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Impact Crater

 

 

 

The location of the Wetumpka Astrobleme —“star-wound”— originated from a cosmic event that occurred some 80 to 83 million years ago. It was confirmed only recently, after more than two years of extensive investigation and deep earth core drilling conducted on site. It is one of the few above-ground impact crater locations in the United states and one of only about six in the entire World. Even more unusual is the fact that the structure is actually exposed (as you can see from the rim evidence in these photographs). Despite the weathering that has occurred through millions of years, the crater walls are still prominent, so the rim was obviously much higher at one time. The projectile of the meteor impact was probably travelling between 10 and 20 miles per second. So this means the impact would have produced winds in excess of 500 miles per hour, and the meteor most likely struck at a 30-45 degree angle as it came from the northeast. They determined that it came from the northeast by the angle at which the rocks are slanted within the impact area which includes the current flow path of the Coosa River. This can be seen looking from both directions on the Bibb Graves Bridge.

Geologists speculate that the shock waves, the damage, and other effects of the impact explosion radiated out from the strike several hundred miles. Debris may have been thrown as far away as the present Gulf of Mexico. Geologists also theorize that the strike area would have been under a shallow sea, perhaps 300 to 400 feet of water, that covered most of southern Alabama at the time of the impact.

It is estimated that the diameter of the meteorite to be 1,100 feet and could have been as much as three to four times larger. Rock samples were obtained for laboratory analysis for evidence of “shocked quartz.” Quoting from an article in The Wetumpka Herald published on July 1, 1999, “Another piece of evidence confirming meteoritic impact was uncovered …the unusual amounts of iridium, an element relatively common in asteroids and meteorites, but relatively uncommon in the Earth’s crust. Iridium, detected in amounts of approximately 200 parts per trillion within Wetumpka drill-core samples, is considered an anomalously high concentration. This discovery is important proof that an asteroid vaporized upon impact, thus contributing some of its iridium atoms to crater-filling rocks. Discovery of iridium abundance at Wetumpka follows the February 1999 announcement of the discovery of impact-produced shocked quartz in the core samples. Shocked quartz grains are found only in impact craters, and their discovery is considered the most important means of proving meteoritic impacts of the past.

One distinctively unique feature is its horseshoe-shaped ridge of rock which is not submerged in water or covered or eroded beyond visibility. In spite of the millions of years of weathering, the crater walls are still prominent with the rim approximately three to four miles wide.

A panoramic view of the highest point on the crater rim at Bald Knob Mountain is visible from routes into town. The Coosa River flows across the western edge of the crater. From the Bibb Graves Bridge one can easily see the upturned rock tilting in the direction of the crater. Outcroppings of dramatically upturned rock formations are visible along US Highway 231.


There is a Crater Impact Commission consisting of six members—three appointed by the City of Wetumpka and three appointed by the Elmore County Commission. They will be holding public hearings regarding the future development and use of this very rare anomaly in our City, including an interpretative center located on Highway 231 in Wetumpka, AL.

 

 

 

 

 

 

Wetumpka Impact Crater Commission: http://www.wetumpkaimpactcratercommission.com/ 
 

Earth Impact Database - Wetumpka: http://www.unb.ca/passc/ImpactDatabase/images/wetumpka.htm

 

Alabama Impact Crater & Science Center Master Plan: http://www.cityofwetumpka.com/Sites/Wetumpka2/Documents/Attractions/Alabama%20Impace%20Crater%20&%20Science%20Center%20Study2.pdf