The Story Of North America

I have several new things to add to our understanding of the geological natural history of North America and I decided that it is best to weave them into my version of the story of the continent, rather than posting the new additions one by one. I will not discuss glaciation here, but only large-scale tectonic movement.

THE APPALACHIANS

The story begins with the Appalachian mountain chain which extends from the area of Atlanta to that of Montreal. This mountain system is very old and it's peaks were once much higher than they are today but have been worn down by erosion. The one thing that differentiates the Appalachians from similar mountain chains is the extensive ridges throughout the system.

I have made many more detailed about the Appalachians in the posting on this blog, "All About The Appalachians".

The reason that ridges are such an important part of the Appalachian system, instead of just mountain peaks, is that the system was formed by the long-ago collision of two continents, but the collision took place at a relatively low angle and not head-on. The friction between the colliding continents produced the ridges. The so-called "Great Appalachian Valley", between ridges, runs nearly throughout the entire system.

A most interesting fact about the Appalachian Mountains is that there are two fragments of the mountains, one from each end, which have been separated from the chain and are now far away from it.

The Anti-Atlas Mountains of Morocco are known to have once been a part of the Appalachians. The chain was obviously formed before north Africa and North America were broken apart by the volcanic activity beneath, which now forms the Mid-Atlantic Ridge running across the floor of the entire ocean from north to south. The reason that Africa is today well to the south of the latitude of North America is that both were drifting northward but Africa collided with the European Plate, preventing it from going any further north. This collision is what forced up the Rock of Gibraltar.

Here is a map link http://www.maps.google.com/ . Notice how the continetal shelf off the east coast of the U.S. fits nicely with the coast of North Africa. The two were once joined. When they were separated by the volcanic activity of the Mid-Atlantic Ridge beneath the land from the Appalachians to the edge of the North American continental shelf, which had been part of north Africa, remained with North America.

The second mountain fragment that was once part of the Appalachians is the Ouachita Mountains of Arkansas and Oklahoma. These mountains were separated from the Appalachians when the friction of the collision which created them pulled the continent that is now North America apart into two pieces. As the two continental segements were pulled apart, the land in between was pulled upward so that the Appalachians and the Ouachitas are now separated by a wide stretch of lowland.

NEW ENGLAND

The first contact in the collision which formed the Appalachians happened in what is now the Atlanta area and the continent which is now Africa slid northeastward along the collision front, creating the peaks and ridges of the Appalachians. But we can see in a good physical geography world atlas that the ridges of the system curve across eastern Pennsylvania toward New York City. This curve, in my opinion, is the result of the collision front meeting an especially sturdy portion of the Canadian Shield in what is now eastern New York State.

This means that in Pennsylvania, the collision was more directly head-on, instead of at a low angle. The focal point of this more direct collision was right around Harrisburg. This increased pressure of the head-on collision in this area forced land upward on the North America side of the collision front. This land which was forced upward is today known as the Allegheny Plateau. The Catskill Mountains of New York State are actually an eastward extension of this plateau which has eroded unevenly over time so that some areas are higher in elevation than others, thus creating mountains.

This sturdy extension of the Canadian Shield interrupted the southwest to northeast line of the collision front and forced the land on the African side eastward. This land which was forced eastward would have been the first land the make contact with the North American side in the beginning of the collision in what is now the Atlanta area.

This land which had been forced eastward was what is now New England. It later collided with the land of North America further north, most likely following the two continents being split by the volcanic activity beneath. The result of this collision is the Green Mountains of Vermont. For further details, see the section in the posting on this blog "All About The Appalachians", "The Mystery of The Northeastern United States And Eastern Canada".

If we stand a board on it's end and then allow it to fall to the ground, the impact on the board is greatest at the end which had formerly been highest. This is simply because it had further to fall. The same principle applied in this New England collision and we can see that indeed the Green Mountains form a straight line and are higher in the north and fade out as we go southward toward Connecticut.

