Virginia Physical Geography

1. Virginia Physical Geography

2. The Physiographic Provinces of Virginia • Virginia has had a long, complex geologic history, over 1.1 billion years • Events that have led to the formation of a rich diversity of rocks, and events that have folded, faulted and rearranged those rocks in complex patterns. • A physiographic province is a landform region, areas divided according to similar terrain that has been shaped by a common geologic history. • Geographers recognize more than 20 physiographic provinces in North America; five of these are in the state of Virginia.

3. The Physiographic Provinces of Virginia • Each province is characterized overall by its elevation, relief, lithology, and geologic structure. Because of the region’s history of rock formation, deformation, and erosion, specific types of landforms or other geologic features may be associated with a given province.

4. The Physiographic Provinces of Virginia

5. Coastal Plain • The Coastal Plain is a flat area underlain by young, unconsolidated sediments. • Includes all of Virginia East of the Fall Line. • The Fall Line is where Rivers cross from the hard igneous and metamorphic rocks of the Piedmont onto the soft roundest rocks in Virginia. • Deposits of sand, silt and clay including marine fossils deposited by rivers. • Layers of sediment were produced by erosion of the Appalachian Mountains and then deposited on the Coastal Plain.

6. Coastal Plain • The tilted beds of the Coastal Plain extend offshore some 50 to 75 miles to the edge of the North American continent. • During the ice ages of the Pleistocene sea level was lowered, exposing the shelf. Streams flowed across the shelf and carved their valleys into it. One such large valley became Chesapeake Bay when sea levels rose again and flooded the shelf

7. Coastal Plain

8. Piedmont • The Piedmont is an area of rolling hills underlain by mostly ancient igneous and metamorphic rocks. • Igneous rocks are the roots of volcanoes formed during an ancient episode of subduction that occurred before the formation of the Appalachian Mountains. • The Piedmont is underlain by metamorphic rocks of various origins that were folded during the Paleozoic as the North American and African plates converged. Later, in the Mesozoic, it was affected by rifting as Pangaea broke apart and the Atlantic Ocean formed.

9. Piedmont • Largest physiographic province. • Bounded on the east by the Fall Zone, and on the west by the mountains of the Blue Ridge. • Rolling topography, deeply weathered bedrock and rocks are strongly weathered. • Rocks are generally buried under a thick (2-20m) blanket of saprolite. ( a chemically weathered rock) • Topography is more rugged closer to the Blue Ridge.

10. Piedmont

11. Blue Ridge • The Blue Ridge is a high ridge of crystalline rock separating the Piedmont from the Valley and Ridge Province. • The billion-year old igneous and metamorphic rocks of the Blue Ridge are the oldest in the state. • The Blue Ridge province experienced mountain building during the late Neoproterozoic era (750-700Ma). • In central and northern Virginia, the 570 million year old basalts are over sedimentary rock. • Some metamorphism of these rocks occurred during the formation of the Appalachian Mountains.

12. Blue Ridge • The Blue Ridge is composed of complexly folded and faulted igneous (granitic) and metamorphic rocks. These rocks date to the PreCambrian and Paleozoic and represent parts of the basement rock of the North American continent. • When Africa and North America converged during the Paleozoic, these rocks were thrust upward and many miles westward over younger rock materials.

13. Blue Ridge

14. Valley and Ridge • Long parallel ridges and valleys of sedimentary rock which were folded and faulted, and eroded differently. • 540 million years old sandstones are overlain by carbonates that make up a region of limestone and dolomite. • The folding and faulting of the sedimentary rocks occurred during a collision between Africa and North America. • The collision, which occurred in the late Paleozoic, produced the Appalachian Mountains. • Carbonates were deposited in a shallow tropical ocean along the southeast edge of North America. • Carbonates in the Shenandoah Valley create the correct environment for caves and sinkholes (KarstTopography)

15. Valley and Ridge

16. Appalachian Plateau • The Appalachian Plateau has rugged irregular topography and is underlain by ancient, flat-lying sedimentary rocks. • Large folds of rock found in the Valley and Ridge become smaller folds and flat-lying rocks in the Plateau. • Some parts of the Plateau are relatively flat, and some are hilly and rugged. • The area is actually a series of plateaus separated by faults. The upper layers of the Plateau are rich in mineral resources like coal, natural gas, and petroleum.

17. Appalachian Plateau

18. Watersheds of Virginia • Virginia is drained by three watersheds • The Chesapeake Bay watershed which drain the Northern and Eastern portion of the state This includes The James, Rappahannock, Potomac, & York • The North Carolina Sounds drain the south central part of the state include the Chowan, and Roanoke • The Mississippi River drains the western part of the state includes the New and Big sandy Rivers

19. Watersheds of Virginia • Virginia Watersheds