Original subtitles

[narrator] Worldwide, 36 billion cameras are watching us.

On our streets, at work, and in our homes.

They capture things that seem impossible.

Science says this shouldn't happen.

[person] Do you see that?

[narrator] Experts carry out forensic analysis of these unusual events.

Wow, what a blast!

[woman screaming]

This doesn't make sense.

There has to be some sort of explanation.

What else is going on here?

[narrator] Coming up, has the mother of all stink bombs

caused this mystery explosion?

This is horrendous. People were running for their lives.

[narrator] Killer sludge heads for an American town.

Anyone trapped under that would be charred to a crisp.

[tires screeching]

[narrator] And a crashed van spills unexpected cargo.

Seven, eight, nine, ten... Oh my gosh,

how many people are in this van?

There's still more coming out?

How could they possibly have all fit inside?

[narrator] Bizarre phenomenon...

Oh my god. [gasps]

-[narrator] Mysteries caught on camera... -[woman screaming]

What's the truth behind this... Strange Evidence?

Sichuan Province, Central China.

January 28th, 2020.

An early morning in a city shopping district.

A security camera films two young girls playing on the street.

And then, all of a sudden, boom!

The street lunges upward.

It happened so suddenly. Giant concrete slabs flying in the air.

[narrator] The two girls and two other bystanders

disappear under a pile of rubble.

There's a giant cloud of dust, it's pandemonium.

People were running for their lives.

That video is absolutely horrific.

My first thought watching that video is,

"Is that girl okay?"

[narrator] No deaths were reported from the incident,

but the source of the explosion is a mystery.

The scale of this blast is off the charts.

It came out of nowhere.

[narrator] Former NYPD image analyst, Connor McCourt,

notices the innocent looking young girl is up to something.

The woman in the purple jacket bends over,

and it appears she puts something on to the ground.

And seconds later, the entire ground explodes.

[narrator] There had been over 80 terrorist attacks in China since 2010,

but this isn't one of them.

Science journalist Liberty Vittert believes

the girls may be taking part in

a dangerous prank that goes horribly wrong.

There's a widespread trend in China of young children

dropping poppers and other fireworks down manholes.

[narrator] When the black powder in fireworks explodes,

it produces a sonic boom of rapidly expanding gas.

The exploding firework can reach

temperatures of 1800 degrees Fahrenheit.

If this happens inside a confined space like a sewer pipe,

the blast wave can be amplified.

Has she just lit a firework and dropped it down the manhole?

[narrator] But the force of this blast is far greater than the energy

unleashed by a normal sewer fireworks prank.

If you look at previous fireworks explosions,

when it's thrown into a sewer,

the type of explosion you see typically only lifts the manhole cover,

or creates a small, localized explosion.

That's not what were seeing here.

[Connor] The force of this explosion is incredible.

These planters here, they're flown into the air

as the explosion erupts.

[narrator] Engineer Brian Wolshon finds reports of an explosive substance

infesting China's sewers,

a liquid that blights the lives of its citizens.

So one of the hallmarks of Chinese cooking, is deep-frying things in oil.

[narrator] In 2018, the Chinese used over 34 million tons

of vegetable oil over the course of the year,

to prepare more than 1.4 billion dinners per day.

The Chinese are known to dump cooking oil

into sewer systems, down a drain pipe.

[narrator] Cooking oil is a prized possession in China,

and the demand far outstrips the supply.

So criminals have turned recycling into a disgusting money-maker.

Gutter oil is a big problem in China.

[narrator] This deadly, second-hand cooking oil,

is harvested from disease-drenched drains.

So there are criminal gangs

who are actually going into the sewer system,

collecting this oil,

and then selling it back to restaurants for use.

[narrator] It's estimated that 10 percent of all cooking oil in China,

is oil that has been scooped out of the sewers beneath towns

and sold again for reuse.

They'll harvest it, they'll filter a little bit, strain it,

try to make it to where it's presentable again.

And then, they'll sell it back to the restaurants

that probably dumped it there to begin with.

This is horrendous. Sloppy goo from the sewer?