The White Mountains of neighboring New Hampshire are not quite parallel to the Green Mountains. In fact, the White Mountains display the same type of curve as the Appalachian collision front. This is because these mountains are the same curve on the land that was forced eastward by the extension of the Canadian Shield in eastern New York State and later collided back further north. The St. Lawrence River Valley is an incomplete merger of the two land masses.

When the New England land mass stopped moving north, the momentum of the lower part of this land mass forced it into New England and the result is the continuation of the Appalachian ridge system that had curved across Pennsylvania to Long Island and Martha's Vineyard. Cape Cod is a continuation of this ridge line, but when the New England land mass moved westward, resulting in the collision which formed the Green Mountains, it pulled the ridges with it and the result is the bend of Cape Cod which we now see. At the outside apex of the bend, the land was forced upward and it is now called Nantucket Island.

It is important to remember that this land mass included the broad continental shelves off the east coast of North America which we have today.

I cannot believe the articles on Wikipedia about Long Island and Cape Cod that they are solely the result of a glacial moraine because this was the extent that the glaciers moved. If we look on a map, we see that the southern extension at the east end of Long Island forms a direct straight line with Block Island and the Elizabeth Islands off Massachusetts and the parallel northern extension off Long Island forms a line with Fishers Island, just off the state of Rhode Island.

This fits with my concept of the underlying basis of Long Island, Martha's Vineyard and, Cape Cod as a continuation of the ridges of the Appalachian Mountains. The glacial deposits on the ridges were put there much later.

FLORIDA AND THE BAHAMAS

Now, let's go southward to the state of Florida. Unfortunately, I mean that only figuratively and not literally, as there is a frigid cold wind where I live today.

But Florida is vital to this collision scenario because the longitudinal axis of the peninsula of Florida is actually the axis of direction of what is now Africa on the way to the collision which produced the Appalachian Mountains. Following this line, it collided with the land mass which is now North America about where Atlanta is now, at the southwest beginning of the Appalachians.

Africa slid along the side of the other land mass, it was not a direct collision, and the result is the extensive Appalachian ridges that we see today. Florida was sea floor that was forced upward by the impact of this collision to above sea level. Notice how the directional alignment of the Allegheny Plateau is diametrically opposite to that of Florida. It is because both were forced upward by this same collision front.

By Florida, I mean the wide extent of shallow sea all around the peninsula, particularly off the Gulf coast of Florida, as well as the land. The land area of the state today is no more than about 40% of what it must have been at one time. The lowland has been eroded away by the sea to produce the wide shallow water all around. The whole Florida Platform consists of limestone atop bedrock, the limestone being built up gradually as sediment.

There are many lakes in Florida, but notice how the lakes get larger the further south we go. This shows how the terrain must be somewhat lower in the southern part of the state, which was the furthest from the Appalachian collision, because it was forced up to a lesser extent. Lake Okeechobee is the largest lake and is far to the south. The swampiness of Florida tells us that it is too low and flat for good drainage, which fits with it being a former sea floor, and that the largest swamp of all, the famous Everglades, is far to the south of the state.

I explained in the posting "The Atlas Barrier" on my meteorology blog, http://www.markmeeklife.blogspot.com/ why there is far more shallow continental shelf to the west of Florida than there is on the Atlantic side. It is because the hurricanes which regularly batter the state also build up barrier islands, which stem erosion by waves. Without these barrier islands, Florida would most likely be gone today or would be a chain of small islands.

The Bahamas, to the east of Florida, are a part of this scenario also. The islands of the West Indies; Cuba, Hispaniola and, Puerto Rico, are volcanic in origin and so do not move with the continental tectonic drift. The Bahamas were once a southward extension of Florida, also forced upward by the Appalachian collision until the westward movement of the entire continent caused what is not The Bahamas to collide with the tectonic plate of the West Indies, called the Carribean Plate. This collision held The Bahamas back while North America continued westward.

One piece of evidence to support this scenario is the presence of ridges in The Bahamas. The islands are mostly flat, as we would expect raised former sedimentary sea floor to be, except for a number of ridges up to 15-20 meters in height.

Why would there be ridges on the flat islands of The Bahamas? Remembering how ridges were formed in the Appalachians by the friction of an indirect collision, isn't it logical to presume that these ridges were formed by an indirect collision with the Carribean Plate, as I have described?

