# Anyone know about plate tectonics?



## John Galt (Aug 4, 2015)

I'm planning a project and was wondering a few things: 
1. The inciting incident involves someone magically "lifting" a tectonic plate to form a wall of sorts. What would the consequences be of this movement? (The intended city to be walled has ocean on all sides save for one which faces land) What would be the consequences for the land and oceanic plates specifically? (local to the area and global)
2. For the above consequences, how could they be "remedied"/"countered"?
3. As more of a point of interest, if - hypothetically - there were a few plates. Could they (or would they) move more frequently and could they be shifted around like geo-fortresses?
4. Any random interesting facts/phenomenon or theoretically possible situations.

Thanks.  :icon_cheesygrin:


----------



## Blade (Aug 4, 2015)

You can't get there from here.:dejection: Tectonic plates are huge and could only be relocated with a vast and directed input of energy. The plates are, on average, about 100 km. thick and move slowly about on their own. 

Plate motions range up to a typical 10–40 mm/year (Mid-Atlantic Ridge; about as fast as fingernailsgrow), to about 160 mm/year (Nazca Plate; about as fast as hair grows).[SUP][4][/SUP] 
Wikipedia.

In any case moving a plate would have unpredictable consequences which could be catastrophic. :blue: Since no one seems to really understand plate behaviour and how interaction is performed on a global scale intervention could have consequences like huge volcanic eruptions or earthquakes either nearby or some unsuspected remote point.



> 2. For the above consequences, how could they be "remedied"/"countered"?



Point is that they couldn't be. If you moved a plate on the Pacific rim and giant earthquakes suddenly happened in Alaska you would just be stuck with it. Messing with the plates could result in serious personal unpopularity and would likely even be life threatening.](*,)



> What would be the consequences for the land and oceanic plates specifically? (local to the area and global)



Unknown but serious and irreversible.:worked_till_5am:


----------



## Cran (Aug 4, 2015)

John Galt said:


> I'm planning a project and was wondering a few things:
> 1. The inciting incident involves someone magically "lifting" a tectonic plate to form a wall of sorts. What would the consequences be of this movement? (The intended city to be walled has ocean on all sides save for one which faces land) What would be the consequences for the land and oceanic plates specifically? (local to the area and global)


OK. I'm guessing this is not an Earth setting; at least not the Earth as we know it. 

Further Assumption: magic or super technology can achieve anything you want.

With those out of the way, let's look at what you are asking here: lifting a tectonic plate to form a wall of sorts. Yes, tectonic plates can be lifted by other tectonic plates. Most - oceanic/continental plate interactions - form active volcanic regions. The one well-known continent/continent interaction is that of the Indian sub-plate sliding under the Asian plate, forming the Himalayan mountains and the Tibetan Plateau.  

I doubt a tectonic plate is what you are looking for here; even a microplate is a bit too large to tilt to a vertical alignment without looking ridiculous or staying stable for very long before gravity does its thing. What you want is block fault movements, which commonly occur within plate boundary fault zones, but also occur within plates if the conditions are right ... dangerous for those caught up in the moment. For the block elevation shift to make an effective wall, it would be a catastrophic earthquake locally.

In any event, to make the changes you want would mean severe earthquakes, and likely complete disruption of the city you want to protect. Raising pieces of oceanic plate relative to a continental edge do happen (ophiolites), but it means a very active subduction zone offshore and lots of the nastiest volcanic activity on land. And mass slumpings (or mass wastings - like avalanches but with entire mountains or large portions thereof). And earthquakes. 

It looks like you want a headland - that takes care of the sea-bound sides - then ... some sort of natural wall between the tip of the headland and the mainland. 

Hmm. Sure you don't want a moat instead? That would be easier. In other words, it is easier to undermine the surface layers and trigger a collapse in this layout than to trigger a fairly small-scale (geologically) reverse block fault that leaves a wall. 

If it didn't have to be created; ie, if it was there from before the time of the story or the city, then you could have an impressive rock wall from the natural processes of folding and erosion, leaving the hardest layer(s) standing. These rarely turn up singly, so it would more likely be a maze-like parallel series of natural walls. 





