we have talked a lot about the formations of mountains and volcanos
when plates are running into each other or one plate is being
subducted under another, but that isn't the only place
it is the dominant place or the most likely place to find the mountains or volcanos on the surface of
the earth. But that's not the only place that mountains of volcanos can form and probably the biggest example
of volcanic activity or the most popular one, this might be a slightly American, Amero-centric point of view.
But the most, often cited example of volcanic activity away from a plate boundary is Hawaii.
Hawaii, so this right here, these are the hawaiian islands, this is the big island of hawaii, and it is,
it is experiencing active, an active volcano. Lava is or magmas flowing from underneath the ground that
once its surfaces we called it lava, and that lava is actively making the island,is actively making the island bigger, so where is
that volcanic activity coming from and how can we think about that volcanic activity or that kind of heat
rising from below the surface of the earth to explain some of the geological features we see around
hawaii. So what we think is happening once again, this is all theory right here, is that hawaii is
sitting on top of a hot spot, in particular, the big island of hawaii is sitting on the top of the hot spot
right now, and this hot spot,this hot spot there is different ways or different theories on how it that
emerge, but we think that at the mantle, at the mantle core boundary. I don't know if this diagram were
intended this white area to be the core, but that's just say that this is the outter core down here. Let
us just say this is the outter core, outter core for the sake of explaining things.We think it is possible
that kind of plumes of very hot material can kind of.uh, just based on kind of flow dynamics of what
is happening at that mantle outer core boundary that plumes are a really hot material can kind of rise
up,can kind of - let me do this in a darker color - can rise up from outter core. It rises up from the outter core and create
a hot spot underneath the moving lithospheric plate, underneath the plate, now it is not necessary, we don't know
for sure, where these hot spots are being created from, by these mental plumes these materials formed, or heated
up at the outter core mantle boundary, but we do feel pretty confident about is that there is
this hot spot here and it's independent of any of those convection patterns that we saw.
I shouldn't say independent, this is obviously all related, cause we have all these fluid commotion
going on in the mantle, but it's, it's seperate on some degree from all those convection patterns that
we have talked about, that could actually cause the plates to move,and to a large degree or the way we
think about it right now, this is stationary, this hot spot is stationary, relative to the plates. And the
reason why we feel pretty good about thinking that it's stationary relative to the plates, is we see this
notion right here,if you look at the volcanic if you look at the volcanic rock in Kawaii, which is
one of the older inhabited hawaiian islands. The oldest rock we observed there is 5.5 million years old,
and it's all volcanic rock, now the oldest rock we observed on the big island is about 7 hundred thousand
years old, we also know, we also know that the pacific plate, you could look at this diagram right over
here is moving in this general direction, like we know it from, we know it from GPS measurements, is
moving exactly in the direction, that the hawaiian islands are kind of distributed in. So uh,uh, frankly, the
only good explanation for why we see this pattern, why we see this newer land here and then as we go further
and further up the hawaiian island chain we see older and older land actually if we keep going, if we
keep going we have the leeward islands over here as we, as we keep measuring the rock on the leeward island as we get older
and older as you go to the northwest and if you even look at what's below the ocean.
this is the big island of Hawaii
these are the main Hawaiian islands,these are the leeward islands
but you see even beyond that submersed under the Pacific Ocean,
you continue to see a chain of islands. So,
The explanation for what’s happening here,
is that you have a stationary hot spot that is right now underneath the big island of Hawaii
And I just wanna be clear,
the big island is called the island of Hawaii, it is one of the islands in the state of Hawaii.
So I don’t want cause you confusion.
I’ll just call it the big island from here on out.
So the hot spot is right under the big island.
But if you were to rewind 5 million years ago, if you were to rewind 5 million years ago, the entire pacific plate
the entire pacific plate was probably on the order of, you know, about 150, 200 miles,
however far Kawaii is from the big island.
It was probably shifted that much to the southeast, if you go back 5 million years ago. So 5 million years ago
when all of this was shifted down and to the right, then Kawaii, Kawaii was on top of the hot spot.
And so this is how each of these islands are formed.
If you rewind a ton of years, then maybe this area over here in the Pacific plate was over the hot spot.
Island- an island formed there then Pacific plate kept moving to the northwest.
It kept moving to the northwest and new islands,new volcanos kept forming.
Those volcanos would release lava that would keep piling up,
keep piling up keep piling up, eventually, go above the surface of the water,
and form this whole chain of islands, and as whole Pacific plate kept moving to the northwest, it kept forming new islands.
Now the one question you might ask, is well, how come the big island is bigger?
Has the plate kind of paused over there, is it spending more time over the hot spot
so that more lava can kind of form there to form this,
to form this- essentially it’s an underwater mountain that’s now also above the water
and actually if you go from the base of the Pacific Ocean to the top of the big island of Hawaii it’s actually 50% higher than Mt. Everest,
so you could really just view it as a big mountain
But the question is this looks so much bigger than Kawaii they keep getting smaller as you keep going to northwest
is somehow the Pacific plate slowing, is it spending more time here? And the answer is it’s probably not slowing,
what’s happening is, at one time Kawaii was also probably a relatively large island.
If you rewind 5, maybe 5 million years ago,
Kawaii also might been about that big, but over 5 million years it’s just experienced the a ton of erosion.
Remember, once it moved over the hot spot, new land wasn’t being created,
it’s in the middle of the Pacific Ocean, its experiencing weather,
5 million years is a long period of time, and so it just got eroded over that time. So the older the island is,
the more eroded it’s going to be and the smaller it’s going to be.
So if you go these, if you go to these under water mountains up here, that don’t even surface above the ocean
at one time they might have surfaced, but over, due to the ocean and weather
and whatnot they’ve just been eroded over time to become smaller and smaller, just kind of remnants of volcanos
I thought you would find that entertaining, how the Hawaii islands
actually got formed, and how we can actually have these hot spots,
and these, this volcanic activity, and actually even earthquake activity, outside of actually
eh, eh, eh plate boundaries.
Actually while we’re looking at this diagram we talked about,
we talked about the trenches of plate boundaries,
you can actually see it here, cuz this shows the depth,
and the really dark dark dark dark blue, it’s really dark deep parts of the ocean.
So here is the Mariana Trench
then you can see here over the Pacific plate just getting abducted-- not abducted-
-- getting subducted into other plates, underneath and forms these trenches here.
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