LANDFORMS of NORTH CAROLINA
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Purpose: This class provides an overview of the Geomorphology Section of the Course Use it as a "review session" for the First Quiz
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| 1 | Rapid Overview |
| 2 | Mountains |
| 3 | Blue Ridge Front |
| 4 | River action |
| 5 | Piedmont & Fall Line |
| 6 | Coastal Plain |
| 7 | Coast |
| 8 | Conclusions |
Overview
This page is intended to provide access to the slides shown in class. The text linking the slides is just a brief guide so that you can relate the slides to the class material. The breakdown into sections is also designed to help relate the page to the lecture.
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| A schematic cross-section of North Carolina, showing many of the major geomorphic features. | Schematic map showing the location of the major geomorphic features. |
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Land is uplifted and the action of weather - frost, snow, rain, wind, temperature change - begins to weaken the solid rock. The top layer of that weakened rock is familiar to us as soil, which we can see grading into the underlying rock in this view of an 'artificial' road cut. Such cuts frequently lead to landslides, as the weakened rock moves down slope. |
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Running water, collecting in almost any small depression picks up some of the fallen material and uses it to chip away at the rock over which it runs. A gully forms. The chipping action also wears creates ever finer particles as part of the 'load' of the river. The brownish color of many of our Coastal Plain rivers is that eroded material being carried away. |
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Given enough time, enough altitude, and enough material to erode, valleys are formed. Eventually the stream velocity becomes small, the material is deposited, either to form:
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<-- lowland plains or
coastal beaches --> |
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| The mountains were subjected to several uplift and erosion cycles during the last 600 million years. Currently they are being worn away, leading to a generally level skyline. |
Now erosion by running water, the creation of valleys by the rivers that flow in them, is paramount. The ease with which water can erode depends partly on rock type. In places there is soft (relatively soft!) rock which is easily eroded, leading to wide, open valleys.
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Looking across the valley of the Valley River near Andrews
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and looking upstream (eastward) from Andrews -----> |
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Immediately upstream of this is a narrow valley, with little or no valley floor, formed on resistant rock.
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Sometimes rather large rivers have cut down through soft rock and revealed more resistant forms. They may now flow in narrow gorges, which have implications for settlement as well as transportation. |  |
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On a smaller scale, rock type and geological
formations affect individual stream reaches
<-- calm ones suggestive of fishing
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<-- more energetic ones, with waterfalls and rapids, for more energetic pursuits -->
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| Steep slopes and rapid streams also provide the opportunity for hydroelectric generation. |
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3. Blue Ridge Front & Monadnocks
| The Blue Ridge Front is a more or less straight wall of mountains rising above the undulating Piedmont. It is commonly the crest of the Eastern Continental Divide, and streams rising to the west flow, in relatively gentle courses, to the Mississippi and the Gulf, while streams to the east take a shorter, steeped, and more active erosion course directly to the Atlantic. |
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It is not a straight wall - valleys cut into it in several places, many of them providing relatively easy access as transportation corridors.
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It seems that the Blue Ridge Front has been retreating slowly westward for many millions of years. However, where especially resistant rock has been exposed, residual hills -Monadnocks - have been left. |
These can take various forms,
sometimes cylindrical,
sometimes conical,
and a variety of other shapes.
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Nevertheless they are all upstanding above the undulating Piedmont surface. Many are now State Parks.
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Since erosion and deposition by rivers is the major determinant of the detail of a landscape, it is worth looking at them in a little more detail. |
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Rainfall initially flows 'downhill' in a more or less chaotic fashion, but eventually becomes organized into a specific channel - at it smallest this may be a gully. This shows the down cutting action of running water, but the water can also cut sideways when flow is rapid, as well as depositing eroded material when the current drops. |
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The lateral movement gives rise to meanders. The meandering movement of water can also be seen on larger scales, possibly influencing the shape of whole valleys. |
| Commonly the narrow valley of a steep, rushing stream becomes more open as the stream slows and meanders become more common, leading to the creation of a flat valley floor. |
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Most Piedmont Rivers have well marked walls, but even on the
Coastal Plain most streams will have valley walls, although they
may be very small.
Even here, however, rock structure can be important, and cliffs are not uncommon. However, on the northern Coastal Plain geologically recent sea level rises mean that river banks, let alone valley walls, are virtually absent. |
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In other parts of the ears there have been some recent land
uplifts, which have usually produced some rather small-scale features. A gently
meandering coastal plain stream may have started to flow a little faster as the
land rose, cutting a small valley within the existing valley,
or, in the Piedmont, leaving a slight cliff-like feature on the valley side. |
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| Indeed, since there has been plenty of time, many of the Piedmont rivers have cut these rejuvenated valleys. |
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The Piedmont is generally characterized as a region with undulating landscape. This is true throughout, but there are regions, such as those associated with monadnocks, which are much more undulating than others. This is also the area of most of the major cities of the state. Undulations are not just rural features, they occur in urban areas as well.
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For much of the eastern United States the Fall Line represents the junction between the Piedmont and the Coastal Plain. This is not very well developed in our state. The Triassic Basins near the eastern edge of the Piedmont make most of a gradual transition, although there are some rapids in the area. Further, the Sandhills, with its own characteristic landscape, covers parts of both regions. |
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| Note in this Sandhills region, where the underlying material is very easily broken down into sand grains, there is little fine material for the rivers to carry unless they are in flood, so that the rivers in this region normally run rather clear. |
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The Coastal Plain is often divided into two major sections:
Tidewater, which has the true flat coastal plain.
This is best developed in the north, where marine terraces, ancient cliff-lines, are present, along with some more recent 'cliffs'. These can be seen in the Gatesville - Elizabeth City Field Trip. Now the land is generally sinking and the estuaries and Sounds of this region are indicative of the sinking.
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Cape Fear Arch: In the south is the area of the 'Cape Fear Arch'. Rivers most definitely flow in banks. The banks themselves show evidence of various layers of sediment, some beach sand, some swamp vegetation, some drier organic material.
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The rivers in this area still have flood plains, although that often have a swampy character.
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Beach Dunes
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At the Coast wave action replaces running water as the agent for erosion, deposition, and sediment movement. Most waves are benign, but storm waves can do a large amount of damage. Although the beach sand is readily moved by wind and waves, vegetation tends to stabilize dunes.
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Nevertheless, the constant shifting, especially if the vegetation or dune structure is disturbed, can lead to a renewal of erosion. Further, human actions may change natural ones, with severe impacts on structures which even sandbags find difficult to prevent.
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A few comments in conclusion:
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Human actions not by no means confined to the coast - we can and do modify the landscape everywhere, where through a gravel pit, a new house, or a town. The physical landscape may play a major role in influencing the nature and location of human actions - particularly when there is a shortage of flat land in the mountains.
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The study of physiography (Geomorphology) is only one part of natural environment, climate soils and vegetation and their interactions make the total physical landscape.
