Editing Appalachian Mountains (section)

==Geology==
{{Main|Geology of the Appalachians}}
Plate tectonics over the period dating back at least 1 billion years led to geological creation of the land that is now the Appalachian Mountain range. The continental movement led to collisions that built mountains and they later pulled apart creating oceans over parts of the continent that are now exposed.<ref>{{Cite journal |last=Keppie |first=J. D. |date=2006 |title=Avalonian terranes of the Appalachian orogen: A review |journal=Geological Society of America Bulletin |volume=129 |issue=9/10 |pages=1195–1208 |doi=10.1130/B31595.1}}</ref>

===Grenville Orogeny and formation of Supercontinent Rodinia===
The first mountain-building tectonic plate collision that initiated the construction of what are today the Appalachians occurred at least a billion years ago when the pre-North American [[craton]] called [[Laurentia]] collided with at least one other craton - [[Amazonian craton|Amazonia]]. All the other cratons of the earth also collided at about this time to form the supercontinent [[Rodinia]] and were surrounded by one single ocean.  (It is possible that the cratons of [[Kalahari craton|Kalahari]], and [[Río de la Plata craton|Rio Plato]], were also part of that early collision since they were present as Rodinia broke up). Mountain-building referred to as the [[Grenville Orogeny]] occurred along the boundaries of the cratons.<ref name="Thomas 2021"/><ref name="auto">{{Cite book |last=Clark |first=Sandra H. B. |url=https://pubs.usgs.gov/gip/birth/birth.pdf |title=Birth of the Mountains: The Geologic Story of the Southern Appalachian Mountains |publisher=United States Geologic Survey |year=1996 |pages=4 }}</ref> The present Appalachian Mountains have at least two areas which are made from rock formations that were formed during this orogeny - the  [[Blue Ridge Mountains]] and the [[Adirondack Mountains|Adirondacks]].
[[File:Grenville extent.gif|thumb|Land added to Laurentia during the Grenville orogeny]]

===Breakup of Rodinia and formation of the Iapetus Ocean===
After the Grenville orogeny, the direction of the continental drift reversed, and the single supercontinent Rodinia began to break up. The mountains formed during the Grenvillian era underwent erosion due to weathering, glaciation, and other natural processes, resulting in the leveling of the landscape. The eroded sediments from these mountains contributed to the formation of sedimentary basins and valleys. For example, in what is now the southern United States, the Ococee Basin was formed. Seawater filled the basin. Rivers from the surrounding countryside carried clay, silt, sand, and gravel to the basin, much as rivers today carry sediment from the midcontinent region to the Gulf of Mexico. The sediment spread out in layers on the basin floor. The basin continued to subside, and over a long period of time, probably millions of years, a great thickness of sediment accumulated.<ref name="auto"/> Eventually, the tectonic forces pulling the two continents apart became so strong that an ocean formed off the eastern coast of the Laurentian margin. This was called the [[Iapetus Ocean]] and was the precursor of the modern Atlantic Ocean. The rocks of the Valley and Ridge province formed over millions of years, in the Iapetus. Shells and other hard parts of ancient marine plants and animals accumulated to form limey deposits that later became limestone. This is the same process by which limestone forms in modern oceans. The weathering of limestone, now exposed at the land surface, produces the lime-rich soils that are so prevalent in the fertile farmland of the Valley and Ridge province.<ref name="auto"/>

During this continental break-up, around 600 million to 560 million years ago, volcanic activity was present along the tectonic margins. There is evidence of this activity in today's Blue Ridge Mountains. [[Mount Rogers]], [[Whitetop Mountain]], and [[Pine Mountain (Appalachian Mountains)|Pine Mountain]] are all the result of volcanic activity that occurred around this time.<ref>{{Cite book |last=Rankin |first=James W. |title=The volcanogenic Mount Rogers Formation and the overlying glaciogenic Konnarock Formation: Two late Proterozoic units in southwestern Virginia |publisher=USGS |year=1993 |doi=10.3133/b2029}}</ref> Evidence of subsurface activity, dikes and sills intruding into the overlying rock, is present in the Blue Ridge as well. For instance, mafic rocks have been found along the Fries Fault in the central Blue Ridge area of Montgomery County, VA.<ref>{{Cite book |last=Kaygi |first=Patti Boyd |title=The Fries Fault near Riner, Virginia: an example of a polydeformed, ductile deformation zone |publisher=VT Works |year=1994}}</ref>

===Taconic Orogeny===
[[File:Taconic orogeny.gif|thumb|Taconic orogeny]]
The Iapetus continued to expand and during that time bacteria, algae, and many species of invertebrates flourished in the oceans, but there were no plants or animals on land. Then, during the middle [[Ordovician Period]] about 500 to 470 million years ago, the motion of the crustal plates changed, and the continents began to move back toward each other. The once-quiet Appalachian passive margin changed to a very active plate boundary when a neighboring Iapetus oceanic plate containing a volcanic arc collided with and began sinking beneath the [[North American craton]]. Volcanoes grew along the continental margin coincident with the initiation of [[subduction]]. Thrust faulting uplifted and warped older sedimentary rock laid down on the passive margin. As the mountains rose, erosion began to wear them down over time. Streams carried rock debris downslope to be deposited in nearby lowlands.<ref name="auto1">{{Cite book |last=Clark |first=Sandra H. B. |url=https://pubs.usgs.gov/gip/birth/birth.pdf |title=Birth of the Mountains: The Geologic Story of the Southern Appalachian Mountains |publisher=United States Geologic Survey |year=1996}}</ref>  The Taconic orogeny ended after about 60 million years, but built much of the land mass that is now New England and southwestward to Pennsylvania.

