All language subtitles for S42E13 - Sinkholes; Buried Alive

NARRATOR:
They can occur suddenly

and catastrophically.

WOMAN:
Oh, my God, do you see it?

NARRATOR:
They have swallowed cars,

animals

and people.

They have destroyed homes.

MAN:
Our house and also
our neighbor's house

is completely gone.

NARRATOR:
And for an unlucky few
have become graves.

These are sinkholes.

All across the globe,

enormous sinkholes have cracked
the earth's surface

like an eggshell,
devouring every type of terrain

with a destructive force
that defies imagination.

In Louisiana,
a 40-acre monster

has been consuming the bayou
for two years.

In Spain, sinkholes are
cracking apart historic towns

and leaving others in ruins.

NARRATOR:
And in Florida,

a sinkhole becomes
one family's worst nightmare.

MAN:
We heard my brother scream.

There was no floor,
no ground, no nothing.

Everything was gone.

Everything was gone.

NARRATOR:
Why is the ground under our feet
collapsing?

What dangers lurk
beneath the surface?

Whose home will be next?

"Sinkholes: Buried Alive,"
right now on NOVA.

Major funding for NOVA
is provided by the following:

At Cancer Treatment Centers
of America,

Supporting NOVA and promoting
public understanding of science.

And the Corporation
for Public Broadcasting,

and by PBS viewers like you.

operty
in Seffner, Florida,

is all that remains of a tragedy

that will haunt the dreams
of Floridians forever.

A home had stood on this spot
for over three decades.

But that all changed
on February 28, 2013.

The house had been occupied
by Jeremy Bush,

his wife Rachel,
and their daughter Hannah.

Rachel's sister Janell
and Jeremy's brother Jeff

were also living there.

That night, Rachel and Jeremy
had finished a late dinner,

were washing up,
and about to go to bed.

Janell had just gone into
her bedroom for the night,

and Jeremy's brother Jeff was
already asleep in his room.

It had been a long day
for everyone.

When we were just fixin'
to lay down,

that's when it happened.

NARRATOR:
The time was 11:01 p.m.

(rumbling)

It sounded like somebody came
and hit the house with a truck.

(man screams)

Then we heard my brother scream.

RACHEL:
We ran down the hallway.

I flicked on the light
and opened up the door.

JEREMY:
There was no floor,
no ground, no nothing.

Everything was gone.

Everything was gone.

NARRATOR:
And everything
was still sinking.

But Jeremy makes
an instant decision.

I automatically just
jumped into the hole

and started screaming
and yelling for my brother.

And all I could see was
the corner of my brother's bed.

That was it.

His TV, his dresser
and everything was gone.

I started digging
with my hands and stuff,

trying to get to my brother

because I thought I could
hear him yelling and screaming

for me to help him.

NARRATOR:
Rescue teams were too late
to save Jeff Bush,

but did manage to pull Jeremy
from the ravenous hole.

The next day,
cautious authorities

stretched a pole camera through
Jeff Bush's bedroom window.

The sinkhole
was more than 20 feet deep

and completely empty.

No bed, no body, just dirt.

Wary of more sinkholes,

the house and two neighboring
homes were demolished.

Jeff Bush's body
was never recovered.

The slab and hole
mark his grave.

But ironically, his death
may have prevented another.

JEREMY:
Two months before my brother
moved in,

it was my daughter's bedroom.

Hannah's bedroom.

NARRATOR:
Sinkhole fatalities
like this one are rare,

a remarkable fact

given the scores of sinkholes
that occur each year.

MIKE FASANO:
Florida is very lucky
that more people

haven't been seriously injured
from sinkholes,

where they were sleeping
in their home

or apartment complex

and they did not get out
in time.

NARRATOR:
Although sinkholes threaten
many regions of the world,

Florida is particularly
vulnerable.

In 1981, one of the largest
ever witnessed

ate two square blocks
of Winter Park near Orlando,

including an unfortunate
Porsche Dealership.

Sinkholes are usually
not this big.

But why does Florida have
so many?

Its placid surface
offers no clue.

