Hi. It’s Mr. Anderson
and this is environmental science video 3.
It is on geology,
which is the study of rocks and how they change over time.
And in this class more appropriately
how that affects human society.
Now the problem with rocks is that they change slowly.
They change over geologic time
and we simply do not live long enough to see all of these changes occur.
You could imagine how this sandstone is being shaped by the wind
but you cannot see it.
And it is not until we see lava
that we really start to understand the dynamic earth.
And to understand these systems on the earth
we should really understand how the earth is put together.
And so if we look at the layers,
on the inside we have the inner and outer core.
We then have the mantle and finally we have the crust.
And we live on the crust.
And we have only been able to
dig just a little bit into the crust.
And so we have been able to figure out everything else
by looking at how earthquake waves move through the earth.
And we know this,
that the crust is made up of rocks and minerals.
Rocks are made of minerals,
which in turn are made of molecules and atoms.
They are constantly being reshaped.
And we can measure that through the rock cycle.
But crust itself is made up of these large continental and oceanic plates.
And they float on the mantle itself.
And so this is rock under here,
but it is rock that is moving.
As we generate heat,
as it moves up, it is pushing those plates around.
They move very slowly,
about the same rate that your fingernails grow.
But they have huge force and therefore huge impacts.
And so when those plates run into each other we have boundaries.
An example of that would be the ring of fire.
So if you look around the Pacific Ocean
you have this area where almost all of the earthquakes and volcanoes take place.
We also have what are called hot spots.
And those are going to be areas where
a plate will move over a hot area in the mantle,
and we can form islands like Hawaii.
Now if we look at where those boundaries
occur we will have structures like volcanoes and mountain chains.
But we will also therefore
have hazards around those areas
where it can impact human society
and we will discuss a lot of those.
And so to understand what is going on on the earth
we should really understand what it looks like on the inside.
So we have a solid inner core,
a liquid outer core and
then we have what is called the mantle.
Now around 85 percent of the volume of the earth
is going to be in this mantle.
So it is rock, but it is rock that is moving.
We are generating a huge amount of heat down here.
And then we finally get up to what is called the crust.
That is where we live.
And so on that crust we have rocks.
And those rocks are constantly
being shaped from one into another.
And so if we take a look at this rock cycle,
since it is a cycle you could start anywhere.
Let’s start with an igneous rock.
So an igneous rock,
is going to be formed when we have crystallization of magma.
as it crystallizes you can see those crystals right here.
So this granite is made up of minerals.
So I can see for example this quartz
and this pink feldspar and we have this mica.
So these are the minerals that make up the rock itself.
But, this could experience erosion.
So erosion on the planet, water, wind,
can cause it to break down into sediments.
therefore after it has done that it could get squeezed
for a long period of time and
we could have a sedimentary rock,
which is going to be compressed sediments.
Now that it could be squeezed,
we could squeeze it under the surface of the earth using heat and pressure.
It could form something like quartzite.
Or we could take that igneous and we could squeeze and
make something like gneiss.
And so g-n-e-i-s-s,
it is a type of metamorphic rock
that is formed by the squeezing of granite.
Now you can see those minerals are still there
but has a different shape.
And so the rocks on our planet
are continually recycled over and over and over again.
But if we get back to the structure of the earth,
what is driving all of this
are going to be convection currents within the mantle itself.
And so if you look at this and say this is some boiling water,
so if we generate a little bit of heat underneath it,
that heat is going to be transferred through the water,
so if you held your hand up here
you would feel some of that heat above it.
But if we look inside the water itself
we are going to have these convection currents,
areas where we are heating it up.
And so we are decreasing the density
and then it cools down and then it is going to sink again.
So we are going to find the same thing in the mantle itself.
It does not occur as quickly
as it does in the boiling water,
but it has huge implications on the crust above.
So if we look at that crust it is actually made up of plates.
And so if I trace out a plate like this,
this would be a continental plate.
And so it is being pushed to the left
and the reason why it is being pushed is
because this convection current is moving like that.
It is forcing the plate in that direction.
And it is running into another plate.
So we have an oceanic plate.
The oceanic plates are going to be more dense
and they will be pushed underneath a continental plate.
And what we are going to get, right along this
margin is going to be a convergent plate boundary.
They are running into each other.
But we could look over here
and maybe there is another oceanic plate that is moving in the other direction.
Why is it moving in the other direction?
Because the convection current is pushing it here.
Or pushing it there.
And so we could have this mid-Atlantic ridge or this mid-oceanic
ridge being formed right there.
So we have known this for a long time.
If you look at the ring of fire,
we find around the Pacific Ocean we have an aggregation of volcanoes and earthquakes,
something like 75 percent of all volcanoes,
90 % of earthquakes are found in this area.
If we start plotting where those
earthquakes are we can start to see where
those plates exist.
And if we look at the plates on our planet it is hard to wrap your
head around this picture for a second.
So this is North America right here.
And it sits on this giant north american plate.
