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Welcome back to week three's videos. We are going to continue on and talk about
coastal processes,
that are occurring
along the edges of the continents. And in this video
what we are gonna
continue with
are
some of the
major
coastal landforms that are associated with the different types of coastlines. And
remember these
types are: the emergent, the sub-mergent and the fairly stable
coastline. So
last video we did a little bit of a Google Earth kinda intro.
So we are going to continue on
and take a look at some of these
different areas, some of the things we see at active margins. And then we'll
talk about what's happening at passive margins.
So again we looked here at
Point Reyes, California. If I kinda zoom in on Point Reyes you can see that
rocky coastline. Very irregular surface here. You can
see waves crashing if we zoom in
really, really far in and kinda move around a little bit
you can really see
the topography here, the rocks out in the ocean water.
So the next place
that we will visit
is actually right around the corner from here.
And that's Soqueal Cove,
California and if I
search, we'll
fly right over, which is super fun,
we zoom way in on that cove, but again we don't want to be looking at the water.
You actually want to be looking
at
the edge of this continent. So we're
kind of passing by the city of Santa Cruz
and what we kinda
see here, just outside of Santa Cruz,
we see this highway passing
through.
And on the
north side of that highway we see kind of a mountainous environment.
See rivers flowing out.
Not a lot of development.
But right along the
edge
of the coastline, here in the south side of the highway, we
see lots of
farmland. Farmland tends to be
fairly flat.
They like to build farms in places that are pretty flat
to begin with. They don't want to be.. have to, you know, level things out.
This part of the coast here
was flat before these farms came through
and started cultivating.
And what this flat surface is is one of these wave-cut benches.
So this
part of the coast used to be
underneath
the ocean. So the waves
would have been crashing right about where that highway
passes
through
that farmland to the south and the more mountainous environment to the north.
So this is active tectonics.
We're in California, this is where the San Andreas fault is.
So we have things
actively moving. And in this part
of the country, the
continent is actually rising up out of this sea. And know that because we see these
wave-cut
platforms.
I have a little
example
for you of what that looks like.
So in those emergent coastlines-
continents rising out of the ocean we get
the wave cut platforms that we just saw in Google Earth.
And we see rocky coastlines, headlands, and sea stacks.
So what happens here, if we start out
with our
continent at this dotted line,
topography surface. We
force the ground surface up and out of the ocean. What we do is we take
that surface that was once being eroded by the waves,
and we raise it up above sea level. So we take
that wave cut bench or wave cut platform
and we move it up higher.
So in this picture here
we've had
two events where the coast has been,
the continent has been
pushed upwards um... pulling those wave cut
platforms up out of the ocean.
So some other examples of headlands and sea stacks to show you,
so we can see those here.
Headlands this is a rocky
outcrop. It juts out into the water. Usually
we have these kinda fingers sticking out into the ocean and then a bit of a sandy
beach in the middle a little bit more protected.
We see these in Maine, Oregon, California, Washington.
um...
And then we also tend to see sea stacks. So here's another headland sticking
out
here. Another
headland with a little sea stack.
Sandy beach in between.
And then here another sea stack.
All of these on the actual Oregon
coast.
So to kinda look at Google Earth,
and we can toggle over
to that screen.
So I zoomed into Astoria, Oregon and then moved further south towards
Seaside
and what we can see around Tillamook Rock if I zoom in closer.
What we start to see popping out are some of these steep
uh... rocky
uh... headlands stick out into the ocean with some
sea stacks
out in the water. And this is
uh... Ecola
State Park
where you can see a lot of different types of coastal features. Which is
kind of neat.
We can probably move further to the south, you can see another headland with some of
those sea stacks out in
the ocean.
We can also go to Cannon Beach
as well.
And see what that looks like there.
Just um... about
where we are.
And we can see there, someone's taken some photos. I'm going to get rid
of those
photos
so we can see things a little bit better. And I can zoom in
and there you see Haystack Rock
and the shadow that it casts
on the beach.
Kinda neat. Those headlands
um... which are
um... the uh...
sticking out, starting to erode, breakdown and then we start leaving these little chunks of
that solid rock behind.
Which creates
these um...
these rocks like Haystack Rock
sticking out.
So to look at submergent coastlines where we see the continent appearing to
sink below
the ocean.
um... What happens here is we start out with that dotted line profile,
ground surface lowers,
and drops
below sea level a little bit. So what happens right along the edge
of that continent is any low-lying area gets flooded.
