/ Modified feb 3, 2014 4:31 p.m.

Remnants of Volcanoes Across AZ, Geologist Says

In Arizona's geologic history, there have been several major periods of volcanic activity, last one between 15-30 million years ago.


In Arizona’s geologic history, there have been several major periods of volcanic activity, said Jon Spencer, a senior geologist at Arizona Geological Survey.

The last one, between about 15 and 30 million years ago, delivered a huge amount of volcanic rock to the landscape and modified it enormously, he added.

Although volcanoes in Arizona are not active any more, their remnants are all over the state.

“Some ranges, such as the Chiricahua, Galiuro, and Superstition Mountains, are largely composed, or almost entirely, of volcanic rocks that were produced at that time,” Spencer said.

Since so much of the landscape consists of volcanic rocks, volcanoes have been quite important in forming it.

“With younger rocks, especially like up around the San Francisco volcanic field near Flagstaff, we still have the craters and peaks that represent volcanos,” Spencer explained.

If there was a potential for a volcanic eruption, Sunset Crater would be the likely place, he said.

“But we would have plenty of warnings, before it happened, such as small earthquakes to signal the ascend of a new magma,” he said. “It wouldn’t be a really dangerous eruption… and it would be a great touristic attraction."

To learn more about this topic, you can also watch an excerpt from an hour-long documentary "Under Arizona" by Eight, Arizona PBS in Phoenix.

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