Also, notice on the map how the combined length of Florida and The Bahamas is just about exactly equal to the main collision front along the Appalachians.

THE DISSOLUTION OF FLORIDA

The recent fatal sinkhole in the Tampa area provides more proof of the scenario that I presented in "The Story Of North America" on the geology blog, www.markmeekearth.blogspot.com . Sinkholes in Florida are the rule, rather than the exception. They occur all over the state.

Florida is a product of the tectonic collision between what is now North America and what is now Africa that formed the long chain of mountains and ridges known as the Appalachians. When this long-ago collision took place, it forced up trailing sea floor in the same way as the sudden halt of a long train would affect the cars which still have their forward momentum. There is a large area of former sea floor that was forced upward by the collision. What is now the peninsula of Florida is only a minor portion of the total area that can be seen on a map showing the sea depths, there are wide areas of shallow sea on both sides of the state.

Sea floors in warm areas, or that were formed in warm areas before moving tectonically, tend to be formed of limestone. This is a rock formed by the bodies of countless microscopic life forms, and is chemically known as calcium carbonate. Limestone does not last indefinitely, and can be slowly dissolved by flowing water. This is what forms caves. The stalactite formations, hanging like icicles from cave ceilings, are composed of limestone that has been dissolved in moving water and then recrystallized.

Florida consists of a bed of such limestone, covered by a layer of clay because there was once a warm period between ice ages when sea level was higher than it is now so that low, flat Florida was covered by water. South Florida has so much marshland because it is lower in elevation, being further from the Appalachian tectonic collision it was forced upward less than the northern part of the state.

Florida has numerous small lakes, similar to the terrain in Canada or Sweden or Finland, but which are not glacial in origin. Florida's lakes can be seen to be either circular in shape, or elongated along the flow of groundwater, and not elongated from northwest to southeast like glacially-formed lakes tend to be. If these lakes were somehow glacial in nature, maybe formed by glacial ice originating from the Appalachians to the north, the lakes would continue into Georgia. Yet, this is not the case.

The reason is that Georgia was part of the original land mass, while Florida was formed from limestone seafloor being forced upward by the momentum that continued after the collision began. Florida's many lakes  are the result of sinkholes that formed in the same way as caves. Water gradually dissolved limestone to create an underground cavern, until the roof collapses to form a sinkhole. These sinkholes then grow, and may merge with other sinkholes over millions of years.

There is a large lake in south Florida, Lake Okeechobee. Aside from being a good computer password, it is also the future of Florida. Sinkholes will continue to appear, grow and merge until, in the distant future, the entire state is gone.

What do you suppose that Tampa Bay is? It looks to me like two large sinkholes that have grown along the flow of groundwater before merging, with the peninsula remaining between them upon which Macdill Air Force Base is located. You can see in the satellite imagery on the map that traces of the former coastline remain. Sinkholes do not go very deep, you can tell that Tampa Bay is relatively shallow because it is spanned by several bridges with abutments set in the water.

Sinkholes like this are also found in southern Quebec, and in Mexico's Yucutan Peninsula which is a kind of geological sibling to Florida. The Gulf of St. Lawrence and the St. Lawrence Valley is formed by land masses that came into contact, but did not completely merge. But this would have forced seafloor upward that was between them, and that is why sinkholes in the limestone are found here as well.

The Florida Keys, to the south of the state are actually coral and are not related to this.

THE LOWLANDS OF THE U.S. MIDWEST AND SOUTH

The next question becomes; if the Appalachian Mountains were formed by continental collision, why do they stop abruptly in the Atlanta area?

The answer is revealed by the fact that much of America's deep south, like Florida, is low-lying swampy ground. Most of the southern states are former sea floor which was forced upward by this collision which produced the Appalachians.

As I described near the beginning of this article, the sliding collision with the continent that is now Africa tore the continent which is now North America in two. But this was a good thing because the land in between the two pieces of North America was pulled upward and is now the vast lowland region in America's midwest and south shaped approximately like an upside-down V. This lowland is the watershed of the Mississippi River.

