84 million years ago, a massive meteorite strikes ancient Alabama

This story is part four of the AL.com series “Ancient Alabama,” examining the natural forces that made Alabama what it is over the past 500 million years, and how those forces still shape the state today.

There are parts of the small city of Wetumpka, Alabama, that make you feel like you’re on another planet.

From Valley Brook Park and the Wetumpka Farmers Market, you can see stones in the Coosa River, jutting out at strange angles over the water. They point toward a massive hillside that looms over the Elmore County Courthouse and the Wind Creek Casino.

A hill like this would be commonplace in north Alabama, but here among the former cotton fields surrounding Montgomery, it stands out like a sore thumb.

From downtown, it’s a short but steep drive up to Bald Knob Road and the top of that hill. I’ve driven many switchback mountain roads, but usually they offer solid ground on at least one side. Bald Knob has places where the ground seems to fall away from you on either side, like you’re driving on the rim of a volcano.

Geologists in Alabama have puzzled over these strange formations since the 1890s, but it took more than 100 years before the geological community accepted that this weird hillside in Wetumpka and these strange rock formations weren’t created by anything found on Earth.

The features around Wetumpka were signs of an astrobleme, or “star wound,” created when a piece of space debris came crashing down to Earth.

Driving back down from the summit at dusk offers a sunset view far better that it has any right to be, as the ridge stands hundreds of feet higher than anything else off to the west, letting you see the flat, anthill countryside of the Black Belt stretching all the way to Mississippi.

On the other side of that hill, you’ll see strange-looking “cliffs” of white rock swirled with veins of deep red as rainwater eats away at the hillside, exposing the earth beneath. Further down in the canyon floor, yellow-orange ridges reach up toward the sky like some miniaturized version of Badlands National Park, but with more pine trees.

As early as 1891, Alabama’s state geologist called the unusual formations in Wetumpka “difficult to explain.” Finally, in 2002, the geological community accepted that this hillside was created by something from the heavens above.

For that 2002 publication, Auburn University geology professor David King and others, drilled down hundreds of feet below the surface to find trace elements left behind from the extraterrestrial object and show evidence of a massive shockwave that could only be explained by a massive meteorite strike.

Research by King and others showed that about 84.5 million years ago, a meteorite -- perhaps a quarter mile in diameter -- hit at about 12 miles per second, or 43,000 miles per hour. The impact blast created enough force to vaporize the invading object, whether a comet or an asteroid, instantly.

“It’s not like a meteorite that falls in someone’s yard today, a chunk of rock that hits the ground,” King said. “This was going way too fast. The physics of it, it just comes apart, molecule by molecule.”

Calamitous impact

The force of that impact has been estimated at about 175,000 times the strength of the Hiroshima bomb, and would have vaporized the Wetumpka meteorite instantly.

This part of Alabama was still underwater at the time, as the great Western Interior Seaway separated the eastern half of North America from the west. King said the impact occurred “tens of miles” offshore, in water that was maybe 100 feet deep.

“It penetrates [the water] and it basically blows up,” King said.

The impact thrust the bedrock hundreds up several hundred feet into the air, poking above the water line.

“The rim would have been sticking out afterwards,” King said. “It would have been like a little circular archipelago, or maybe islands.”

The northeast part of the state would have featured the Appalachian mountains, taller than today, but still weathered significantly from their highest points. The land in between the mountains and the shoreline would have been dominated by tropical jungles, where dinosaurs like Appalachiosaurus roamed.

“When it explodes, some of the elements get trapped in the bedrock and we’ve detected them there,” King said. “It sends a tsunami wave that probably killed hundreds of thousands of dinosaurs and other creatures in the area, marine life, birds, whatever.”

The smoking gun that proved that Wetumpka was hit by a meteorite was shocked quartz, which is created when rocks are exposed to extremely high pressure shock waves at limited temperature. The shock wave sent out by the impact blast damages the quartz in ways that are still visible 84 million years later.

