Shenandoah And Great Smoky Mountains National Parks example essay topic

The Appalachian The Appalachian Mountains The Appalachian mountain system dominates the Eastern United States and separates the Eastern seaboard from the interior with a belt of uplands that extends nearly 1,500 miles from northeastern Alabama to the Canadian border. ; They are old, complex mountains, eroded from much older and greater ranges. The present topography is a result of erosion that has carved the weak rocks away, leaving a skeleton of resistant rocks behind as highlands. Because of this weathering, geologic differences are reflected in topography. In the Appalachians these differences are sharply demarcated and neatly arranged, so that all the major subdivisions except for New England lie in strips parallel to the Atlantic and to one another. The Appalachian mountains were formed due to several collisions between the African, Eurasian and North American Plates.

Africa and North America were joined into one super continent. The collision of these land masses over 1 billion years ago metamorphosed the original rock producing the Pedler gneiss and Old Rag granite which can be observed in the Shenandoah National Park. In late Precambrian time this super continent began to rift apart under the tensional forces producing the Catoctin rift basalts that can be observed in the Shenandoah. As they rifted apart, they created a growing ocean called the proto-Atlantic or Iapetus after the father of Atlas, for whom the Atlantic Ocean is named. Towards the end of the Precambrian, the tensional forces changed to compression and subduction began. Volcanic islands grew as a result of andesitic volcanism associated with the subduction.

With continued subduction and convergence, volcanic islands collided with North America and those rocks were thrust up on the continental margin. Deformation, metamorphism and magmatism accompanied this collision and gave rise to the Taconic Orogeny. Rocks metamorphosed and deformed in this event are seen in the Blue Ridge and Piedmont provinces. This all occured during the Ordovician time, about 425 million years ago. As North American, African, and Europe convergence continued, a small microplate known as the Avalon terrane, collided with North America producing a second phase of deformation, metamorphism and magmatism known as the Acadian Orogeny.

This event had the largest effects in the Northern Appalachians and it's effects are very visible in the Acadia National Park in Maine, but not easily seen in the Shenandoah and Great Smoky Mountain National Park to the south. This all occured during the Devonian time, about 380 million years ago. With continued subduction, finally collision of the African continent with North America occured causing intense folding, which is most pronounced in the Valley and Ridge province, and metamorphism. The European and South American plates were also converging with North America at this time to form a super continent called Pangea. This all occured during the Alleghenian Orogeny during the Pennsylvanian time. Pangea began to break up in Jurassic time about 200 million years ago as the present Atlantic Ocean opened up.

The rifting occured at slightly different locations from the original boundaries between the North American, African, European and South American Plates, leaving behind small crustal pieces of these plates attached to North America. We see these rocks exposed in the Acadia National Park. All of this had finished taking place in Mesozoic time. The Appalachian mountains are classified as a fold and thrust mountain. A fold and thrust mountain is a mountain that develops when two continental plates collide. In places, they produce exceptionally high mountain systems, sometimes two miles or higher in elevation.

Typically, these rocks consist mostly or marine sediment that have been intensely folded, thrust-faulted, and, sometimes, metamorphised and intruded by large plutons. The Appalachians were once connected to Europe, but through continental drift, they have been disconnected. When the Northern Hemisphere's plate boundaries are reconstructed, we find that the Appalachians actually extended to the Caledon ides of of western Europe. The Appalachians width of 400 miles covers what are described as three principal provinces, seperated by major thrust faults. Each province developed at different at a different time and has certain rock formations that are apparently distinct. They were all affected by the same series of mountain building episodes.

West to East, the Valley and Ridge province consists of a thick sequence of relatively unmetemorphosed Paleozoic sediments that were folded and thrust to the northwest by compression from the southeast. The Blue Ridge province includes highly metamorphosed Precambrian and Cambrian crystalline rocks with the highest relief in the Appalachians. These rocks were thrust over rocks of the Valley and Ridge province to the west. Both Shenandoah and Great Smoky Mountains National Parks are located in this province. The Piedmont province consists of metamorphosed Precambrian and Paleozoic sediments and volcanic rocks that were intruded.

There is an additional province called the Appalachian Plateau, which dips gently to the west. It contains a lot of limestone units. There are three major National Parks in the Appalachians, which all have distinct and interesting geological features. Shenandoah National Park was established in 1926 to restore a badly misused area. A dominant feature in this park are shallow angle reverse faults, also known as thrust faults. The Precambrian and Cambrian rocks of the Blue Ridge province were thrust over younger sedimentary rocks of the continental margin.

Movement along these faults is believed to be as large as 150 miles westward. Few good rock outcrops exist in the park due to abundant vegetation and severe weathering due to the humid environment. The precambrian metamorphic and igneous rocks are the dominant rock types exposed in the park. These are the Catoctin metamorphised basalt, the Pedler gneiss and the Old Rag granite. The geology of the Great Smoky Mountains National Park is very similiar to the Shenandoah National Park. The Acadia National Park, which is located along the coast of Maine, has a few major differences than the other two parks I have discussed.

Glaciers covered much of this area during the past million years and glacial erosion has stripped away much of the vegetation and soil to expose abundant rock exposures. This region significantly experienced the Acadian Orogeny during the Devonian time when a "suspect terrane' called the Avalon terrane, lodged itself against northern North America. A suspect terrane is defined as a province with geologic features that sharply contrast with those of nearby provinces. The Avalon terrane which docked itself next to North America during the Acadian orogeny fits this description. Its rocks are very different from those of adjacent regions.

These rocks are exposed throughout the park and consist primarily of metamorphosed sedimentary and volcanic rocks. Abundant igneous activity associated with the Acadian orogeny produced large amounts of dioiritic and granite igneous rock also exposed in the park.