View Full Version : Does the Earth's Spin effect the movement of the continental plates?

04-08-2011, 08:46 AM
Hello all,

This is my first posting (other than my introduction post), and there will probably be a few more in times to come.

Anyways, the title of this thread is pretty self explanatory. I know that weather patterns are effected by the Coriolis Effect, but what about tectonic plate movements? Do they have a tendency to move east/west instead of north/south?

Thanks in advance for any replies.

04-08-2011, 04:41 PM
Interesting question Thurlor, I am not a geologist, but I am quite well versed in quoting that oh-so-accurate-and-never-erroneous reference known as Wikipedia.

Regarding the driving mechanism of the plates various models co-exist: Tectonic plates are able to move because the Earth's lithosphere has a higher strength and lower density than the underlying asthenosphere. Lateral density variations in the mantle result in convection. Their movement is thought to be driven by a combination of the motion of seafloor away from the spreading ridge (due to variations in topography and density of the crust that result in differences in gravitational forces) and drag, downward suction, at the subduction zones. A different explanation lies in different forces generated by the rotation of the globe and tidal forces of the Sun and the Moon. The relative importance of each of these factors is unclear, and is still subject to debate (see also below).

I'm sure you could read the rest of the article yourself, but in general there is very little evidence for a directional preference of tectonic motion. Recently scientists have determined that there is a slightly Westward bias to the total motion of all tectonic plates (there are plates moving in all directions though), but it is unclear if this is actual or just a result of the dominance of the increasingly large pacific plate (which is expanding westward from its ridge).

Wish I could be more help.

Edit: Again, take all this with a grain of salt. I am only summarizing what I just read on wikipedia.

04-08-2011, 04:43 PM
Common sense would say yes but I don't think that it actually does. North America is sliding to the northwest and at the same time spinning counter clockwise. Our west coast is moving the same way but faster. India and Africa are moving north. The Saudi Arabian peninsula is spinning but I don't remember which way it is moving. In a few billion years they all come back together to form something called pangea ultima (or something like that). I got that all from some of the tv shows on either History or Science channels and I'm simplifying things as well but that's the main gist of things. If you want to compare the entire crust's movement to the core, then it's possible that things are always sliding from east to west due to spin but I don't think that there's anyway to verify that. I'm sure that those with more knowledge can expand or counter.

04-08-2011, 04:55 PM
Pangea Ultima (http://en.wikipedia.org/wiki/Pangaea_Ultima), that sounds like a great idea for a mapping challenge to me! :)

04-08-2011, 05:01 PM
May be a nice challenge, yes. Or even a nice lite challenge.

04-08-2011, 07:44 PM
If I had to guess I'd say there wasn't enough 'slip' for the continental plates to freely slide at the time scale of days. If I had of actually thought about this properly I would have come to this conclusion myself, as Earth doesn't have all of it's continents spread along the equator.
Anyways, thanks for the replies.

04-09-2011, 04:17 PM
I know that weather patterns are effected by the Coriolis Effect, but what about tectonic plate movements? Do they have a tendency to move east/west instead of north/south?Yes, tectonic plates (like everything that exhibits large-scale motion on the Earth) are affected by Coriolis forces; they have a tendency to rotate clockwise in the Northern hemisphere, counterclockwise in the Southern. However, the fact that the plates are solid mitigates this effect, as does the fact they run up against each other (like two meshed gears can't both rotate the same way).

However, the Coriolis effect is not the primary cause of the east-west pattern in weather systems. That is the division of the atmosphere into convection cells; six bands along the Earth where hot air rises at one latitude, travels north and south high in the atmosphere, then sinks at a different latitude. The tropical cell is driven by hot air rising at the equator and falling in the subtropics; the polar cell is driven by cold air falling at the poles and rising in subpolar latitudes. The third cell in each hemisphere is the temperate cell, which runs in the opposite direction from what you'd expect, because it's driven by the other two; the air falling from the tropical cell moves towards the pole, then pulled up when it meets the air from the polar cell. (There's a pretty good illustration here (http://wisp.physics.wisc.edu/astro104/lecture11/F08_22.jpg).)

Because of the Coriolis effect, the circulation of air in the convection cells causes general air movements along lines of latitude, especially in the mid-latitudes (where the tropical cell meets the temperate cell). However, the convection effect is nonexistent in the tectonic plates; even in the mantle, which has some effect on the motion of the plates, the convection cells are a lot deeper (as there's a lot more mantle than atmosphere) and aren't smeared out into bands by the Earth's rotation.

Basically, then, the Coriolis effect should be, at most, only a minor influence on the motion of the tectonic plates, and you shouldn't expect to see more east-west than north-south motion in any event.

04-09-2011, 09:26 PM
Thank you Gilgamec, that answers most of my questions quite nicely.