- These are all of the volcanoes in the world.

You've got this big strip here in Ethiopia,

a big cluster up in Iceland,

and a long strip down the west coast of the Americas.

But there's one spot that has more volcanoes

than anywhere else on Earth, right here in Indonesia.

And it's not even all of Indonesia,

this country of 17,000 islands.

It's really this belt right here.

This is called the Sunda Arc.

And it's where the majority of volcanic activity

in Indonesia is happening.

It's where the violence, the intensity,

the beauty of all of these blasts is taking place.

I want to show you some of the most striking volcanoes

on Earth, and I'm doing this

because I want to try to better understand

why they are so deadly and why millions of people

live right in the shadow of these sleeping dragons.

(suspenseful music)

Okay. Let's quickly go over why volcanoes exist.

Maybe you've heard this before, but I'm going to try

to explain it in a way that makes sense.

It's important to remember that the ground

under your feet is actually a giant plate

a hundred kilometers thick,

one of many plates floating around on molten lava.

They're all moving in certain directions

and at different speeds.

There are seven main plates on Earth

and a bunch of smaller ones.

And they're always moving.

When these plates move into each other, they make mountains.

When they spread apart, they make underwater volcanoes

that cool and turn into rocks and we call them islands.

When they slide against each other

they make terrible earthquakes.

And when they run into each other

and one gets forced below the other,

they make volcanoes.

- [Narrator] A whole series of volcanoes begins to pop up

along the edge of the continent, parallel to the trench.

- So the real reason why this one strip of land in Indonesia

has so many volcanoes is because this plate

is slamming into this plate at a rate

of seven centimeters a year,

which is one of the fastest movements

of plates in the world.

So you're getting a ton of this,

which results in a ton of this.

(exciting music)

If you zoom into one of these volcanoes,

you're going to see a lot of this dark green

around the volcano where no one lives.

But all of this, each one of these little dots,

are villages where tons of people live.

And they're right in the strike zone of this volcano.

Volcanoes kill people when they suddenly erupt,

but it's not the lava that kills them.

It's the ash.

This huge column of ash and gases first goes up

and then it eventually falls down.

As it falls it gains momentum on these steep mountain sides.

And eventually that will slam into villages

up to three kilometers in radius from the volcano.

If you were standing in the way of one of these massive

ash avalanches, you will die.

And then if it rains, it gets really bad,

because the ash and the rain make these horrifying

mud rivers that cut through the mountain

and flood villages all around the region.

Okay, before we go any further

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and let's get back to volcanoes.

Every volcano has its own personality.

And I want to show you some of the most striking volcanoes

along this strip and in the process,

explain how and why humans live so close

to these sleeping dragons.

(exciting music)

First, let's talk about Kawah Ijen.

This volcano blew up really bad 3,000 years ago,

and left a one kilometer wide crater that is now full

of this bright blue, very acidic water.

The most acidic lake on Earth, because under the surface

there is a huge deposit of sulfuric gas

that is venting out of this crack in the earth.

All of this sulfur gas means that when this thing

erupts with lava, it burns that gas

and ignites it in this mesmerizing blue flame.

All of this gas also means

that there is some money to be made.

The locals have installed these ceramic pipes

to catch the gases and force it to condense into a liquid.

It flows down here to where it cools

and turns into a solid which can be harvested by locals.

My friend Christian is there right now,

covering the realities of this job.

I'm going to let him show you

what this work is actually like.

- Hey, Johnny.

So right now we are inside of Kawah Ijen, a active volcano.

And this crater is full of life.

You can see all the steam rising off of the water,

this insane plume of yellow smoke,

and this yellow smoke is what creates the sulfur.

And with me here are the bad-ass, hardworking dudes.

No other way to put it. They're literal superheroes..

- [Man] This here is Supano. What's up Supano?

- I've had this amazing opportunity to just pick his brain,

try to understand a little bit better

why is it that these guys are taking on

some of the most challenging work conditions

on planet Earth.

What is the heaviest weight that you'll take up the hill?

- 75 kilogram. - 75 kilograms.

I just tried 40. I could barely manage it.

I mean, you look at these guys,

they're not bodybuilders, but they're strong minded.

They're incredibly driven

and they've got a good purpose for it.

- How much money? For one kilo only 1,250.

- [Christian] So how much do you make at the end of the day?

- 300,000.

- If you were to convert that to you U.S. dollars

that's about 20 to $21 for the entire day's worth of work.

(exciting music)

- These workers make it into town

where they sell this sulfur to factories,

which mainly use it to bleach sugar so that it's white.

It's back-breaking, dangerous work.

Christian made a whole video from this mine

and the realities of this work.

I will link to that in the description.

Next up we have Mount Merapi or Fire Mountain.

This volcano has killed more humans than any other.

It erupts all of the time, like every few years.

Here it is erupting just last year.

This thing is happening over the course of five minutes.

This time-lapse was recorded by VolcanoYT and Frekom,

two different YouTube channels that we'll link to

in the description.

The reason why this volcano is so deadly

is because like I said before,

there are millions of people living around it.

And not just remotely around it,

like right up against the mountain.

Here's the volcano.

And these are all the villages right up against it.

Which raises an important question

I had going into this story,

which is why do so many people live here?

Like so many people.

The answer is that this is an amazing place to live.

(upbeat music)

Indonesia has mild warm weather.

It rains super hard for a few months

and that rain is effectively stored in these mountains.

And it provides water to these people throughout the year.

And then there's the fact that this is perfect fertilizer,

all mashed up and broken down,

ready to make this soil incredibly fertile.

This is some of the most fertile land on Earth.

You get three rice harvests from this soil every year

because the soil is like magic.

So yeah, the people living here are sort of

in a high risk, high reward situation.

They live on a sleeping dragon

that could wipe them out at any moment.

And yet, as long as it doesn't,

they have some of the best weather

and growing conditions on Earth.

Next up is Krakatau.

What you're looking at here is actually

like a graveyard of what used to be a big island.

It used to look a lot more like this,

but a hundred years ago, it blew up.

We think this is the most explosive volcano

in modern history.

10% of the world could hear the blast, it is so intense.

Tens of thousands were killed in the ash

and the ash exploded so high into the air

that all the way in Europe the sky was red and hazy.

Which has led some to speculate that it was this event

that inspired the red hazy look of this painting,

one of the most famous paintings in the world

called "The Scream".

(exciting music)

The volcano that grew out of Krakatau has kept erupting

over the years, breaking this island down further

and further until the whole thing just eventually collapsed

and caused a huge tsunami that killed hundreds.

Just a couple of years ago, the island went

from looking like this to this.

And today it's one of the fastest growing

volcanoes in the world, and will certainly

be back for more destruction.

Okay, the last one I want to talk about

is this set of volcanoes.

This one is Mount Bromo and this one is Mount Semeru.

First off, these two volcanoes are some of the most

stunning volcanoes I've ever seen in my life,

but they also represent the deep religious symbolism

that volcanoes have come to symbolize over time.

This mountain, Mount Semeru, is named after

the mythical Mount Meru,

which is a sacred five-peaked mountain

in the cosmology of three religions;

Hindu, Jain, and Buddhism.

It is considered to be the center of the physical

and metaphysical and spiritual universes.

The neighboring volcano is also deeply symbolic.

It's called Bromo, which in Javanese is the name

for Rama or the Hindu god of creation.

Every year, Hindus hike up this mountain

and make an offering of vegetables and plants and animals

to the gods embodied in this volcano.

(gentle music)