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North Carolina's Geologic History
Transcript of North Carolina's Geologic History
The mountains (Blue Ridge)
Upper/Lower Coastal Plain
Sandhills Indeed there are. These mountains are called the Blue Ridge mountains, and are a subdivision of a much larger range called the Appalachians. Well, by definition, a Piedmont is an area of less steep land than the mountains it exists around, but also more unlevel than a flat plain. These areas are sometimes called foothills. Coastal plain is just a fancy word for the flatter land in North Carolina that borders the Atlantic Ocean. Geologic History of North Carolina So what accounts for all these regions, and their distinct features? Sandhills How old do you think North Carolina really is? The Blue Ridge Mountains began to form more than 400 million years ago. (Process later explained.) Why are they called BLUE Ridge? From far away, these mountains actually appear to be blue. Trees that reside along the mountainsides are responsible for this. Trees release a substance called isoprene into the air that causes the blue haze you see along the mountains. In North Carolina, the Piedmont region is directly between the more mountainous west, and the flat, coastal east. The Piedmont region consists of gently rolling countryside, small mountain ranges that have over time become severely eroded, and hills. (Process/causes later explained.) Some of the characteristic eroded areas of the Piedmont region include
the Uwharrie Mountains,
the Brushy Mountains,
and the South Mountains. Believe it or not, the Piedmont region of NC is the most densely populated of the three, and plays a crucial role in our society. Coastal Plain? Who Says our coast is plain? Piedmont regions tend to have land formations called plateaus, or high land with a flat surface. The Coastal Plain of North Carolina is usually subdivided into Outer and Inner Coastal Plain.
The inner Plain is more elevated, and less wet than the outer, and begins west of the Tidewater region. Included in this subregion are things called sandhills, which are exactly what they sound; sandy hills. It is within these hills that the highest elevation in the Coastal Plain is located. The outer Plain is comprised of the Outer Banks and Tidewater areas. Converging Plates- The entire Earth is subdivided into large sections of its crust and upper mantle called tectonic plates. These plates are in constant motion. With all these huge pieces of crust floating around, what are the chances of a collision?... Quite high, actually. When two plates collide, a number of things can happen. Two continental plates colliding presents the issue of both having the same or similar density. Thus, neither can really be subducted, or forced under the other one. What can't go down must then go up. Think about it. As we said before, these are huge sections of crust/mantle. When these collide, tremendous force is involved. The two plates can then buckle as they are forced upward, causing something called a fold to happen. As the plates continue to be thrust upward, they continue to buckle and fold, causing what we refer to as folding mountains... Like the Blue Ridge ones in North Carolina! Erosion Piedmont areas generally form at the bases of mountains. They are the results of a combination of the same forces that form mountains, and erosion. Over time, this less extreme, but still rolling landscape can be eroded and worn down, creating distinct features like plateaus. Sedimentary Rocks and Water's Impact The Coastal Plain region of North Carolina is comprised primarily of sedimentary rocks. The closer you get to the coast, the smaller the sediment that comprises these rocks get. Why is this? Water plays an important part in this concept. Water is great at eroding things, and is in fact some (a lot) of the force that caused the erosion in the Piedmont region. Tidal forces are huge. The tides are continually moving, rolling in and out. AS they do so, they carry small bits of sediment along. Water can also chemically weather, dissolving many substances in rocks and soil. Over time, the combination of chemical and physical influences exerted by tides can strip land into a much flatter formation. This is evident when you look at the Coastal Plain, and its much flatter landscape, combined with its sandy soil. A further look into specific terms...
And other stuff! :D Ancient remnants of sand dunes left behind as proof that the coastline used to be farther inland. The great seas/lower land of the past left this geologic landmark divisor that now generally separates the Coastal Plain from the Piedmont region. Fall Line The border line between the Coastal Plain and Piedmont regions. On one side is softer, sedimentary rock. On the other is harder, rougher mountain-like rock. There is no general term for the line that separates the mountain and Piedmont regions of NC. Coastal Plain regions are formed when Marine sedimentary rocks are brought upwards, and over time eroded by wind/water/etc. (More detail later.) Geological Timeline: 4500 bya Earth formed 4000 mya stable crust with oceans formed 3800 mya crust started to shift and erosion started from glaciers bya - billion years ago
mya- million years ago 1700 mya land to form North Carolina started to form 1300 mya First mountains in North Carolina formed, called Grenville Mountains. They eroded away. 1000 mya North Carolina pulled apart and created an inland sea. Volcanic islands formed along the Virginian and North Carolinian border all the way to Georgia. 750 mya 540 mya 444 mya 344 mya 320 mya 260 mya 251 mya Part 1 The King Mountain Belt formed and the Piedmont moved into the continent. North America and Eupore/Africa still move toward each other causing rock to move upward and buckle. North America and Europe/Africa start to move toward each other. The Appalachian Mountains form, and as mountains form, streams also did. They carried sand and sediment filling the sea. North America and Europe/Africa collided, thus creating Pangea. This is the end of the building of the Appalachian Mountains. The Piedmont and Coastal Plain regions move up. The Appalachian Mountains are complete. Pangea breaks apart, North Carolina at this time is near the equator. Geological Timeline: 200 mya Part 2 When the tectonic plates were moving the Coastal Plains sunk, causing the difference between the Piedmont and Coastal Region. The Appalachian Mountains start to erode creating the Piedmont. 145 mya 18000 1.7 mya 1.8 mya 5.3 mya 23.0 mya 33.9 mya 55.8 mya 65.5 mya All of the Coastal Plains are above sea level. The Coastal Plains start to sink again, the ocean comes up to where the modern Piedmont would be then recede again. The ocean retreats completely from the modern day Coastal Plains The ocean recedes and the Coastal Plain surfaces. The youngest ranges of the Rocky Mountains form. The ocean rises as far as modern day New Bern. Glaciers recede, and the barrier islands form. The Ice Age begins and sea levels fall. The Sand Hills form. Streams bring sediment to the Coastal Plains. The ocean rises then recedes again creating the fall line. The Blue Ridge Mountains and Piedmont look as they do today; shallow seas cover the Coastal Plains then recede. North Carolinian Mountains http://www.steveshamesphotos.com/tripback41.htm North Carolina Piedmont http://placesofvalue.com/best-places-to-live-in-north-carolina/north-carolina-piedmont-area/ North Carolina Barrier Islands http://hatterasblog.surforsound.com/all-posts/geography-gone-wild/ El Fin