| Origins of the Blue Ridge |
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The story of the Blue Ridge is tied to the history of the Appalachian Mountains and continental drift. About 450-500 million years ago, the ocean to the east of what is now North America began to get smaller as continents moved closer together. The name of this ocean was the Iapetus Ocean; the Atlantic would not form until later. About 280 million years ago, the ocean disappeared as Africa collided with North America. | |
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The energy of collision gave rise to the Appalachian Mountains. The Blue Ridge was formed as a part of this process. It is composed of ancient rocks originally part of the deep "basement" of our continent. They were forced up to 100 miles westward, up over younger rocks along an enormous fault line. | |
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The collision was part of the process creating the super continent Pangea. The Blue Ridge was in the middle of this continent, far from the sea. About 220-180 years ago, Pangea began to break up as the forces of continental drift pulled its parts way from each other. A new ocean, the Atlantic Ocean, began to open up east of the Blue Ridge. | |
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The forces of the collision and the later pulling apart gave the rocks of the Blue Ridge their present structure. It was the slow erosive effects of rivers and streams that carved the land, creating its present appearance. | |
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The Blue Ridge is not all mountains. South of Roanoke it widens into a broad plateau. | |
"Tombstones"
Parkway Milepost 169,
opposite the visitor info station.
The rock in these tombstone formations is harder than the surrounding rock, which eroded away more quickly. They are made of schist, a type of rock originally formed from mud that heat and pressure turned into slate. The forces of the collision later turned the slate into schist. Schist has lots of mica in it. The mica crystals are oriented in a plane perpendicular to the direction of the collision. The mica easily weathers and erodes away along this plane, creating the broad flat surfaces of these tombstone formations. |
Watch continents collide
Here are a couple of web sites that provide information about continental drift and plate tectonics. They also provide animated maps of continental drift. to see the formation of Pangea and its subsequent break up, Click one of the animations for the last 750 million years. to see higher quality plate tectonics animation. You can also download these files for use off-line. |