The Taconic Orogeny was the second of four mountain building plate collisions that contributed to the formation of the Appalachians, culminating in the collision of North America and Africa (see [[Alleghanian orogeny]]).<ref name="usgs">{{Cite web |url=http://geomaps.wr.usgs.gov/parks/province/appalach.html |title=Geologic Provinces of the United States: Appalachian Highlands Province |publisher=USGS |url-status=dead |archive-url=https://web.archive.org/web/20130311111217/http://geomaps.wr.usgs.gov/parks/province/appalach.html |archive-date=March 11, 2013 |access-date=July 19, 2010}}</ref>

===Acadian Orogeny===
The third mountain-building event was the [[Acadian orogeny]] which occurred between 375 and 359 million years ago.<ref>{{Cite journal |last=Hatch |first=N. L. |date=2009 |title=The Acadian orogeny: A review |journal=Geological Society of America Bulletin |volume=121 |issue=5–6 |pages=639–678}}</ref> The Acadian orogeny was caused by a series of collisions of pieces of crust from the Avalonia Terrane, sections broken off from continent of [[Gondwana]], with the North American Plate. The collision initiating this orogeny resulted in the closing of the southern [[Iapetus Ocean]] and the formation of a high mountain belt. After the Acadian collision took place, Gondwana began to retreat from Laurentia with the newly [[Accretion (geology)|accreted]] [[Avalonia]]n [[terrane]]s left behind. As Gondwana moved away, a new ocean opened up, the [[Rheic Ocean]], during the Middle to Late Devonian, and subsequently its closure would result in the formation of the [[Alleghanian orogeny]].

===Alleghenian Orogeny and Supercontinent Pangea===
As the continental plates moved closer together, fragments of oceanic crust, islands, and other continental masses collided with the eastern margin of ancestral North America. By this time, plants had appeared on land, followed by scorpions, insects, and amphibians. The ocean continued to shrink until, about 270 million years ago, the continents that were ancestral to North America and Africa collided during the formation of the [[Pangaea|supercontinent Pangea]].<ref name="auto1"/>

Because [[North America]] and [[Africa]] were once geographically connected, the Appalachians formed part of the same mountain chain as the [[Little Atlas]] in [[Morocco]]. This mountain range, known as the [[Central Pangean Mountains]], extended into [[Scotland]], before the Mesozoic Era opening of the [[Iapetus Ocean]], from the North America/Europe collision (See [[Caledonian orogeny]]).

[[File:Appalachian fault.jpg|thumb|Old [[fault (geology)|fault]] exposed by roadcut near [[Hazleton, Pennsylvania]], along [[Interstate 81 in Pennsylvania|Interstate 81]].]]

By the end of the [[Mesozoic|Mesozoic Era]], the Appalachian Mountains had been eroded to an almost flat plain.<ref name="usgs" /> It was not until the region was uplifted during the [[Cenozoic Era]] that the distinctive topography of the present formed.<ref>{{Cite journal |last1=Poag |first1=C. Wylie |last2=Sevon |first2=William D. |date=September 1989 |title=A record of Appalachian denudation in postrift Mesozoic and Cenozoic sedimentary deposits of the U.S. Middle Atlantic continental margin |journal=Geomorphology |volume=2 |pages=119–157 |bibcode=1989Geomo...2..119P |doi=10.1016/0169-555X(89)90009-3 |number=1–3}}</ref> Uplift [[rejuvenation (river)|rejuvenated]] the streams, which rapidly responded by cutting downward into the ancient bedrock. Some streams flowed along weak layers that define the folds and faults created many millions of years earlier. Other streams [[downcutting|downcut]] so rapidly that they cut right across the resistant folded rocks of the mountain core, carving canyons across rock layers and geologic structures.

