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Folding and the Ozarks

The Appalachian Mountain Range is still the dominant mountain system in the eastern US. It was created by the intense folding of sedimentary rock. In some places, younger rocks were pushed completely over older rock as Africa and North America shifted and slid against one another. The Ozarks and Ouachita Mountain systems west of the Mississippi formed the southwest end of the Appalachian system. More intrusive igneous rock is located in the northeast portion, where the Appalachians continue into New Brunswick and Newfoundland in Canada and across to northern Ireland, Scotland, and Norway (this area was connected to North America over 200 million years ago).

The Appalachians Today

The Appalachians generally stopped growing after the continents separated from one another 200 million years ago. Continuous erosion has now brought most of the peaks down to under 5,000 feet in elevation. Narrow valleys, steep hillsides, and thin soils have resulted in low population densities and has kept cities small. This scenario holds true for the Ozarks and Ouachitas. Metamorphic metallic minerals (especially copper and iron ore) have been largely mined out of the Appalachians, though coal still remains in abundant supply.

The Appalachian Mountains form a wide belt which runs from Newfoundland in the northeast to Alabama in the southwest. The Appalachian Mountains can be divided into three sections: (1) a northeastern section which covers northern Maine and the Maritime Provinces of Canada, (2) a New England Section, (3) and the Appalachian Mountains proper.

The Maritime Provinces and New England Appalachians

The maritime provinces of Canada and northern Maine were also subjected to mountain building processes which involved huge intrusions of igneous rock (known as batholiths). These formations constitute the Central Highlands of New Brunswick and Nova Scotia, as well as pockets of Newfoundland Island. The hard rock underlying this land has experienced considerable scraping and erosion from continental glaciers and resembles the landscapes of the Canadian Shield. The St. Lawrence River and the Gulf of St. Lawrence form a water boundary between the northern Appalachians and the Canadian Shield of Quebec and Labrador.

The New England section of the Appalachians extends north and east of the Hudson into central Maine. Two north-south trending mountains dominate this area, both of which are a mix of folded sedimentary and intrusive igneous rock. Granite (igneous) and marble (metamorphosed limestone) rock are both quarried here. The Green Mountains in the west are lower in elevation. Its peaks have been rounded due to continental glaciers that once covered them. The higher White Mountains include Mount Washington, the tallest peak in the northeastern US at 6,288 feet (in New Hampshire). The uplands of New England drop gently eastward to the sea. Here can be seen lone peaks called monadnocks which are remnants of mountains eroded by continental glaciers.

Even though this part of the Appalachian Mountains is close to the coast, the climate is continental because of the west-to-east flow of air. Thus, cold polar air masses from the Canadian Shield regularly blow across the northern Appalachians region, bringing winter snows all the way to Boston Harbor. The climate is generally one of mild summers and cold winters in the northern portion, with hot summers and cool winters farther to the south.

The Appalachian Mountains Proper

In the south, the Appalachians proper are found. The eastern side of the mountains here are made of ancient Precambrian igneous and metamorphic rocks. On the west, they are made of a new belt formed by the upthrust edge of the carboniferous swamp that covered the interior lowlands of North America 300 million years ago. These old swamp lands form the basis for the rich coal deposits found throughout the Appalachians proper.

Where the Appalachians meet the Atlantic Coastal Plain the old rocks have been severely eroded to form a gently sloping dissected plateau surface known as the Piedmont. The edge of the piedmont is known as the fall line, due to the presence of waterfalls along rivers flowing from the higher inland elevations. The piedmont rises gradually to 1,200-1,500 feet, where it merges with the first chain of wooded mountains, the Blue Ridge Mountains. These mountains reach an elevation of over 6,000 feet in the section known as the Great Smoky Mountains along the North Carolina and Tennessee border. (The Smokies are the highest mountains east of the Rocky Mountains, with the highest peak being Mt. Mitchell at 6,684 ft.) In northern Virginia and Pennsylvania, however, the Blue Ridge Mountains subside, becoming low and discontinuous.

In the west, the mountains are heavily folded in parallel lines known as ridge and valley topography. This corrugated area is 25-80 miles wide. The north-flowing Shenandoah River and the south-flowing Tennessee River run through it. West of the fold zone and above a high scarp face, known as the Allegheny Front in Pennsylvania, lies the plateau section. The two main plateaus are the Allegheny Plateau in Pennsylvania and the Cumberland Plateau of Tennessee, West Virginia, and Kentucky. They generally rise to about 2,000 feet, although the Cumberland Plateau reaches over 4,000 feet in West Virginia. The Allegheny Plateau stretches almost to the Great Lakes and has the richest coal deposits in the US.

Heavy precipitation falls in the high Great Smoky Mountains/Blue Ridge Mountains in the southern portion of the Appalachians proper. A rainshadow area of low precipitation exists in the central portion of the lateral mountain chains. Most of the Appalachians proper, however, experience a hot summer and cool to cold winter.

The Ozarks and Ouachitas

The Ozark Plateau and Ouachita Mountains consist of a group of low mountains sometimes called the interior highlands. The Ozark Plateau is composed of a domed plateau flanked by rocks of the Carboniferous Age. On the southern edge of the plateau are the Boston Mountains, the peaks of which are exposed Precambrian granites. To the south, beyond the Arkansas River, are the Ouachita Mountains, a folded belt that resembles the ridge and valley of the Appalachians. At the highest point, the area does not exceed 2,700 feet. The climate of the Ozarks and Ouachitas is similar to that of the surrounding lowland South. This is in part because they are an east-west trending system, which benefits little from altitudinal zonation and rainshadow impacts.

Earthquakes in the Eastern US

Although earthquakes are more commonly associated with the western US, in fact the strongest earthquakes to ever occur in the US were in the Memphis, Tennessee, and Madrid, Missouri, area in 1811 and 1812. Other devastating quakes have occurred in Charleston, South Carolina, Jamaica Bay (New York City) in the past 100 years. Geologists estimate an 85% probability of a destructive earthquake occurring in the eastern US before the year 2000 (which did not happen), and a near 100% chance of one by the year 2010. Because earthquakes are so infrequent in the East none of the buildings have been constructed to resist tremors, as they have in California.

Date: 2015-02-16; view: 614

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