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  • We've talked a lot about the formations of mountains

  • and volcanoes when plates are running into each other,

  • or when 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 mountains and volcanoes on the surface of the Earth,

  • but that's not the only place that mountains or volcanoes can

  • form.

  • And probably the biggest example of volcanic activity,

  • or the most popular one-- this might

  • be a slightly American, Amerocentric point of view,

  • but the most often cited example of volcanic activity

  • away from a plate boundary is Hawaii.

  • So this right here, these are the Hawaiian Islands.

  • This is the big island of Hawaii,

  • and it is experiencing an active volcano.

  • Lava or magma is flowing from underneath the ground,

  • and once it surfaces we call it lava.

  • And that lava is actively making the island bigger.

  • So where is that volcanic activity coming from?

  • And then 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, and once again, this

  • is all theory right here, is that Hawaii

  • is sitting on top of a hot spot, and in particular,

  • the big island of Hawaii is sitting on top of the hot spot

  • right now.

  • And this hot spot, there's different ways,

  • different theories on how it might emerge.

  • But we think that at the mantle core boundary--

  • and I don't know in this diagram whether they intended

  • this white area to be the core, but let's just

  • say that this is the outer core down here.

  • Let's just say that this is the outer core

  • for the sake of explaining things.

  • It's possible that just based on the fluid dynamics of what's

  • happening at that mantle outer core boundary,

  • that plumes of really hot material can kind of rise up.

  • Let me do this in a darker color.

  • They could rise up from the outer core,

  • and then create hot spots underneath the moving

  • lithospheric plates.

  • Now, we don't know for sure whether the hot spots are being

  • created by these mantle plumes, these material formed or heated

  • up at the outer core mantle boundary.

  • But what 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.

  • It's obviously all related because we

  • have all this fluidic motion going on in the mantle,

  • but it's separate on some degree from all of those convection

  • patterns that we talked about that would 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 rock in Kauai, which

  • is one of the older inhabited Hawaiian Islands, the oldest

  • rocks that we've observed there is 5.5 million years old,

  • and it's all volcanic rock.

  • Now, the oldest volcanic rock that we've

  • observed on the big island is about 700,000 years old.

  • We also know that the Pacific Plate,

  • you could look at this diagram right over here,

  • is moving in this general direction.

  • We know it from GPS measurements.

  • It's moving exactly in the direction

  • that the Hawaiian Islands are kind of a distributed in.

  • So frankly, the only good explanation

  • for why we see this pattern, why we see newer land here,

  • and then as we go further and further up the Hawaiian Island

  • chain we see older and older land,

  • and actually if we keep going, we

  • have the Leeward Islands over here.

  • And as we keep measuring the rock on the Leeward Islands

  • they get older and older as you go to the Northwest.

  • And then 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 want to 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 to 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,

  • the entire Pacific Plate was probably

  • on the order of about 150 to 200 miles,

  • however far Kauai 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

  • Kauai 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

  • on the Pacific Plate was over the hot spot.

  • An island formed there.

  • Then the Pacific Plate kept moving to the Northwest.

  • It kept moving to the Northwest, and new islands, new volcanoes

  • kept forming.

  • Those volcanoes 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 the 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 a 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?

  • 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 Mount Everest.

  • So you could really just view it as a big mountain.

  • But the question is this looks so much bigger than Kauai,

  • and they keep getting smaller as you

  • keep going to the Northwest.

  • Is it 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 Kauai was also probably also

  • a relatively large island.

  • If you rewind maybe 5 million years ago

  • Kauai also might have been about that big.

  • But over 5 million years it's just

  • experienced a ton of erosion.

  • Remember, once it moved over the hot spot and new land

  • wasn't being created it's in the middle of the Pacific Ocean.

  • It's 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 to these underwater mountains

  • up here that don't even surface above the ocean, at one time

  • they might have surfaced, but due to the ocean and weather

  • and whatnot they've just been eroded over time

  • to become smaller and smaller kind of remnants of volcanoes.

  • So anyway, I thought you would find

  • that entertaining of how the Hawaiian Islands actually got

  • formed, and how we can actually have

  • these hot spots, and this volcanic activity,

  • and actually even earthquake activity

  • outside of actual plate boundaries.

  • Actually, while we're looking at this diagram,

  • we talked about the trenches at plate boundaries.

  • You can actually see it here because this shows the depth.

  • And the really dark, dark, dark, dark blue

  • is really deep parts of the ocean.

  • So this right here is the Mariana Trench.

  • And you can see over here the Pacific Plate just

  • getting abducted.