===Mineral resources===
[[File:Cliffs above Gauley-27527.jpg|thumb|Cliffs overlooking the [[New River (Kanawha River)|New River]] near [[Gauley Bridge, West Virginia]]]]
The Appalachian Mountains contain major deposits of [[anthracite]] [[coal]] as well as [[bituminous coal]]. In the folded mountains the coal is in metamorphosed form as [[anthracite]], represented by the [[Coal Region]] of [[northeastern Pennsylvania]]. The bituminous coal fields of [[western Pennsylvania]], [[western Maryland]], southeastern Ohio, eastern Kentucky, [[Southwest Virginia|southwestern Virginia]], and West Virginia contain the sedimentary form of coal.<ref name="coal">{{Cite web |url=http://pubs.usgs.gov/pp/p1625c/CHAPTER_A/CHAPTER_A.pdf |title=Executive Summary—Coal Resource Assessment of Selected Coal Beds and Zones in the Northern and Central Appalachian Basin Coal Regions |last=Ruppert |first=Leslie F. |publisher=USGS |url-status=live |archive-url=https://web.archive.org/web/20100715045305/http://pubs.usgs.gov/pp/p1625c/CHAPTER_A/CHAPTER_A.pdf |archive-date=July 15, 2010 |access-date=July 19, 2010}}</ref> The [[mountain top removal]] method of [[coal mining]], in which entire mountain tops are removed, is currently threatening vast areas and ecosystems of the Appalachian Mountain region.<ref name="Palmer et al 2010" /> The surface coal mining that started in the 1940s has significantly impacted the central Appalachian Mountains in [[Kentucky]], [[Tennessee]], Virginia and West Virginia. Early mining methods were unregulated and mined land reclamation research, including [[acid base reaction]], was led by the [[West Virginia University]] in the 1960s and 1970s. West Virginia developed rigorous [[mine reclamation]] standards for state coal mines in the late 1960s. Regulations were introduced by most states to protect the Appalachian Mountains by the late 1960s. Social and political activism brought about the [[Surface Mining Control and Reclamation Act of 1977]].<ref>{{cite book |title=Legislation, Technology and Practice of Mine Land Reclamation |last=Hu |first=Zhenqi |publisher=CRC Press |year=2014 |page=3 |isbn=9781315732138}}</ref>

The [[Drake Well|1859 discovery]] of commercial quantities of [[petroleum]] in the Appalachian Mountains of western Pennsylvania started the modern United States [[petroleum industry]].<ref name="appBasin" /> Recent discoveries of commercial [[natural gas]] deposits in the [[Marcellus Shale]] formation and [[Utica Shale]] formations have once again focused oil industry attention on the Appalachian Basin.

Some plateaus of the Appalachian Mountains contain metallic minerals such as [[iron]] and [[zinc]].<ref>{{cite book |url=http://quarriesandbeyond.org/articles_and_books/min_res_appalachian_region/tc_intro.html |title=Mineral Resources of the Appalachian Region |publisher=USGS |year=1968 |id=Professional Paper 580}}</ref>

===Drainage===
[[File:Eastern North American Paleogeography Middle Devonian.gif|thumb|[[Palaeogeography|Paleogeographic]] reconstruction showing the Appalachian Basin area during the Middle Devonian period<ref name="url">{{Cite web |url=http://jan.ucc.nau.edu/rcb7/nam.html |title=Paleogeography and Geologic Evolution of North America |last=Blakey |first=Ron |website=Global Plate Tectonics and Paleogeography |publisher=Northern Arizona University |url-status=dead |archive-url=https://web.archive.org/web/20080621201253/http://jan.ucc.nau.edu/rcb7/nam.html |archive-date=June 21, 2008 |access-date=July 4, 2008}}</ref>]]
There are many geological issues concerning the rivers and streams of the Appalachians. In spite of the existence of the Great Appalachian Valley, many of the main rivers are transverse to the mountain system axis. The [[drainage divide]] of the Appalachians follows a tortuous course that crosses the mountainous belt just north of the [[New River (Kanawha River)|New River]] in Virginia. South of the New River, rivers head into the Blue Ridge, cross the higher Unakas, receive important tributaries from the Great Valley, and traversing the Cumberland Plateau in spreading gorges ([[water gap]]s), escape by way of the [[Cumberland River]] and the [[Tennessee River]] rivers to the [[Ohio River]] and the Mississippi River, and thence to the [[Gulf of Mexico]]. In the central section, north of the New River, the rivers, rising in or just beyond the Valley Ridges, flow through great gorges to the Great Valley, and then across the Blue Ridge to tidal estuaries penetrating the coastal plain via the Roanoke River, [[James River (Virginia)|James River]], [[Potomac River]], and [[Susquehanna River]].<ref name="EB1911" />

In the northern section the height of land lies on the inland side of the mountainous belt, and thus the main lines of drainage run from north to south, exemplified by the [[Hudson River]].<ref name="EB1911" /> However, the valley through which the Hudson River flows was cut by the gigantic [[glacier]]s of the [[ice age]]s—the same glaciers that deposited their [[terminal moraine]]s in southern New York and formed the east–west [[Long Island]].

[[File:Appleorchardmountain.jpg|thumb|[[Apple Orchard Mountain]] peak in the [[Blue Ridge Mountains]], which stretch from southern [[Pennsylvania]] in the north through [[Georgia (U.S. state)|Georgia]] in the south]]The Appalachian region is generally considered the geographical divide between the [[East Coast of the United States|eastern seaboard]] of the United States and the [[Midwestern United States|Midwest]] region of the country. The [[Eastern Continental Divide]] follows the Appalachian Mountains from Pennsylvania to Georgia.