South American 'Pompeii': Volcanic eruption 22 million years ago preserved a snapshot of the Andes forming

A volcanic eruption 22 million years ago froze a snapshot of the Andes in their youth, revealing a slow-and-steady formation of this formidable mountain range.

The eruption, which originated from the Lauca Caldera in what is now northern Chile, blanketed the landscape in a formation known as ignimbrite. This rock is left over after a pyroclastic flow ‪—‬ a mix of rock, volcanic gas and ash that sweeps over the landscape like a broiling tsunami. Pyroclastic flow is what buried the Roman town of Pompeii after the eruption of Mount Vesuvius in A.D. 79, preserving buildings and people where they fell.

Now, a new study published Sept. 11 in the journal Science Advances extrapolates the landscape under this Andean ignimbrite, revealing that it must have buried rolling foothills rather than craggy peaks.

"Pompeii shows how volcanic eruptions can freeze a moment in human history," By...