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February 26, 2017 Weekly Geology Guest, Plate Tectonics

February 25, 2017
Greetings from the Bluff Park Back Porch, way up yonder on Shades Mountain (1,109′) in Alabama:

We will now dive into the realm of Plate Tectonics.

>    There is a lot of material with this subject.

“Continental drift is the movement of the Earth’s continents relative to each other, thus appearing to “drift” across the ocean bed.[2]”

“Plate tectonics (from the Late Latin tectonicus, from the Greek: τεκτονικός “pertaining to building”)[1] is a scientific theory describing the large-scale motion of 7 large plates and the movements of a larger number of smaller plates of the Earth‘s lithosphere, over the last hundreds of millions of years.”

Plate Tectonics is the current accepted geological theory while continental drift is the older theory.

“The lithosphere, which is the rigid outermost shell of a planet (the crust and upper mantle), is broken up into tectonic plates. The Earth’s lithosphere is composed of seven or eight major plates (depending on how they are defined) and many minor plates. Where the plates meet, their relative motion determines the type of boundary: convergent, divergent, or transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries. The relative movement of the plates typically ranges from zero to 100 mm annually.[2]  ”  Wikipedia

By USGS –, Public Domain,

Types of Plate Boundaries

Divergent Boundary (Constructive)

“Active zones of Mid-ocean ridges (e.g., Mid-Atlantic Ridge {Iceland} and East Pacific Rise), and continent-to-continent rifting (such as Africa’s East African Rift and Valley, Red Sea) are examples of divergent boundaries.”

By domdomegg – Own work, 2016, CC BY 4.0,

“Convergent boundaries (Destructive) (or active margins) occur where two plates slide toward each other to form either a subduction zone (one plate moving underneath the other) or a continental collision.

At zones of ocean-to-ocean subduction (e.g. Aleutian islands, Mariana Islands, and the Japanese island arc), older, cooler, denser crust slips beneath less dense crust.”

By domdomegg – Own work, 2016, CC BY 4.0,

Other type of boundaries include Transform Boundaries, like the San Andreas Fault; and Plate Boundary Zones.

Driving forces may include plate motion, mantle dynamics, gravity, and earth rotation.
Note:  Plate Tectonics is still a young science with a lot of pieces of the puzzle that still need to be worked out.

With all this vectoring, jostling, convergence, and divergence, it appears that we are going to have a collision of continents in the near geologic future.

Detailed map showing the tectonic plates with their movement vectors.

By Eric Gaba (Sting – fr:Sting) – Background map: NGDC World Coast Line dataData: Prof. Peter Bird’s map, CC BY-SA 2.5,

With the shear abundance of Continental Drift images, I will let you graze through the forest.;_ylt=A0LEVjHFX6pYkckAdxwPxQt.;_ylu=X3oDMTByMjB0aG5zBGNvbG8DYmYxBHBvcwMxBHZ0aWQDBHNlYwNzYw–?p=Plate+Tectonics&fr=yhs-befrugal-002&hspart=befrugal&hsimp=yhs-002

Plate Tectonic Video:

>    Search:  Continental Drift, Plate Tectonics, North American Plate, Geology of Iceland, Icelandic Plume, Divergent Boundary, Mid-Ocean Ridge, sea floor spreading.

References include:

–    Wikipedia


Editors Note:  It is the intent of this site to keep this discussion as simple as possible, so as to educate the interested general public and not to discuss with the geology crowd the latest geologic theories and nuances.  Thanks, R
“No copyright infringement intended.
The rights belong to their respective owners”

Copyright Disclaimer: Under Section 107 of the Copyright Act 1976, allowance is made for “fair use” for purposes such as criticism, comment, news reporting, teaching, scholarship, and research. Fair use is a use permitted by copyright statute that might otherwise be infringing. Non-profit, educational or personal use tips the balance in favor of fair use.


Author’s Request:  If you see any pictures that you know the source and photographer, let me know immediately.  Thanks!  R

Images have been searched by TinEye Reverse Image Search.
Next week, I will dive on into earthquakes and volcanoes that are caused by plate tectonics.
Enjoy the adventure!
And for my and our amusement I will attach some plate tectonic cartoons.  The choice of cartoons were made by me so any atta-boys or rocks should be thrown my way.






"Looks like the 'Big One' finally hit."

“Looks like the ‘Big One’ finally hit.”







'Before we start our field tests, could somebody placate the Mountain God.'

‘Before we start our field tests, could somebody placate the Mountain God.’

'If our calculations are correct, Dr. Pinkerton, continental drift is speeding up much faster than anyone thought.'

‘If our calculations are correct, Dr. Pinkerton, continental drift is speeding up much faster than anyone thought.’

'I want to report an earthquake.'

‘I want to report an earthquake.’

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