Plate Tectonics -- Geological Features of Divergent Plate Boundaries
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- Before we go into possible theories
- as to why plates actually move,
- what I want to do in this video is
- think a little bit about why we see the
- geological features we do see
- at plate boundaries, and in particular
- I want to focus on the
- features we see at divergent plate boundaries,
- where the plates are moving away
- from each other, where new land is being created
- like we saw in the mid oceanic ridges,
- where we see new land being created right in the center
- and moving outwards from them.
- So to do that let's think about the different layers
- and actually I want to make one quick correction
- on the last video.
- Over here I had drawn these arrows going in that direction
- and based on how I defined them, they should
- be going into the page and so they should've
- had these Xs here.
- Now with that out of the way
- let's draw a little diagram
- of what happens at the early stages
- of these divergent plate boundaries.
- So you might have your
- here you have just your crust,
- and maybe it's continental crust...
- This right here is the earth's crust,
- and then you have the solid part of the mantle.
- And the combination of them is the lithosphere.
- And then you have the liquid part, the superhot part
- of the mantle, this down here is magma.
- It hasn't solidified, it's hot enough to be in the liquid state.
- And all of this combined, this right here,
- we consider the mantle.
- Now, there's some debate, and we'll talk about
- this in the next video, of how hotspots actually form
- it could be these mantle plumes that start
- at the border between the mantle and the core,
- it could be some type of convection current
- in the actual mantle, we'll talk more about that in
- the next video or maybe a few videos from now.
- But let's take it for granted that hotspots form
- in the mantle, so let's say we have an area
- of magma right here, that is particularly hot.
- Let me draw it in in another color... pink.
- So this is particularly hot magma here.
- And we know, or maybe we don't know,
- if you take the same material and you make it hotter,
- it's going to become less dense
- because the particles essentially are going to
- bump into each other with more kinetic energy
- and have more space in between them
- and so this really hot part of the magma
- or this really hot part of the mantle
- it is going to move upwards,
- because it is less dense, it will have buoyancy.
- And as it moves upwards, it'll heat up
- the things around it and it'll
- eventually make its way into the lithosphere
- and it'll be able to break through the lithosphere
- because it's so hot it can melt its way through.
- So let's fast forward this a little bit,
- so this is Step 1 up here.
- Now Step 2, this hot magma is