# What moves the tectonic plates? **URL:** \ **Category:** Factual Questions\ **Created:** [February 24, 2006, 1:05am UTC](https://boards.straightdope.com/t/what-moves-the-tectonic-plates/345870 "2006-02-24T01:05:56Z")\ **Posts on this page:** 10\ **Page:** 2
**Author:** ![Excalibre](https://avatars.discourse-cdn.com/v4/letter/e/898d66/32.png) [@Excalibre](https://boards.straightdope.com/u/Excalibre)\ **Post date:** [February 25, 2006, 7:56am UTC](https://boards.straightdope.com/t/what-moves-the-tectonic-plates/345870/21 "2006-02-25T07:56:44Z")
> [@Stranger On A Train](#): > > Sorry, but this book is full of urban legend and misapprehension; to excerpt from it would be perpetuating inaccuracies and misunderstandings. Bryson, despite claims to have conferred with “experts in the field”, seems to have failed to have the manuscripted throuroughly vetted before publication. A recent discussion of Bryson’s techincal merits can be found [thread=356705]here[/thread], but if you search back you can find plenty of criticisms of Bryson’s allegeded knowledge of science. I don’t specifically recall his coverage of plate techtonics, but his explainations of natural selection and modern physics are so badly mangled that hey may do far more damage than good. To say that his knowledge in these areas is limited is an understatement. > > Stranger I picked up a pop-linguistics book of his on the history of the English language at the bookstore on a whim. I wasn’t impressed with that, I must say. You’d think someone attempting to write a book pertaining to linguistics would attempt to learn at least the basics first. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [February 25, 2006, 3:11pm UTC](https://boards.straightdope.com/t/what-moves-the-tectonic-plates/345870/22 "2006-02-25T15:11:53Z")
> [@CC](#): > > One of the most remarkable is the mid-Atlantic ridge, where the material keeps coming out, spreading across the ocean floor and then dives back down under the continental plates, I’m pretty sure that that is not happening with the material from the mid-Atlantic ridge. None of it is “diving back down”, SFAIK. > [@Stranger On A Train](#): > > Sorry, but this book is full of urban legend and misapprehension; to excerpt from it would be perpetuating inaccuracies and misunderstandings. It’s not all bad 🙂 ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [February 25, 2006, 4:25pm UTC](https://boards.straightdope.com/t/what-moves-the-tectonic-plates/345870/23 "2006-02-25T16:25:30Z")
Well, I don’t think I’d do well challenging Stranger to a contest over the accuracy of Bryson’s assertions. I’m sure there are plenty of inaccuracies, particularly from the point of view of the cutting edge experts in the various fields. However, for the person who wants to know how plate tectonics works vis a vis a pot of boiling stew, I would still say you could do a lot worse that consulting a very readable and essentially correct discussion of it in his book. As to excerpting from it for 7th and 8th grade, I believe that in many instances the large picture is well enough stated that even if the fine points are, in fact, wrong in some places, the piece has value. Mentock, I have lent the book out, but as I remember, his point about the material diving back down is that if it were not doing so, where is it? It’s been spreading from the mid-Atlantic ridge for hundreds and thousands of years. And at the same time, sediment from the east coast has been building up along the coast for hundreds and thousands of years. Where is all that material? It’s all being subducted at the line where the plates meet and the spreading ocean floor is subducted under the continental plate. Anyway, in the absence of a book like that, there isn’t much that the average science naive but curious person can look to to help understand nature. I still recommend it. xo, C. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [February 25, 2006, 6:00pm UTC](https://boards.straightdope.com/t/what-moves-the-tectonic-plates/345870/24 "2006-02-25T18:00:18Z")
> [@CC](#): > > Mentock, I have lent the book out, but as I remember, his point about the material diving back down is that if it were not doing so, where is it? It’s been spreading from the mid-Atlantic ridge for hundreds and thousands of years. And at the same time, sediment from the east coast has been building up along the coast for hundreds and thousands of years. Where is all that material? It’s all being subducted at the line where the plates meet and the spreading ocean floor is subducted under the continental plate. No, it’s not. There is no subduction along the east coast (of the United States). The east coast and the atlantic seabed are considered one plate, moving west together. As the old supercontinent opened up, creating the atlantic ocean, it continued to move away. The cooling atlantic ocean crust has not subducted, it continues to move away with the continental crust. There is subduction in other part of the world. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [February 25, 2006, 6:25pm UTC](https://boards.straightdope.com/t/what-moves-the-tectonic-plates/345870/25 "2006-02-25T18:25:54Z")
