Portage Escarpment
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The Portage Escarpment is a major landform in the
U.S. state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its so ...
s of
Ohio Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...
,
Pennsylvania Pennsylvania, officially the Commonwealth of Pennsylvania, is a U.S. state, state spanning the Mid-Atlantic (United States), Mid-Atlantic, Northeastern United States, Northeastern, Appalachian, and Great Lakes region, Great Lakes regions o ...
, and
New York New York most commonly refers to: * New York (state), a state in the northeastern United States * New York City, the most populous city in the United States, located in the state of New York New York may also refer to: Places United Kingdom * ...
which marks the boundary between the Till Plains to the north and west and the
Appalachian Plateau The Appalachian Plateau is a series of rugged dissected plateaus located on the western side of the Appalachian Mountains. The Appalachian Mountains are a range that run from Nova Scotia in Canada to Alabama in the United States. The Appalachi ...
to the east and south. The escarpment is the defining geological feature of New York's
Finger Lakes The Finger Lakes are a group of eleven long, narrow, roughly north–south lakes located directly south of Lake Ontario in an area called the ''Finger Lakes region'' in New York (state), New York, in the United States. This region straddles th ...
region. Its proximity to
Lake Erie Lake Erie ( ) is the fourth-largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and also has the shortest avera ...
creates a narrow but easily traveled route between upstate New York and the
Midwest The Midwestern United States (also referred to as the Midwest, the Heartland or the American Midwest) is one of the four census regions defined by the United States Census Bureau. It occupies the northern central part of the United States. It ...
. Extensive industrial and residential development occurred along this route. It is also called the Allegheny Escarpment in its southern portion after it diverges from Lake Erie in Ohio.


General description

The Portage Escarpment forms the northern and western boundary between the Appalachian Plateau and the Till Plains of the Central Lowland physiographic section of the United States. The escarpment begins in eastern New York. Nevin Fenneman placed its starting point between
Cayuga Lake Cayuga Lake (, or ) is the longest of central New York's glacial Finger Lakes, and is the second largest in surface area (marginally smaller than Seneca Lake) and second largest in volume. It is just under long. Its average width is , and i ...
and Seneca Lake, where the Onondaga Escarpment transitions to the sandstone of the Portage Escarpment. But New York state officials concluded that it began east of
Auburn, New York Auburn is a city in Cayuga County, New York, United States. Located at the north end of Owasco Lake, one of the Finger Lakes in Central New York, the city had a population of 26,866 at the 2020 census. It is the largest city of Cayuga County, the ...
. As it approaches
Buffalo, New York Buffalo is a Administrative divisions of New York (state), city in the U.S. state of New York (state), New York and county seat of Erie County, New York, Erie County. It lies in Western New York at the eastern end of Lake Erie, at the head of ...
, it turns to the southwest and hugs the shore of
Lake Erie Lake Erie ( ) is the fourth-largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and also has the shortest avera ...
. The escarpment moves across northwest Pennsylvania, continuing close to the shoreline. In Ohio, the escarpment gradually moves further away from shore. At
Cleveland Cleveland is a city in the U.S. state of Ohio and the county seat of Cuyahoga County. Located along the southern shore of Lake Erie, it is situated across the Canada–U.S. maritime border and approximately west of the Ohio-Pennsylvania st ...
, Ohio, it turns sharply southward. It proceeds in an undulating south-southwest direction across Ohio,
Kentucky Kentucky (, ), officially the Commonwealth of Kentucky, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Illinois, Indiana, and Ohio to the north, West Virginia to the ...
, and
Tennessee Tennessee (, ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...
. In these latter two states it is known as the
Highland Rim The Highland Rim is a geographic term for the area in Tennessee, North Alabama, and Kentucky which surrounds the Central Basin. The Central Basin is a geological dome which has subsequently fractured and eroded to produce a basin. The Highland R ...
. The landform's name is derived from attempts by the French to establish a
portage Portage or portaging ( CA: ; ) is the practice of carrying water craft or cargo over land, either around an obstacle in a river, or between two bodies of water. A path where items are regularly carried between bodies of water is also called a '' ...
over the escarpment in the 1750s which would link their Great Lakes forts with their fort at Pittsburgh.


