Asheville Natural History
Geology
Asheville is located 2134 feet (650 meters) above sea level on a moderate-height plateau formed by the Great Valley of the Appalachian Mountains. Among the oldest mountain ranges in the world, the Appalachians are actually two parallel chains, the Alleghenies and the Blue Ridge. The dual ranges form a substantial feature of the eastern United States and Canada from Maine to Quebec. The geological process of mountain-building which created these ancient highlands is a fascinating story.
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Map of the Great Appalachian
Valley (Click to Enlarge) |
Beginning in the late Silurian period (Cayugan epoch) around 420 million years ago, Western North Carolina was an utterly different world. The eastern seaboard of the North American craton (tectonic plate) was merely a narrow chain of windswept hills separating the deep Iapetus Ocean from shallow inland seas covering the modern midwestern states. On the extreme eastern boundary of these hills, small rivers tumbled rapidly downstream into the ocean, carving primordial river channels destined to dominate these regions for the ages. Hundreds of miles further east, the volcanic Avalonia island chain was washed by the roaring waves of the Iapetus Ocean. These islands moved incrementally and unstoppably closer to the North Armerican craton across the millennia, eventually impacting the larger landmass with enormous force. By 370 million years ago, the late Devonian period (Chautauquan epoch), this momentum had created the towering Allegheny peaks and supporting Allegheny plateau. The process also buoyed interior regions of the craton, raising the modern midwest from the shallow depths.
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Map of regional
mineral composition (Click
to Enlarge) |
The most dramatic changes were yet to come--by the middle Carboniferous period (Mississippian epoch) a behemoth landmass of continental proportions was destined to smash the comparably-sized North America. Around 320 million years ago, the continent known as Gondwana (comprising prehistoric Africa and Europe), was rapidly approaching North America--and closing the Iapetus Ocean in consequence. As Gondwana crushed against the North American craton, massive lifting forces were once again released, tossing up still-higher Blue Ridge peaks which then rivaled the modern Himalayas. This collision signaled the creation of a single supercontinent dubbed Pangaea ("all-lands") by geologists. Lands once drowned beneath miles of ocean were thrown upward, older rocks were twisted and metamorphosed, and rivers changed course forever. This geological wreck was complete by the late Permian period (Ochoan epoch) around 250 million years before the present.
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Map of regional
mineral resources (Click
to Enlarge) |
These great collisions, known as the Alleghenian Orogeny, were complete, but the Appalachian Mountains were still unrecognizable. Another 250 million years of erosion--by forces of wind, rivers, and glaciers--would be required to shape the ancient knobs and horns familiar to modern visitors. The high-altitude plateau created between the Alleghenies and Blue Ridge would have been the roof of the ancient world--much like modern Tibet, and the embryonic rivers which drained this region would trace meandering paths toward the newly-created Atlantic Ocean. Others would later fall westward, toward a great gulf forming over modern Mississippi and Tennessee. Millennium after millennium, aeon after aeon, the constant force of water and wind reduced these mountains to a fraction of their former stature. Rivers grew in scale as they carved increasingly deep gorges. The Great Valley of the Appalachians formed, continuous across more than 1500 miles (2500 kilometers) of territory. Here beside the highest remaining pinnacles, astride the eastern continental divide, the first human inhabitants of Western North Carolina began a powerfully mystical relationship with the geography.