Surely, that can't be healthy.

[narrator] This highly flammable sewer grease

isn't just revolting, it's a health risk.

Gutter oil often contains poisons that can cause everything

from diarrhea to abdominal pain.

It's even been linked to cancer of the colon,

stomach, breast, kidneys and intestines.

[narrator] The people of China use over two million tons

of illegal gutter oil in their cooking every year.

Street food vendors are the number one consumers of gutter oil,

but they're not the only ones.

Manufacturing facilities, restaurants, supermarkets,

even school cafeterias have been known to purchase this product.

[narrator] Gutter oil is such a health hazard in China,

that the authorities have even introduced capital punishment

for criminals caught collecting and selling this slop from the sewers.

In 2014, Zhu Chuanfeng was sentenced to death

for masterminding a gutter oil empire

that netted him over $4 million.

Criminals fearing the firing squad are now deterred

from scooping out filthy fat from the sewers.

But this has simply created a new, explosive headache for the Chinese authorities.

The Chinese people are walking on ticking time bombs.

[narrator] Coming up, the ultimate dirty bomb lurking in suburban sewers.

What might be beneath your house

just waiting for a firecracker to set it off.

[narrator] And is this fur evidence

a polar predator is at large in Washington state?

Given the opportunity, they'd attack humans as well.

[narrator] In China, two young girls are tossed into the air

when a fireworks prank goes horribly wrong.

Historian Martin Morgan believes their firecracker

has ignited the filthy waste oil

that's been poured down the city's drains.

A reality of the modern era is the fatberg.

The idea that you get a big buildup of fat

from cooking fats that have been dumped in the sewer system,

that all conglomerate and congeal together.

[narrator] Already, they are a massive problem in the west.

In 2017, a giant fatberg is discovered

blocking up the Victorian sewers of London.

This fetid mass of fat, oil, feces, needles and diapers

is over 200 yards long, and weighs the same as 11 school buses.

It takes nine weeks to dig it out.

Now, these greasy monsters are growing

right beneath Chinese citizens' feet.

These big, congealed fatbergs,

they are potentially explosive.

[narrator] Fatbergs contain cooking oil, methane and hydrogen sulfide,

a potent cocktail that could turn into

a fat-ferno, if ignited by fireworks.

There's yet another horror for you to imagine

each night when you lay down to go to sleep.

What might be beneath your house, is a fatberg

just waiting for a firecracker to set it off.

[narrator] It's not known exactly what caused

the fireworks prank to end in such a catastrophe

but China has now told it's cities to clean up their act,

and decreed that sewers must be swept,

and their sludge turned into clean energy,

perhaps in a belated attempt to stop tragedies

like this one from happening again.

Just think, those sewers could be full of 10 years

of decomposing nitrates and ammonia,

a dangerous cocktail, waiting to explode.

[narrator] Now, Gifford Pinchot National Forest, Washington.

January 12th, 2013.

A lone hiker deep in the forest,

finds and films a mysterious white fuzz on a tree branch.

[Kevin] It's weird, the entire stick is covered

with this strange, glacial, white fur.

It looks like there's a stick that's somehow grown a long coat of white fur.

Trees don't grow fine strands of hair, what is this?

[narrator] Gifford Pinchot National Forest is over a million acres of

mountains, thick forest, and deep lava tube caves.

Deborah Hyde wonders if the branch

has snagged the hair of a polar predator hiding out in the wilderness.

You often find tufts of fur from animals

just caught on a piece of tree as they've gone by.

This looks like an extremely fine fur.

Sort of, beautifully white like a polar bear fur.

[narrator] The polar bear's North America's apex predator.

Over 12 feet long, it can easily outrun a human,

and a single swipe of its enormous paw can decapitate a man.

And in recent years, they've been migrating

closer to urban areas in search of food.

In 2018, two Canadian men are killed in separate attacks by polar bears.

It's not hard to see how some might connect this

white fur to these terrifying creatures.

[Jon] Even though they live in one of the coldest climates in the entire world,

polar bears will shed their fur,

their entire coat, once a year.

