In some places the folding was so sharp that the strata were torn apart along great fractures, called faults. There are probably hundreds of such breaks in the rocks of the park. They can be seen in the cliff of Alum Cave where thin quartzite layers in slate have been buckled into S-shaped folds and torn apart. But nowhere in this area is there a large fault displayed as well as in road-side exposures on Tennessee State Highway No. 73, about two and a half miles southeast of Townsend, in Tuckaleechee Cove.1 Here the dark colored slates of the mountains rest on top of blue-grey limestone. The limestone is known to be younger than the slate. The cove is everywhere underlain by limestone but around its margin the old slate is found resting on top of the younger rock. The old mountain rocks must have been shoved up and over the younger valley rocks along a great fault. Geologists have estimated the displacement on the fault to be as much as 35 miles. Erosion has cut through the overthrust mass leaving Tuckaleechee Cove as a window through which the structure of rocks beneath the mountains can be seen. No man knows the cause of these great deforming forces, but when they were spent the area became solid land subject to slow but repeated uplifts and continuous erosion.
The visitor from his vantage point looks out over the panorama of the Great Smoky Mountains; the clouds of the past have cleared away; below he sees the tortuous channel of Little River, the cascading waters of Roaring Fork, the sharp cleft of West Prong, the Oconaluftee, the Cataloochee, and a hundred more rivers, streams, and brooks. Running water, the sculptor of the mountains, is at work, grinding with the sand and gravel in the stream bed, cutting valleys ever deeper. If it were not for repeated uplifts of the land, these streams long since would have reduced the entire area to a lowland. If it were not for erosion, the area would be a high plateau. Erosion has dug its deep trenches through which land waste is carried back toward the sea. The Mississippi delta can be thought of as the other half of the Great Smokies.
Erosion Has Dug Its Deep Trenches
The erosional part of the story starts when the rain first falls on the ground, on mountain top and valley walls. Part of the water soaks into the ground, following cracks and crevices, later to emerge as mountain springs, but in its underground course this water has effected an alteration of the rocks. At Alum Cave, on one of the trails to Mount LeConte, a white to yellow powder fills crevices in slate, deposited there by ground water. This material is mainly of sulphates of aluminum, iron, and magnesium. Veins of white quartz in rocks along the road from Newfound Gap to Forney Ridge likewise have been deposited by ground water in a past age. Here it is clearly seen that seeping water both precipitates and dissolves minerals. Rock cracks have been wedged open, partly by frost, partly by growing tree roots, and these cracks are filled with spongy "rotten" rock. From the hard firm rock at the base of these road cuts, gradations can be found into the loose, friable soils above.
All rocks exposed to the weather are thus loosened and altered, but all are not equally susceptible. Hard quartzite is extremely resistant to weathering and thus areas underlain by this rock make prominent ridges and high peaks, like Forney Ridge and Clingmans Done. The slates of the area form lower but sharper peaks, such as the Chimneys and Charlies Bunion. Limestone, the most soluble of all common rocks, has come to occupy the lowest ground and is found only in the coves, as near Townsend, Tennessee. The form and position of most of the mountains in the park are actually a reflection of the character of underlying rocks.
Once time foundation rocks have become loosened by weathering, they start their relentless downward journey to the sea. True enough, erosion in a heavily, forested park is slow --- slow by the human clock. Does not the ancient spruce deny that the mountain slopes are being washed away? It is slow when compared even to the life span of forest trees. But every year literally millions of tons of soil and rock are carried down the slopes, some by sudden landslides (they scar the sides of Mount LeConte), some by slow hillside creep.
The Great Smoky Mountains National Park is young, one of the youngest of the park system, but the mountains themselves are old, older than the hills. The keenest visitor will see from his vantage point more than a three-dimensional panorama; he will see a fourth dimension of time and a kaleidoscopic change of scene that starts "millions of years ago."
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regional_review/vol5-2-3c.htm Date: 04-Jul-2002 |