> 2. For the above consequences, how could they be "remedied"/"countered"?


Easiest that doesn't involve magic or super technology? Don't Be There.

Otherwise, geological activity on the sort of scale you want can't be countered by any means available to us. The recent devastation in Nepal was from a relatively small block shift. The tsunamis which caused Japan such grief or the Indian Ocean nations such terrible losses, were from relatively small block shifts. Large shifts tend to come from a series of smaller shifts over longer than human lifetimes. 

To compress the time/rate of these things means a world more like ours in its earliest times, not conducive to complex life or cities.   





> 3. As more of a point of interest, if - hypothetically - there were a few plates. Could they (or would they) move more frequently and could they be shifted around like geo-fortresses?



Well ... yes, if they were microplates and if you could bear a world that only sci fi and fantasy worlds could be, with open seas of glowing lava and steam clouds rather than liquid water. In other words, a world more like ours in its earliest times, not conducive to complex life or cities.


----------



## Bloggsworth (Aug 5, 2015)

The resultant tsunami would wipe out most life on earth, you need know no more than that.


----------



## ppsage (Aug 5, 2015)

I think perhaps we are not looking at tipping whole plates on edge here. A tiny percent rise, or a small tilt such as has made the Dover cliffs, properly engineered to reduce seismic effects, would create an impressive redoubt against man (alien?) made ground assault. This could possibly be worked out to SF plausibility requirements; fantasy ought to be a cinch.


----------



## John Galt (Aug 6, 2015)

@ppsage: You're right - I'm not planning on tipping the entire plate at 90 degrees, just bringing up the edge so as to make passage to the city (and its grain fields) incredibly difficult by human means. This is for fantasy, so most of it's accounted for in the magic, but I like to write the magic as scientifically as possible. 

@cran: The city can be destroyed; in fact, if its inhabitants weren't killed by the crash of the plates, the persons responsible would go around and kill everyone within. The point of the wall isn't to protect, but to keep people out (and stop them from finding a thing). Moat wouldn't work as well, I think; the thing I'm trying to hide is a sizable tree. It has to be created, but as more of an inciting incident - "wall" comes from nowhere, earthquakes and the lost grain fields cause war within the country, which adds conflict to the post-war plot.


----------



## Cran (Aug 6, 2015)

John Galt said:


> @ppsage: You're right - I'm not planning on tipping the entire plate at 90 degrees, just bringing up the edge so as to make passage to the city (and its grain fields) incredibly difficult by human means. This is for fantasy, so most of it's accounted for in the magic, but I like to write the magic as scientifically as possible.
> 
> @cran: The city can be destroyed; in fact, if its inhabitants weren't killed by the crash of the plates, the persons responsible would go around and kill everyone within. The point of the wall isn't to protect, but to keep people out (and stop them from finding a thing). Moat wouldn't work as well, I think; the thing I'm trying to hide is a sizable tree. It has to be created, but as more of an inciting incident - "wall" comes from nowhere, earthquakes and the lost grain fields cause war within the country, which adds conflict to the post-war plot.



In that case, you do want a very localised reverse (or thrust) fault shift to lift the headland (or at least enough of it) relative to the mainland. To those outside of the city/headland, it would appear as an unbroken wall or sheer cliff. As a localised thrust shift, it would include some tilting of the block. None of the building levels would be left horizontal; those left standing would have a distinct lean away from the fault line. 

In broader terms, it would indicate a larger converging boundary of tectonic plates. 

It suggests the other plate is also continental (think Africa moving towards Eurasia, or South America moving towards North America - in both cases forming long peninsular mountain chains orthogonal (normal, at 90 degrees to the movement, think Italy) which eventually form isthmuses (think Central America), which makes sense if the setting is a large headland.

If the other plate is oceanic, there would be a subduction zone offshore and a boundary chain of volcanic islands (examples of these are found in and around East Asia; eg, the Korean peninsula and the Japanese island group).


----------

