About the Watershed

Part 2: Geology of the Chesapeake Bay Watershed

Part II. Geology of the Chesapeake Bay Watershed

Geologists divide the land into regions that are similar in topography and geology, two factors that affect the types of soils, flora, fauna, stream patterns, climate, and even land use.
Five different physiographic provinces compose the Bay watershed, and each makes its own contribution to the state of the Bay.
1. While often considered mountainous, the Appalachian region is actually an elevated plateau that has been heavily cut by rivers. Around 280 million years ago, the region was a marshy sea filled with horsetail ferns. As the landscape changed, these ferns were compressed and now form the coal seams that run throughout the mountains. Not surprisingly, coal mining was a major industry in this area. The Appalachian Plateau has many forests and, of all the provinces in the Chesapeake Bay watershed, gets the greatest amount of rainfall each year.
2. The Ridge and Valley province is formed by a band of mountains and high plateaus that are slightly lower in elevation than the Appalachian region. Sedimentary rocks underlay the changing topography. The deep limestone soils make this region extremely fertile for farm fields and add to the buffering capacity of local waterways.
3. The Blue Ridge region consists of a narrow line of low mountains with ancient hard rocks, making it the most rugged of the provinces. Throughout the Blue Ridge there is a variety of soils and vegetation.
4. The Piedmont is a rolling, hilly terrain dotted with many dairy farms. The Piedmont's fertile, yet erodable, soil overlays hard and resistant crystalline rocks. The type of rock under the soil can subdivide the Plateau. In the eastern part of the Piedmont are highly metamorphosed sedimentary rocks and igneous rocks of volcanic origin; in the western part are moderately to slightly metamorphosed igneous rocks.
5. The youngest land of all forms the Coastal Plain. Its generally flat surface makes flooding a recurring problem. Vegetation is primarily oak-associated, and the soil is composed of weak sands and clays. To the west of the Bay and before the Fall Line, the Plain is higher in elevation than on the eastern shore of the Bay, which results in the distinction between the Upper Coastal Plain in the west and the Lower Coastal Plain in the east.
There are processes and forces that cause the earth to change.
1. The water cycle causes watersheds to form through many years of water running over the land.
2. Weathering and erosion are processes that cause watersheds to change.
3. Scientists are studying the influence of the Chesapeake Bay bolide on the geological and hydrological processes of the coastal plain.
Bay shores have undergone constant modification by erosion, transport, and deposition of sediments.
1. Erosion is the wearing away or disintegration of earth material (soil and rocks) by the physical force of moving wind and water. As water or wind moves across the earth's surface, particles are loosened and become mobile.
2. The amount and speed (velocity) of the water influences the rate of erosion. The faster and larger amounts of water mean greater and faster erosion.
3. Erosion begins the process of sediment transport.
4. Vegetation, such as trees and grass, limit the amount of erosion that takes place.
5. Sediments are loose particles of clay, silt, sand, and other substances suspended in the water. Sediment eventually settles to the bottom (deposition) after it has been transported through a water body.
6. During the process of erosion and sedimentation, areas of strong relief, like peninsulas and headlands, are eroded and smoothed by currents and tides, and the materials are deposited in other parts of the Bay. Sediments may be deposited in channels.
7. Sediments, carried by the river currents, also are left at the margins of the Bay and major tributaries, resulting in broad, flat deposits of mud and silt.

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Resources

"The Chesapeake Bay Bolide Impact: A New View of Coastal Plain Evolution." U.S. Geological Survey. <http://marine.usgs.gov/fact-sheets/fs49-98/>.

The Chesapeake Bay Bolide: Modern Consequences of an Ancient Cataclysm. U.S. Geological Survey. <http://woodshole.er.usgs.gov/epubs/bolide/>.

Color Landform Atlas of the United States: Virginia. Johns Hopkins University Applied Physics Laboratory. <http://fermi.jhuapl.edu/states/va_0.html>.

Geology of the Chesapeake. Chesapeake Bay Program. <http://www.chesapeakebay.net/ecointr.htm>.

The Geology of Virginia. College of William and Mary. <http://web.wm.edu/geology/virginia/>.

Virginia Places: The Natural Setting. <http://www.virginiaplaces.org/>.

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