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.

Or not abducted, getting subducted into other plates

underneath and forms these trenches here.

Anyway, hopefully you found that entertaining.