Brooks Mitchell is an earth science educator and geologist who is currently the Education Coordinator for the Space Science Institute in Boulder, Colorado.
Updated April 18, Featured Video. Cite this Article Format. Mitchell, Brooks. Geology of the Appalachian Mountains. Appalachian Plateau Geology and Landmarks. Geologic Maps of the 50 United States. New York Geological Attractions and Destinations. Rock Provenance by Petrologic Methods. Get to Know 24 Types of Sedimentary Rock. Your Privacy Rights. To change or withdraw your consent choices for ThoughtCo.
At any time, you can update your settings through the "EU Privacy" link at the bottom of any page. These choices will be signaled globally to our partners and will not affect browsing data. We and our partners process data to: Actively scan device characteristics for identification. This regional view shows the striking visual effect of the valley-and-ridge topography of the Appalachian Mountains as viewed from the International Space Station. The image shows more than kilometers miles of this low mountain chain from northeast Pennsylvania top right to southern West Virginia, where a dusting of snow covers a patch of land lower left.
Sunglint reflections reveal details of Chesapeake Bay and the great bend of the Potomac River. The farm-dominated Piedmont Plateau is the light-toned area between the mountains and the bay. The Appalachian Mountains appear striped because the ridges are forested, providing a dense and dark canopy cover, while the valleys are farmed with crops that generally appear as lighter-toned areas. Farmland is even lighter than usual in this image because the fields are fallow after the harvest.
Geologically, the valleys are the softer, more erodible rock layers, much the preferred places for human settlement.
Not only do the larger rivers occupy the valley floors, but the soils are thicker, the slopes are gentler, and the valleys are better protected from winter winds. The rocks that form this valley-and-ridge province, as it is known, are relatively old to million years old and were laid down in horizontal layers when North America was attached to Europe in the ancient supercontinent of Laurasia. During this time Gondwanaland—an ancient supercontinent that included present-day Africa, India, South America, Australia, and Antarctica—was approaching Laurasia under the influence of plate tectonics.
The Appalachian chain is a barrier to east-west travel as it forms a series of alternating ridgelines and valleys oriented in opposition to any road running east-west. Definitions vary on the precise boundaries of the Appalachians. A common variant definition does not include the Adirondack Mountains, which geologically belong to the Grenville Orogeny and have a different geological history to the rest of the Appalachians. The range is mostly located in the United States but extends into southeastern Canada, forming a zone from to mi to km wide, running from the island of Newfoundland 1, mi 2, km southwestward to Central Alabama in the United States.
The range covers parts of the islands of Saint Pierre and Miquelon, which comprise an overseas territory of France. The system is divided into a series of ranges, with the individual mountains averaging around 3, ft m. The highest of the group is Mount Mitchell in North Carolina at 6, feet 2, m , which is the highest point in the United States east of the Mississippi River. The term Appalachian refers to several different regions associated with the mountain range.
Most broadly, it refers to the entire mountain range with its surrounding hills and the dissected plateau region. However, the term is often used more restrictively to refer to regions in the central and southern Appalachian Mountains, usually including areas in the states of Kentucky, Tennessee, Virginia, Maryland, West Virginia, and North Carolina, as well as sometimes extending as far south as northern Georgia and western South Carolina, as far north as Pennsylvania and southern Ohio.
The Ouachita Mountains in Arkansas and Oklahoma were originally part of the Appalachians as well, but became disconnected through geologic history. During the earliest Paleozoic Era, the continent that would later become North America straddled the equator.
During this interval, the region was periodically submerged beneath shallow seas. Thick layers of sediment and carbonate rock were deposited on the shallow sea bottom when the region was submerged. When seas receded, terrestrial sedimentary deposits and erosion dominated. During the middle Ordovician Period about million years ago , a change in plate motions set the stage for the first Paleozoic mountain building event Taconic orogeny in North America.
The once quiet Appalachian passive margin changed to a very active plate boundary when a neighboring oceanic plate, the Iapetus, collided with and began sinking beneath the North American craton. With the creation of this new subduction zone, the early Appalachians were born. Along the continental margin, volcanoes grew, coincident with the initiation of subduction.
Thrust faulting uplifted and warped older sedimentary rock laid down on the passive margin. As mountains rose, erosion began to wear them down. Streams carried rock debris downslope to be deposited in nearby lowlands.
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