But underground,
the answer becomes clear.

In many places,
the bedrock is far from solid

and riddled
with water-filled caves.

The caves are carved out of
a porous rock called limestone,

and it's this water-soluble rock

that gives Florida its unique
and dangerous footing.

At the surface, a quarry
is one of the few places

where we can see Florida's
hidden geology.

And this one near Tallahassee

has attracted Geological Survey
specialist Harley Means.

This fossil clam
is over 30 million years old.

And this is the fossil remains
of an organism

that lived in a shallow sea.

Well, we're standing
above sea level currently,

so how did this deposit
get here?

How did it form?

Well, it turns out Florida
has been shaped primarily

by the processes that drive
sea level fluctuations.

NARRATOR:
The landmass
we now know as Florida

stayed submerged
for millions of years.

Although ocean levels
rose and fell,

periods of global freezing
expanded ice caps,

froze glaciers and eventually
lowered sea levels,

exposing the land.

The emerging surface became
a dynamic mix of seawater,

wind-blown sediments

and the remains of countless
marine organisms.

MEANS:
So what happens is

these critters live,
they die,

and they accumulate
on the sea floor,

and then they get buried,
they get compressed,

and ultimately,
they can become rock.

That's what we're
looking at here.

So... one of the properties
that makes this rock

so susceptible
to being dissolved away

is the ability for water
to move through this.

And it has something to do with
how well it's cemented together.

There's not a lot in the way
of mud and whatnot

to impede the ability
of this material

to transmit a whole bunch
of ground water.

NARRATOR:
Landscapes where water
erodes limestone like this

and other rock types
are called karst.

Rainwater becomes acidic

when it absorbs carbon dioxide
in the air and ground

and over time
can eat away the rock,

creating caverns, caves
and sinkholes.

But how do sinkholes
actually form?

Back in the quarry,

we can see soil
above the layers of limestone.

When it rains,
water passes through the soil

and enters the rock layer
through cracks and fissures.

So here's one of these
fracture features

that we've been talking about--

you can see it all the way
from the top of the section here

right down through
right in front of me here--

that plays such
an important role

in the development of karst
in Florida.

What happens is,
rocks are brittle,

and over geologic time,

they can fracture
like this has right here,

and then they provide
a preferred pathway

for groundwater to flow.

NARRATOR:
Rainwater from the surface
passes through the cracks,

eroding the limestone
and carving out a hollow space.

When the growing void reaches
the underside of the soil layer,

dirt will begin to drop
into the hole.

If the soil is loose or sandy,
the surface will begin to sink,

gradually forming
a bowl-shaped depression

called a subsidence sinkhole.

But if the soil contains clay,
which is more cohesive,

the surface will not sag

even as the void underneath
grows larger

until without warning,
it suddenly collapses.

(loud crashing)

MEANS:
These are called
cover collapse sinkholes.

These are the ones that
really do most of the damage,

not only in Florida,
but all over the world.

NARRATOR:
Globally, many regions
contain limestone,

and virtually all
are vulnerable to sinkholes.

Beside sinkholes, these areas
are often characterized by caves

hollowed out over geologic time
by water.

Because many of Florida's caves
are still filled with water,

they are magnets
for intrepid cave divers,

like this team
led by Brett Hemphill.

Once we get to 160 feet,
this should clear up real good.

We should be good.

NARRATOR:
Today, the team will enter
a cave system near Gainesville.

After suiting up,

they slip into a leafy looking
pond called Mill Creek Sink.

The pond is actually
a very deep sinkhole

and one of many portals

into Florida's vast
and underexplored cave system.

HEMPHILL:
With all the cave systems
that we're aware of in Florida,

believe it or not,

the ones that we can dive
and actually get into

represent less than one percent

of the caves
that actually exist underground.

NARRATOR:
Brett and other divers have
explored this section before.

As always, they will look
for cracks in the walls

big enough to swim through,

hoping they can find
unexplored territory.

Along the way,
they often find surprises.

HEMPHILL:
Caves are time capsules.

