The Blue Ridge Mountains are known for having a bluish color when seen from a distance. Trees put the "blue" in Blue Ridge, from the isoprene released into the atmosphere.[3] This contributes to the characteristic haze on the mountains and their perceived color.[4]
Although the term "Blue Ridge" is sometimes applied exclusively to the eastern edge or front range of the Appalachian Mountains, the geological definition of the Blue Ridge province extends westward to the Ridge and Valley area, encompassing the Great Smoky Mountains, the Great Balsams, the Roans, the Blacks, and other mountain ranges. In North Carolina, two lower elevation ranges to the east, referred to as foothills, are also often included as "spurs" of the Blue Ridge: the Brushy Mountains and the South Mountains. In Virginia the Southwest Mountains are an anticlinal range that similarly parallels the Blue Ridge.
The Blue Ridge Mountains as seen from Blowing Rock, North CarolinaThe Blue Ridge near Massies Mill, Nelson County, Virginia
The Blue Ridge contains the highest mountains in eastern North America south of Baffin Island. About 125 peaks exceed 5,000 feet (1,500 m) in elevation.[6] The highest peak in the Blue Ridge (and in the entire Appalachian chain) is Mount Mitchell in North Carolina at 6,684 feet (2,037 m). There are 39 peaks in North Carolina and Tennessee higher than 6,000 feet (1,800 m); by comparison, in the northern portion of the Appalachian chain only New Hampshire's Mount Washington rises above 6,000 feet (1,800 m). Southern Sixers is a term used by peak baggers for this group of mountains.[7]
The Blue Ridge Parkway runs 469 miles (755 km) along crests of the southern Appalachians and links two national parks: Shenandoah and Great Smoky Mountains. In many places along the parkway, there are metamorphic rocks (gneiss) with folded bands of light-and dark-colored minerals, which sometimes look like the folds and swirls in a marble cake.
Most of the rocks that form the Blue Ridge Mountains are ancient graniticcharnockites, metamorphosed volcanic formations, and sedimentary limestone. Recent studies completed by Richard Tollo, a professor and geologist at George Washington University, provide greater insight into the petrologic and geochronologic history of the Blue Ridge basement suites. Modern studies have found that the basement geology of the Blue Ridge is made of compositionally unique gneisses and granitoids, including orthopyroxene-bearing charnockites. Analysis of zircon minerals in the granite completed by John Aleinikoff at the U.S. Geological Survey has provided more detailed emplacement ages.
The northernmost extension of the Blue Ridge Mountains, in northern Maryland
Many of the features found in the Blue Ridge and documented by Tollo and others have confirmed that the rocks exhibit many similar features in other North American Grenville-ageterranes. The lack of a calc-alkaline affinity and zircon ages less than 1.2 billion years old suggest that the Blue Ridge is distinct from the Adirondacks, Green Mountains, and possibly the New York–New Jersey Highlands. The petrologic and geochronologic data suggest that the Blue Ridge basement is a composite orogenic crust that was emplaced during several episodes from a crustal magma source. Field relationships further illustrate that rocks emplaced prior to 1.078–1.064 billion years ago preserve deformational features. Those emplaced post-1.064 billion years ago generally have a massive texture and missed the main episode of Mesoproterozoic compression.[8]
At the time of their emergence, the Blue Ridge were among the highest mountains in the world and reached heights comparable to the much younger Alps. Weathering, erosion, and mass wasting over hundreds of millions of years has resulted in much shorter peaks.[9]
History
The Blue Ridge Mountains, looking especially blue in the background, seen from Lynchburg, Virginia
At the foot of the Blue Ridge, various tribes including the SiouanManahoacs, the Iroquois, and the Shawnee hunted and fished. A German physician-explorer, John Lederer, first reached the crest of the Blue Ridge in 1669 and again the following year; he also recorded the Virginia Siouan name for the Blue Ridge (Ahkonshuck).
At the Treaty of Albany negotiated by Virginia Lieutenant Governor Alexander Spotswood with the Iroquois between 1718 and 1722, the Iroquois ceded lands they had conquered south of the Potomac River and east of the Blue Ridge to the Virginia Colony. This treaty made the Blue Ridge the new demarcation point between the areas and tribes subject to the Six Nations, and those tributaries to the colony. When colonists began to disregard this by crossing the Blue Ridge and settling in the Shenandoah Valley in the 1730s, the Iroquois began to object, finally selling their rights to the valley, on the west side of the Blue Ridge, at the Treaty of Lancaster in 1744.
Flora and fauna
View of Blue Ridge Mountains from Grandfather Mountain in North Carolina
The Blue Ridge Mountains have stunted oak and oak-hickory foresthabitats, which comprise most of the Appalachian slope forests. Flora also includes grass, shrubs, hemlock and mixed-oak pine forests.[10]
While the Blue Ridge range includes the highest summits in the eastern United States, the climate is nevertheless too warm to support an alpine zone, and thus the range lacks the tree line found at lower elevations in the northern half of the Appalachian range. Statistical modelling predicts that the alpine tree line would exist at above 7,985 feet (2434 m) in the climate zone and latitude of the southern Appalachians.[11] The highest parts of the Blue Ridge are generally vegetated in dense Southern Appalachian spruce-fir forests.[citation needed]
^Leighty, Dr. Robert D. (2001). "Blue Ridge Physiographic Province". Contract Report. Defense Advanced Research Projects Agency (DOD) Information Sciences Office. Archived from the original on May 21, 2008. Retrieved December 29, 2007.
^Medina, M.A.; J.C. Reid; R.H. Carpenter (2004). "Physiography of North Carolina"(PDF). North Carolina Geological Survey, Division of Land Resources. Archived(PDF) from the original on December 16, 2007. Retrieved December 29, 2007.
