"Where the Star Fell"
- A panoramic view of the highest point on the crater rim at Bald Knob 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 rocks tilting in the direction of the crater.
- Outcroppings of dramatically upturned rock formations are visible along U.S. Highway 231.
What is the Wetumpka Impact Crater?
Wetumpka, Alabama, sits right on the bull’s eye of the greatest natural disaster in Alabama’s history. The hills just east of Downtown are the eroded remains of a five mile wide meteor Crater that was blasted into the bedrock of Elmore County. The mighty blast occurred near the end of the Age of the Dinosaurs, about 83 million years ago. All around the circular pattern of hills that make up the remaining rim of the crater, the hard rocks of the Piedmont are bent sharply up and pointing toward the center of the impact. The normally horizontal layers of more recent surface rocks are mixed in and around the crater suggesting an incredible explosion that would have destroyed all life for a radius of about forty miles.
How was it discovered?
Geologically speaking, something is wrong with the vaguely circular patch of hills located immediately south and east of Wetumpka. Normally in this area, the soft sedimentary rocks of the Costal Plain smoothly overlap the harder and older metamorphic rocks of the Piedmont, but at Wetumpka, this is not the case. In the crater area, rocks of more than two hundred million years difference in age are intermixed. At Bald Knob, where communication towers overlook Wetumpka, a curved ridge of very old metamorphic rock protrudes seven hundred feet above its normal level through jumbled layers of much younger rocks. Below the surface, the entire area is surrounded by concentric rings of fractures and zones of shattered rock. Nowhere else along the 2,250 mile border of the Piedmont does anything similar exist.
In 1891, State Geologist Eugene Allen Smith noted the unusual nature of the Wetumpka area, and for many years the area was marked on geological maps as “structurally disturbed”.
In 1972, Geological Survey of Alabama Geologist Tony Neathery was heading a team that was making detailed geologic maps of Elmore County. They had been mapping for several months, but as they approached Wetumpka, they started finding rock layers that were bent at dramatically different angles and directions than other rocks in the area. As they measured and mapped, it became clear that all these features were pointing toward the hills east of Wetumpka. When they looked at these hills, the rocks in the center seemed chaotically disturbed and intermixed, very unlike the evenly horizontal rocks surrounding the area.
In 1976, they published their finding, calling the feature an Astrobleme, literally, a “star wound”. For a number of years, this conclusion was greeted with skepticism by most geologist. During 1998 two wells were drilled into the bedrock and core samples were extracted for testing. Geologist hoped to find materials proving the “star wound” theory. The research team was headed by Dr. David T. King Jr. Professor of Geology, Auburn University. The researchers indeed found the core contained shocked quartz, which can only be formed by an enormous explosion such as a large meteor impact would cause. Dr. Peter Schultz , a Brown University authority on impact craters visited the site in 1999 and affirmed the previous findings. Christian Koeberl Institute of Geochemistry, University of Vienna, an international expert on impact craters also examined the evidence and confirmed the presence of shocked quartz and other minerals that would definitely confirm the site as an impact crater. In the fall of 2002 the scientist published the evidence and established the site as an internationally recognized impact crater. It is believed that at the time of the impact the area was covered by a shallow sea of up to 100 feet in depth, making this the best preserved marine impact crater in the world.
How big was it?
As a rule of thumb, a hypervelocity projectile causes a crater of about twenty times it’s diameter. Given the diameter of the Wetumpka crater and using this formula, the meteorite is estimated to have had a diameter of about 1000 feet. Since no fragments of the meteorite have been recovered (most of it probably vaporized upon impact), the composition of the object is not known, but since stony meteorites are far more common than iron meteorites, the former would seem to be the best guess. To give one some idea of how large this object was, the Wetumpka meteorite is said to have been large enough to fill the entire bowl of Jordan-Hare Stadium at Auburn University.
The enormity of the Wetumpka explosion is hard to comprehend. The impact of a large object traveling at 40,000 miles per hour would cause an explosion that would dwarf even the largest thermonuclear weapons.
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