Middlesboro
Key facts
- Country
- United States
- Diameter
- 6 km
- Age
- less than about 300 million years
- Location
- 36.62° N, 83.73° W
A round basin about 6 km across in the Appalachian Mountains of south-eastern Kentucky, surrounded by ridges. The town of Middlesboro is built inside it.
Middlesboro, in Bell County, south-eastern Kentucky, in the United States, is one of very few towns built inside an impact crater. The town sits on the floor of a round basin about 6 km across, ringed by the ridges of the Appalachian Mountains, close to the Cumberland Gap.
What it hit. The target was a thick sequence of Pennsylvanian sandstones, shales and coal seams, about 300 million years old. The impact broke and tilted these layers, and in the centre lifted older rocks. Since then, erosion has worn down the surrounding mountains, but the softer, broken rocks of the crater were eroded more easily, leaving a basin.
Proof of impact. Geologists noticed in the mid-twentieth century that the rock layers in the basin were strongly disturbed in a round pattern unlike anything else in the region. Later study found quartz grains with planar deformation features, microscopic sets of planes that form only under shock, which showed that an impact was responsible.
Age. The youngest rocks affected are Pennsylvanian, so the impact happened less than about 300 million years ago. Its exact age is unknown.
Why it matters. Middlesboro shows how an impact can shape a landscape long after the crater itself has eroded, creating a flat basin in the middle of rugged mountains. The impactor is unknown.
Visiting. Signs in the town explain the crater. The basin's shape is best seen from the surrounding ridges.
Did you know?
The town of Middlesboro is built inside an impact crater.
The crater forms a flat basin in the middle of the Appalachian Mountains.
It lies close to the Cumberland Gap, a famous pass through the mountains.