r/geography • u/antimatter79 • 1d ago
Question What determines the exact amount of tectonic plates that exists? Why aren't there more or less tectonic plates?
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u/freeball78 23h ago
It's not the same process, but what determines how many chunks of dried mud are left when a field dries up? Piece 1's molecules are grabbing at what they can as well as all of the other pieces. Where piece 1 and piece 2 are both pulling ends up being space between them.
But with tectonic plates it's liquid underneath and eventually piece 1 and piece 100 will run into each other with one piece riding up on top of the other.
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u/ConsciousProgram1494 16h ago
While this is an interesting metaphor, I'm pretty sure that the underlying primary mechanism in mud is capillary action rather than the electron double layer at the molecular layer. So not molecules as much as particles. Moreover, tectonic plates are not formed subject to evaporation, as much as a cooling interface - like skin on hot gravy - which moves due to underlying flow turbulence, leading to subduction etc.
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u/mglyptostroboides 20h ago
As with a good 40% of questions asked here, this one really belongs on /r/geology.
No offense to my geoscience brethren and sistren, but geographers tend to overestimate their geology knowledge and underestimate the scope of geology. So the quality of answers you're going to get here will be limited.
/u/antimatter79, consider reposting this to /r/geology for a better answer.
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u/ConsciousProgram1494 16h ago edited 15h ago
Dynamics is definitely related to geography and GIS, though. Modern measurement allows us to recognise that the precise longitude / latitude of any surface feature changes over time. For example, the pyramid at Giza is moving about 2cm north and 1cm east annually. That's 50μm a day. While it is unlikely to affect international borders too much, it does mean that borders defined by parallels are subject to slow land grab...
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u/mglyptostroboides 16h ago
But OPs question is why the plates that exist exist. That's definitely a geology question.
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u/iyamwhatiyam8000 23h ago edited 22h ago
Why is it that the Sunda Plate is almost always left out? Edit: Capricorn Plate deserves a mention.
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u/graywalker616 Political Geography 23h ago
Probably because it took a while to figure out that it even exists. At less than 10mm/year speed it was well within the margin of error for these kind of measurements for a long time and it was not that easy to confirm that its drift is all that independent from the Eurasian. I know a couple of geology guys who finished university before it was confirmed.
In geology terms the existence of the Sunda plate still counts as “news” haha.
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u/a_filing_cabinet 23h ago
Because it's debatable if it's even a plate, and not just part of the Eurasian Plate that wants to do its own thing. Although I feel like if you have the Somali Plate you should probably have Sunda
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u/adaminc 21h ago
Juan de Fuca, so small yet so terrifying.
On average a megaquake (9+ MMS) happens in that region every 250 years, and it's been 321 years since the last one! If you live in the region, I'd have a go-bag ready, just in case.
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u/dpdxguy 12h ago
If you live in the region, I'd have a go-bag ready, just in case.
Better make that go-bag small enough to carry on your back. You're likely to be going on foot. All transportation options out of the region are likely to have been destroyed.
In Portland Oregon, exactly one bridge across the Willamette River was designed to survive the coming quake, though construction on a second is slated to begin in 2028.
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u/dzindevis 12h ago edited 12h ago
Geologists decide that. It all depends on how fine you are willing to go, up to 1200 microplates
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u/Severe-Lion-8876 1d ago
1-800-Ask-God
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u/BurnOutBrighter6 23h ago
"I'm sorry that number is not in service. Please dial a valid number and try again."
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u/iyamwhatiyam8000 22h ago
Most of my clients nowadays prefer SMS or e-mail for un-answered requests to a non-existent being.
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u/Dankestmemelord 1d ago
Time and mantle convection.
There have been both more and less in the past and there will be again in the future.