Dreams of Summer: Living Under the Threat of Destruction at Wupatki

The San Francisco Peaks, a gigantic stratovolcano, rises beyond the ruins of the Citadel at Wupatki National Monument.

There is a huge difference between living close to the Earth without advanced technology and living in a highly technological society. Well, lots of differences actually, but today I'm thinking about living in ignorance of geological hazards. The thought arose because of our visit to the rather fantastic pueblos of Wupatki National Monument in the region east of Grand Canyon. There are lots of archaeological remains of the people who lived in the Colorado Plateau over the last 12,000 years, but few of them are as spectacular as the pueblos that were built between 1,100 and 1,285 AD. Many, maybe most, were fortresses. Some of these people seemed to be living in fear.

The Citadel ruin at Wupatki is built on the eroded remains of a basalt lava flow.

There has been a mountain of speculation about why the Ancestral Pueblo people and other cultures took such a defensive posture in their architecture. It is well known that most of the Colorado Plateau was abandoned in the late 13th century, and the hypotheses are numerous. There were a series of droughts, including a 25-year-long monster. These was evidence of warfare in a few places. Soils had washed away in many places. There could have been religious or cultural forces in place that caused migrations. It's an interesting issue that will keep archaeologists busy for a long time.

The view of the San Francisco Peaks from the top of the Citadel ruin.

Archaeology played a special part of our summer field studies journey across the Colorado Plateau. Half our students were majors in the subject (or possessed a lot of interest in the subject) who were learning geology. And our geologists were learning archaeology. I've been doing joint trips with our anthropology professors for a decade now, and we find a lot of common scientific ground as we travel through this fascinating landscape.

The hundred room pueblo at Wupatki

Wupatki National Monument preserves structures and sites of numerous ancient cultures, but the most visible were built by the Sinagua people, whose descendants still live in the region (the Hopi, Zuni,  Pima, Tohono O'odham, and Yavapai people). The region was a crossroads of sorts, and direct evidence suggests habitation as early as 500 AD. People lived at the site for 600 years, perhaps never suspecting that they were living on volcanic ground.

That changed in 1085 AD or so when Sunset Crater, a basaltic cinder cone, erupted, sending out lava flows, cinders and ash over a region totaling about 800 square miles (the longest lava flow was 6 miles long). Lava flows covered several villages.

It's possible that some cultural recognition of volcanism existed in the stories and traditions of the people who lived in the path of destruction, but maybe not. Can you imagine the impact of seeing a volcanic eruption in progress for the first time as a people? What kind of stories would be told explaining the phenomenon? Many of the old ruins are built on older volcanic deposits. Did the logical thinkers among the people recognize in a flash the origin of the ground and rock on which their homes were constructed?

In any case, the region was abandoned for a few decades, but settlers came back, finding that the ash had rejuvenated the soils. A gift of the gods? One wonders. They lived and built homes in the region for two more centuries before leaving the land for other places. Although the abandonment was part of a regional pattern, one can wonder if those two centuries included a healthy fear of the fires from down below in the crust?

Sunset Crater, the youngest volcano in the San Francisco Peaks Volcanic Field. It erupted about 1085 AD

The Sinagua people of Wupatki may or may not have known about volcanoes prior to 1085 AD, but in our highly technological society, we understand a great deal about volcanoes, and geology has provided us the tools to figure out the probabilities of future eruptions. Likewise, we are able to calculate to a reasonable degree the probabilities of earthquakes within given time frames (over a 30 year period, for instance). We can calculate flood probabilities before a particular storm arrives.  But that also means we live with a certain amount of fear. This is good in the sense of allowing the society to prepare. But fear can also be manipulated.

I can imagine a shaman or other kind of leader of the Sinagua threatening his or her people with the return of the legendary fire gods of the volcano to achieve some nefarious end. Can we imagine anyone who would be tempted to manipulate scientific knowledge into a fear of volcanoes (can you say "SUPERVOLCANO" nice and loud?) or earthquakes (can you say CASCADIA?) to achieve influence and power?

Source: http://www.cosmostv.org/2014/08/yellowstone-super-volcanoresent-rumors.html (actually, this is good article)

Nah, I'm sure no one would fan the flames of fear in modern society...the internet and other mass media has brought knowledge and wisdom to us all.