You have to understand that
because there's no rain or sun

that will erode away stuff,

in a cave,
things are locked in time--

bones, fossils,
just many things.

NARRATOR:
Cave diving is very dangerous.

Currents and conditions
can change quickly.

Any physical
or equipment problem,

and there's no quick way
to get to the surface.

Some divers never come back.

Although most cave systems
are well below ground,

some get so close to the surface

they can create
a sinkhole threat.

HEMPHILL:
Divers can get a sense
of what's occurring above them

in these particular areas

because as we're moving
through the conduit underground,

you can see that the ceiling
starts to become eroded away.

Many times when
we're in the caves,

we can be at 80 feet,

and the conduit
can be like a tube,

and all of a sudden, there's
literally less than 20 feet

between us and the surface.

And these are areas that are
very prone to sinkholes.

NARRATOR:
The land around Florida's
picturesque lakes

is also prone to collapse

because many lakes are
themselves ancient sinkholes.

And there are regions where
if you peeled away the surface,

it would look like Swiss cheese.

So building houses
above these areas

makes sinkhole problems
almost inevitable.

Usually, there are warning signs

the ground is sinking
or shifting.

The driveway had collapsed.

The sinkhole just dropped out.

This door used to open.

It is a significant buckling.

This crack.

Truck fell in
the test point hole.

(loud crash)

NARRATOR:
But sinkholes can also occur
with no warning signs,

especially during heavy rains
and flooding

when water oversaturates
the land,

or when farmers irrigate
and draw too much water

from the underground aquifer.

Then disasters happen.

Guys, let's fill
the tank.

NARRATOR:
That is why Ming Ye and a team
from Florida State University

are creating this sandbox model.

Be careful about the water
content in the clay.

NARRATOR:
They want to speed up
the time it takes

for sinkholes to form
in different soil environments.

YE:
We put sands and rocks
to mimic the geology,

and also we put water to mimic
the hydrology in the field.

NARRATOR:
Once the layers
are stacked correctly,

the team adds some extras
and fills the model with water

because today's test will focus
on drawing too much water

from the underground aquifer.

So we are testing
one tipping point,

that is, change of water level
in the subsurface environment.

NARRATOR:
The top two layers
are sand and soil.

Below are limestone layers
where a small void is forming--

the first step
in the sinkhole process.

This process takes place

when a lot of water is drawn
through the limestone layer

and begins to dissolve it.

You can't see water flowing
in the sponge-like limestone,

but it is there, just as it is
in the network of caves below.

HEMPHILL:
A lot of people think
of the Floridian aquifer

as this enormous void of water.

When you look at limestone,
you think it's absolute,

but it is a very porous media,
and water can move through it.

NARRATOR:
The aquifer is Florida's
main source of drinking water

and also provides water
for irrigation.

In severe winters, farmers will
often irrigate day and night

to keep fruit from freezing,
and that's when problems emerge.

MEANS:
It turns out when you start

to draw down the surface
of the groundwater table,

those void spaces that might
have once been filled with water

are now filled with air,
and air does not provide

as much support
as water does

and we can see
more sinkholes occur.

NARRATOR:
In 2010, massive pumping
in Plant City

produced 60 sinkholes in this
one East Tampa community.

Ming has patterned his model
on the Plant City experience

and is drawing water
out of the aquifer

to simulate
the overpumping there.

As a result, a large sinkhole
has developed under the surface,

just like the ones
in Plant City.

That's because the soil layers
and deteriorating limestone

are sliding downward,
causing the surface to subside.

Then the team
turns things around

and begins to add water
at the top

as if a big storm followed
overpumping of the aquifer.

The water pools
into the void space,

triggering
an almost immediate collapse.

For Ming Ye, there is one
unmistakable conclusion.

YE:
It would be a disaster

if you pump too much water
from the limestone layer

and at the same time,
you have a thunderstorm,

and that pours too much water
on the ground.

NARRATOR:
To predict sinkholes
in various soil conditions,

the team will have to do
the experiment many times.

Their results could inform
future development

and water regulations.

