Fall line

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A fall line (or fall zone) is the area where an upland region and a coastal plain meet and is noticeable especially where rivers cross it, with resulting rapids or waterfalls. The uplands are relatively hard crystalline basement rock, and the coastal plain is softer sedimentary rock. [1] A fall line often will recede upstream as a river cuts out the uphill dense material, forming "c"-shaped waterfalls and exposing bedrock shoals. Because of these features, riverboats typically cannot travel any farther inland without portaging, unless locks are built. The rapid change of elevation of the water and resulting energy release make the fall line a good location for water mills, grist mills, and sawmills. Seeking a head of navigation with a ready supply of water power, people have long made settlements where rivers cross a fall line.

Contents

Geography

Diagram showing the Fall Line. USGS figure. Bulletin 426 Fig 2 Fall Line.jpg
Diagram showing the Fall Line. USGS figure.

The slope of rivers crossing fall zones affected settlement patterns. For example, the fall line represents the inland limit of navigation of many rivers. As such, many cities along a fall line grew as a result of demand for transferring people and goods between land-based and water-based transportation at that place. [2]

North American Atlantic Seaboard Fall Line

The Atlantic Seaboard Fall Line, or Fall Zone, is a 1,400-kilometre (900-mile) escarpment where the Piedmont and Atlantic Coastal Plain meet in the eastern United States. [3] Much of the Atlantic Seaboard fall line passes through areas where no evidence of faulting is present.

The fall line marks the geologic boundary of hard metamorphosed terrain—- the product of the Taconic orogeny—- and the sandy, relatively flat outwash plain of the upper continental shelf, formed of unconsolidated Cretaceous and Tertiary sediments. Examples of the Fall Zone include the Potomac River's Little Falls and the rapids in Richmond, Virginia, where the James River falls across a series of rapids down to the tidal estuary of the James River. Columbia, South Carolina, is similar as well with the Congaree River.

Before navigation improvements such as locks, the fall line was often the head of navigation of rivers due to rapids and waterfalls, such as the Little Falls of the Potomac River. Numerous cities were founded at the intersection of rivers and the fall line. U.S. Route 1 links many of the fall line cities.

In the USA, Mid-Atlantic and Southern fall line cities include:

Canada

The Laurentian Upland forms a long scarp line where it meets the Great Lakes–St. Lawrence Lowlands. Along this line numerous rivers have carved falls and canyons (listed east to west):

The River Jacques-Cartier and River Saint-Maurice lack such noticeable feature because they cross the scarp through U-shaped valleys. The falls of the lower Saint-Maurice (as well as those of the River Beauport, in Quebec City) are due to the fluvial terraces of the Saint Lawrence river rather than the Laurentian Scarp.

See also

Related Research Articles

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<span class="mw-page-title-main">Atlantic Seaboard Fall Line</span> Escarpment in the Eastern United States

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<span class="mw-page-title-main">Croche River (La Tuque)</span> River in Quebec, Canada

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The Rivière aux Chevreuils is a tributary of the south shore of the rivière du Chêne which empties on the south shore of the St. Lawrence River, in the administrative region of Chaudière-Appalaches, in Quebec, in Canada.

The Saint-Georges river is a tributary of the south shore of the Chêne River which flows on the south shore of the St. Lawrence River. The Saint-Georges river flows in the municipality of Sainte-Agathe-de-Lotbinière, in Lotbinière Regional County Municipality, in the administrative region of Chaudière-Appalaches, in Quebec, in Canada.

<span class="mw-page-title-main">Bras Saint-Nicolas</span> River in Chaudière-Appalaches, Quebec (Canada)

The Bras Saint-Nicolas is a tributary of the south-eastern bank of the rivière du Sud (Montmagny), which flows north-east to the south bank of the St. Lawrence River.

References

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  2. 1 2 "The Fall Line and major cities of the Eastern U.S."
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  5. 1 2 3 4 5 6 7 Dunkerly, Robert; Boland, Irene (2017). Eutaw Springs. Columbia: The University of South Carolina Press. p. 24. ISBN   9781611177589.
  6. "A Summary of the Geologic History of Delaware". The Delaware Geological Survey. Retrieved 25 January 2017.
  7. "Maryland Geology". Maryland Geological Society. Retrieved 25 January 2017.
  8. 1 2 3 4 "Geology of the Fall Line". Virginia Places. Retrieved 25 January 2017.
  9. 1 2 3 "Fall Line". NCpedia. Retrieved 25 January 2017.
  10. 1 2 3 "Fall Line". The New Georgia Encyclopedia. Retrieved 17 October 2011.
  11. 1 2 3 "Fall Line". Encyclopedia of Alabama. Retrieved 25 January 2017.