Arizona Hot Spot

When your daughter and family move to a house situated smack dab on the Pacific Rim of Fire, you can bet you're going to be interested in volcanoes. Of course, I've been intrigued by volcanoes for many years; in fact, I put the Kamchatka Peninsula on my list of remarkable places in the world I'd like to visit but never will.

And so it was that I joined the crowd at the Sharlot Hall Museum this afternoon to hear Wendell Duffield's quite informative lecture on Northern Arizona volcanoes. More specifically, the San Francisco volcanic field surrounding Flagstaff. Full house -- people in Prescott are interested in the subject. After all, we have a couple of tired old relics in the area and lava flows here and there, even in town.

Admittedly, Yavapai County, with its odds and ends of vulcanism, isn't going to interest geologists when next door there's an incredible field of mountains and cones. Every one of those dots on the map above is a volcanic eruption of some sort; the current count is over 600, dating from 6 million years ago up to 1250 AD. And, no, the field is not dead; it is moving to the northeast at the rate of about 2 inches per year and could spring into action one of these days. It is sufficiently un-dormant that Duffield was part of a US Geological Service team who recommended it as a potential source for geothermal energy.

Flagstaff is located at the foot of San Francisco Mountain, at roughly 12,600 ft. tall the high spot in Arizona. Presumably it was a stratovolcano that blew out its side about one million years ago, a la Mt. St. Helens. Probably a good 16,000 ft. in elevation before the big event. Incidentally, Duffield pointed out that the mound in the lower right dates from only about 400,000 years ago.

Here's another feature of the field, in a Landsat image. The black cone is SP crater, with a major lava flow to the north. Don't miss all the volcanic cones at the bottom of the image.

Two types of mountain projected at the lecture. The illustrations are from a book written by the speaker.

Here is evidence to remind us of the recency of vulcanism in Arizona -- Indian corn left an imprint in a piece of lava found near Sunset Crater, our latest volcano. But even more intriguing is the pottery shard embedded in lava (below) from the most recent flow from a cone at the foot of remote Mt. Trumbull, which is located at the west end of Grand Canyon Natl. Park on the north rim. Both these relics are believed to be in the same age range, said Duffield.

Judging from the questions the audience threw at the speaker, there's really a lot of interest in local vulcanism, which doesn't make it into most discussions, such as these from the US Geological Service (here and here.) Of course I bought a copy of Duffield's book, Volcanoes in Northern Arizona. And one of these days I might pull together a post about a few of the volcanic features of our local area.