THE GREAT SMOKY MOUNTAINS OVERTHURST
by Dorothy Hussey
Western North Carolina has the largest variety of minerals and flora in the world.
Mountains usually rise from volcanic action or shifting of tectonic plates. Over millions of years, mountains rise, then erode, filling sea troughs. Parts of them even sink into the sea. Sediment builds up as much as six miles thick and becomes too heavy for the crust of the earth to support. A gradual shifting upward creates new mountains which will again erode.
Our mountains have no fossils, which means that they formed before life began, the Precambrian age. They were old when the Alps, Himalayas and Tetons were gestating in the bottom of the sea. The earth is 4.5 billion years old. Grandfather Mountain, elevation 5,160 is 1.8 billion years, the oldest rock formation in the world.
In the beginning this area was a vast plain. On the far east was a five-mile high mountain called Appalachia. On the west was a geosyncline trough, running from Alabama to Canada, connected to the sea on both ends. Troughs are created by upheavals beneath them. This sea is believed to have been 45,000 feet deep; no one can conjecture as to how wide it was. The mountain range eroded very rapidly due to steep sides and lack of vegetation. Boulders and large rocks tumbled across the plain and into the sea where they metamorphosed into conglomerates of quartz and feldspar. Volcanoes poured molten rock into cracks which formed narrow bands of quartz. These can be seen in roadcuts, river banks, gorges and canyons. The last volcano was near Knoxville. The mountains eroded to harder rocks. These went more slowly and became sand, which settled in layers in the sea and hardened into sandstone.
Eventually the mountain had eroded and there was a flat plain. The sea extended across it as the water became clear from mud cast into it for millions of years. Life began. Fossils of this early life can be found across the mountains in eastern Tennessee. We have collected fossils of crinoids, trilobites, worms, sponges, snails, pectines, brachiopods and others. For millions of years the sea animals multiplied, changed forms, died and cast their dead bodies to the bottom of the sea. They changed into lime which hardened into limestone. Pick up a piece of limestone out of the driveway, observe with a hand lens. Often one, can see small fossils, "fish houses" as a four old friend of mine calls them.
Four hundred million years ago the Paleozoic era dawned, a period of mountain making. The Blue Ridge Mountains, which include the Black Mountains and the Great Smoky Mountains were aborning. Slowly they formed and then erupted in giant upheavals. They moved at least one hundred miles northwest from their site in the sea. Plate Tectonics pushed them in twists and turns, buckles, folds, loops, ribbon-like waves, and all sorts of convolutions which are evident in rock formations today. They compressed to about half their original size as they settled on the top of the limestone bed, reversing the usual way mountains form. Most come up from the depths formed from eroded material. This is called THE GREAT SMOKY MOUNTAIN OVERTHURST. Stand on a mountain top and observe the twists, turns and loops the mountains took as they settled. It sometimes appears that a giant threw them out like pickup sticks. They run in all directions.
Our Precambrian rocks are as they formed originally as they were never ground down and reformed. Also in the days of Panagea, when the world was all connected, this area was attached to France. High mountains there eroded and cast their stones on what is now our area. The mountains were originally five miles high; they eroded to their present height and are now slowly eroding. Minerals landed and stayed instead of going into the sea. The Eastern side was mostly sandstone which washed into the Piedmont, filling rifts and creating fertile plains. The Triassic era of 200 million years ago filled the rift valleys, similar to those in Africa, with mud and shale which turned into slate. The rifts were caused by volcanic activity in the depths of the ocean.
On the west of the new range, rocks were harder and eroded more slowly, creating deep gorges, canyons and tall waterfalls. Cades Cove is a prime example. Now a part of the Smoky Mountain National Park, it is preserved as a monument to the hardy pioneers who settled and prospered there. Nantahala Gorge has limestone deposits which metamorphosed into marble. Hot Springs and the Mills River Valley have deposits of limestone. Some of these "windows" were created by faults. There are many, including the Oconoluftee near Cades Cove, the Greenbrier at the foot of Mt. LeConte. The most notable is the Brevard fault which starts in Georgia, runs through Brevard, the Mills River plains and is most evident in the Mitchell, Avery and Yancey area with their vast areas of giant pegmatite dikes of feldspar, quartz, mica and many related minerals. One mine there has 54 different minerals. Faults appear as if a giant knife sliced the earth, rearranged it, and put it back after tumbling.
Coves were created when streams cut down to limestone; hollows appeared as the limestone was washed out.
The Cambrian era brought traces of plant life as algae crept out of the sea and turned into fungi. By the Traissic era, life became abundant; new species developed and the mountains were covered.
The Pleistocene era of a million years ago brought the Ice Ages, which lasted about half a million years. A recent New York Times article states that ocean drilling off the coast of Labrador reveals six layers of gravel which indicates six different Ice Ages. Drilling off the coast of France at 13,000 feet reveals gravel from Canada at six layers also. Ice two miles high piled up in the Hudson Bay area.
Warming trends caused the ice near the earth to melt. Huge glaciers broke loose and traveled over land and dumped into the ocean, scouring everything in their path. Their melting caused floods. The ocean rose 350 feet each time. Ensuring floods dumped minerals and seeds of plants into our area. With each cold spell, plants were damaged. Many didn't survive, but there finally evolved plants which could survive all sorts of climatic conditions. More than half of our trees and many of our other plants originated in Canada. Botanical studies have shown that a large diversity of plants growing thickly survive stresses better than sparsely planted areas. For every 1,000 feet of elevation, it is equal to going 300 miles north. Vegetation on lower levels is often different from that at higher elevations. Some plants and some minerals are found in only one location. The rare rubies and sapphires of Cowee Valley are found in small gravel under large river-washed rocks about three feet underground. The mother lode has never been found. Did they wash down during one of the meltdowns, the last of which occurred about 10,000 to 20,000 years ago?
Thousands of rockhounds come to this area each year. Information on collecting can be had from members of S.A.M.S., area rock shops, rock shows, the Franklin Mineral Museum or the Mineral Museum on the Parkway at Gillespie Gap.
Reprinted from Mountain Mineral Monthly, Vol.63 Number 5, May 1994. Used by permission.