Oh. Ok. So, where is all the sediment that has flowed off of the east coast? And where is the material that has spread westward from the ridge? Where does all that stuff go? Now you have me wondering, too. At one point, I was taught that the weight of the sediment had caused the rising of the Appalachians. I think it was referred to as the geosyncline. Sort of a seesaw effect. But I thought that idea had been rejected. So - where’s all this material going to? ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [February 25, 2006, 7:00pm UTC](https://boards.straightdope.com/t/what-moves-the-tectonic-plates/345870/26 "2006-02-25T19:00:57Z")
> [@CC](#): > > And where is the material that has spread westward from the ridge? Where does all that stuff go? It goes “west”. Seriously. The North American plate is being pushed west as the mid-Atlantic ridge expands. You are right that it eventually gets pushed back down into the earth but in the case of the North American Plate the subduction happens in the Pacific (not sure exactly where as some of the west coast is a transform boundary [slide sideways against each other] and other parts subduct). The North American plate is mostly riding over the top of the plates in the Pacific I believe. ---
**Author:** ![Khan](https://avatars.discourse-cdn.com/v4/letter/k/3ab097/32.png) [@Khan](https://boards.straightdope.com/u/Khan)\ **Post date:** [February 25, 2006, 7:20pm UTC](https://boards.straightdope.com/t/what-moves-the-tectonic-plates/345870/27 "2006-02-25T19:20:32Z")
> [@CC](#): > > Oh. Ok. So, where is all the sediment that has flowed off of the east coast? And where is the material that has spread westward from the ridge? Where does all that stuff go? Now you have me wondering, too. At one point, I was taught that the weight of the sediment had caused the rising of the Appalachians. I think it was referred to as the geosyncline. Sort of a seesaw effect. But I thought that idea had been rejected. So - where’s all this material going to? That sediment IS, among other things, the Appalachians, and it’s found its way into the soil of the eastern seaboard as well as to wherever the Atlantic currents took it. And the ridge is what’s responsible for the existence of the Atlantic. It started as a crack between what is now North/South America and Europe/Africa that expanded and filled with seawater. As such the material you’re looking for is the floor of the Atlantic ocean. Could you please elaborate on your question about the weight of the sediment causing the Appalachians? Where was that sediment? ---
**Author:** ![JRDelirious](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jrdelirious/32/9531_2.png) [@JRDelirious](https://boards.straightdope.com/u/JRDelirious)\ **Post date:** [February 25, 2006, 7:21pm UTC](https://boards.straightdope.com/t/what-moves-the-tectonic-plates/345870/28 "2006-02-25T19:21:06Z")
> [@CC](#): > > Oh. Ok. So, where is all the sediment that has flowed off of the east coast? On the continental shelf of North America; some of it makes up the East’s coastal plains (Carolinas, Florida, Chesapeake region); some was reshaped by the glaciers. To elaborate on **Whack-a-Mole** ’s explanation: on the North Aerican side of the collision between North America and the Pacific Plate, the NA plate crumples upward, resulting in the Rockies, Cascades and Sierras. Much of the Rockies, in turn, erodes into the Mississippi Valley and Gulf Coast. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [February 25, 2006, 7:38pm UTC](https://boards.straightdope.com/t/what-moves-the-tectonic-plates/345870/29 "2006-02-25T19:38:44Z")
> [@CC](#): > > Oh. Ok. So, where is all the sediment that has flowed off of the east coast? And where is the material that has spread westward from the ridge? Where does all that stuff go? Most of the sediment that has flowed off the east coast since the formation of the Atlantic, starting about 200 million years ago, is still there. [This map](http://mahi.ucsd.edu/Gabi/sediment.html) shows the sediment thicknesses, which are 7-15 km thick over the oldest sea floor off the east coast, and virtually nil out in the middle of the Atlantic, over the newest sea floor near the ridge. Note also that there is very little sediment near the west coasts of the Americas, despite very high levels of erosion off high mountains, since subduction is going on along most of this margin and swallowing the sediments that fall into the trenches. > [@](#): > > At one point, I was taught that the weight of the sediment had caused the rising of the Appalachians. I think it was referred to as the geosyncline. Sort of a seesaw effect. But I thought that idea had been rejected. That was the former explanation, but it has pretty much been discredited by the discovery of plate tectonics. ---
**Author:** ![Doobieous](https://avatars.discourse-cdn.com/v4/letter/d/da6949/32.png) [@Doobieous](https://boards.straightdope.com/u/Doobieous)\ **Post date:** [February 27, 2006, 3:13am UTC](https://boards.straightdope.com/t/what-moves-the-tectonic-plates/345870/30 "2006-02-27T03:13:30Z")
> [@Colibri](#): > > Note also that there is very little sediment near the west coasts of the Americas, despite very high levels of erosion off high mountains, since subduction is going on along most of this margin and swallowing the sediments that fall into the trenches. In California, much of the sediment coming off of the Sierra Nevadas and the ranges along the western edge, have washed into the great central valley, which has very deep sediment thicknesses (I can’t find numbers, but they are thousands of feet deep). The valley has acted like a bowl, containing the sediments. [Previous page](https://boards.straightdope.com/t/what-moves-the-tectonic-plates/345870.md?page=1)