But for many Floridians,
the die is already cast.

Richard and Betty Theodore
live in a modest house

in Spring Hill, Florida.

You know, this thing
is really getting worse.

NARRATOR:
Like many residents, they
came here from the Northeast

to live out their golden years

in the warmth
of the Sunshine State.

BETTY:
We lived in a little town
in Massachusetts

called Acushnet,

And we found a nice house
and we bought it.

NARRATOR:
But they didn't know
they had moved into an area

locals call Sinkhole Alley.

BETTY:
There were at least seven houses
in this immediate area

that are sinkhole houses.

NARRATOR:
And then it happened
to their house.

RICHARD:
One day, I went outside,
and I see all different cracks

on the side of the house,
and come to find out

we did have a sinkhole
underneath the house.

When we got the house,

we didn't know
we had a sinkhole.

Oh, send a bill.

408 has numerous problems.

NARRATOR:
Former State Senator Mike Fasano

has been Florida's leading
advocate for sinkhole victims.

FASANO:
The homeowners
in many of those homes

who happen to be seniors
feel very vulnerable.

They've invested every dime
they have in that home,

so if a sinkhole were to occur,

this is the last home they're
going to be living in probably

until they die.

NARRATOR:
The Theodores would like
to sell their house

and move somewhere safer,

but they believe they will get
very little money for it now,

so they're staying put

and hoping the house
does the same.

BETTY:
When we moved here, we expected
to enjoy our retirement

and just see some sights.

I love Florida.

I just don't love sinkholes.

NARRATOR:
Although Florida is
extremely prone to sinkholes,

especially in the central
portion of the state,

globally, it is hardly alone.

In Spain, there are communities

that have been living
with sinkholes for centuries.

This is the medieval city
of Calatayud.

Founded and fortified by Muslim
Moors in the eighth century

and conquered
by the Christian king

Alphonso the Battler
in the 12th century,

today, it is a charming jewel
cursed by a plague of sinkholes.

FRANCISCO GUTIERREZ:
A peculiar aspect of this city

is that most the buildings
have been built on gypsum,

and this is a soluble rock,

and that's the reason
why sinkhole problems

are quite common.

NARRATOR:
Gypsum surrounds and underpins
this city.

As another form of karst,
it is easily dissolved by water,

but is more porous
than limestone

and dissolves even faster.

So the city's buildings
are constantly cracking.

GUTIERREZ:
Problems affect the daily life
of the people.

NARRATOR:
Several of the city's
most beautiful buildings

are endangered.

But structural fixes here are
difficult and very expensive,

so damage everywhere
keeps reoccurring.

GUTIERREZ:
Cracks are very common,

and obviously people try
to repair them with plaster,

but obviously that does not
solve the problem.

It's just a makeup.

It improves the aesthetics.

(church bell ringing)

NARRATOR:
In an effort to save
a leaning church tower,

engineers lopped off the top,

hoping the surgery would keep it
from crashing down.

The storks don't seem
too concerned.

Like the people of Calatayud,

they are simply making the best
of their tilted world.

GUTIERREZ:
The development of the sinkholes
will keep on occurring,

but people here get used
to that problem.

They can obviously cope with it.

NARRATOR:
Although Calatayud has managed
to survive its unstable ground

for centuries,

other towns in the region
have not been as fortunate.

This is an aerial photograph
of Puilatos,

a sparkling new town
built in the 1950s

to provide better housing
for local farmers

and their families.

Today, it's just piles
of rubble,

the victim
of a sinkhole-laced terrain.

(translated):
It was a neighborhood of houses.

A street went through here.

This is all very changed now.

NARRATOR:
Javier Rome was one of the
town's original inhabitants.

ROME (translated):
Here, we still see a manhole
cover that was built in 1962.

This was the end of the town.

The water ran
around the perimeter.

We came in 1956.

The problems with the cracks
and the sinking

started a few years later.

NARRATOR:
Like most people in Puilatos,

Javier came from a family
of farmers.

In fact, he still is one.

Unlike his ancestors,
he tills the fields

with the machines
of modern agriculture.

