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>> Hi, everyone.
This is Keith Meldahl.
We're going
to review here some
of the major motions
that happen
at the different tectonic
plate boundaries.
We'll start here
with the divergent boundary.
These are the mid-ocean ridges
of the world.
These are the places
where the plates separate
from each other,
allowing hot magma to come
up from the asthenosphere,
the mantle underneath.
The magma congeals along the
mid-ocean ridges
in volcanic eruptions,
forming pillow lava
or pillow basalt.
There are lots of earthquakes.
And the new ocean floor forms
and spreads away
from the ridges
like two oppositely moving
conveyor belts.
So the seafloor grows
and spreads
from these divergent
boundaries called the
mid-ocean ridges.
Now, the opposite process
happens at the convergent
boundaries of the world.
These are marked
by the deep ocean trenches,
deep creases
on the ocean floor.
And these creases are formed
because one plate dives
down beneath another one
in the process
that we call subduction.
One plate, the ocean floor,
dives beneath the other plate.
As it does that,
it makes frequent earthquakes.
As the plate gets
to a certain depth
in the mantle,
it triggers melting
of the mantle,
which causes magma to rise
and form a line of volcanoes
that we call a volcanic arc:
a line of volcanoes that rises
and runs parallel
to the ocean trench.
So we call these
convergent boundaries.
They are the locations
of subduction, and they occur
at the ocean trenches
of the world.
The third kind
of motion is called transform
motion, or a transform
boundary, and this is
where the plates slide side
by side past each other.
The main thing
that happens here
is earthquakes.
We don't have the creation
of the Earth's crust;
we don't have its
destruction either.
We simply have side
by side sliding.
The San Andreas Fault
of California and a number
of other very large faults,
including on the ocean floor,
are characterized by this kind
of motion.
In this final animation,
what we can see here is
that as the new ocean floor is
created at the mid-ocean
ridges, it spreads
and slides along for a while
and eventually slides
down an ocean trench
and is consumed
in the Earth's mantle.
But not before making lots
of earthquakes and rising
to form magma that erupts
and forms volcanoes.
So that's plate tectonics
in a nutshell.
コツ:単語をクリックしてすぐ意味を調べられます!

読み込み中…

Motion at Plate Boundaries

664 タグ追加 保存
羅紹桀 2015 年 7 月 30 日 に公開
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