THE GEOLOGIC AND GEOMORPHIC HISTORY OF
THE APPALACHIAN FALL LINE IN SOUTH CAROLINA
By Alicia Fischer
What is a Fall Line?
• Geomorphologic unconformity
• A high, crystalline area and a sedimentary coast
• Waterfalls and/or rapids
• Lack of knowledge
The Fall Line and SC
• The state most influenced by the fall line is South Carolina
• Divides SC in half (Columbia)
• Key role in the formation of the state
Characteristics of the Fall Line
• Spans 135 miles across SC
• The boundary between the Piedmont and the Coastal Plain
• Geologically – is made of bedrock
• Geomorphically – the last appearance of bedrock downstream
• Decrease in elevation from erosion (Piedmont vs Coastal Plain)
• Reliefs up to 300 feet in a short distance
Characteristics of the Fall Line (cont.)
• Quick deep drops disrupt river flow
• Rivers downcut to reach the low Coastal Plain
• High river gradients
• Rough character with rapids, gorges, and waterfalls
• Fluvial erosion (Piedmont) and deposition (Coastal Plain)
Geologic/Geomorphic History of SC: Pre-Cambrian
• Lava World
• 1.2 billion years ago, the first rocks created in what will become South Carolina
• The Grenville Orogeny created the eastern U.S. (SC’s Blue Ridge)
Geologic/Geomorphic History of SC: Paleozoic
• Appalachian Orogeny: most important in SC’s formation
• Alleghanian orogeny formed the Appalachian Mountain
• Rapid uplift and deformation in Blue Ridge (crystalline)
• Half of present-day SC formed during the Alleghanian
Orogeny (Piedmont)
Geologic/Geomorphic History of SC: Mesozoic
• Reinvigorated Grenville and Appalachian materials
• Fault-prone rift basins (erosion)
• Reversed rivers to east (drainage divide)
• Waves of erosion deteriorated Appalachian peaks
• Rivers deposit sediment to Mesozoic shoreline (Coastal Plain)
Geologic/Geomorphic History of SC: Cenozoic
• Sediment continually deposited by gravity and fluvial processes
• Epeirogeny across the Blue Ridge and Piedmont (erosion)
• Spans the Coastal Plain past Mesozoic shoreline (120 miles)
Geologic/Geomorphic History of the Fall Line
• Resistant crystalline Blue Ridge (31 meters per million years)
• Piedmont metasedimentary peneplain (16 meters per million years)
• Flat sedimentary Coastal Plain (depositional area)
• Fall line lies between Piedmont and Coastal Plain
• Made of bedrock and was the old Mesozoic shoreline
Fall Line Formational Hypothesis #1:Faulting
• Numerous faults lie in the fall line
• Small localized faults exist throughout SC
• Crosscut South Carolinian geological terrain
• Faulting exists only in a few sections of the fall line
• False Hypothesis
Fall Line Formational Hypothesis #2:Coastal Emergence/Erosion
• Coastal Plain once extended over Piedmont
• Rivers did not erode the Coastal Plain
• Regional disruptions created its hilly topography
• Through-flowing rivers caused Coastal Plain’s erosion
• Restricted to the coast and east of the Piedmont
Fall Line Formational Hypothesis #2:Coastal Emergence/Erosion (cont.)
• Research shows this coverage was too overstated
• Drainage patterns in some locations support this hypothesis
• Upland – dendritic
• Coastal Plain materials 40 km above the fall line
Fall Line Formational Hypothesis #3:Peneplain intersection and unconformity
• Two ancient peneplains crosscut
• The fall line is Piedmont’s stripped face
• Only Piedmont existed (uplifted and tilted into Atlantic)
• Deposition and extension of Coastal Plain on Piedmont
• Rivers flowed from the Piedmont to the Coastal Plain
• The erosional contact exposed bedrock
Fall Line Formational Hypothesis #3:Peneplain intersection & unconformity (cont.)
• Deep drilling into the Coastal Plain exposed the underlying Piedmont
• Coastal Plain depth extends from 0 feet to over 4,000 feet
• Hypotheses 2 and 3 explain fall line’s origin
Figure 11-4, South Carolina “Fall Line ”
Relocation and Possible Disappearance
• (1) Fall line bedrock erodes between 6 and 9 meters per million years
• (2) Upland gravels above the fall line
• (3) Gradients show the fall line is stable
• Shifting plates and erosion/deposition in several million years (move FL)
• Next million years, the fall line should remain stable
The fall line’s significance
• Historically, the fall line was important in navigation and settlement
• First noticed when traveling by boat
• Colonized area to control trade and transportation (Columbia)
• Potential for hydrologic power and irrigation from fall line’s rivers
• Farms and SC’s economy
Pictures Cited• http://www.virginiaplaces.org/regions/fallshape.html
• Snipes et al., 1993
• https://pangaeablues.wordpress.com/author/pangaeablues/
• https://www.pinterest.com/xadams2/precambrian-hadean-4600-3800-miljoen-v-chr/
• http://bullet-magnet.deviantart.com/art/Planet-Icarus-Erebosian-Eon-48325388
• http://paristampablog.com/tag/paris-bassin/
• http://www.rci.rutgers.edu/~schlisch/103web/NJcontext/ENAhistory.html
• http://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Earthquakes-and-Faults
• http://en.wikipedia.org/wiki/Fall_line
• http://www.postandcourier.com/article/20150411/PC1002/150419855/1022/stand-strong-for-sc-coast
• Odum et al., 2013
• http://www.georgiaencyclopedia.org/blog/2013/08/13/rolling-line
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