Flynn Creek crater facts for kids

Flynn Creek crater is a fascinating impact crater located in Jackson County, Tennessee, USA. It's about 8 kilometers (5 miles) south of Gainesboro. This huge hole in the ground was made around 360 million years ago when a space rock crashed into Earth.

When it first formed, the crater was like a shallow, saucer-shaped bowl. It was about 3.8 kilometers (2.4 miles) wide and around 150 meters (490 feet) deep. The impact created a large hill in the middle, and the rock layers around the edge were bent and broken. There was also a thick layer of broken rocks, called a breccia lens, about 40 meters (130 feet) deep.

The crash broke up and mixed over 2 square kilometers (0.77 square miles) of flat rock layers. These rocks were mostly old types of limestone and dolomite. The impact broke them down to a depth of about 200 meters (660 feet). At least half of these broken rocks were thrown out of the crater. The rocks left inside range from tiny grains to huge chunks, some as big as 100 meters (330 feet) long! Amazingly, rock layers 100 meters (330 feet) below the original crater floor were not disturbed.

What's Inside the Crater?

In the very center of the Flynn Creek crater, you can find a large hill. This hill is made of ancient Ordovician limestone and dolomite layers. These layers were pushed up about 100 meters (330 feet) by the impact. They are now steeply tilted, bent, and broken. Some of these rocks even have special cone-shaped marks called shatter cones. These cones only form when rocks are hit by extreme forces, like a meteorite impact.

The Crater's Edge

The rim, or edge, of the crater also shows signs of the massive impact. The limestone layers here were pushed up about 10 to 50 meters (33 to 164 feet). They are also tightly folded into shapes that look like hills and valleys, all circling the crater walls. In some parts of the rim, the folding squished the rocks inwards by as much as 35%. You can also see many breaks in the rock layers, called faults, which also follow the curve of the crater.

In the southeastern part of the rim, a large section of rock actually slid over another part. This section was pushed out from the crater and lifted about 50 meters (160 feet). It partly covers a sunken block of land, called a graben, which dropped about 100 meters (330 feet) and moved towards the crater. On top of this sunken area, there's a layer of broken rocks. This layer is believed to be what's left of the "ejecta blanket"—all the material that was thrown out of the crater during the impact.

How the Crater Was Preserved

After the crater formed, most of the ejected material was worn away by erosion. However, the part covering the sunken graben remained. Within just a few million years of the impact, the entire crater was covered by mud and shale from an ancient sea called the Chattanooga Sea. This covering helped to preserve the crater incredibly well, making it one of the best-preserved ancient impact structures we know today.

Later, erosion along Flynn Creek slowly uncovered a large part of the crater. The area around the crater is also known for its Karst features, which means it has many caves and sinkholes formed in the limestone. Some of these caves are linked to the impact features. One special cave, Hawkins Impact Cave, is the only known cave to be found in the central uplift of an impact structure.

Flynn Creek Crater Quick Facts

• Size: About 3.8 kilometers (2.4 miles) wide.
• Depth: Around 200 meters (660 feet) deep, not counting the broken rock layer.
• Water: The area likely had about 15 meters (49 feet) of water when the impact happened.
• Broken Rock Layer: The average thickness of the broken rock layer (breccia) is about 40 meters (130 feet).
• Impact Speed: The space rock that hit could have been traveling between 11.2 and 72 kilometers per second (7 to 45 miles per second).
• Formation Time: The initial crater formed in less than 60 seconds!
• Central Hill: The rocks in the central hill were pushed up about 300 meters (980 feet) from their normal position.
• Shape: The crater has a rough polygonal (many-sided) shape.
• Discovery: Tiny sea creatures called conodonts found in the crater's infill show it was a marine (ocean) environment.