Sunday, November 18, 2007

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.

9 comments:

Bill said...

Would love to learn more about Yavapai's volcanoes! Glassford Hill is well known, of course, but others?

Your blog is one of my few daily must-reads, Granny J, and I enjoy it immensely.

Karen of Scottsdale said...

There is an area along Interstate 8 traveling between Maricopa and Yuma which looks like a lava flow because all the rocks are black and scraggy and so different from all the areas around it. Did that gentleman say if there were any volcanoes in Southern Arizona?

Granny J said...

Welcome, bill -- me too! I know that Glassford Hill, Martin Mountain over by Skull Valley and Blowout Mountain down by Yarnell were all volcanoes & there are lava flows all over the place, but nothing has ever been pulled together. Wish someone would do it in my lifetime!

karen -- sounds like basalt... there's a rather neat book, Roadside Geology of Arizona which might answer your question. And the AZ Dept. of Mineral Resources has put out a bunch of county maps that show the source of the surface material .. these are good for locating the lava flows. The Chiricahuas are volcanic.

sheoflittlebrain said...

Interesting post GJ, but scary too! The corn and pottery in the lava tell some of the old story, while the new one is boiling, unseen beneath the earth's crust..

Granny J said...

brain -- fortunately, up there, not here. Probably. On the other hand, what better way for the old earth to ward off excess heat than by letting a few big ones blow?

smilnsigh said...

"...and lava flows here and there, even in town."

It does?????!!?????

Mari-Nanci

Granny J said...

SnS -- it did, many eons ago! Difficult word, that -- you can't call them f-l-o-e-s, for they aren't nearly cold enough. I should have said, "one can spot lava flows here and there about town..."

RE IN AZ said...

I'm sorry I missed this event. So many cool things going on in our little town. Thanks for the highlights.

Granny J said...

Hi, RE -- Better coverage in today's Courier. It does sometimes happen!

 
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