America's Volcanic Past -
Virginia

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Volcanic Highlights and Features:
[This list is just a sample of various Virginia volcanic features or events and is by no means inclusive.]

• Virginia
• Virginia Regions
• Virginia's Volcanic Rocks
• Appalachians
• Appomattox Court House
• Blue Ridge Mountains
• Blue Ridge National Parkway
• Great Falls of the Potomac
• Green Springs
• Monticello
• Mount Rogers National Recreation Area
• Old Rag Granite
• Piedmont Province
• Shenandoah National Park
• White Top Mountain

Albermarle County Pillow Basalts:¹
The Catoctin also outcrops in the southeastern Blue Ridge, Albemarle County, shows a pillow structure within the greenstone, implying that these basalts erupted under water.

Catoctin Greenstone:¹
The Catoctin greenstone outcrops in many places along Virginia's Skyline Drive in the northeast Blue Ridge. The rocks contain fractures such as the columnar joints that indicate genesis as a subareal basaltic flow. The Catoctin also outcrops in the southeastern Blue Ridge. Catoctin in Albemarle County shows a pillow structure within the greenstone, implying that these basalts erupted under water.

Charnockite Granite:¹
Charnockite is a type of granite that is widespread in the Virginia Blue Ridge.

Old Rag Granite:¹
A distinctive granite containing alkali feldspar (white) and quartz (blue) is another common rock type in the Virginia Blue Ridge. The Old Rag granite is an example.

Volcanic Rocks of the Blue Ridge Province:¹
The Blue Ridge physiographic province includes the Blue Ridge proper, located immediately southeast of the Valley and Ridge, as well as terrain characterized by lesser ridges and rounded hills that extends as much as 20 miles to the east and south. The Blue Ridge contains the northwesternmost exposures of metamorphic rocks in Virginia, and is physiographically analogous to the Great Smokey Mountains of Tennessee and North Carolina, the Green Mountains of Vermont and Quebec, and the Long Range of Newfoundland. The central portion of the Blue Ridge contains one billion-year-old granites and gneisses that are among the oldest rocks in Virginia. Metamorphosed volcanic and sedimentary rocks overlie the older basement granites and gneisses on the northwest and southeast flanks of the Blue Ridge. These rocks formed on the edge of North America as an ancient ocean basin, "Iapetus", opened to the east. (See more Blue Ridge below)

Volcanic Rocks of the Piedmont Province:¹
The Piedmont of Virginia extends eastward from the Blue Ridge to the Fall Line, where Paleozoic-age and older igneous and metamorphic rocks are covered by unconsolidated sediments of the Atlantic Coastal Plain. The Virginia Piedmont is part of the greater southeastern Piedmont, which extends from northeastern Alabama through Georgia, South Carolina, North Carolina, Virginia, Maryland, and southeastern Pennsylvania. The Piedmont is characterized by deeply weathered, poorly exposed bedrock and a high degree of geological complexity, making it one of the last frontiers of North American regional geology. Geologists compete with beavers to locate bedrock outcrops in stream bottoms. The Piedmont contains a collage of rock associations or terranes that are bounded by northeast-trending regional faults. In the western Piedmont, a volcanic arc terrane known as Chopawamsica is separated from the Blue Ridge by metagraywacke and melange that formed as Chopawamsica moved towards North America (Laurentia) during Cambrian time (about 550-475 million years ago). (See more Piedmont Province below)

Appomattox Court House:⁴
Appomattox Court House, where the Nation reunited in 1865, is located in the Piedmont province. It lies astraddle the Chatham fault on a body of transported rock known as the Smith River allochthon composed of metamorphic schists and gneisses, typical of the Piedmont.

Blue Ridge Mountains:³
Most of the rocks that form the Blue Ridge are ancient granitic and metamorphosed volcanic formations, some exceeding one billion years in age. By comparison, humans have been associated with this land only about 9,000 years.

