Hi everyone, Cody here, and I have a piece of plasterboard.
This is otherwise known as sheetrock; it is a gypsum-based material,
and we put it up on the walls because it is very fire resistant, insulating, and it can handle water fairly well.
Now one thing about this is the fact that a small piece like this is fairly rigid.
You can see it's fairly stiff, and if I try to bend it,
[snap]
it'll just snap.
You know, the paper might not, but the...
the plaster, the gypsum,
since it a... actually is a rock,
it... can't handle the bending very well.
But that's only in small scales.
[Drop plasterboard to the ground]
If we take a long piece, like this,
you can see,
that it's very flexible.
See that?
Now this actually reminds me of geologic processes.
You see, rocks, on a small scale
are fairly brittle.
If you ever struck at a rock with a hammer, it breaks.
But if you have a very large slab of rock,
it bends and deforms.
Kind of like this.
Of course, the material is actually bending on the small scale,
it's just that small arc segments of very large circles, look flat.
And so the amount that this bends before it breaks
is imperceptible, because I'm looking at such a small piece.
[Plasterboard hits the floor]
If you take a large piece and try to bend it, you'll see that the...
amount that it's bending here is also still imperceptible.
But if you zoom out a little bit and look at the whole thing,
you can see that there is a definite curve to it...
as it does actually bend.
In fact, in order to model geologic processes on a small scale,
geologists usually use a material like sand,
to simulate what the rocks do on the very large scale.
I was reminded of an experiment we did back in my Structural Geology class,
and I actually made a video of my own little project that I did off on the side,
but I realized that I never published the video.
So, here it is.
So I want to run to experiment to simulate the fact that crustal rocks are actually floating on the semi-liquid mantle.
Initially, I wanted to use Mercury, because Mercury is incredibly dense,
fluid, and rocks will actually float on it because it's so dense,
but the school thought that would be a terrible idea
so I'm actually using a very lightweight material. This is Perlite.
See here.
And uh... this is basically obsidian that's been puffed out.
So it's mostly air, and, uh, Silica.
uh, If you've seen Pumice, it's very similar to Pumice, although not quite as hard.
So it, it's got a very low density, and it'll actually float on water.
And so what I'm going to do is put a bunch of Perlite in here,
and then add some water to make it float.
That way, it'll simulate the crustal rocks which are floating on the mantle.
And as for the marker beds, I'm going to use some carbon here,
some activated charcoal in fact,
just to give us a nice big contrast, but without changing the density of the material very much.
And, like I said before, the fact that it's basically sand will simulate rocks on a large scale.
So we've got the perlite and carbon in, as you can see.
It's got a nice dark band right through the perlite there, simulating a marker bed in the rock.
Now, I'm actually going to put the water in now,
rather than having it in before...
[Water flowing]
because I think it was much easier to spread out this way.
I'm just going to let this fill up slowly. The water will just run in and should just lift this all up.
Okay, so we've installed the water,
and everything looks like it's still good, it just floated straight up.
So now, it's time to start squishing it.
You know, this actually looks a lot like what happens when you run two continents together,
like this would be the Himalayas here, you know?
The crust just gets super thick and you get a big pile of material that ends up being the mountains.
And now we've run out of water here, so now it's just going to be...
regular old thrust folding.
It's interesting how it's like, coming down here, see that?
Kanyon: It's basically what happened at the beginning again.
It's got kind of a weird pinch over here.
Yeah.
It's kind of like, going up and pinching the top right here.
Yeah!
Oh, it's squishing over here now! See that?
Look at this up here, up at the top.
See that?
How it's like, pushing it under?
[Screw squeaking]
So you can clearly see that there are two thrust faults: here and here.
But what is kind of odd is the fact that the thrust faulting does not extend down into the marker bed.
You know, you should see a sharp break if this was indeed a fault.
I didn't realize it at the time, but I now realize that what we're seeing here is actually a brittle-ductile transition.
See, at the surface, the grains of perlite...
are able to slide past each other because there's not very much confining force pushing them together, so there's not very much friction there.
But as you go deeper into the material, the pressure is higher,
and so the Perlite grains don't rub past each other as easily,
and so rather than breaking and forming a brittle fracture,
like a... thrust fault,
you rather see these compressional folds.
And what's really cool about this is that this is exactly what you see on a full scale, in real life.
You see folding down in the basement crystalline rocks,
where the temperatures are higher and the confining stress is incredibly high,
but up at the surface you see thrust faulting.
See, we ended up with just this wavy, folded structure, see that?
How the black layer has...
got these folds in there?
And they seem to increase in amplitude towards the... thing that was pushing.
See, it tapers off over here.
So like over here it didn't move at all, but this got just squished, and it "accordioned" together.
And the whole thing just got thicker.
That's cool.
I thought it was really interesting up here,
How this material was actually going underneath of this material.
So it's actually...
almost like...
a triangular fault. So you've got faults going this way,
and this way here, see that?
There's two faults right there.
Well, should we run it backwards and see how it turns out that way?
Alright, so basically what we have here is like the basin and range... extension,
and then material that still hasn't really moved a whole lot,
so this would be like your Wasatch fault into the Rockies,
into Colorado.
So the crust is like, super thin right here, but it's still rather thick up here.
And, er, if you look up in the top here,
you've got these blocks of material that are just floating,
and then, surrounded by areas that are lower.
So you've got a block of material here,
a low area,
block of material here,
and a low area.
So this is like the Horst and Graben structure,
that you see with these extensional regions.
So you've got like normal faults here, here,
here, and here obviously.
So these high areas would be your mountains,
and the low areas would be your valleys.
Alright, so this is all cleaned out,
and we've removed the water.
I'm thinking maybe I'd like to do a run with the Perlite without the water, to see how much of a difference it actually makes.
I'm out of activated charcoal, so I'm going to have to use like a red clay for the marker bed,
but... shouldn't make that much of a difference, right?
[Pouring of perlite]
So I guess this would be simulating like a smaller scale.
So you're not like continental scale, this is more like...
you know, top of the continent
or whatever.
Got a nice cylindrical fold going here, see that?
[Screw squeaking]
Of course the low density material makes it so it doesn't have very much... weight to it, you know?
[Screw squeaking]
You definitely have a thrust fault right in here.
Hehe
There's a normal fault going, see?
Hehe
So in conclusion, by floating the material on top of a liquid,
I was more accurately able to simulate the processes that formed the basin and range of Utah and Nevada.
You see, 40 million years ago,
the crust was compressed, so you had, er, thrust faulting, and also
folds going on deep down in the crust,
and then the crust was extended,
forming the valleys and ranges.
The Basin and Range.
Doing the test inside of a sandbox that is completely dry,
your faulting gets shifted over a little bit, because you've got drag on the bottom of the box.
Also, the water, since it's able to float on it, it gives another place for the material to go,
so it's able to go down as well as up,
which is the case in real life.
A completely dry sandbox is good for simulating the upper part of the crust which is in the...
Brittle Zone.
But, in order to get the full Brittle Zone and the Ductile Zone which is many miles down,
You kind of have to use this method with the lower friction on the bottom, because that's how it is in real life.
Anyway, hope you all enjoyed. I'll see you next time.