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Arizona has a rich and fascinating geologic history. The illustrations on the next page give a brief overview of its progress courtesy of The University of Northern Arizona’s Geology Department. These are the best illustrations available I’ve found. You'll also find additional links at the end of this article.
Illustrations of the Paleogeography of the Southwest
Chris Scotese's Brilliant Animation of Earth 250 Million Years in the Future!
Heavy iron and manganese materials are in the center of the Earth. Lighter minerals “float” on top.
Now, imagine a pan of slowly boiling chicken soup with the characteristic film on top. As the heavy lower liquid moves from the heat, the film on the top moves, wrinkles and changes shape.
You’ve just watched plate tectonics at work. The same principles apply.
The lithosphere is a collection of those lighter minerals. It forms the land we see and the 12 plates that form the Earth. Deep beneath it is a slow moving, heavy, hot liquid moving the lighter tectonic plates.
Basalt is iron and manganese rich so it’s heavy, spreading out in black puddles around the opening hence the term “shield”. .
Silicic or stratovolcanoes are the ones we normally think of as volcanoes with the tall, conical shape. Lighter silica, a quartz like material, liquefies and spews from the opening. As it cools, the silica becomes hard and bottles up the opening. The pressure builds again and it erupts. Sometimes, the “cap” is large enough to hold, forcing the material to find a new path to release the pressure, forming side vents. It’s almost always accompanied by steam.
Chris Scotese's Brilliant
Animation of Earth 250 Million Years in the Future! |
 Map of Arizona
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 Map of the reservations and Four Corners
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