Dispatches from the Road: Pictures I Missed Before

Nothing of great consequence, but I got some pictures on our holiday journey that I wished I had a few months ago. Our road took us through the San Francisco Peaks Volcanic Field, which I discussed in my series on the geologic history of the Colorado Plateau. I had a post on the volcanoes, but my photo archives revealed hardly any usable shots of the San Francisco Peaks (I borrowed some photos from the USGS). As we drove from Grand Canyon to Flagstaff on Highway 89, we passed the massive stratovolcano, topped by Humphreys Peak, which at 12,643 feet is the highest point in Arizona. The mountain, seen above, has a massive east-facing basin that may have formed in the same explosive manner as the crater at Mt. St. Helens. Prior to the destruction of the peak, it may have been the highest mountain in the contiguous United States, at something over 16,000 feet.

The meadow in the foreground lies along the entrance road to Sunset Crater National Monument, which preserves one of the youngest volcanic features in Arizona. A look east from the same meadow reveals Sunset Crater itself.

The crater erupted over a period from 1040 to 1100 A.D., and disrupted life for some of the Ancestral Pueblo/Sinagua people who lived in the area at the time. The monument is a marvelous place to see evidence of recent basaltic volcanism, and adjacent Wupatki National Monument is one of the most spectacular places to see evidence of the ancient Sinagua people.

Time Almost Not Beyond Imagining: Recent Volcanism on the Colorado Plateau

Top photo shows the San Francisco Peaks looming over the ancestral Sinagua ruins at Wupatki National Monument near Sunset Peak. Bottom diagram is a digital topographic map of the San Francisco Peaks Volcanic Field from the USGS Fact Sheet 017-01.

Six million years ago, the Colorado River was just beginning to carve the Grand Canyon. The rest of the Colorado Plateau had risen to thousands of feet above sea level, and was being vigorously eroded, but around the edges, other things were happening: the land was falling away, so to speak. The Basin and Range (and the related Rio Grande Rift) were being stretched, and in response the crust split into numerous fault blocks, some bobbing upwards into mountain ranges, and some blocks sinking to form deep basins (the deepest, such as Death Valley, eventually sank below sea level). Such stretching of the crust is a prelude to the breakup of the North American continent. The splitting of the continent is not an instantaneous process; it has been evolving over the last 20-25 million years as convergence was ending on the west coast of the continent, and the San Andreas fault system was slowly expanding.

The stretching and thinning of the crust released the pressure on the underlying mantle rocks, allowing them to partially melt and start rising through the overlying crust. The faults of the Basin and Range provided an easy avenue for magma to reach the surface, and so volcanism has played a prominent part of the landscape visible to us today on the Colorado Plateau. Recent lava flows and volcanoes can be seen in the Zion National Park area, especially near the towns of St. George and Hurricane, and at Mt. Taylor in New Mexico. But two areas of volcanic activity especially stand out: the San Francisco Peaks Volcanic Field in Arizona, and the Jemez Caldera in New Mexico.

The San Francisco Peaks Volcanic Field is an immense region (around 2,000 square miles) of lava flows and cones that is dominated by the edifice of the San Francisco Peaks, a huge stratovolcano reaching 12,633 feet above sea level. The volcanoes started erupting in the west side of the field about 6 million years ago, with later eruptions in a more eastward direction, culminating in the eruption of Sunset Crater just 1,000 years ago, making it the youngest volcanic feature in the state of Arizona. Humans witnessed (and suffered from) the eruption, since part of the flow covered an Anasazi village. The origin of the magma remains an enigma, but the eastward progress of the eruptions is suggestive of a hot spot, but this is by no means settled as an explanation.

The 600-plus cones in the volcanic field include all manner of cinder cones and lava domes, with compositions ranging from dark black basalt to light colored rhyolite. There is but a single stratovolcano, the San Francisco Peaks, but it dominates the landscape for many miles around. It is the prominent peak seen on the horizon from either rim of the Grand Canyon, and is one of the four sacred peaks of the Navajo people. The mountain grew during a period lasting from about a million years to 400,000 years ago.

There is a gigantic east-facing bowl forming the summit of the mountain. For a long time, geologists thought that it formed as a result of slow erosion of the summit of the mountain by way of streams, mass wasting and glaciation, but the eruption of Mt. St. Helens in 1980 gave them a new hypothesis: it may have formed from a giant explosion and subsequent collapse of the summit towards the east. Certainly a comparison of the summit regions of the two volcanoes lends support to the idea (photo of St. Helens by Garry Hayes, summit bowl of San Francisco Peaks courtey of the USGS).

Even more intriguing is the idea that we are looking at what may briefly have been the highest point in the lower 48 states and Hawaii. Projecting the lava flows along the broken edge of the summit ridges upwards produces a former volcanic summit that may have reached as high as 16,000 feet, about a quarter mile higher than Mt. Whitney in California.