The lowland created by the Appalachian collision is approximately bisected by a line from Decatur, Illinois-Memphis-Jackson, Mississippi-New Orleans. On the west side of this lowland are, of course, the Ouachita Mountains of Arkansas and Oklahoma which were, as I described, one a part of the Appalachians but were pulled away by the friction of the collision.

So, this simple scenario that I have described here explains the Appalachian Mountains with the extensive ridges, the Green Mountains of Vermont, the White Mountains of New Hampshire, the St. Lawrence and Hudson Valleys, the lines of Long Island to Martha's Vineyard and Cape Cod, the curve of the Pocono Mountains, the vast central lowland region of the U.S., the Ouachita Mountains in Arkansas and Oklahoma, the Allegheny Plateau, Florida, the ridges in the Bahamas and the swamps in much of the southeastern U.S.

For more about New England, see the section on this blog of "All About The Appalachians", The Mystery Of The Northeastern U.S. And Eastern Canada".

WESTERN NORTH AMERICA

I will not go into as much detail with the western part of the continent as I have with the east. But all of the Rocky Mountains in the U.S. and Canada are former sea floor, with deep sedimentary layers that were forced upward by tectonic collision with the Pacific Plate. This collision happened far more recently than the one which formed the Appalachians.

These sedimentary layers can easily be seen in the landscape formations across the American west. Such compacted sediment is easily eroded and the region has been shaped by glaciers from the mountains and from rivers. The Grand Canyon demonstrates how readily the landscape is cut away by the flow of a river. The variety of landscape formations are the result of uneven erosion.

The far western U.S. has crossed the expansion zone at the boundary with the Pacific Plate. This expansion zone is basically a line around the world shaped roughly like a W. It is where the earth's crust is spreading which is, I believe, the driving force behind earthquakes. I described this in the posting "Insights Into Earthquakes And Tectonic Plates" on this blog.

The line includes the Mid-Atlantic Ridge, goes around the southern part of Africa into the Indian Ocean, a branch of the lines runs northward to the Red Sea which was created by this sea floor spreading, the line goes south of Australia and meets North America at the Gulf of California (or Sea of Cortez) on the west coast of Mexico. This was formed by sea floor spreading in the same way as the Red Sea.

The western U.S. crosses this expansion line and the result is not only Mexico's Gulf of California, but also the vast San Joaquin and Sacramento Valleys of California, the coastal lowland along the coast of Oregon and Washington State and, the Columbia Basin of Washington State.

MEXICO

Now, on to Mexico. There are two distinct branches of the Rocky Mountains here, known as the Sierra Madre Occidental (west) and the Sierra Madre oriental (east). If the mountains all along the west coast of the Western Hemisphere were formed by simple tectonic collision with the Pacific Plate, then why should Mexico have two separate branches of these mountains?

One look at the map provides an obvious answer. The much larger chain, the Sierra Madre Occidental, was formed by the tectonic collision. The somewhat lesser Sierra Madre Oriental was formed because the Pacific Plate extends eastward at the latitude of Mexico and the entire country was thus "pushed" east relative to the rest of North America and the Sierra Madre Oriental was formed by the resulting compression along the eastern side of Mexico. This can be easily seen on a map.

The Yucutan Peninsula in the southeast of Mexico, and the wide continental shelf all around it, was formed when sea floor was pushed upward when this area collided with the Carribean Plate as Mexico struck the Pacific Plate but the rest of North America continued westward due to the curve in the Pacific Plate boundary. There is a similarity in principle between the Yucutan Peninsula and both the The Bahamas and Cape Cod.

THE ARCTIC

The only major non-glacial feature of North America that remains to be explained is the mountains in the far north of Canada and Alaska, which are aligned more east-west than the northwest-southeast of the mountains formed by the great collision with the Pacific Plate. These are from one of the Continental Asteroids, described in the posting on this blog, "The Story Of Planet Earth". At this point, I believe these rocky and mountainous islands to be from the Second Continental Asteroid, which formed the Original Impact Line.