Blue Ridge in Virginia:⁴
In Virginia, the oldest rocks in the Blue Ridge province are different types of granite which date back over one billion (1,200,000,000) years. Some of the rocks in the Blue Ridge were there before there was even life on Earth! Younger rocks from the Paleozoic era cover the eastern side of the Blue Ridge. The rocks that make up the Blue Ridge have been shoved over the rock layers of its neighbor to the west, the Valley & Ridge province. The rocks were moved to the northwest when (what today is) Africa and North America got sandwiched together, pushing the Blue Ridge on top of the Valley & Ridge along a fault line. By being deformed, older igneous and metamorphic rocks show that the continents crunched together and split apart many times during the Paleozoic. In central and northern Virginia the Blue Ridge mountains rise to elevations over 1,200 meters (4,000 feet). The local relief (difference in height) on the east side of the Blue Ridge is up to 1,000 meters. In the southern Blue Ridge of Virginia, a broad table-like region rises over 500 meters above the Piedmont province. Mount Rogers in the southwestern Virginia Blue Ridge, at 1,746 meters, is the highest peak in Virginia.

Blue Ridge Parkway:²
The Blue Ridge Parkway extends 469 miles along the crests of the Southern Appalachians and links two eastern national parks: Shenandoah and Great Smoky Mountains.

Skyline Drive Columnar Basalt:¹
The Catoctin greenstone outcrops in many places along Virginia's Skyline Drive in the northeast Blue Ridge. The rocks contain fractures such as the columnar joints that indicate genesis as a subareal basaltic flow.

Great Falls of the Potomac, McLean, Virginia:⁷
Located just 15 miles from the Nation's capital, the Great Falls of the Potomac (a name given the area by the first European colonists) is considered the most spectacular natural landmark in the D.C. metropolitan area. Here, the Potomac River builds up speed and force as it falls over a series of steep, jagged rocks and flows through a narrow gorge. This dramatic scene makes Mather Gorge, named after the first director of the National Park Service, a popular site with local residents and tourists from around the world who are visiting the Washington area. The falls consist of cascading rapids and several 20 foot waterfalls with a total 76 foot drop in elevation over a distance of 3500 feet. Arising from a calmer and much broader flow upstream, the Potomac constricts at Great Falls from 2500 feet just above the falls to between 60 and 100 feet along the gorge for over a mile. The Great Falls of the Potomac display the steepest and most spectacular fall line rapids of any eastern river. The geologic history of the falls is an interesting one. After the last ice age, the ocean levels dropped forcing the Potomac river to carve deeper in its path to the sea. The overlying rock was eroded away exposing a much harder, resistant rock formation called the Piedmont. This hard layer is principally made up of highly metamorphic and igneous rock, and may be seen throughout the park. For thousands of years the Potomac river has eroded the bedrock, causing the falls to recede upstream from a point 9 miles downstream near Chain Bridge to its current position at Great Falls. Joint fault plains, natural fissures in the rock substrata where shifting has occurred, exist in many places in the Piedmont Formation between Chain Bridge and the Great Falls. These areas of faulting have loosened the rock, forming areas of weakness. The force of the river has eroded along these areas changing the river's course to its current position. As one walks along the cliff tops, evidence of the ancient river beds can be seen in well-rounded boulders, smoothed surfaces and grooves, and beautifully formed potholes which were once formed on the ancient riverbed. The metamorphic rocks provide jagged rocky surfaces and high-walled cliffs, stark and pristine against the crashing waters of the Potomac at the falls and along Mather Gorge.

Green Springs National Historic Landmark District:
Located on 14,000 acres, Green Springs National Historic Landmark District is located on the western piedmont of central Virginia. It is a natural basin caused by erosion of a volcanic intrusion resulting in particularly fertile soil, which has sustained grassland farming for over 270 years. On this land, man has built homes and dependencies which represent a continuum of rural Virginia vernacular architecture, respectful of location and scene, preserved virtually unaltered in its original context, where the land has been enhanced rather than despoiled by the presence of man. The Green Springs Historic District is six and one-half miles long, four and one-half miles wide, bounded by Route 15 and Route 22 in the western end of Louisa County. Its farms, buildings, and families represent many generations of agricultural, architectural, and social history. In 1841 Cyrus McCormick chose to test his reapers on the wheat fields of Green Springs.

Monticello

Monticello:⁴
Thomas Jefferson's home of Monticello, resting on a hill of 570 million-year-old Catoctin greenstone--the remnants of ancient lava flows. The hill can be easily seen from I-64, just east of Charlottesville.

