Triad Geology

Triad Geology

3:05pm Jan 10, 2014
Pilot Mountain with the Sauratown Mountains in the background.
Molly Davis


From a geologic perspective, we don’t usually think about the North Carolina Piedmont as being very exciting. There are no tall mountains or volcanoes right nearby. But what if I told you that much of the area was once dominated by towering mountains and active volcanoes? In fact most of the piedmont was made up of a series of volcanic islands, or “island Arcs” much like Japan or Indonesia today. These separated themselves from the early continents, eventually collided and were squeezed together as the supercontinent “Pangea” was being formed. This same thing happened up and down most of the East Coast of the United States. Any time you find actual granite exposed at the surface, it was once part of a magma chamber located deep within the earth, likely feeding the region’s volcanos that were formed in these collisions. The Greensboro area has a lot this.

Winston-Salem is a bit different. There is a great deal of black or black and white rock that looks like was layered together (though it wasn’t) and squished up. This kind of rock, called gneiss w  as formed under tremendous pressure in the core of an enormous mountain range that may have rivaled the Himalayas in size. Over hundreds of millions of years the overlying rock has eroded away exposing the core - the rocks you see today. If you set your time machine back and land anywhere in the North Carolina Piedmont, you would materialize deep inside this mountain range.

There’s more amazing geology right in our back yard! Have a look at Pilot Mountain. It’s not a volcano as some people believe. In fact, the white quartzite cap at the top was once beach sand along the shores of an ancient ocean! If you climb to the top you can find sand piles where the material has eroded and dropped to the ground. Eventually some of this sand will make its way into the rivers and to the ocean where it will become beach sand once again. This is true at Hanging Rock, as well.

Here’s something to think about: When you’re standing in the The Dan River Valley, you‘re in a break in the continent, called a “rift valley”. It was formed when the supercontinent Pangea was separating into North America and Africa. There are bunch of these along the East Coast. But the most successful one formed further East and became the Atlantic Ocean. Just think, if it worked out a little differently, everything east of the Dan River valley might have become part of Africa!

After the rift valleys formed, they began to fill up with debris from the eroding Appellations, which may have once stood taller than Mt Everest. Meanwhile, the separating continents continued to stretch, thinning out the crust which cracked in places like an eggshell. Dark colored Magma, rich in Iron, began to squeeze up through the cracks which can be seen all up and down the North American and African coasts. The magma cooled into a rock we call diabase and remained in place as a formation called a dike. As you're floating down the Dan River these dikes cross in front of you, looking like short black walls. This is a great place to see them, because softer sediments of the rift valley have been washed away by the river, leaving the harder diabase exposed. SciWorks Radio will continue weekly at this time, exploring the science happening in North Carolina. In the coming weeks we’ll talk with experts about fracking, 3D printing human organs, and moths who talk to bats. We’ll talk to a local astronaut and we’ll learn how the future safety of football may evolve. We’ll also learn why the diversity of species in our state is unique.

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