Other than a meteorite strike, there’s no other natural process known to create shocked quartz. Underground nuclear blasts can also do it, but given that the impact was dated to 84.5 million years ago, a meteorite strike seems much more likely.

A meteor is a small piece of an asteroid or comet that breaks off and enters Earth’s atmosphere, sometimes creating a great light show in the sky. When a meteor doesn’t burn up completely on entering the atmosphere and reaches the ground, it’s called a meteorite.

King said it’s not 100 percent certain what crashed into Alabama.

“We know it was an object from space,” King said. “We assume it was a small asteroid, but there’s no way to know whether or not it was a small comet.”

But whatever the source of the Wetumpka meteorite, it left a scar still visible today.

Seeing the crater

There are plenty of locations around Wetumpka where you can still see impacts of the meteorite. A self-guided tour map is available from the Wetumpka Impact Crater Commission, founded by city and county officials to promote tourism to the site.

Bald Knob offers a great view of everything, at an elevation of 587 feet above sea level, compared to just 185 feet in the city itself. Looking west offers a spectacular view of the rest of the countryside -- what this area should look like if not for the meteor. The view to the east shows the crater valley floor, how steep that drop-off is.

From downtown, you can follow U.S. 231 past the casino to Harrogate Springs Road to get inside the bowl of the crater. The first view, across the utility right of way, is of the “cliffs,” stark red and white bands where clay and sand sediment slid back into the crater after the impact.

The actual crater floor, where the meteorite impacted, is far below the surface. Most of the strange rocks on the interior of the crater were blasted up on impact and slid back down on top of the cavity left afterwards.

The driving tour then takes you to the center of the impact site and the eastern rim, and the distinctive rock formations caused only by objects falling from space.

The next big meteorite impact

While the explosion and tsunami undoubtedly devastated the wildlife nearby, King says there’s no evidence that it triggered a widespread extinction event.

That was not the case about 18 million years later, when a much larger meteorite crashed into the Gulf of Mexico near the Yucatan. That was around 65 million years ago, and that impact triggered the mass extinction event that wiped out the dinosaurs.

King said that the Yucatan meteorite is estimated to have been about 10 kilometers in diameter, or about 30 times larger than the Wetumpka meteorite.

Scientists believe that impact killed off the dinosaurs and a whole lot else. Some studies estimate that the meteorite wiped out more than 90 percent of the oceanic plankton of the time, gravely damaging the marine food chain. Scientists estimate that 70 percent or more of all species living at that time were lost.

The science continues

For the 2002 publication proving the impact crater, King drilled nine boreholes down into the crater at depths ranging from 70 to 700 feet.

He did not get all the way to the bedrock where the actual meteorite struck. He estimates that’s probably a full kilometer beneath the surface and said he didn’t have the money or equipment to get that far.

He calls the concept of drilling to the crater impact spot a “million-dollar project” that he has not been able to get funded. His first drilling project was funded to prove that the geology was caused by a meteorite, but King says there’s still more to be learned.

A 2010 study published by King and other collaborators compared the Wetumpka crater to craters on Mars.

Because craters are noticeably different when the object strikes water vs. dry land, studying Alabama’s crater can help scientists determine where oceans once were on Mars.

“There are marine craters similar to Wetumpka on Mars that have been found with Mars imagery,” King said. “There’s kind of a planetary connection because Mars had an ocean at one time, so we studied that a little.”

Next time…

In the next installment of Ancient Alabama, we head back up north and back in time to visit Alabama’s own Grand Canyon at Little River Falls, a majestic site that was once an ancient coral reef.

More Ancient Alabama

• Part One: Ancient Alabama once had mountains higher than Everest
• Part Two: In search of Appalachiosaurus, T-rex’s Alabama cousin
• Part Three: Stunning White Cliffs of Alabama hint at the forces that shaped the Black Belt
• Part Four: 84 million years ago, a massive meteorite strikes ancient Alabama
• Part Five: Alabama’s spectacular Little River Canyon was formed by ancient sea mud
• Part Six: Hunting the largest shark ever in ancient Alabama