Hi cboerner,
Thank you for a very interesting question.
The Appalachian are a complex mix of mountains formed by a series of
continental collisions that took place over a period of more than 1
billion years. They are among the oldest mountains on Earth and are
divided into parallel chains that include the Allegheny, the Blue
Ridge and Catskill Mountains. The highest peaks in this Mountain Range
are located in the Great Smoky Mountains National Park (North Carolina
and Tennessee).
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http://www.jamestown-ri.info/geological_history.htm
(Scroll to middle of page)
"This collision was one of several that formed a supercontinent,
Pangaea about 306 million years ago.
For more than 100 million years most of the world's land was united.
Jamestown was located thousands of miles from the ocean, deep within
that huge supercontinent. This was the time when dinosaurs appeared.
The layers of shale and coal that are common in the Narraganset Bay
area were formed during this period.
About 200 million years ago, Pangaea broke up. The Atlantic Ocean
formed and slowly widened.
(http://www.jamestown-ri.info/atlantic.htm - Scroll to THE ATLANTIC
COASTAL PLAIN AND CONTINENTAL SHELF EVOLVE)
As the Appalachians eroded, land on both sides of the mountain chain
was covered with sediment. To the east and south, the layers of
sediment formed the coastal plain and the (now underwater) continental
shelf.
During the past 75,000 years, Jamestown was visited by glaciers at
least twice. They gouged out channels in the Narragansett Basin and
left deposits of rocks and soil throughout the area.
The last glaciers left the area about 12,000 years ago.
At that time, sea level was hundreds of feet lower than today. As
additional glaciers melted around the world, the sea rose.
Vegetation and animals that had been driven south, returned to the
barren-post glacial area.
Humans arrived. They were driven from coastal areas and river valleys
to higher elevations as the rising sea covered the continental shelf
and eventually filled Narragansett Bay."
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Geologic History of the Appalachian Mountains
http://www.appalachiantales.com/geologic_history.htm
"As dinosaurs rose during the Triassic and Jurassic Periods, Pangaea
began to break up and the Appalachians began to erode once again. By
the beginning of the Jurassic, nearly 200 million years ago, the
continents had begun moving toward their current configuration with
the Atlantic Ocean in between. Two hundred million years of wind,
water, and ice has eroded the Appalachian mountains to about half of
their original height."
(see image)
"Now the movement of continents was not the only major geologic event
in the history of the Appalachians. Several glaciers have covered
parts of the Northern Appalachians over the last three million years.
Glaciers are large moving sheets of ice. The last glaciation is the
one we know the most about since its marks still remain on the land.
The Wisconsin glacier (so-named because it started in present-day
Wisconsin) began about 18,000 years ago and reached as far south as
New York's Long Island before retreating about 10,000 years ago. This
glacier was more than a mile thick in places so you can imagine that
the land underneath was compressed significantly under the weight.
The ice carved valleys, streams, rivers, and lakes, rounded mountains
and pushed the eroded sediments hundreds of miles to the south."
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Geological History of Jamestown, Rhode Island - Building the Northern
Appalachian Mountains and New England
http://www.jamestown-ri.info/northern_appalachians.htm
Scroll to 3/4 down the page: About 220 Million Years Ago:
Rifting Creates the Atlantic Ocean
"By the time North America began to pull away from Africa, about 220
million years ago, weathering had greatly reduced the size of the huge
mountains that had been created in the Alleghenian Orogeny. Land that
had been compressed and metamorphosed by the energy of collision was
now stretched, cracked and rearranged as the land masses separated.
The (Relatively) Recent Past:
Glaciations and Rising Seas Reshape the Coast
The most recent changes to the Appalachian mountains, and all of New
England, have been driven by erosion and glaciations, rather than
orogeny."
(Please scroll through the rest of article to the bottom of the page
for more information to present day - with images.)
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http://wrgis.wr.usgs.gov/docs/usgsnps/province/appalach.html
"The breaking of a supercontinent
Pangea began to break up about 220 million years ago, in the Early
Mesozoic Era (Late Triassic Period). As Pangea rifted apart a new
passive tectonic margin was born and the forces that created the
Appalachian, Ouachita, and Marathon Mountains were stilled. Weathering
and erosion prevailed, and the mountains began to wear away.
Old mountains, young topography
By the end of the Mesozoic Era, the Appalachian Mountains had been
eroded to an almost flat plain. It was not until the region was
uplifted during the Cenozoic Era that the distinctive topography of
the present formed. Uplift 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 downcut so rapidly that they
cut right across the resistant folded rocks of the mountain core,
carving canyons across rock layers and geologic structures."
See image from NASA.
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http://www.themoonlitroad.com/tailypo/tailypo_cbg002.asp
"The Appalachian Mountains are a narrow and extensive mountain system
that parallels the eastern coast of North America for approximately
1,212 miles. Formed about 250 million years ago, it is one of the
oldest mountain systems on Earth."
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Best regards,
tlspiegel |
