Serpent Mound Disturbance
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The Serpent Mound Disturbance is a geological feature in Adams County, Ohio. It is a complex crater 5 miles in diameter. A complex crater is one that features a central uplift, a transition zone, and a ring graben (a trough surrounding the periphery of the crater), as opposed to a simple crater, which is just a bowl-like structure.
The Serpent Mound Effigy is located at the edge of the site, but there is no known connection between the effigy and the disturbance.
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[edit] History and Study
Dr. John Locke discovered the Serpent Mound Disturbance. It was mapped by August Foerste in 1919, by W.H. Bucher in 1920, and by Steve Rydell in 1973.
Two core holes have been drilled into the structure, and seismic lines have been placed across it.
[edit] Origin Theories
A number of theories have been put forth as explanations for its origin, including: crypto-volcanic, tectonic, hydro-tectonic, kimberlite intrusion, impact by meteorite or comet, and multiple deformation events before and after an impact. Geologists from the Ohio Division of Natural Resources Division of Geological Survey and from the University of Glasgow (Scotland) concluded in 2003 that a meteorite strike was responsible for the formation after studying core samples collected at the site in the 1970s. Further analyses of the rock core samples recovered at the site indicated the meteorite impact occurred during the Permian Period, about 248 to 286 million years ago. [3]
http://dnr.ohio.gov/geosurvey/pdf/ri146.pdf
[edit] Features
A number of unique features are found in the Serpent Mound Disturbance.
- The rock layers beneath the site are broken (“breccia”) and fractured (“tipped”). There are also a number of radiating local faults, where rock structures have shifted relative to each other. Faults are common in both volcanic and meteorite impact events.
- Shatter cones have been found within the rock layers. These are formed by seismic waves passing through rock.
- Vertical bedding is evident at the site. Normal rock layers in the Ohio bedrock are horizontal. Where vertical bedding occurs, it is as though the bedrock has been turned up on its side. A plot of bedding dips from one of the core samples shows normal bedding at 2700 feet gradually changing to vertical bedding near the surface. A plot of bedding dips from the other core sample shows a cone-shaped anomalous bedding structure. In this case, the team taking the second core sample drilled through the side of the structure and into the normal bedrock.
- Normally, the deeper the origin of a rock sample, the denser the sample (because of the increase in gravity at depth). At the disturbance site, some samples show a negative gravity anomaly: that is, rocks from deeper within the structure are less dense. In other words, rocks from higher in the structure have been “driven down”.
- Some rock samples exhibit planar deformation features (the crystal lattice within the quartz has been melted, so that it no longer exhibits a crystalline structure). This is the strongest evidence for the extraterrestrial impact origin theory, as planar deformation is unique to meteorite impact. Other melt structures have also been found.
Not all evidence points to a meteorite impact: magnetic anomalies at the site are not of the type that would be expected in a meteorite impact. However, in the case of this conflicting evidence, scientists apply the 90/10 rule: 90% positive evidence vs. 10% negative evidence means that the negative evidence can probably be safely ignored, as geology is not an exact science.
[edit] The Event
- This assumes an extraterrestrial origin.
This event occurred about 230 million years ago. The original meteorite is estimated to have been 100 meters in diameter, and is believed to have been traveling at 15 miles/second when it struck the earth.
Here is how the crater was formed: when the meteorite struck the earth, its speed suddenly changed from 15 miles/second to zero. All of its energy was transferred to the earth. This energy transfer caused the rocks at the site to undergo massive transformation. They broke up, and a great deal of material was blown out, forming the crater. The central uplift was formed by a “rebound” during the energy transfer.
[edit] Sources
- The original version of this article was compiled by Wikipedia editor "Jfcarr" from notes of a public lecture given at Miami University by Greg Schumacher on November 13, 2004.
