The Appalachian Mountains constitute the oldest mountain system in North America. Lying in the Northeast of the United States, they form a long belt of ranges and ridges, valleys, plateaus and tableland. They extends for 2,600 km (1,616 miles) in a southwest-northeast direction, from 33° north latitude to 49° N lat. The width of this orographic system varies from 300 km (186 miles) to 500 km (311 miles), The main ranges of the Appalachians are the Blue Ridge Mountains, White Mountains, Adirondacks, and Green Mountains. The Appalachian Plateau should also be noted. Their altitude ranges from 1,300 to 1,600 m, with the highest peak being Mount Mitchell, which is 2,037 m (6,683 feet) high.
The rivers of the Appalachians run through deep valleys. The flow is abundant all year round, providing considerable reserves for hydro-power AC generation. The largest rivers are the Connecticut, Hudson, Susquehanna, and Tennessee. They overflow their banks frequently because of melting snow in the spring and heavy rainfall in the summer. The major rivers of the northern Appalachians are navigable. As they fall from the eastern edge of the Piedmont, most of the rivers form rapids and waterfalls (the so-called fall line), which are used in part for power production.
Climate
The weather of the Appalachian Mountains is modified by the influence of the Atlantic Ocean and especially of the warm ocean current of Gulf of Mexico (or America). It is temperate in the north and subtropical in the south. The average temperature in January ranges from - 12°C in the north to 8°C in the south; in July the average ranges from 18°C to 26°C. Annual precipitation is from 1,000 to 1,300 mm. In the winter there are heavy frosts in the upper zone of the mountains, and much snow falls. The valleys are drier and warmer. The summers are humid and cloudy; rainfall is abundant, especially on the western slopes. The clearest and sunniest weather comes at the end of summer and beginning of autumn.
Geological History
The Appalachians were uplifted on the site of a geosynclinal system which developed actively in the Paleozoic era on a late Precambrian folded foundation. Millions of years later, the mountains were leveled during the Jurassic Paleocene period. Mountains reappeared again in the Neocene-Anthropogenic period, when the territory of the modern Appalachians underwent a domed uplift, which resulted in the vigorous breakup of the surface and the formation of the modern terrain. The ranges consist of folded rocks and boulders and are divided by intermontane erosional valleys and basins.
The northern Appalachians border on the Canadian Shield in the northwest, along a huge fault (the Logan line). They lack frontal sag and consist of a narrow belt of lower Paleozoic sedimentary deposits in the northwest and a wider belt of igneous, intrusional magmatites and metamor-phic rock in the southeast. The main tectonic periods for the northern Appalachians were the Taconic (at the end of the Ordovician) and the Acadian (at the end of the Devonian). During the Carboniferous-Permian period intermontane sag developed in the interior, filled mainly with continental deposits, first coal-bearing and then red in color.
During the Anthropogenic period, the northern partion of the Appalachians underwent glaciation, while the southern part remained in a temperate (mild) and humid climate. As a result, forests of broad-leaved and evergreen trees were able to survive there and subsequently to spread over a large part of the Appalachians. By structure and development the Appalachians are divided into the northern and southern regions (with the borderline approximately at the latitude of New York City).
 |
| Above, a map of North America showing the Appalachian Mountains. |