Atlantic Seaboard fall line | |
|---|---|
 Map showing part of the Eastern Seaboard Fall Line, where the pale-colored coastal plain meets the brightly coloredPiedmont | |
| Location | United States |
| Formed by | New Jersey,Virginia, theCarolinas,Georgia,Alabama, U.S.[1][2][3] |
| Dimensions | |
| • Length | 900 mi (1,400 km)[3] |
TheAtlantic Seaboard Fall Line, orFall Zone, is a 900-mile (1,400 km)escarpment where thePiedmont andAtlantic coastal plain meet in theeastern United States.[3] Much of thefall line passes through areas where no evidence offaulting is present.
Thefall line marks the geologic boundary of hardmetamorphosed terrain—the product of theTaconic orogeny—and the sandy, relatively flatalluvial plain of the uppercontinental shelf, formed of unconsolidatedCretaceous andCenozoicsediments. Examples of fall zone features include thePotomac River's Little Falls and the rapids inRichmond, Virginia, where theJames River falls across a series of rapids down to its tidalestuary.
Before navigation improvements, such aslocks, rapids or waterfalls along the fall line were generally thehead of navigation on rivers and necessitatedportage around them. Numerous cities initially formed along the fall line because of the easy river transportation to seaports, as well as the availability of water power to operate mills and factories, thus bringing together river traffic and industrial labor.U.S. Route 1 andInterstate 95 link many of the fall-line cities.
In 1808,Treasury SecretaryAlbert Gallatin noted the significance of the fall line as an obstacle to improved national communication and commerce between the Atlantic seaboard and the western river systems:[4]
The most prominent, though not perhaps the most insuperable obstacle in the navigation of the Atlantic rivers, consists in their lower falls, which are ascribed to a presumed continuous granite ridge, rising about one hundred and thirty feet above tide water. That ridge from New York toJames River inclusively arrests the ascent of the tide; the falls of every river within that space being precisely at the head of the tide; pursuing thence southwardly a direction nearly parallel to the mountains, it recedes from the sea, leaving in each southern river an extent of good navigation between the tide and the falls. Other falls of less magnitude are found at thegaps of theBlue Ridge, through which the rivers have forced their passage...
Gallatin's observation was sound, though simplified and limited by the knowledge of his time. The limits of the fall line are subject to some dispute. In the north, the fall line is usually understood to have its northern limit atNew Brunswick, New Jersey, a geologic continuation in fact crosses theHackensack andPassaic rivers at the cities of those names, to which navigation was possible. In the south, some such as Gallatin and the USGS,[1] imply its end to be in theCarolinas orGeorgia, and to include only rivers running to the Atlantic; others trace it farther west through Georgia andAlabama as its geologic continuation.[5][6]
Only the principal city of an area is listed below. However, two cities may belong on one river, if the one downstream is at the effective head of navigation and the one upstream at the site of useful water power.
Cities that lie along the Piedmont–Coastal Plain fall line include the following (from north to south):
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{{cite web}}: CS1 maint: url-status (link)[dead link]Lock 31 is there because of the fall line. That's where everything changes right there. That one spot right there is a paradigm shift.
The location of the Wetumpka Astrobleme —"star-wound"— originated from a cosmic event that occurred some 80 to 83 million years ago. It was confirmed only recently, after more than two years of extensive investigation and deep earth core drilling conducted on site. It is one of the few above-ground impact crater locations in the United States and one of only about six in the entire World. Even more unusual is the fact that the structure is actually exposed (as you can see from the rim evidence in these photographs). Despite the weathering that has occurred through millions of years, the crater walls are still prominent, so the rim was obviously much higher at one time. The projectile of the meteor impact was probably travelling between 10 and 20 miles per second. So this means the impact would have produced winds in excess of 500 miles per hour, and the meteor most likely struck at a 30-45 degree angle as it came from the northeast. They determined that it came from the northeast by the angle at which the rocks are slanted within the impact area which includes the current flow path of the Coosa River. This can be seen looking from both directions on the Bibb Graves Bridge. Geologists speculate that the shock waves, the damage, and other effects of the impact explosion radiated out from the strike several hundred miles. Debris may have been thrown as far away as the present Gulf of Mexico. Geologists also theorize that the strike area would have been under a shallow sea, perhaps 300 to 400 feet of water, that covered most of southern Alabama at the time of the impact. It is estimated that the diameter of the meteorite to be 1,100 feet and could have been as much as three to four times larger.
George Ellicott House: A block away is the 1789 George Ellicott House at 24 Frederick Road., which has been saved, moved out of the flood plain, and restored. The Ellicott family settled here along the fall line of the Patapsco River in 1772 and built an innovative, water-powered flour mill