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

04-08-2011, 09:46 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, 05:41 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, 05:43 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, 05:55 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, 06:01 PM
May be a nice challenge, yes. Or even a nice lite challenge.

04-08-2011, 08:44 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, 05:17 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, 10:26 PM
Thank you Gilgamec, that answers most of my questions quite nicely.

Hannah Ophiuchus
11-19-2015, 08:11 AM
if coriolis effected land masses what would you expect to find?an indentation of the coastline at equador?horse latitude cracks in the land masses like the mediterranean?different minerals upsurging on the earth on the equator and subducting at horse latitudes?this would be a bit less than 30 degrees due to oblateness.you might expect a pattern to earthquakes like a japan quake followed by a NZ quake in succession being opposite sides of the equator.maybe cyclones would pick up power if they travel to latitudes 2/3 of the way to the pole- i figure there would be a counter rotating band above this region.do people keep quiet about this so they can exploit the minerals?are the electron shells the coriolis pattern of atoms?as above so below.are "plate" tectonics and "particle" physics NLP obfuscations?i have pet theory of pangaea forming at the pole which initially pointed towards the sun of an earth acreted from a sphere of material and major geologic upheavals occuring as the earths tilt went past 45 and 33 degrees.i'm predicting the continents to spread equidistantly across the planet when the tilt reaches 18degrees and the arabian peninsula can no longer act as a lynch pin.how could noah predict the flood and why do they predict armageddon?

11-19-2015, 09:23 AM
Yes, theoretically it does, but on a scale so small as to be undetectable, and completely overwhelmed by other factors.

Consider your bathtub drain, a common example for Coriolis Effect. Theoretically, the water will always swirl going down the drain in the same direction (depending on which hemisphere you are in), but in practice it you watch and record it, the water will swirl left 50% of the time and right 50% of the time on average. Why? Because other factors such as movements in the water, even bubbles in the drain, affect it more strongly than the Coriolis Effect does.

Another common question is whether rivers are affected by CE. Rivers do not tend to flow more westward because of CE even on very flat land, because the terrain they flow through overwhelms any CE. Rivers do, however, tend to flow more heavily toward the westward side when constrained by heavy terrain, so that in mountain passes, most of the erosion is on the west side. On flat land, where the river meanders, the meandering goes both directions because the softer terrain lets the flow overwhelm any CE.

11-19-2015, 12:18 PM
The Coriolis pseudo force is no force at all.
It is just a manifestation of a non inertial (e.g rotating) frame of reference.

Imagine an immobile disk with an ant crawling from the center to the edge following a radius.
The trajectory you would see is a straight line because an immobile disk is an inertial frame of reference and as there is no force acting on the ant supposing its motion is balanced by friction (so according to Newton F=m.a => m.a = 0 => a=0 and the movement is a line).

Now same ant but you make the disk rotate to clockwise.
Obviously the trajectory you would see is a curved one because the ant is not only moving along a radius but is also carried by the rotating disk clockwise.
If you try to use Newton again, it doesn't work (from your point of view the acceleration a is obviously non zero, yet Newton says it is 0) and it shouldn't because you must not apply Newton to a non inertial frame of reference.
If you insist and want to write Newton all the same, you must add a non physical correcting factor - let's call it Fc.
E.g you would write F+Fc=m.a. F is still zero but because of the non zero Fc, you obtain a non zero a. And you obtain indeed a curved trajectory.
This correcting factor is called the Coriolis "force" but as you see it is no real force at all - it is just a trick that allows to use Newton for a rotating frame of reference. It's just convenient and makes the trajectory calculations easier.

So now as the Earth rotates, every single object moving on its surface will be subject to this Corolis pseudo force.
It is true for oceanic currents, atmospheric circulation, continents and ants.
Now the value of this pseudo force is very small because the Earth rotates slowly and the trajectories we observe are generally small.
In practice it has only an influence on very large movements like atmospheric cells, cyclonic rotations and oceanic currents.
It has no influence at all on slow movements (like continents) and small movements (like Chick rightly said bathtub drains don't rotate differently in N and S hemisphere)