But every generation
has worked on land

where layers of porous rock
lie just beneath the soil.

And when farmers irrigate,
the water pours onto the surface

and then down
to mineral deposits

that here are composed
primarily of salt.

In geologic terms,
salt is an evaporite

and, like gypsum,
can dissolve very easily.

One of the characteristics
of the evaporative areas

is that the dissolution
processes may be very fast

and the probability
of occurrence of sinkholes

may be very high.

NARRATOR:
Just walking the fields
in places like these

can be extremely dangerous.

Experienced farmers
used to wear long wooden sticks

tied to their shoulders.

The sticks had nothing to do
with tending crops.

They had a far more important
function...

(gasps)

...keeping farmers from entirely
disappearing into sinkholes.

(grunting)

MIGUEL LIZAGA (translated):
When I was a kid, I knew some
elders who carried the sticks

because they made them
feel safer.

I know people who fell in one
and got hurt,

and also machinery.

When the sinkhole was big,

whole harvesters
have fallen inside.

NARRATOR:
By the 1970s, there were
so many sinkholes in Puilatos,

the government condemned
the once model community

and tore it down.

ROME (translated):
We lived here for 19 years.

It was not very pleasant
to leave.

We were nostalgic
for what we were leaving behind.

NARRATOR:
The sinkholes
that destroyed Puilatos

did not disappear
with the village.

Today, in the shadow
of the destroyed town,

a growing, water-filled sinkhole
threatens a major highway.

A team from the University
of Zaragoza

is using Ground
Penetrating Radar

to assess the effect
of the sinkhole on the highway.

GPR uses radio waves

to create a kind of sonogram
of conditions under the ground.

GUTIERREZ:
Here, we have a very large
sinkhole.

This sinkhole is more than
200 meters across.

We can see that the ground
and also the overlying highway

is subsiding by sagging.

And this is the kind of sinkhole

that's very difficult
to remediate

because it's related to the
dissolution of salt at depth,

and that's something
you cannot stop.

NARRATOR:
As in Florida, sinkholes in
Spain are a constant threat

and not just to roads
and houses.

Just before its famous
high-speed train was to make

an inaugural run, a sinkhole was
discovered under the track.

With speeds approaching
180 miles per hour,

any deviation in the track
alignment

could cause a derailment
and bring results

similar to this 2013
operator-caused catastrophe.

Globally, as more sinkholes
emerge near infrastructure,

housing and other forms of
development, one thing is clear.

GUTIERREZ:
Sinkholes can be accelerated

or even triggered by various
human activities.

NARRATOR:
Poorly designed and overloaded
sewage systems helped create

this enormous sinkhole in
the center of Guatemala City.

Damming the Jordan River

has made the desert edge
of the Dead Sea

look like the surface
of the moon.

And melting permafrost
from global warming

could be responsible
for spectacular holes

in far Siberia.

20% of the earth's land surface
contains the soluble rocks

of karst terrain.

This means there are millions
of acres in scores of countries

where human activities can
increase the risk of sinkholes.

That is why Francisco Gutierrez
studies these areas

so intensively.

These rare limestone monsters
are extremely old,

probably forming long before
any human activity.

But as it turns out, we can
create our own sinkhole monsters

and in a mere fraction
of that time.

There's no better example
of human-created sinkholes

than in southern Louisiana's
Bayou Corne.

Bayous are home to marshes
and slow moving rivers,

slender-rooted cypress trees,

birds, fish, insects
and, of course, alligators.

Here, the natural world is
interlaced with metal roots:

giant pipelines transporting
gas, oil and salty brine

to the region's many
petrochemical plants.

PATRICK COURREGES:
One of the keystones of our
economy has always been

development
of the natural resources.

NARRATOR:
Patrick Courreges works

with the Louisiana Department
of Natural Resources.

Louisiana has always been rich
in oil and natural gas,

which are very critical
to almost everything we do.

NARRATOR:
Bayou people, like longtime
resident Dennis Landry,

are not too concerned about all
the oil and gas operations,

except when they see bubbles
like these.

