Fall line
Afall line(orfall zone) is the area where an upland region and acoastal plainmeet and is noticeable especially where rivers cross it, with resultingrapidsorwaterfalls.The uplands are relatively hardcrystalline basement rock,and thecoastal plainis softersedimentary rock.[1]A fall line often will recede upstream as a river cuts out the uphill dense material, forming "c" -shaped waterfalls and exposing bedrockshoals.Because of these features, riverboats typically cannot travel any farther inland withoutportaging,unlesslocksare built. The rapid change of elevation of the water and resulting energy release make the fall line a good location forwater mills,grist mills,andsawmills.Seeking ahead of navigationwith a ready supply of water power, people have long made settlements where rivers cross a fall line.
Geography
[edit]
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]
 | The examples and perspective in this sectiondeal primarily with the United States and do not represent aworldwide viewof the subject.(November 2016) |
North American Atlantic Seaboard Fall Line
[edit]TheAtlantic Seaboard Fall Line,orFall Zone,is a 1,400-kilometre (900-mile)escarpmentwhere thePiedmontandAtlantic Coastal Plainmeet in the easternUnited States.[3]Much of the Atlantic Seaboard fall line passes through areas where no evidence offaultingis present.
The fall line marks the geologic boundary of hard metamorphosed terrain—- the product of theTaconic orogeny—- and the sandy, relatively flat outwash plain of the upper continental shelf, formed of unconsolidatedCretaceousandTertiarysediments.Examples of the Fall Zone include the Potomac River'sLittle Fallsand the rapids inRichmond, Virginia,where theJames Riverfalls across a series of rapids down to the tidal estuary of the James River.Columbia, South Carolina,is similar as well with theCongaree River.
Before navigation improvements such as locks, the fall line was often thehead of navigationof rivers due to rapids and waterfalls, such as theLittle Fallsof thePotomac River.Numerous cities were founded at the intersection of rivers and the fall line.U.S. Route 1links many of the fall line cities.
In the USA, Mid-Atlantic and Southern fall line cities include:
- Paterson, New Jersey,on thePassaic River[citation needed]
- Trenton, New Jersey,on theDelaware River[3]
- Philadelphia, Pennsylvania,on theSchuylkill River[4][5]
- Wilmington, Delaware,onBrandywine Creek[6]
- Baltimore, Maryland,on theJones Falls,Gunpowder FallsandGwynns Falls[7]
- Washington, D.C.,on thePotomac River[8][5]
- Fredericksburg, Virginia,on theRappahannock River[8]
- Hanover, Virginia,on theNorth Anna River[citation needed]
- Richmond, Virginia,on theJames River[8][5]
- Petersburg, Virginia,on theAppomattox River[8]
- Weldon, North Carolina,andRoanoke Rapids, North Carolina,on theRoanoke River[9]
- Rocky Mount, North Carolina,on theTar River
- Raleigh, North Carolina,on theNeuse River[9][5]
- Fayetteville, North Carolina,on theCape Fear River[9]
- Camden, South Carolina,on theWateree River[5]
- Columbia, South Carolina,on theCongaree River[2][5]
- Augusta, Georgia,on theSavannah River[10][5]
- Milledgeville, Georgia,on theOconee River[10]
- Macon, Georgia,on theOcmulgee River[10]
- Columbus, Georgia,on theChattahoochee River[3]
- Tallassee, Alabama,on theTallapoosa River[11]
- Wetumpka, Alabama,on theCoosa River[11]
- Tuscaloosa, Alabama,on theBlack Warrior River[11]
Canada
[edit]TheLaurentian Uplandforms a long scarp line where it meets theGreat Lakes–St. Lawrence Lowlands.Along this line numerous rivers have carved falls and canyons (listed east to west):
- Saint Anne FallsandCanyon Sainte-Anne(River Sainte-Anne-du-Nord)
- Chaudron à Gaudreault (Rivière aux Chiens)
- Unnamed falls (Rivière du Sault à la Puce)
- Canyon of theRiver Cazeau
- Montmorency Falls(River Montmorency)
- Kabir Kouba Fall(River Saint-Charles)
- Chute Ford (River Sainte-Anne)
- Sainte-Ursule Falls (River Maskinongé)
- Chute à Magnan (Rivière du Loup)
- Chutes Émery and Chute du Moulin Coutu (Rivière Bayonne)
- Les sept chutes (River de L'Assomption)
- Dorwin Falls(River Ouareau)
- Wilson Falls (Rivière du Nord)
- Long Sault, now flooded by theCarillon hydroelectric generating station(Ottawa River)
- TheChaudière Fallsrun over the unrelated Eardley Escarpment of theOttawa-Bonnechere Graben.
TheRiver Jacques-CartierandRiver Saint-Mauricelack such noticeable feature because they cross the scarp throughU-shaped valleys.The falls of the lower Saint-Maurice (as well as those of the River Beauport, inQuebec City) are due to thefluvial terracesof theSaint Lawrence riverrather than the Laurentian Scarp.
See also
[edit]References
[edit]- ^Schneider, Craig W.; Richard B. Searles (1991).Seaweeds of the southeastern United States: Cape Hatteras to Cape Canaveral.Duke University Press. pp. 5–7.ISBN978-0-8223-1101-0.Retrieved17 November2010.
- ^ab"The Fall Line and major cities of the Eastern U.S."
- ^abcFreitag, Bob; Susan Bolton; Frank Westerlund; Julie Clark (2009).Floodplain Management: A New Approach for a New Era.Island Press. p. 77.ISBN978-1-59726-635-2.Retrieved17 November2010.
- ^Shamsi, Nayyar (2006).Encyclopaedia of Political Geography.Anmol Publications. pp. 92–93.ISBN978-81-261-2406-0.Retrieved17 November2010.
- ^abcdefgDunkerly, Robert; Boland, Irene (2017).Eutaw Springs.Columbia: The University of South Carolina Press. p. 24.ISBN9781611177589.
- ^"A Summary of the Geologic History of Delaware".The Delaware Geological Survey.Retrieved25 January2017.
- ^"Maryland Geology".Maryland Geological Society.Retrieved25 January2017.
- ^abcd"Geology of the Fall Line".Virginia Places.Retrieved25 January2017.
- ^abc"Fall Line".NCpedia.Retrieved25 January2017.
- ^abc"Fall Line".The New Georgia Encyclopedia.Retrieved17 October2011.
- ^abc"Fall Line".Encyclopedia of Alabama.Retrieved25 January2017.
External links
[edit]- .Encyclopædia Britannica(11th ed.). 1911.
