Meteor Crater at Serpent Mound

Meteor Crater at Serpent Mound

by Michael Earl Patton

Indians built one of the largest mounds in the shape of an animal in the world, inside an ancient large meteor crater about an hour east of I-275. Many people have heard of Serpent Mound, the mysterious earthen mound built centuries ago. Far fewer have heard that it is inside a crater that was formed by a meteor that struck about 300 million years ago. The crater itself is hard to see partly because it is so big – about 5 miles across. It is also badly eroded and woods often prevent one from seeing landscape that far away. I was at Serpent Mound this past August 20 during its annual “Archaeology Fair” where I got a chance to see the Mound and the small museum at the site, talk to some very knowledgeable collectors of Indian artifacts that can be found in this area, and listen to a couple wonderful talks by experts. One of the experts was Keith A. Milan of Ohio University, who has studied the meteor crater for years. But first, a little bit about the Serpent Mound itself.
Although Serpent Mound may have been an important site during Indian times, today it is fairly remote from major roads and cities. I think the easiest way to get there is to take Ohio 32 east to Ohio 41, which goes to Peebles, Ohio. There is a sign on Ohio 32 alerting visitors that this is the way to Serpent Mound. Drive through Peebles and turn left onto Ohio 73 at the next town, Locust Grove. The entrance to the historical site is a few miles on the north (right) side of the road.
When Serpent Mound was built and what Indians built it is debated back and forth, with proposed construction dates ranging from about 300 B.C. to 1070 A.D. c_usersmichaelearlpattonpicturesserpent-mound-schematic

Likewise we do not know why it was built or how it was used. There are no burials in the mound, so possibly it was used for ceremonial purposes. We do not know how it was used because the site was abandoned by the time settlers of European descent arrived in the area. The Indians who were in the area were probably not direct descendants of those who built the mound. And above all, the population of Indians in what became the United States appears to have been decimated due to some great calamity shortly before the arrival of European settlers, probably due to smallpox and other diseases brought by the first explorers.

Because of its size and that the ground slopes down by its tail and its head, it is impossible to obtain a photograph of the entire serpent from the ground or even from the observation tower. Visitors are asked not to walk on the mound, but there is path encircling it.
There is a small museum at the site which explains a little about the culture and daily life of the Indians who built the mound. The museum itself is little more than a single room, but worthwhile and the attendant is helpful. A painting in the museum shows a reconstruction of an Indian village. Dr. William Kennedy of the Dayton Society of Natural History was another of the interesting speakers at the archaeology fair. He talked about trying to reconstruct how such a village looked when there are virtually no historical records. He especially talked about thatching the roofs, which today is almost a lost art. We know the Indians in this area used thatch, and even the type of grass used, due in part to an accidental survival of a mud wasp nest. The nest was built in the thatch, which later caught fire and baked the nest to a kind of low-grade ceramic. An imprint of the thatching was found on the nest, and from that archaeologists could show that the Indians used a type of prairie grass that was once common in the area. That was the easy part to figure out. How to properly thatch a roof and what it probably looked like was much harder.

Dr. Keith Milam gave a wonderful talk about the meteor crater, and how long it took for scientists to realize that it was indeed a meteor crater. Geologists in the mid-20th century could see that it looked like a meteor crater – like the Moon has in abundance – but it was a big conceptual step to realize that such craters could be here on Earth, too. The first theory was that it was some kind of ancient volcano, and indeed there were bits of molten glass found, but in general it did not look like a typical volcano. So it was called a “crypto-volcano,” that is, a volcano but a somewhat secret one. When no volcanic rock could be found, there was a new theory of the crater being the result of a huge explosion of natural gas escaping from deep inside the earth. In fact, I still have a brochure from my first visit to Serpent Mound in the 1980s which says it is known as a crypto-explosive structure.
Now it is known for certain that it is the result of a meteor impact, probably about 300 million years ago. Not only are the limestone rock layers buckled and fractured, but geologists have found “shock cones.” These are rock formations that are only produced during intense compressive stress such as in a nuclear explosion or large meteor impact. The shock cones were found in a small peak near the center of the crater, the peak itself being the result of the rock being pushed down by the meteor and then springing back up. Similar peaks can be seen in some of the larger craters on the Moon.

I have shown the apparent size of the crater as about 5 miles across, which is what most sources use. Dr. Milam explained why he thinks it could possibly be twice as large, based on comparisons of the central peak with the overall crater size on the Moon and other bodies in the Solar System. And there are other geological features that far out which may have been shaped by the meteor impact. Extensive erosion makes the work of deciphering all of this difficult. In fact, some scientists do not even call the remains a crater but an “astrobleme.” This is a rather poetic name which literally means “star wound.” But rather than use a word which almost no one knows what it means, and which one has little chance to use elsewhere, I will continue to call it a crater.
At this point we do not know what hit. Dr. Milam, in his Guide to the Serpent Mound Impact Structure, South-Central Ohio, gives a couple possibilities. One is a comet traveling at 31 miles/second, another is an asteroid traveling at 11 miles/second, both about a half-mile in diameter and impacting the Earth at an angle of 45 degrees. The resulting explosion would have been over 2 million times that of the atomic blast at Hiroshima. He cautions that these are only two of the many possibilities. I bought the guide at the museum gift shop. Although it is only 40 pages and cost $20 (Dr. Milam said even at that price he doesn’t get any royalties), for me it was worth it as the guide contains a wealth of technical information, clear photographs, and charts.

I thoroughly enjoyed my day at the Serpent Mound Archaeology Fair. The presenters and exhibiters were all very knowledgeable and enthusiastic about their subjects. It was an example of what good science education can be. I will certainly be back for the fair next year if at all possible.