And bubbles in this very spot

began a saga
few here will ever forget.

LANDRY:
My wife Pat and I were
just taking

a leisurely boat ride

and when we got close
to the pipelines here,

I saw some unusual bubbling
in the water.

So I looked up and I could see
a pipeline sign,

so I immediately thought,

"Well, surely it's got to be
the pipeline leaking."

NARRATOR:
Pipelines from natural gas wells

crisscross the undersurface
of the bayou.

Natural gas is odorless,
highly flammable

and explosively dangerous...

so reports of unusual bubbling
go directly to John Boudreaux,

the Assumption Parish director
of emergency management.

BOUDREAUX:
We received a call
about bubbling

that was occurring
in Bayou Corne,

and yes, there was bubbling

and it was right near
the pipeline crossing.

NARRATOR:
But Boudreaux had to eliminate

the possibility it was swamp
gas, which results

from rotting organic matter
and is not a threat.

So, like a forensic detective,

he sped to the site to take
the gas's fingerprints.

Boudreaux had to catch
the bubbles with a funnel

and feed the data
to a methane detector

to see if it was natural gas
from a leaking pipeline

or just swamp gas.

BOUDREAUX:
The methane detector indicated
it was not swamp gas--

that it was a natural gas
from a deep source.

NARRATOR:
But almost immediately,
more bubbles began to appear

in too many places to originate
from a single leaking pipe.

Then they had bubbles coming up
in the neighborhood.

It's not just in the bayou.

They were coming up right down
the road over here,

bubbling up like Alka-Seltzer.

NARRATOR:
And then the swamp began
to tremble with earthquakes.

Very unusual to have earthquakes
here in south Louisiana.

NARRATOR:
As the earthquake activity
increased,

the community began getting
very nervous.

COURREGES:
We have natural gas bubbling,
but the pipelines are okay.

We're feeling tremors.

It's kind of a mystery because
the clues don't really add up.

NARRATOR:
Then in the predawn hours
of August 3, 2012...

the bayou cracked open
in a giant circle

as if the land had been struck
by a colossal meteor.

LANDRY:
There was a huge hole
in the middle of the swamp,

at least a couple
of football fields.

BOUDREAUX:
I have never seen trees

that have turned over

and the root system is now
pointing up.

LANDRY:
I could smell a strong smell

of diesel or petroleum
or something.

BOUDREAUX:
I'd never seen anything
like it.

NARRATOR:
What was once a shallow,
tree-filled swamp became a lake,

covered with an oil slick.

(tree trunk cracking)

Boudreaux used an amphibious
vehicle to reach the middle

so he could measure the depth
of the sinkhole that created it.

BOUDREAUX:
That initial depth

that I checked was 384 feet.

NARRATOR:
The hole was
almost 40 stories deep.

What could possibly
cause this to happen?

The immediate suspect was
fairly close to the sinkhole

and lay under this clearing:

the mile deep,
and previously abandoned,

Texas Brine salt cavern.

There are several caverns
in Bayou Corne

because it sits atop
an enormous geologic formation

called a salt dome.

Salt domes are ancient salty sea
beds that rise up like pillars

when downward pressure
from accumulating sediment

forces the buoyant salt upward.

They are extremely valuable

because oil and gas can get
trapped on their perimeters.

And of course, there's the salt.

Mined for centuries to help
preserve food

and enhance its flavor,

today salt is also processed
into chlorine gas,

a major component for making
plastic, bleach and paper.

But traditional mining
is expensive,

so companies like Texas Brine
brine it.

Water at high pressure is sent
down a pipe.

It easily dissolves away the
salt and creates a watery cavern

that grows larger
as brining increases.

The salty brine is then pumped
to the surface, stored in tanks

and piped to chemical plants.

COURREGES:
It's a mechanically simple way
to get it and deliver it

to flush fresh water down,
bring salt water up

and ship that salt water up
for further processing.

NARRATOR:
Sinkholes on salt domes have
happened before.

