Using Cereal Bowls and Car Crashes to Understand Virginia Geology

Virginia has grown in size over the last 2 billion years. Volcanoes spewed lava onto the surface, oceans deposited sediments, continental collisions added clumps of land, and sediments eroded from uplands to form new land at the edge of the waters (or underneath the water). We also shrank: continental collisions pushed rocks over each other and folded up Virginia like an accordion, and erosion has washed away the land particle by particle.

The process by which the landmass has expanded/contracted is fascinating, but geology terminology can be as challenging as computer manuals. Here's a different way to grasp the formation of Virginia's rocks and ridges:

Imagine you have a bowl of milk in front of you. Add Cheerios, so you have one clump floating in milk on one edge of the bowl.

Watch some Cheerios dissolve and sink into the milk. Then add another clump of cereal - Rice Krispies, this time - on the other edge.

Swirl the milk a little with your spoon, and watch the two clumps collide together.

Swirl the milk again, and see that the clumps separate... but some Cheerios drift away with the Rice Krispies, while some Rice Crispies stay behind with the Cheerios lump.

That's the basic process, and it affected the entire eastern coast of North America. The crystalline bedrock underneath the more-recent limestone in Florida was once part of Africa, for example. That bedrock was part of Gondwana (the African plate), before it smashed into Laurentia (the North American plate) to form Pangea. When the continents split up, the Florida chunk of the African plate was left behind, attached to North America.¹

Now put on your thinking cap and follow the links below.

• The Grenville Event and Virginia Geology
• The Orogeny Zones and Virginia Geology
• The Rest of the Story About Virginia Geology

(Whew, did you look at all three? Long description, lots of words... and it's only a short, not-exactly-perfect abbreviated version. Considering that you covered 1.8 billion years in a few minutes, that's a pretty good compression ratio.)

References

Great North Mountain (Shenandoah County)