New York

In New York state, the Portage Escarpment (also known as the "Finger Lakes sedimentary deposit") consists of
sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...
interbedded with
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...
. The base is almost all black and gray soft shale, while the upper portion is interbedded sandstone and shale. Because the more durable sandstone is not a capstone, the escarpment does not have a sharp, defined cliff or crest. This geologic makeup gives it a slope instead, and it often appears as two or more parallel terraces. The Portage Escarpment's eastern end is in the Finger Lakes region, where it is the dominant topographic feature. Prior to the
Wisconsin glaciation The Wisconsin glaciation, also called the Wisconsin glacial episode, was the most recent glacial period of the North American ice sheet complex, peaking more than 20,000 years ago. This advance included the Cordilleran Ice Sheet, which nucleated ...
(the last ice age), roughly 24 major rivers flowed north over the escarpment. The Wisconsin glaciation began about 85,000 years ago, and the ice reached its southernmost point approximately 25,000–21,000 years ago during the
last glacial maximum The Last Glacial Maximum (LGM), also referred to as the Last Glacial Coldest Period, was the most recent time during the Last Glacial Period where ice sheets were at their greatest extent between 26,000 and 20,000 years ago. Ice sheets covered m ...
. The ice sheet could not overcome the Portage Escarpment. Instead, the ice scoured downward, creating 11 long gouges in the earth. When the ice age ended about 10,000 years ago, these gouges filled with water coming down the escarpment and became the 11 Finger Lakes. The Portage Escarpment essentially runs along the southernmost tips of each finger lake. The glacial gouging and subsequent erosion by rivers and streams has led to the creation of deep valleys which extend southward as far as the southern tip of the Finger Lakes. This makes the escarpment appear to weave north and south in deep loops. The Wisconsin glaciation's scouring of the land in front of the escarpment in the Finger Lakes area has left the escarpment with a steeper slope than elsewhere in New York state. Here, the escarpment can be in height. West of the Finger Lakes region, the Portage Escarpment is relatively straight. The interbedded sandstone and shale here has suffered extensive erosion. In
Livingston County, New York Livingston County is a county in the U.S. state of New York. As of the 2020 census, the population was 61,834. Its county seat is Geneseo. The county is named after Robert R. Livingston, who helped draft the Declaration of Independence a ...
, this has left it much less well-defined. The Tonawanda Plain lies along the north side of the escarpment from its eastern terminus to Lake Erie. This
lacustrine plain A lacustrine plain or lake plain is a plain formed due to the past existence of a lake and its accompanying sedimentation, sediment accumulation. Lacustrine plains can be formed through one of three major mechanisms: glacial drainage, differentia ...
is bounded on the north by the
Niagara Escarpment The Niagara Escarpment is an approximately discontinuous, arc-shaped but generally northward-facing escarpment, or cuesta, in Canada and the United States. The escarpment begins south of Lake Ontario and circumscribes the top of the Great Lake ...
. Although quite wide at the eastern end of Lake Erie, the plain narrows considerably along the lake's southern shore. Here, the plain continues to be bounded by the Portage Escarpment, which turns southwest in a series of indefinite hills at
Hamburg Hamburg (, ; ), officially the Free and Hanseatic City of Hamburg,. is the List of cities in Germany by population, second-largest city in Germany after Berlin and List of cities in the European Union by population within city limits, 7th-lar ...
, Orchard Park, and East Aurora.


Pennsylvania

The Portage Escarpment continues to hug the southern shoreline of Lake Erie in Pennsylvania. It passes solely through Erie County, where it is from the lake. Here, Mississippian sandstone predominates over shale, and the escarpment rises to between in height. From
Erie, Pennsylvania Erie is a city on the south shore of Lake Erie and the county seat of Erie County, Pennsylvania, United States. It is the List of municipalities in Pennsylvania, fifth-most populous city in Pennsylvania and the most populous in Northwestern Pen ...
, to Cleveland, the escarpment is a little further from the shore, about .


Ohio

The Portage Escarpment also largely controlled where the Wisconsin glaciation stopped in Ohio. The lacustrine Erie Plain lies beyond it to the northwest and west. The escarpment continues to hug Lake Erie until it reaches Cleveland. In this portion, the escarpment rises in three distinct terraces: A first terrace, which is about above the plain; a second terrace, about higher than the first terrace; and a third terrace, about higher than the second terrace. In total, it ranges from in height, and is wide, giving it a slope of per . East of Cleveland, much of the lower portions of the escarpment are covered in glacial
moraine A moraine is any accumulation of unconsolidated debris (regolith and Rock (geology), rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a gla ...
. Both the upper and lower parts are cut by numerous dry ravines, rivers, and streams. This makes the escarpment somewhat discontinuous. The upper terrace of the escarpment is difficult to distinguish from the Appalachian Plateau beyond, because both are eroded so deeply by water. Where the escarpment meets the Erie Plain, it is much more well-defined. Where the escarpment meets the valley of the Cuyahoga River, it bends southward and begins moving even further away from the shore. It is distant from the shore between the Cuyahoga River and the Rocky River, and distant from the shore west of the Rocky River. Here, the escarpment rises between in a single step. The much lower height of the escarpment has allowed glacial
till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...
to build up and cover much of the escarpment's topography. This part of the escarpment is extremely discontinuous, as it is broken by the broad river valleys of the Great Miami and Scioto rivers. Southwest of the Scioto River, the escarpment forms the western boundary of the Shawnee–Mississippian Plateau region, the most rugged area in Ohio.


Cultural and historic importance

That portion of the Erie Plain between Lake Erie and the Portage Escarpment connects the Central Lowland of the Midwest with the
Mohawk Valley The Mohawk Valley region of the U.S. state of New York is the area surrounding the Mohawk River, sandwiched between the Adirondack Mountains and Catskill Mountains, northwest of the Capital District. As of the 2010 United States Census, ...
in the east, and provides the only natural, low-lying route north of the Gulf Coast to the North American interior from the Atlantic seaboard. Consequently, this area is heavily populated. Settlement of Ohio largely occurred along the Erie Plain, following the natural route created adjacent to the Portage Escarpment barrier.


See also

*
List of escarpments A list of escarpments follows below. Planets Earth Africa * Elgeyo Escarpment (Kenyan Rift Valley, Great Rift Valley) * Great Escarpment, Southern Africa **Including the Drakensberg and God's Window in Mpumalanga's Eastern Escarpment * Bandiag ...


References

;Notes ;References


Bibliography

* * * * * * * * * * * * * * * * * * * *{{cite book, last1=Wilson, first1=Michael P., last2=Boria, first2=William T., chapter=Quaternary Geology and Water Supply Issues, title=Field Trip Guide for the 71st Annual Meeting of the New York State Geological Association, location=Albany, N.Y., publisher=New York State Geological Association, date=1999, url=http://www.nysga-online.net/download/1990s-nysga-guidebooks/?wpdmdl=94&ind=NaUAB2S4UEeI5eGAsMfzh9GcorpX1auCJ67m31nnSKUuHIbXPuPEvs6euafoDNr7UHSdOWzWstiFJzQsszK2YZs2ugRZk7LucEUw1G_deIvlgqJjIjQncQnk4ASI6abq Escarpments of the United States Landforms of New York (state) Landforms of Ohio Landforms of Pennsylvania