So what happens, especially at river mouths, is we see
that um... the
ocean kinda invades into that river mouth and we get
things like estuaries. Which
we can see at different places such as
as the Oregon Coast. And here you can see a picture of Alsea Bay,
just one section of that estuary.
And then this Google Earth image, it's focusing on Astoria and that body of water
that you
see here.
Estuary flooded and then the river coming out.
And then Willapa Bay up further north. You can see
that low lying area
that has been flooded,
creating one of these estuaries, where
the water kinda goes
back-and-forth between
freshwater and saltwater. So then they mix together,
we call that brackish. So when
tide goes out we have more
fresh water coming down from the rivers, so that those
estuaries tend to get
a little bit fresher.
And then when tide comes in, saltwater
moves in, and the estuaries gets a little bit more salty. So kinda fluctuates
back and forth.
So when we have stable areas, where we have very little to
no change,
what we have here is that gradation happening. We have the land surface slowly eroding,
depositing material out into the oceans.
And we have that wave action on the coastline transporting sediments from
place to place.
So in these kinda
stable areas we end up with more beach environments. And
depending on
the wave energy
on that beach we might have smaller particles. Like you can see the sand in my hand in
that picture.
Pretty small,
sand sized or if the waves are really big, lots of energy,
we can transport larger particles and then we can get cobble beaches.
Overall however at some of these stable environments we get more of
the sandy beaches. So here there are some parts of the Oregon coast, which are
fairly stable. They're not
really rising or sinking.
There are
parts that are rising and parts that are sinking, producing some of these headlands
and sea stacks.
But in some places we have these nice sandy beaches building up.
And the Florida east coast is a good example
of where we have some of these stable environments.
So some of the features that we can get
looking at some of these screen captures looking at this Barrier
island in Maryland.
So you have an actual sandy island that
runs parallel
to the mainland
with that little uh... lagoon
kinda area or bay in between the barrier island and the mainland.
We can produce hooks
and we can produce spits. And these are all
made out of loose
sediment, loose sand
that's being transported.
In the spit picture we're moving from the top from the north to the south.
And in that hook picture
things are kind of rotating around
that hook.
Moving on the bottom
from
west to east and then from north to south to north
kind of around that hook. That
movement of sand and water is what we call long shore drift.
And how that works is basically
you see these green lines are wave fronts moving into the coast. They start out
maybe at an angle, because the winds blowing
the water uh... towards the land.
We get these
wave fronts coming at an angle. As soon as the bottom of that wave starts to
interact with the
ocean floor it starts to slow down and it starts to kinda
bend and wrap
around and kind of lap up onto that beach.
And what happens is because those waves are striking at an angle,
as they wash up on the beach,
the material they're carrying and the water itself moves in the direction of those white
arrows. So kind of at an angle
up the beach.
And then once those waves roll back out again, they're gonna
fall straight out,
um perpendicular to the beach face,
and that line
in between the ocean and the beach.
So we have a zig-zag pattern. So the sediments are moving,
following those arrows. Following the white,
then going back out.
The black following the white
back out to the black.
And so we see this overall direction of movement
in that red arrow. So that's what we call the long shore drift direction.
Since sometimes when you're looking at Google Earth, you can actually see the direction
of the waves. You can see the angle of their striking the beach.
But you can also see
different types of features. Like these spits or hooks
that tell you
the direction that the long shore drift is going in. And for the case of spits
and hooks that are actually
extending out and growing
in the direction of
long shore drift. So here you can see those black and white arrows again moving
the sediments and you can see the spit kinda getting
larger and larger
moving towards the left.
So when we actually
put some barriers in there. In some locations. Maybe there's a structure
put in maybe there's a headland that sticks out.
Well what happens is that barrier
traps the sediment that long shore drift that's coming from
the right side
gets trapped on the right side of that feature
once those waves wrap-around
that barrier,
they don't have anymore sediment
so they start to erode away on the opposite side of that feature. So one side we get
deposition the other side
we get erosion.
So when you're trying to determine the direction of long shore drift you can look for
spits and you can look for structures that
will show you
uh... which way we have erosion which way we have deposition and that will
directly relate to the direction
that the materiel is moving.
So to kinda wrap things up we looked at
major types of
coastal landforms that are associated with
the emergent and submergent and stable environments.
So what we'll do is sign off from
this video and we will come back and
talk about some of the hazards
that exist on coastlines as well as how they are
mitigated or fixed.