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How an Undersea Eruption Created Jerome, Arizona

You may hear jokes about “oceanfront property in Arizona,” but in the distant past, it really existed. In fact, 1.75 billion years ago, the area was undersea. However, there was a lot going on down there where tectonic plates were colliding.

I don’t know if you can imagine an undersea caldera eruption. There’s the sea floor, suddenly torn apart, with boiling clouds of ash billowing through the water. Had there been fish back then, they would have been tremendously inconvenienced; also, cooked. Fortunately for them, this was before the Age of Fishes. When the magma chamber emptied, the whole shebang came crashing down. A huge series of fractures propagated in a huge, irregular ring miles in diameter. Sea floor, seamounts, volcanic domes, newly-emplaced Cleopatra tuff and all fell into the chamber magma had so recently vacated.

But that was just the beginning of the turbulent geologic history that led to the settlement we know as Jerome, Arizona. The legacy of its volcanic history was a rich vein of valuable copper, which drew miners. Now the mines are an open record of the catastrophic events that created the place.

Read a lot more of this story at Scientific America.