Dreams of Summer: The Bad Star Strikes! What happened at Canyon Diablo 50,000 Years Ago

It might be heresy for me to say it, but there are some places where the geology appears to be kind of...monotonous. Flatlands covered by soils are sometimes not all that interesting. I can even be accused of thinking this way about my very own home valley, the Great Valley of California. I've spent a long time teaching my students that our valley isn't actually boring at all. It's just that the best parts are beneath the surface.

Just the same, parts of the Colorado Plateau can be a bit monotonous too. The region between Flagstaff and Holbrook is a case in point. There just isn't much to see as you travel east on Interstate 40 except for the San Francisco Peaks Volcanic Field receding in the distance. The sage and grass-covered plains don't offer much in the way of interesting sights. But there is one really big exception. At Canyon Diablo there are some hills visible south of the highway that seem a bit out of place. They aren't high, but there is nothing like them elsewhere in the area.

Disasters happen. Sometimes, the nature of the disaster is predictable, as when one sees a river rising prior to flooding. A volcano that is shaking and producing ash suggests that an evacuation might be smart. We had just left such a place a few hours earlier, at Wupatki and Sunset Crater National Monuments. Sometimes disasters happen, and there's simply no way to be warned.

50,000 years ago, this barren plain was slightly less barren. The region was a savanna/woodland populated by horses, bison, antelope, sloths, and mammoths. They were hunted by American Lions, Sabertooth Cats, Dire Wolves and Cave Bears. The sky lit up, maybe for a moment brighter than the sun. The incoming meteor would not have appeared to move across the sky, because it was headed directly at this spot, at a speed estimated between 28,000-45,000 mph. Maybe the light would have grown in brightness and in size, but there were only a few seconds to respond. And what to do? There was nowhere to run. The chunk of rock was about 160 feet across when it impacted with the surface. The explosion was comparable to a large atomic explosion. The resulting crater was about 3,900 feet (1,200 meters) in diameter, and some 570 feet deep (170 meters). The chunk of iron and nickle was obliterated into small bits (in the early years efforts were made to drill for the large chunk thought to be buried within the crater). The largest piece found so far is the Holsinger Meteorite, which weighs 639 kilograms (1,409 lb).

The Holsinger Meteorite at the Meteor Crater Museum

The word "disaster" has an interesting etymology. It literally translates as "bad star". Meteors may be called falling stars, but they are made of the leftovers from the formation of the Solar System. On the other hand, the raw materials of meteorites, the iron, nickle and other elements, were forged in the core of gigantic stars, so in a sense it is fair to think of a meteorite as a "bad star".

A large impact can be a horrific disaster. A few years back in 2013, astronomers were monitoring an asteroid chunk that was going to make a close pass by Earth, but that same day a different chunk several yards across hit the atmosphere from another direction. It exploded with the strength of a large atomic bomb, shattering thousands of windows in the Russian town of Chelyabinsk. It was about 65 feet (20 meters across). If such a chunk hit the surface near a city, the effects would be incalculable. A large strike in the oceans has the potential to produce destructive tsunamis. A meteorite several miles wide probably caused the extinction of the dinosaurs and around 60% of all species of life known from 65 million years ago.

In the big picture, Meteor Crater was a localized event. It destroyed life over an area of 100 square miles (260 square kilometers) or more. And yet the scale of the hole is hard to appreciate. Look at the white patch in the bottom of the crater in either of the pictures above. The spots are fenced off, and the owners have placed a life-sized astronaut for scale. Can you see the astronaut below?

The crater is privately held, but the owners have done a nice job of preserving the crater and have constructed an extensive museum and viewing area. They are very accommodating for geology field trips if you contact them in advance. For more information about visiting the crater, check out http://www.meteorcrater.com/.

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.