About 83 million years ago, a cosmic object (an asteroid or comet estimated to have been about 1,250 feet, or 380 meters, in diameter) struck what is now Elmore County, Alabama, on the eastern side of the city of Wetumpka. All that remains of the meteoritic impact crater formed by the collision is a crescent-shaped ridge of hills rising up to 300 feet above the surrounding river plains. Bald Knob, the highest point on the rim, and other parts of the crater remnant are clearly visible to travelers entering Wetumpka on US Highway 231 and Alabama Highway 14.
The crater structure was first noted in 1969 by a group of geologists from the Geological Survey of Alabama, including team leader Thornton L. Neathery. In 1976 Neathery and his co-workers published a paper proposing that a meteor had created the feature, which they called the Wetumpka astrobleme. Its origin was not proven conclusively until 1999, when a team of scientists, including Neathery and Auburn University geologist David T. King Jr., completed a 630-foot-deep drilling operation at the crater's center. The scientists found that the minerals contained in the subsurface samples revealed evidence of deformation characteristics resulting from high pressure and massive sudden impact. Such minerals are found only in structures formed by cosmic impacts and at nuclear-test sites. In addition to the physical analysis, the material was subjected to geochemical testing at a laboratory in Vienna, Austria, which revealed meteoritic elements such as iridium, cobalt, nickel, and chromium and confirmed their meteoric origin. In 2002 the research team published its results in Earth and Planetary Science Letters and officially established Wetumpka as the 157th known impact crater on Earth.
The Wetumpka impact crater, which is approximately 4.7 miles (7.6 km) wide, formed during a time in geological history when the sea level was much higher than it is today. Much of southern and central Alabama was under the shallow waters of the northern Gulf of Mexico, and the shoreline ran roughly from Tuscaloosa County to northern Elmore County and eastward to northern Russell County. The Wetumpka impact thus occurred about 15 miles (25 km) offshore in water about 100 feet (30 m) deep. The rim is made of hard, crystalline rocks, and the interior area is composed of softer, sedimentary materials. There is also an area of highly disturbed sediments outside the crater's rim on the southern side of the crater that were washed into place by the catastrophic resurgence of sea water forced away from the area by the impact.
The Wetumpka impact was the greatest natural disaster in Alabama history. Energy released by the impact was roughly 175,000 times greater than the nuclear explosion in Hiroshima in 1945. The collision produced a huge earthquake, a tsunami, an atmospheric blast wave (hurricane-force, straight-line winds), and a cascade of falling rocks that would have blasted out of the developing crater bowl. Many thousands of living things, including dinosaurs, other reptiles, and aquatic life, along the Gulf shoreline of Elmore County were decimated by this event. The Wetumpka impact did not have global consequences, however, and is not linked to any global extinction of animals or plants in the geological record.
Wetumpka, which means "rumbling waters" in the Creek language, is an appropriate name for an impact crater formed in sea water. The crater is celebrated annually by the city of Wetumpka, which sponsors lectures and public tours. In 2002, the Alabama Historical Commission erected a roadside historic marker that describes the crater on U.S. Highway 231 in front of the Elmore County Health Department.