded tree stumps, perhaps a foot or two high. The casual observer first sees them as cut trees, but on closer observation discovers they are made of stone.
In his book “Volcanic Successions,” published in 1987, Wright calls them steam pipes or paleo-fumarolic pipes, formed ages ago when water vapor percolated through thick layers of hot ash.
“The steam bubbles altered the ash chemically, precipitating minerals harder than the surrounding ash,” says Wright. “Wherever bubbles rose, smooth cylinders of rock, perhaps over 20 meters in length, were created beneath the surface.”
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