And then we would have the pacific plate right here.
And so those plates are constantly moving around.
You are probably familiar with Pangea
which was a time when all of the continental plates had come together.
So what happens when plates meet is
that they can do one of three things.
They can slide past one another
in this transform boundary.
They could move apart.
We call that a diverging boundary or
they could run into each other.
That is converging.
And so if we look at an example of that, right
here we have a convergent plate boundary.
So what is going on?
We have this oceanic plate,
which is being pushed of subducted underneath a continental plate.
I described that just a second ago.
What is happening is we are melting that rock
and that is forming this volcano chain
that goes all the way back here.
An example could be the Cascades in Washington state.
We could also have a convergent boundary right here
where you have an oceanic plate going underneath another oceanic plate.
And we get this island arc like the Aleutian Islands in Alaska.
We could have divergent boundaries.
An example could be right here.
So we have this oceanic plate moving away
from this oceanic plate so we get this mid-oceanic ridge.
We could have a rift valley
where this continental plate is being pulled apart.
We could have transformed boundaries.
Here would be an example where they are sliding past one another.
San Andreas fault is a good example of that.
But we could also have structures where this no boundary.
So if we look right here we have what is called a hot spot.
Remember that is going to be an area where
the mantle is close to the surface.
And so for example
Hawaii was formed as the plate slid over a hot spot.
And let me show you what that looks like.
So if we imagine that is the hot spot,
it is going to be underneath the plate and
what has happened to Hawaii over time,
is it slowly slid over the hot spot.
Hot spot stays in the same location.
And so we have had volcano after volcano after volcano.
And so this the most recent volcano and
we will have another island right here.
And the reason they are smaller islands out here is that there is more erosion.
Yellowstone National Park is another example
of a hot spot and a plate simply sliding over the surface.
Now we get to humans and human society and
how we start to interact with the structures of the earth.
And so living around these boundaries can be dangerous.
It is just a matter of time.
And so an example could be volcanoes.
Some volcanoes, like the ones we would find in
Hawaii can ooze out.
And as long as we are able to move out of there quickly
we are going to be fine.
But some are highly explosive.
And it depends on what minerals make up that
rock that determines the explosiveness of the volcano.
A very explosive one I remember
was Mount St. Helens.
And so this is a picture of Mount St. Helens in Washington.
This is the day before it exploded.
And so just take a second to imagine that is the structure
of the volcano and now it is gone and rebuilding again.
And so it literally blew apart.
If you were on or near that you died.
Earthquakes are another example of a natural hazard.
We have our faults and this would be a fault right here.
And we have one plate, in this
case transformed fault, where it is sliding past one.
We could also have a divergent boundary,
so these two are moving away from each other.
And so we have what is called a normal fault.
It is slipping down.
Or we could have a reverse or thrust fault,
when we have an convergent
between these two areas on either side of the fault.
Now the names are not as important.
Really understanding what is going on in an earthquake is.
If you think about it, if we
have two plates that are pushing
on each other eventually they are going to build up pressure
and it is going to slip.
And as it does that we have an earthquake.
So if we watch this right here,
let’s say there is pressure in this direction,
in this direction and eventually it builds up
and we have a slide along that fault line.
Now it is not like it stopped.
There is still pressure there.
We could have another earthquake in the future.
And another earthquake in the future.
As these move past each other
it is just going to move in small slips.
And every time we do we have an earthquake.
Now if you are standing on the surface and
there is an earthquake you are going to be fine.
The problem is if we build structures
on that and it is not earthquake ready then those fall
in and humans are going to be impacted.
We could also look at tsunamis which are caused by earthquakes.
What we have here is a subducting oceanic plate.
This would be a continental plate.
And what is happening is this is being
pushed underneath, but it will just stick.
And so it is not going to release.
And it sticks then we build up pressure.
And eventually when it slips what
we get is a huge push up on the water above it.
So you get this vertical motion
in the ocean and that leads to these giant tidal waves.
And so if you are near the ocean
you would also suddenly notice the ocean is going way
out and then it is going to come way in and there are really bad consequences
from that. We could also have mass wasting.
So an example could be a landslide moving across this road.
This is a picture taken before and then watch it, after a landslide.
Now it does not occur really quickly.
It could be triggered by an earthquake, but generally
if we get a lot of water in an area,
it can not support that weight.
And so did you learn about earth systems?
Can you stop the video and try to fill in the blanks right now?
I would pause the video.
But if not, I would say we have a center core.
We have a mantle and a crust.
The crust is made up of rocks which
in turn are made up of minerals, which
is reshaped using the rock cycle.
These plates move on the surface.
We call that plate tectonics.
An example would be the ring of fire.
Where we have boundaries we can build up structures
like volcanoes, mid-oceanic ridges.
But we could also have natural hazards.
And remember not along boundaries,
but just within the plate we can have hot spots.
So I hopeyou learned all of that.
And I hope that was helpful.
Hi. It’s Mr. Anderson