Too much brining
in Daisetta, Texas,

caused the top of this dome
to crack apart

and the surface above to subside
into a large sinkhole.

The Bayou Corne sinkhole
was far deeper than Daisetta

and its origin mysterious.

Although Texas Brine's
salt cavern

was not directly
under the sinkhole,

the state ordered the company
to inspect the cavern

to see if it triggered
the collapse.

They sent down a drill
that encountered no problems

for the first 1,000 feet, but
then struck rock and sediment.

This material had to come
from outside the salt cavern--

meaning the company had brined

too close to the edge of
the dome, cracking it open.

Soil and rock had cascaded
through the breach,

filling the deep cavern,

and this in turn sucked down the
surface in a massive sinkhole.

COURREGES:
What we know now is

the bubbling appearing
over a widespread area,

the tremors people were feeling,

those were the indicator
that that cavern had begun

or was well into
the process of collapsing.

NARRATOR:
With several lawsuits pending,

Texas Brine refused to talk
to us on camera.

The company does accept
responsibility for the sinkhole,

but denies their negligence
caused the accident.

Using independently created
three-dimensional measurements,

the company points out that
the wall of the salt dome

curved farther inward
than anyone realized.

So as their brine cavern
expanded,

they couldn't have known it had
gotten too close to the edge.

Although the legal process
is ongoing,

for months, Bayou Corne
was a hellish place.

Rising waters quickly
overwhelmed a protective berm,

and gas shot
out of the vent wells.

John Boudreaux patrolled
the site every day

because his instincts told him

the sinkhole trouble was
far from over.

Then, almost a year after
it all began, he got a call

from the seismic
monitoring station.

He says, "Something's happening
at the sinkhole.

I can see it on our equipment."

NARRATOR:
Boudreaux arrived at the edge
of the sinkhole just in time.

BOUDREAUX:
I saw the bubbling
in the tree areas

and it looked like those trees
were sinking, and they were.

Pulled out my iPhone.

MAN:
They're moving, John.

BOUDREAUX:
Yep, I got it.

I got it.

NARRATOR:
The video that John Boudreaux
shot that day

made Bayou Corne a national
news story and a YouTube hit.

Despite the real
and present danger,

some residents never left
their bayou homes.

Dennis Landry has stayed
throughout

in the community he founded
and calls Sportsman's Paradise.

LANDRY: It was a dre

to develop a beautiful
waterfront community

here in beautiful Bayou Corne.

NARRATOR:
He believes residents
are reasonably safe.

LANDRY:
We were assured

that the hole would be monitored
24 hours a day.

They started putting in vent
wells to vent the gas,

to get the gas
out of the aquifer.

They came in, they put air
monitors in our homes,

and like that they gave us
some sense of security

that if gas would get into our
homes we would know about it

in plenty of time to get out.

NARRATOR:
There's still a lot of gas,
with one of the biggest pockets

right under the emergency
command center.

But recently things have
started to calm down.

The sinkhole appears
to be plugging up.

The gas flares are less intense.

And most of the oil is gone.

Unfortunately,
so too are the people,

especially in the older
community across the highway

from Sportsman's Paradise.

Over the past two years,

Texas Brine bought out
homeowners afraid to return

and settled a class action
lawsuit from others

angry their homes
were now worthless.

But it's little solace

for the people
who once called this home.

MIKE SCHAFF:
My friends over here,
Janet and Jerry,

lived here for 30 years.

They were bought out in the
first round by Texas Brine.

NARRATOR:
Mike Schaff is one of
the last people leaving

this once lively community
now going to seed.

SCHAFF:
We didn't have much choice.

Pretty much everybody
decided to leave.

Bayou Corne is not going
to be what it was before.

It's never going to be
the vibrant community it was.

The other day I had to decide
whether or not to save my house,

to stay here or not,

or turn it over to Texas Brine
so they could tear it down.

It felt, to be honest with you,
it fellike turning her over

to... an innocent person
over to the executioner.

NARRATOR:
With most of the houses
abandoned,

is the saga of the Bayou Corne
sinkhole over?

Will a vibrant community
ever return?

