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Hawaiian Islands Formation : Hawaiian Islands formed by stationary hot spot under Pacific plate
相關課程
- 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
- So anyway
- 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.
- Anyway hopefully you found that entertaining.
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