[narrator] Image analysis of the thin white strands

show that they are up to two inches long and densely packed together.

A polar bear's thick coat of 10,000 hairs per square inch

is made up of similar looking strands.

Could there be a polar bear in these woods shedding its fur?

[narrator] Polar bears can prowl areas the size of Texas

and there's evidence that they're heading down from the Arctic.

In March 2021, a bear in Russia wanders 675 miles south,

terrifying villagers in Dzhebariki-Khaya

before it is lured into a cage, baited with seal fat.

But in the Americas, it's highly unusual for polar bears in the wild

to travel this far from their usual Arctic hunting grounds.

James Bay, in northern Ontario in Canada,

is the furthest south a polar bear has ever been spotted,

and that's hundred of miles away from this forest

in Washington state, where we find this furry tree.

As we say in Texas, that ain't no polar bear.

[narrator] Coming up, is this a case of tree-monic possession?

[Kevin] This tree is a zombie tree.

It's both dead and alive.

[narrator] And seen on a highway camera,

a small van crashes, and over 40 people get out.

How could so many people fit in the back of one van?

[narrator] In a Washington forest,

a hiker discovers a tree covered in mysterious white hair.

And as the white tufts come into contact with the man's skin,

something strange happens.

It literally melts away at the touch of his fingers.

[Deborah] This stuff looks like animal fur, but it doesn't behave like it.

If you touch it, it melts away into the background.

[Ashanti] As I look a little bit closer of this branch,

you can see that one end of this kind of fuzzy, white mass,

is actually attached to the branch, as if it were growing out.

This is not something that trees normally do.

This lead me to believe that this is caused by some sort of fungus.

[narrator] What looks like strands of hair, is actually ice,

produced by a fungus slowly attacking the tree.

It's a very rare and unique case of fungi, called Exidiopsis effusa.

[narrator] The fungus is eating the tree from the inside out.

This process produces carbon dioxide,

which forces water out of the wood.

Normally in cold temperatures, water would freeze like regular ice.

But the presence of the Exidiopsis effusa fungus,

causes the water to freeze into hair-like strands.

These icy strands are a ghoulish byproduct

of the fungus's deadly battle with the tree.

This tree is a zombie tree,

it's both dead, and alive.

[Jon] The fungus pushes the moisture out of the rotting wood,

into the atmosphere, and it freezes.

And as it continues to do this,

the strands of ice grow longer and longer.

[narrator] As the fungus in the wood eats its way through,

it releases recrystallisation inhibitors,

similar to antifreeze proteins,

that keep the hairs in their unique shape.

The reason for this, a mystery.

But scientists do know fungi have developed many strategies to lure and consume prey.

Fungi are both clever and deadly,

and that is a very dangerous combination.

Given the opportunity, they'd attack humans as well.

[Kevin] They are linked to all sorts of medical ailments,

and medical science is struggling to keep up.

[narrator] Fungal infections kill three times more people than malaria each year.

In 2019, eight patients die in British hospitals,

infected with a deadly shape-shifting fungus called Candida auris.

It was first discovered in Japan in 2009.

It causes lethal blood infections,

and has already spread across the globe

killing half the people who contract it within 90 days

and it's impervious to most drugs and disinfectants.

So, fungus is incredibly lethal to human beings.

[Jon] Fungi cells are very similar to our own,

so it's very hard to make medicines

that kill fungal cells without also killing human cells.

[Ashanti] I've seen some weird things growing out of trees,

but I've never seen one growing a beard.

I'm never gonna look at mushrooms the same way again.

[narrator] Now, a busy highway on the outskirts of Vienna, Austria.

August 15th, 2015.

A traffic camera records a regular rush hour.

Okay, so we're seeing some traffic cam footage here.

-[narrator] When suddenly... -[tires screeching]

[Jayde] Oh, wow.

Well, that was a big crash, with this white panel van running into the railing.

Wow, the front end is totally messed up.

[narrator] The van spins to a stop right in front of oncoming traffic.

Smoke billows out of its smashed hood.

Okay, so we can see the driver gets out of the van.

