THE TOPOGRAPHY OF NORTH CAROLINA

 

Overview: 

North Carolina's topographic regions

Human Actions & Changing Topography

 

Detailed Sections

Geologic Forces shaping our land

The work of rainy weather

Landscapes created by rivers 

The work of wind and waves

 

 

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NORTH CAROLINA'S TOPOGRAPHIC REGIONS

 

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The six topographic regions of North Carolina (from the 'North Carolina Atlas' - UNC Press) 

 

     The topography of North Carolina has developed over many millions of years.  The processes creating the topography seem to act very slowly, and certainly topography changes little from year to year.  Throughout the period of human occupation there have been three more or less distinct topographic areas in our state: Mountains, Piedmont, Coastal Plain. Because they change little during a human lifespan, and because they are so obvious and visible, they have become the basic regions for the division of our state for a whole variety of purposes. We refer to them in many different parts of this site, but here we look at them as their basic form, as topographic features of hills, valleys, plains and coast.

 

 

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     Despite the seeming unchanging nature of topography, the landscape in fact changes from day to day.  Changes are usually microscopically small, but over a long period of time they could have a great impact.  For example, it is not unusual for a windy spring day to remove about 1/100th of an inch of topsoil from a field ready for planting on the Coastal Plain. Other actions, usually involving either gravity or water flow, move soil downhill and into rivers, eventually depositing the soil particles into the ocean.

     Even if we think of a loss of 1/100" in a year, that is over 800 feet in a million years.  Since our mountains have been around for over 200 million years, major changes have been occurring.  If nothing else, the mountains were once much higher.

     Most changes are slow and virtually invisible. Sometimes, of course, changes are spectacular, with landslides carrying away material in the mountains, floods sweeping all before them in virtually any part of the state.

A Coastal Plain river carrying away sediment - evidence that the landscape upstream is being worn away - albeit very slowly.

 

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A sketch map of North Carolina showing the major topographic regions and some of the major features within each region.  Each of the features is explained in the text. The junction between the Piedmont and the Coastal Plain at Weldon, Halifax County.  In much of North Carolina this junction is hard to identify

 

     The easy visual way to separate the regions - so that you can immediately describe the topography in a shorthand way, is to specify the relative relief:

the relative relief is the difference in altitude between the lowest and highest points in a local area.  This is, deliberately, a rather general and somewhat vague term. Usually this simply means that if you stand in a fairly open area the relative relief is height difference between the highest and lowest points you can see.  A rough estimate of this height is all we need here - you could use a topographic map to identify exact differences in a particular area. 

     

     In the broadest way (and using numbers which are designed as much to be memorable as precise) we can say that relative relief is:

 

            Mountains - 1000m  (3000 ft)

            Piedmont - 100m (300 ft)

            Coastal Plain - 10m (30 ft)

 

      While relative relief doesn't change very much anywhere in the Mountains, it decreases from west to east as we cross both the Piedmont and the Coastal Plain

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Three reasonably typical scenes, showing the relative relief, in the Mountains, Piedmont and Inner Coastal Plain.

 

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The Blue Ridge Front separates the Mountains from the Piedmont.  It is seen here on a misty morning.

Sketch cross-section through the state, showing many of the features indicated on the above map and suggesting the relative relief of the regions.

 

    

 The major features of the topography of the state - the three regions suggested above - have been produced by geologic forces. These forces, originating deep in the earth's interior, create huge moveable rock plates on the earths surface.  The movement, plate tectonics, creates mountains when plates collide, oceans when they separate.  The movement, combined with volcanic action, creates a variety of rock types. The movement is slow and acts on a time scale of hundreds of millions of years. 

 

     Rocks exposed at the surface are subject for another, much faster acting, set of forces.  The weather breaks down exposed solid rock, gravity moves the pieces down slope and wind, rivers, glaciers and waves move it about. When these forces remove the material from the surface, we have erosion.  That dominates our mountains, which are slowly being eroded away.  Deposition occurs along our coastal sounds and estuaries, which has been building out eastward for millions of years.

 

 

 

 

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Schematic diagram showing the major processes involved in the formation of the topography of North Carolina.

   

 

    For most of the state, the dominant force of erosion and deposition is river action - creating fluvial landscapes.  Erosion dominates in the mountains and Piedmont and over the Inner Coastal Plain.  Deposition, combined with a long-term rising sea level is responsible for the outer part of the coastal plain - here called Tidewater.  For one region, the coastline itself, wind and waves provide the motive force creating the topography.  Finally, there is one small area - the Sandhills - where both running water and wind action are equally important.

 

 

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Three regions often considered simply part of the Coastal Plain, but here separated from the Inner Coastal Plain illustrated above, because of significant topographic differences.  From left to right, they are the Sandhills, Tidewater, and the Coastline.

 

 

 

 

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HUMAN ACTIONS AND CHANGING TOPOGRAPHY

 

    Whenever humans change the land surface - clearing land, damming rivers,  building structures - they also automatically alter the local fluvial, wind, or wave processes in some way.   Sometimes we can forecast the changes which we will cause, but often they are complex and extremely difficult to predict.   Just looking at the landscape is unlikely to be sufficient - measurements, tests and calculations are probably needed to get near to the correct prediction. Nevertheless, looking in an informed way can help to identify potential problems, so we conclude with some examples of human actions at work changing the topography of our state.

 

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Construction is the great changer of topography - almost any city, or even any village, shows that.  This area of Asheville  was a hill that was leveled to create a shopping arcade.  Since this was done almost a century ago, we think of the current topography as 'natural'.  However, the removal of the hill, and the construction of the building, had some impact on the mass wasting and fluvial processes of the area.

Damming a river, here the Catawba River on the Alexander-Catawba County border, changes the downstream water flow and sediment load characteristics.  For the topography this may mean less downstream erosion.  There might also be a gradual decrease in sandbar size somewhere along the river.  The sand which would have been deposited is now likely to accumulate in the lake behind the dam.   

 

 

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Because soil creep occurs virtually everywhere, and virtually continuously, any structure built on a slope is liable to have problems unless special precautions are taken. Indeed, any structure will influence the type and intensity of mass wasting occurring the slope, almost certainly having an impact can occur both upslope and downslope of the change.  Sometime the impacts are predictable, but this is not always the case.

Soil creep leading to a larger landslip in Haywood County.  Cutting the road through the base of the slope has disrupted the previous natural flow of water through the soil, leading to a change from continuous soil creep to a single slip event. This makes the whole slope vulnerable to more rapid movement than would occur naturally.

 

 

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Road construction is turning US 321 in McDowell County from a two lane road to a divided super-highway.  Every time it rains there is likely to be removal of soil from the unprotected slopes, something which did not happen on the forested slopes prior to construction. Sand traps at the bottom of the slopes - including in this project the planting of the grasses seen at the left center - prevents undue removal of the soil into local streams.  

 

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Downstream of a construction project soon after a rainstorm.  Soil has been removed from the site and entered the stream flowing from the center background.  The stream color contrasts with that of the stream entering from the left, which flows in a valley well away from the construction. 

The same stream junction some days later.  There has been no rain, and the stream coming from the center is clear - indeed, it seems clearer than that coming from the left.

 

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Beach development is highly vulnerable to wave action.  Structures on or close to the dunes disrupt the natural flow of sand, usually impeding its normal movement.  Frequently this means a dearth of beach material.  In a time of rising sea level, this makes the structures especially vulnerable.

 

 

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One of the best known impacts of a changing topography - probably largely natural, but a process speeded up by human actions - was the need to move Cape Hatteras lighthouse or let it fall into the ocean.  The stone slabs indicate the old position. 

 

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