Sunset Crater and the San Francisco Volcanic Field

No, Fluffy, you can't.  (Image: Morguefile/bandini0

Sorry, Fluffy. (Uncaptioned image: Morguefile/bandini)

Last week, there was some excitement on the Internet that Sunset Crater in Arizona was erupting. It wasn’t. Instead, per reports, the US Forest Service was just conducting a prescribed burn.

Confession: Years ago, when I was first checking out volcano cams, I noticed a bright light at the base of Mexico’s Popocatépetl at night time. All excited, I got onto Usenet and told my group that Popo was erupting. Um, it turned out official monitoring showed that Popocatépetl was not erupting. Someone thought it was probably a brush fire in one of the canyons. A very embarrassing episode! Another time, I saw clouds surging around the top of Mount Vesuvius on a volcano cam. It really did look alarming, and I did not realize that the Bay of Naples area is subject to severe weather. Yep – it was a storm, not an eruption.

Lesson learned: Experts are closely watching many famous active volcanoes. Perhaps you might see something that looks like an eruption on a cam or, as in the Sunset Crater case, on satellite images. Just don’t go blurting it out over the Net. Check first with reputable sources – the USGS, the local volcano observatory (Vesuvius has one and Popo is monitored by CENAPRED), etc.

Sunset Crater and the San Francisco Volcanic Field

Sunset Crater is a cinder cone that sits about a half-hour’s drive from Flagstaff and has become a US national monument (this was done after Hollywood film makers wanted to blow it up – yay for CGI!). It’s about a thousand feet high and a mile wide at its base. Sunset Crater is part of the active San Francisco Volcanic Field and erupted almost a millennium ago. This VEI 4 eruption was unusual large for this type of volcano and it drove nearby native people out of the region.

The San Francisco Volcanic Field, with its 600 vents, is the reason why the ground isn’t flat between Flagstaff and the Grand Canyon. Sunset Crater is its youngest volcano, and San Francisco Mountain, an eroded stratovolcano, at almost 13,000 feet, is the highest point in the field (and in the state). The field has been around for six million years and might be the result of a hot spot – volcanologists say they’re not sure.

The reason there are so many vents there, and only one recent eruption, is because this is a monogenetic volcanic field. Volcanoes usually erupt once and then go extinct, with the next eruption happening elsewhere in the field. Per the US Geological Survey:

Although there has been no eruption for nearly 1,000 years, it is likely that eruptions will occur again in the San Francisco Volcanic Field. With an average interval of several thousand years between past periods of volcanic activity, it is impossible to forecast when the next eruption will occur. U.S. Geological Survey (USGS) scientists believe that the most probable sites of future eruptions are in the eastern part of the field and that the eruptions are likely to be small. These future eruptions may provide spectacular volcanic displays but should pose little hazard because of their small size and the relative remoteness of the area.


Sunset Crater and the Anasazi

Let’s visit Sunset Crater and take a look at what the people who moved in after that eruption left behind when something – no one knows what – made them leave.

Categories: Sunday morning volcano

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