Well, that's good. He looks like he's okay. Phew.

[narrator] Then, the side door slides open.

Look at all those people filing out of the van.

[narrator] Like a dam giving way,

a wave of people spills out onto the blacktop.

[Jayde] Five, six, seven, eight, nine, ten.

Oh my gosh, how many people in this van?

There's still more coming out?

I'm counting 12, 13, 14... It just keeps going.

[Jayde] When you look at the mass of those people,

compared to the volume of the van,

there must be some sort of extra space,

or a trapdoor that we can't see in the footage.

[narrator] Incredibly, nearly a minute after

the first person left the stranded vehicle, they are still coming.

Imagine being one of those cars stopped beside the van,

you would be absolutely shocked.

[narrator] Over 40 people emerge from the damaged van

that's designed to seat just three.

How could so many people fit in the back of one van, and where are they going?

[narrator] Coming up, were these captives in transit to a life of hell?

The slave trade unfortunately, is still very much alive and kicking.

[narrator] And the cable guy gets the shock of his life.

[Carin] It's a living rope

and it's ravenously hungry.

[tires screeching]

[narrator] In Vienna, Austria, a small van crashes on the highway...

and over 40 people spill out on to the road.

[Tracy] So initially when I saw this clip,

what came to my mind were clown cars from the circus,

where it's just clown after clown after clown,

coming out of these small cars.

This scene, with so many people packed into a small van,

looks like an illusion.

[Tracy] But you can see file information on the camera,

and it doesn't look like it's been tampered with.

How could they possibly have all fit inside?

[narrator] Lots of human beings can fit into one vehicle.

In 2014, a group of 27 women

managed to fit into a Mini, in Brighton, England,

-breaking the world record. -[audience applauding]

A Mini has an internal capacity of 19 square feet.

The van in the footage may look significantly larger,

but still has less than 63 square feet of space.

Humans need about 300 square feet to feel comfortable,

but they can survive in far less space.

[narrator] But the women in the Mini were crammed in

for just a few claustrophobic minutes

and the vehicle would never have been allowed to move,

let alone drive on the highway.

Siobhan Deshauer suspects the highway footage

shows something sinister is going on.

[Siobhan] You would never choose to be crammed in like sardines

into the back of a van.

You can see the driver's acting in a suspicious way.

At first, he seems to be pacing back and forth along the van.

Then he grabs something from inside the van and starts running.

He doesn't seem to be concerned about his passengers at all.

Could this be some kind of trafficking operation that's gone wrong?

The slave trade unfortunately, is still very much alive and kicking.

[narrator] The price of human life has never been cheaper.

In ancient Rome, the average price of a slave

cost about $10,000 in modern money.

The average cost of a 21st century slave,

is just $90, the price of a pair of jeans.

The number of modern day slaves in Europe

is one of the highest in the world.

And highways are the backbone of this transcontinental trade in human misery.

There's a human trafficking route that runs from eastern Europe to the Balkans,

and directly into Austria.

Could these people be on their way to a life of forced labor?

[narrator] If their final destination is Great Britain,

then the answer could be yes.

Over 10,000 people live as slaves in the UK,

with the number rising every year.

The people behind this are disgusting parasites.

They're feeding off of desperate people hoping for a better life.

[narrator] Great Britain abolished slavery in 1807,

but two centuries later, shocking cases continue to be found.

A traveler family in Britain kept 18 people as slaves for 25 years.

A lot of these people are actually homeless

and they were promised food, accommodations,

in exchange for a few months of work.

[narrator] The traveler family scours the country

and prey on vulnerable people for their work gangs.

They keep their prisoners in line with savage beatings and malnutrition.

One man is even forced to dig his own grave.

They keep them in squalid conditions,

forcing them to work all day, every day, for no money.

If they complained, they were punished.

One man had a concrete slab thrown in his face.

[narrator] It isn't much better in America,

where up to 400,000 people are trafficked into slavery every year

and around 80 percent of them are women and children.

Sometimes, only the victim's family come to their rescue.

[Jayde] We've all seen the movie Taken.

