Next up, my journey 600 feet into the crater
of a volatile inferno, where scientists
are looking for signs that could end
up saving thousands of lives.
Masaya in Nicaragua is so feared that religious crusaders once
tried to exorcise the devil out of its heart.
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Lake Nicaragua, the largest body of fresh water in Central
America, and home to Jicaro Island,
a "National Geographic" unique lodge.
Nicaragua has 19 active volcanoes,
including Masaya, a ticking time bomb that
could go off at any moment.
That's where I'm headed.
Just look at the size of this volcanic crater.
It's about seven miles across.
And in the center of it, another volcano
was born, Masaya, one of the most volatile in the world,
that's erupted 13 times in just the last 30 years.
I'm making my way around the crater of Masaya volcano
to some volcanologists who risk their lives out
here on this deadly beast.
Part of what makes volcanoes so dangerous
is that they're unpredictable.
And no one really knows when this one will erupt again.
With a million people living just 15 miles away,
geologists have set up shop in the heart of this ticking
time bomb to figure that out.
Guys, nice to see you.
Working on one of the sensors?
Yes, Phil.
Yeah?
We are taking care of the maintenance
of the gas instruments that we use
to monitor the mouth of hell.
(LAUGHING) The mouth of hell.
Yes.
Yeah, where did that name come from, by the way?
It's from the Spanish conquistadors, you know?
PHIL KEOGHAN: Yeah?
A few hundred years ago.
They thought that it was gold and fire coming from hell.
So that's why it's named after that, you know?
PHIL KEOGHAN: Armando and his team
monitor a network of 80 sensors, gauging Masaya's conditions
and surrounding atmosphere so they can try
to predict the next eruption.
It seems to me that without these warning systems,
the people would be really vulnerable.
This is the only means of defense for them?
As you say, when we detect something that is dangerous,
we send information immediately to the local authorities.
PHIL KEOGHAN: In the spring of 2018,
earthquake sensors captured vital data on Hawaii's Kilauea
volcano, which after it erupted, reduced 600 homes to ashes.
That intel is crucial to missions like this.
ARMANDO SABALLOS: It's getting unstable.
You can see--
Yeah, this edge is starting to break away.
Yeah, it's falling apart.
PHIL KEOGHAN: Oh my!
ARMANDO SABALLOS: Yes, that's the mouth of hell.
PHIL KEOGHAN: Oh, my god!
That is really scary-looking.
Where in the world can you see this?
Very few places.
ARMANDO SABALLOS: Yeah, very few places.
PHIL KEOGHAN: The lava lakes that form in active volcanoes
typically don't last long.
But Masaya's has been churning consistently for centuries,
making it one of the most active members of the Ring of Fire.
I've used some volcanic rocks to make a very rough map.
But I want to show you exactly where the Ring of Fire is.
It's 25,000 miles long, and completely circumnavigates
the Pacific Ocean.
It runs right through New Zealand--
that's why there's a lot of volcanoes there--
through Indonesia, Japan, through the top of Russia,
all the way down the west coast of America,
and then down through Central America, where Nicaragua is.
And it continues right down to the end of South America.
Almost all of the volcanoes in the Ring of Fire
occur along the edges of the Pacific tectonic plate.
But Masaya was formed between two smaller plates.
About 20 million years ago, the Cocos plate began sliding
under the Caribbean plate.
The energy from this subduction turns
solid rock into liquid magma.
And when that magma escaped through the Earth's crust,
Masaya was born.
That's a long way down.
So--
So we're good?
It's a 60-story drop into this cauldron of toxic gas.
This mask will actually filter out
the sulfur dioxide that we're expecting down below.
You can also get the gases in your eye.
Then this helmet, for obvious reasons,
'cause at the rim of the crater, there's
a lot of falling debris.
I'm going in to meet up with Rodolfo Alvarez,
the engineer behind this pulley system
built to get scientists in and out of this massive crater.
And it is a lot further down there than it looks.
Everything turned on properly?
This is the exciting part.
Just the enormity of this volcano is incredible, really.
The roar from the volcano is getting louder and louder.
Look at that.
That is absolutely magnificent--
the glow of the lava.
And in the distance, I can see the vent we're heading for.
Descending into this hostile environment
of heat and toxic gas is extremely dangerous.
But for Rodolfo Alvarez, it's as if it's
just another day at the office.
All right.
Rodolfo, how are you doing?
Well, welcome to a gate of hell.
Oh, my goodness me.
That was like-- that was just insane, Rodolfo.
Are you OK?
PHIL KEOGHAN: Yeah, I'm all good.
Wow, it got dark so quick, right?
Why are you not wearing your gas mask?
What's wrong with you?
Oh, because I wear it when I need it.
How do you know?
You watch the gases coming up?
Well, right now you don't need the mask.
But if you want to keep it, it's no problem.
PHIL KEOGHAN: There is an overwhelming odor down here,
like a match that's just been lit.
That's sulfur dioxide.
And when that gas mixes with the moisture in the air,
it forms sulfuric acid.
It eats everything, from the cables ferrying the team in
and out of Masaya, to the sensors that raise
the alarm when there's danger.
This is a box that we got in to protect the sensors,
the sensor inside.
Because of the--
RODOLFO ALVAREZ: The sulfuric acid.
PHIL KEOGHAN: The sulfuric acid.
There are little sensors down the bottom here?
RODOLFO ALVAREZ: Different sensors for different gases.
Those are the ones that are damaged.
The corrosion is really bad, eh?
Yes, actually it's amazing, if you--
All around I see like--
You can look in here.
I mean, this is actually a cable.
And we can--
PHIL KEOGHAN: Wow!
Look at these joints have just completely eroded away.
RODOLFO ALVAREZ: I mean, it's completely destroyed.
PHIL KEOGHAN: And that's from the sulfuric acid?
RODOLFO ALVAREZ: Yes.
You know, you have all this cloud of sulfur,
and you can feel your eyes.
Your eyes will start itching like hell.
PHIL KEOGHAN: Yeah, so it's that strong.
RODOLFO ALVAREZ: I mean, it's not pure sulfuric acid,
but it's very high percentage.
Man, I just want to keep putting on the mask.
And I look at you, you got no mask on.
Right.
I don't know how you do it.
We can go that way and you can actually get to the edge.
We have ropes set up so you can get to the edge.
We're going to go here.
PHIL KEOGHAN: Oh!
RODOLFO ALVAREZ: Now I need a mask.
I just got this swirling of gases.
Yeah, I can feel the heat right here.
Really see it there.
RODOLFO ALVAREZ: Yes.
PHIL KEOGHAN: We got a good look.
I've never seen anything of this magnitude and power.
And you can feel the power in the ground.
What is it about the lava that you love?
People are afraid of this, but this is what
really makes you feel alive.
This is one of those things amazing
of nature or the universe that you can actually see in person.
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