Sediment and Volcanoes:⁸
During the early part of the expansion of the continental crust (about 750 million years ago), a deep basin, known as the Ocoee basin, formed on the margin of the supercontinent what is now the western Carolinas, eastern Tennessee, and Georgia. Seawater filled the basin. Rivers from the surrounding countryside carried clay, silt, sand, and gravel to the basin, much as rivers today carry sediment from the midcontinent to the Gulf of Mexico. The sediment spread out in layers on basin floor. The basin continued to subside, and over a long of time, probably millions of years, a great thickness of sediment accumulated. The sediments of the Ocoee basin now form the bedrock of the Great Smoky, Unicoi, and Plott Balsam Mountains. At the time that sediments were being deposited and mineral deposits were forming in the Ocoee basin, volcanoes were erupting in areas that are now Virginia, the Carolinas, and Georgia. Lava from some volcanoes flowed in slow-moving sheets like lava from the Hawaiian volcanoes, but other eruptions were explosive, like Mount St. Helens. Although volcanic activity ended hundreds of millions of years ago, rocks that formed from these ancient volcanoes are still visible. Fragments that erupted from ancient volcanoes and minerals that filled holes where gas bubbles had escaped can be seen in some rocks at White Top Mountain in the Mount Rogers National Recreation Area of southern Virginia.

Old Rag Granite

Old Rag Granite:⁶
Old Rag Mountain, Shenandoah National Park, in the Blue Ridge province of Virginia. The craggy rock peak is exposed billion year old granitic gneiss called the Old Rag Granite. Blue Ridge to the west is underlain by Late Proterozoic Catoctin Formation which is comprised of massive 575 million year old basalt metamorphosed to greenstone in the Middle Paleozoic. Blue Ridge forms the provincial boundary with the Great Valley of the Valley and Ridge province.

Virginia Piedmont:⁴
The Piedmont is the largest province in Virginia. To its east is the Fall Zone, which separates the province from the Coastal Plain, and to its west are the mountains of the Blue Ridge province. The Piedmont has gently rolling hills, deeply weathered bedrock, and very little solid rock at the surface. Most rocks at the surface become weathered in the humid climate and buried under a blanket of "rotten rock", called saprolite several meters thick. Most places where you can find outcrops of solid rock are usually in stream valleys where the saprolite has been removed by erosion. The land becomes more hilly the closer you get to the Blue Ridge. Many igneous and metamorphic rocks make up the bedrock of the Piedmont. Most of these rocks range in age from the late Pre-Cambrian to Paleozoic and further west make-up the insides of the ancient Appalachian mountains. Triassic sedimentary and igneous rocks can be found in many rock basins that formed when (what today is) Africa and North America ripped apart to create the Atlantic Ocean 245 million years ago. Many of the rocks in the Piedmont have a complex geologic history, and some may have formed in areas outside of North America. Geologic terranes are groups of rock with very different pasts and are separated from one another by faults. The oldest rocks are ~1100 million years old, and can be found just west of Richmond in a place called the Goochland terrane. Rocks of the Goochland terrane are similar to Pre-Cambrian-age rocks in the Blue Ridge province. Other terranes include Cambrian-Ordovician igneous rocks that are thought to be what's left of an ancient volcanic arc (like the present-day Aleutian Islands in Alaska) that collided with and stuck to the eastern edge of North America. Granitic rocks of Paleozoic age are common, and also formed during this time. Many of the terranes became changed by when the volcanic arc smashed into Virginia, making a lot of problems when scientists try to figure out what happened.

Shenandoah National Park:³
Shenandoah National Park lies astride a beautiful section of the Blue Ridge Mountains, which form the eastern rampart of the Appalachian Mountains between Pennsylvania and Georgia. The Shenandoah River flows through the valley to the west, with Massanutten Mountain, 40 miles long, standing between the river's north and south forks. The rolling Piedmont country lies to the east of the park. Skyline Drive, a 105-mile road that winds along the crest of the mountains through the length of the park, provides vistas of the spectacular landscape to east and west. The oldest rocks in Shenandoah National Park were formed between 1 and 1.2 billion years ago. These granitic rocks can be seen at Old Rag Mountain and Mary's Rock Tunnel. Two other major rock types you can see in the park include basalts, made from individual lava flows, each 30 to 90 feet deep, formed about 570 million years ago; and sedimentary rocks (including sandstone, quartzite and phyllite) formed later.

White Top Mountain:⁹
Although volcanic activity ended hundreds of millions of years ago, rocks that formed from ancient volcanoes can still be seen at White Top Mountain in southern Virginia. Some rocks in this area contain angular fragments that had cooled and solidified, then later broke up, and were engulfed in lava flow. Others contain small, irregular, mineral-filled holes that formed as gases slowly bubbled up through hot lava.

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