It was a real life case of a 16 year old girl in Texas that was kidnapped

and would have been forced into a lifetime of slave labor.

Fortunately, her father pulled a real life Liam Neeson,

and was able to track her down and rescue her.

But the reality for a lot of people is that they're not so lucky.

[narrator] But Chad Orzel doesn't think

slave trafficking is what we're seeing here.

[Chad] Looking more closely at the footage,

we see that the people seem to be all different ages.

It looks like there are whole families in there.

Human traffickers prey on individuals, they would separate families.

So this must be something else.

You know, with world conflict the way it is around the world,

you've got a lot of refugees crossing borders.

And they'll do anything to get across.

And something like this is the result.

Maybe that's what we're seeing here.

[narrator] At the end of 2019,

26 million people worldwide are considered refugees.

They come from warring nations.

Syrians who stay in Syria risk being blown apart

by relentless bombing campaigns.

People fled Sudan, because rebels soldiers at any moment

could choose to destroy their villages.

Travelling in a cramped van doesn't seem as big a risk

when you know what you're trying to escape.

[tires screeching]

[narrator] That's until something goes wrong.

[Jayde] So, this footage was taken in August of 2015,

and in the same month, in Austria,

police find another van with the decomposing bodies

of over 70 people that were crammed inside there.

Day after day, people die trying to seek refuge in Europe by land or sea,

but this is one of the worst cases.

[narrator] The men, women and children in the footage

could have been cooped up inside the van for days.

Just imagine if it had been a worse accident,

all those people could have been badly injured, if not killed.

[narrator] Following the crash, the Austrian authorities

take the refugees in for processing

but they do not reveal their identities to the public.

To this day, the whereabouts of the driver who fled the scene remains unknown.

You know, it looks like these people got away with minor injuries,

but they were lucky to get out alive.

[tires screeching]

[narrator] Now, Costa Rica, Central America.

July, 2018.

An electrician is making repairs to a dilapidated village house

when he sees a mysterious cable.

What appears to be a black rope or maybe even a wire.

[narrator] When he approaches, he makes a shocking discovery.

[Shaena] It's moving.

This thing is alive.

I've never seen anything like that before in my life.

[narrator] This is a cable, where there's no cable.

This loop is made up of ants.

I think there's thousands of ''em.

Woah!

This is fantastic!

Are ropes supposed to crawl like that?

On first glance, it looks like the ants

must be crawling over something, like a rope.

But when you check it out more closely,

what you can see is that the ants are climbing over their own bodies.

The rope is made of ants.

[Greg] It looks like they're carrying larvae or eggs.

These ants are hunting.

I can see something that looks like a wasp or a bee nest attached to it.

[narrator] These ants seem to be defying gravity.

[Greg] How did they get from one point to the next?

How did these ants build a rope

from the edge of the house to the wasp's nest,

without anything in between?

How on earth is that created?

[narrator] Coming up, is this evidence

of an ant species suddenly getting smarter?

These living bridges usually only get to be about five inches long.

But this one is absolutely immense.

It wouldn't surprise me if there were thousands of ants in this bridge.

[narrator] And a mysterious black mass

sweeps towards an American town.

Anyone trapped under that would be charred to a crisp.

[narrator] In the Costa Rican jungle,

a man films a gravity-defying living bridge of ants on a feeding frenzy.

Entomologist Kevin Kasky studies the footage

and identifies the ant species.

I think what we're looking at is a colony of army ants.

And what's unique about army ants

is they literally march in a straight line.

Army ants don't build nests in the ground like other ants,

instead, they're constantly on the move.

[narrator] Army ants are half an inch long and practically blind.

They don't sound like a military marvel, but size can be deceiving.

Individually, an ant is not much.

All they do is eat, sleep, follow the queens orders.

But you put them together, they form a cohesive megaunit.

[narrator] When ants get together, they make a gargantuan superorganism.

Some army ant colonies contain as much as 20 million ants,

all controlled by one single, autocratic queen.

[narrator] And this single-minded military machine has no permanent home.

It moves on a relentless march through the jungle,

foraging like a miniature Mongol horde.

