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Welcome back to week 4 and we are going to continue in video 4
discussing some of these internal
processes and more specifically
how these
plate boundaries and plate tectonics are related to
features on the seafloor, coastlines and some of the materials
that we get.
So divergent
boundaries,
this is where we have oceanic crust created at those mid-ocean ridges,
high point on the ocean floor.
Such as the middle of the Atlantic ocean. We see fracture zones.
We also see...
sea mounts
where we end up
connecting he
oceanic crust to the continental crust. That's where we see
the drop-off right at the edge of the continental shelf.
So we see that continental rise steep section
continental slope.
and where we have
plates colliding a lot of the time we create uplifts and volcanic
eruptions. This uplift
accelerates erosion, deposition of
of these sediments and sedimentary rocks.
So where we have
convergent plate boundaries where the crust is moving up or down.
Active coastlines where we have emergent and sub-mergent
features.
So again those active versus passive coastlines. I just talked about active where
you have a boundary,
two plates colliding, pulling apart, sliding past one another such as
the Cascade range,
San Andreas fault.
An example of a passive coastline would be the east coast where we don't have
any
tectonics happening right on the edge of that continent.
Yes we have
some happening
out in the middle of the ocean
but that's too far away from the actual coast.
The activity has to be happening right on that edge of the continent for it
be considered active.
Just to review
a little bit,
active - we have
subduction, divergent,
transform, boundary happening.
Here's examples of
active coastlines here. And this would be an example of a passive coastline. No
plate boundary, no sub-duction, no earthquake activity,
just very calm environment.
And some of the features that we see on those passive
or sorry, on those active boundaries,
we see headlands, we see
sea stacks,
some sandy beaches in some locations, we see
um...
terraces that developed due to the crust uplifting out of the oceans. So we tend
to have a more rocky
coastline
where we have
solid rock exposed to erosion.
uh... And then that solid rock depends on what type it is. Depends upon
the actual geology of that location.
And then we have those eroding away producing the different types of
sediments
that we discussed
back in week 2.
So passive
uh... boundaries, this is where we get lots of beaches built up.
We see these wide sandy beaches, barrier islands, hooks, spits, so on and so forth
in these passive margins like the east coast of the United States. So this is
more
erosional
surface.
So we don't have as many of those rocky coastlines or headlands. We
see mostly just sand because we have
long shore drift
dominating the
geologic process at this location.
uh... moving that sand from one place to another.
So again
zooming in on the
Pacific Northwest
here we've got the convergent boundary right off the coast. Oregon here
Washington up here.
Divergent plate boundary,
active plate margin, lots of rocky coastlines, rocky headlands.
If we look at the seafloor features here, in the next picture, if I remove
those
uh... kind of
change the orientation and remove those boundaries you can see
where the volcanoes are in the ocean floor at that divergent boundary,
where our fracture zone is located. So here you can see that nice ridge that
develops on the ocean floor, the flat abyssal plane, and then where those two
different crusts are combining,
continental slope
and rise. And then the continental shelf on the very edge here
and then the
volcanoes produced from subduction occurring right about
uh... along this
boundary between
our continent and oceanic crust.
So to kinda review things a little bit,
hopefully you're now familiar with the theory of plate tectonics. You could
describe it to me.
You could also list the evidence that exist to support
this theory.
And then you should be able to
identify the different types of plate boundaries, what's happening at each, how
motion uh... is occurring at each of those locations and then some
features related
to tectonics on the seafloor and the coastline and where we see sand, where we see
solid rock.
And here's just a
cool picture of
a vessel that was used to actually
drill into the ocean crust and collect samples from
that ocean floor to tell us a little bit about what's happening down there.
So I will sign off and we will see you in lab.