Anything that stands in their way

will be overwhelmed and potentially destroyed.

The hunting parties of army ants

can kill over 500,000 creatures a day.

[narrator] The army ant's main weapon is their large mandibles

that work like scissors to slice open their prey.

The bite is very painful,

and because their jaws are so strong and lock on,

it's very hard to remove them.

[narrator] Even if the ant body is broken off,

the head will keep biting down in a death grip.

Army ants are champion athletes despite their size.

They race across the ground at over four inches per second.

A human travelling at the same pace

would be going at 37 miles per hour.

Most prey can't outrun them.

When they attack, they swarm over the body,

you may not even know they're there,

until a signal tells them to all bite, nearly at once.

And there is no known way to stop them

once they've started their attack.

At the same time that they're cutting and killing the prey,

they're also secreting an acid

which is sort of digesting the creature outside of the body,

making less work for them, and leaving more time

for them to move on to their next kill.

It would take a while for them to gnaw through your whole body.

But once they get started, there is no stopping them.

As individuals, ants are tiny and weak,

but when they band together like this, they can be deadly.

[narrator] Any creature unable to evade this army will perish.

Hungry army ants have been known to devour

cats and dogs locked in houses.

[narrator] Most horrific of all, they can target small human children.

When a baby was abandoned in a Russian forest,

she was found covered in ants being eaten alive.

But luckily, she survived.

This is just horrific. My skin crawls thinking about it.

[narrator] Even if the colony's prey is raised up off the ground,

these ants can find a way to reach it.

When army ants go hunting,

they can use themselves as bridges

as a way to get over holes or other obstacles that could be in their way.

They don't plan it, it's more of an instinct.

When one ant senses a hole in the ground, it slows down,

but the ant behind it keeps moving and walks up onto its back.

[narrator] When enough ants have done this, the living rope gets stronger.

Like scaffolding, it allows them to climb upwards,

getting closer to the prey above them.

[Shaena] When an ant feels another one on its back, it freezes.

The ant on its back sees the gap and also slows down.

And that process keeps repeating until there's a bridge.

[narrator] Pulling off such a feat requires incredible strength.

An ant can carry around 50 times it's body weight,

the equivalent of an average man

carrying two rhinos on his head.

But an ant bridge like this is one, is an engineering miracle,

even for these unstoppable creatures.

These living bridges usually only get to be about five inches long.

But this one is absolutely immense.

It wouldn't surprise me if there were thousands of ants in this bridge.

[narrator] Scale analysis of the Costa Rican ant cable,

shows that it's six feet in length,

approximately 145 ants long.

That's the equivalent of replacing

the Rio Grande Gorge Bridge with a line of people.

The bridge probably started out much straighter,

but as more ants joined it, it got longer and heavier and dipped further down.

[narrator] But the incredible length of this living chain

suggests that the ants maybe part of a colony of unimaginable size.

There's thousands of ants in this bridge.

That means that there's probably

millions of other ants in the colony out there

to make this bridge worth their time.

I think this could be an ant super colony.

Usually, ant colonies only have one queen.

But sometimes, several colonies will work together

to increase their strength.

[narrator] The ant's main purpose is to kill and eat

every inhabitant of the nest that they are entering.

[Kevin] This is terrifying.

If they could build a bridge that is that long,

think of what they can do if they build a bridge into my house

or worse yet, your house.

[narrator] There are already over 10,000 trillion ants on our planet.

Their next bridge could be to your house.

As they start invading into urban settings,

their numbers increase, and who's next on the menu? You and I.

[narrator] Now, Pima County, Arizona.

July 15th, 2020.

A wildlife cameraman hears a strange noise in a quiet desert landscape.

[liquid gushing]

[narrator] Then, it appears.

[gushing continues]

In the distance, you can see something rolling towards us.

[Jeff] It's kind of alien-looking

and it's just moving really quick.

And it's just, kind of relentlessly just oozing and pouring.

[Ashanti] This is the Arizona desert.

Seeing this black fluid rolling over the parched desert, is so surreal.

[narrator] A mysterious sludge coating everything in sight.

It looks like an avalanche of black goo.

What is this sinister black tsunami and where did it come from?

[narrator] Coming up, a wave of black death sweeps into town.

You think you're finally safe,

but the worst could be yet to come.

[narrator] In Arizona, a tidal wave of black sludge

is filmed rolling towards the city of Tucson.

Journalist Jeff Wise finds reports of weird black goo appearing all over the world.

There's a similar sort of black goo

that's been reported in Caracas, Venezuela.

They call it Le Mancha Negra, the black stain.

[narrator] The black stain first appears in 1986 on a road near the airport.

It's small at first. An inch thick, greasy black blob.

But it slowly spreads to coating

an eight mile stretch of highway.

The consistency of this goo changes with the weather.

It's as if hot weather makes it expand.

[narrator] The black ooze has been blamed

for numerous traffic accidents and even deaths.

Although it's very sort of, oozy, it's also slippery

and that can cause cars to kind of, spin out of control.

It's so dangerous that

taxi drivers refuse to drive here when the phenomenon appears.

They don't want to risk their lives.

[narrator] As the black ooze spreads,

the Venezuelan government becomes more desperate to get rid of it.

They try everything, including pressurized hoses, to try to wash it off,

but nothing works.

They've tried detergents and other chemicals,

but that doesn't work either.

And they've even tried to scrape it off

with a variety of implements,

but the black goo continues to return.

To this very day, they still don't know

what this weird black substance is.

[narrator] But as the raging dark torrent gets closer,

Nick Householder spots a terrifying detail,

that marks it as different to the black ooze that appeared in Venezuela.

It seems like a mixture of mud and sticks,

but it looks like it's steaming hot.

[Jeff] So it's flowing like water and yet it's also smoking.

Like, it's apparently on fire.

It's like this moving, smoking, churning mass.

Anyone trapped under that would be charred to a crisp.

[narrator] Science historian Ashanti Davis finds maps show a forest uphill

from the place where the footage was shot.

[Ashanti] It's just a lot of burnt charred material.

That suggests that it might be the product of a forest fire.

This footage was taken in July which could be prime fire season,

especially in the Arizona desert.

[narrator] Local news reports show that Arizona dealt with

over 2000 wildfires in the summer of 2020.

Thousands of raging infernos sweep across swathes of tinder dry forests,

across the American west coast.

They're propelled by winds of over 60 miles per hour,

making the fires impossible to outrun.

The remains of one man were found

in the driver's seat of his car,

with those of his grandmother sitting next to him.

[narrator] In 2020, more than 30 people are killed

and tens of thousands are forced to evacuate their homes.

Many of these fires were caused by lightning strikes,

but some were set on purpose.

One man claims to have started a fire in California,

to hide the bodies of five of his murder victims.

[narrator] On June 5th, 2020,

a devastating fire breaks out in Santa Catalina mountains in Pima County.

It spreads across over 100,000 acres

and is still burning on the day this footage is filmed.

But how could a fire create a smoking river of goo?

If you look at the background of the video,

you notice that the sky is very cloudy.

It's monsoon season in Arizona so,

lightening, thunder, and just rain, rain, rain.

[narrator] The July storm that swept in that day, didn't snuff out the flames,

it merely stirred up more trouble.

Extreme forest fires can change the physical nature of the soil below them,

almost creating a waterproof layer

that liquid just slides right off of.

This means that even a light rain can turn into

an aggressive flood with very little warning.

Large amounts of burnt material

like ash, silt, rocks and even burnt trees

become loose and start rolling downhill.

[narrator] In 2018, a forest fire followed by storms

sends waist high mud flowing through

California's Santa Barbara County, at 35 miles per hour.

This water doesn't even behave like normal water anymore,

it's more like wet cement.

This is a hardcore mudflow.

It picked up trees, it picked up rocks.

Even picked up cars.

[narrator] 23 people are killed.

The citizens of Tucson were fortunate

that the killer sludge didn't hit the town.

Next time, they may not be so lucky.

As the rate of wildfires increases,

the risk of these additional disasters also increases.