Will there be long-term health
impacts to the bayou

and the people who lived here?

As Louisiana considers
new brining regulations

to guard against future mishaps,

there is a broader question
to answer:

What can be done right now
to protect people everywhere

from the worst consequences
of sinkholes?

Back in Florida, it's hard
to imagine sinkholes forming

under these lovely homes.

But they have.

Jimmy and D'Etta Ferraro
and D'Etta's mother Midge

have lived here for four years,

the last two with confirmed
sinkhole activity that began

with cracking walls
and a subsiding pool deck.

Go! We're good!

NARRATOR:
To stabilize
and strengthen the soil,

the Ferraros' insurance company
wants to pump grout,

a cementlike mixture,
under the foundation.

It's a technique that
has been used successfully

all over the state.

But under certain conditions,

pouring grout has actually
caused huge,

terrifying sinkholes, like
this one in Dunedin, Florida.

The Ferraros want their house
pinned with steel,

an expense the insurance company
is resisting.

Our home is the most expensive
investment that we make

and now I have a home
with a sinkhole,

and I have to worry about my
family's safety all the time.

NARRATOR:
The Ferraros have decided to
bring in a geotechnical team

to analyze the problem.

While the equipment
is being set up,

lead engineer Byron Anderson
begins with a simple test.

ANDERSON:
One of the quick ways
I can determine

whether or not there's a problem
at a property

is by using a fiberglass probe

to just stick it down
into the ground.

And what you would normally
expect to see is that the rod

would just go a few inches deep
and you would get to refusal.

But at this property
what I can find

is there are areas in which
the rod just almost free-falls

down into the ground.

And these areas are
little depressions

that are likely related
to sinkhole activity.

And one of the old wives' tales
that we have often thought of

whenever we're doing
sinkhole investigations

is that the water is being
dropped out of the grass,

going into a sinkhole,
causing the vegetation to die.

As I was doing earlier,
I can just take this probe

and in the center
of what is this void,

you can see that it just very
easily goes down into the earth.

NARRATOR:
There are obvious problems here,

but how extensive
and dangerous are they?

A drilling team is gathering
soil samples

on the other side of the house.

The men will pull up samples
all the way down to bedrock.

If they find loose,
sandy soil at depth,

this could indicate
that upper layers of soil

are dropping down a sinkhole.

BRIAN JORY:
Okay, that was a sample of sand
from a depth of 20 feet.

And that's very typical
of upper soils

down to about 30 feet
in Florida.

NARRATOR:
It could also be typical
of a growing sinkhole.

The team is creating a
Ground Penetrating Radar map

of the entire property

in order to reveal areas
of displaced soil

and detect the extent
of any empty spaces.

From this and other tests,
they create a preliminary sketch

that indicates not one,
but three potential sinkholes

on two sides of the house.

And they can't rule out
the possibility

that there's one giant sinkhole
under the entire property.

The results do not surprise
Byron Anderson.

ANDERSON:
With this property
what concerns me

is that we have this retention
pond area that's off to the left

and we also have a wetland area
that's north of here.

This retention area and wetland
area are old sinkholes

that have formed
in the geologic past.

This is another example

of why you should not have built
houses on this property.

NARRATOR:
Unfortunately, houses aren't
the only structures

Floridians
should be worried about.

Jacki Clark is dodging traffic

along a highway
near Gainesville.

Somewhere underneath her
and the traffic,

Brett Hemphill and his dive team
are in the Alachua Cave system

setting up transponders.

On the surface, Jacki,
a diver herself,

uses a disc-like receiver
to detect their signals

and locate their precise
position.

CLARK:
What we are trying to do is
we're trying to figure out

where Alachua Sink cave passage
actually goes.

So I am using this radio locate
of where it's going

and where in relation
to all these buildings

the cave passage runs.

NARRATOR:
As it turns out,

the divers are indeed swimming
underneath this major highway

and the cave system could go

under several business
establishments.

We've blurred the names

because owners and customers
could get nervous

at the thought that watery caves
might be under their feet.

Each location point becomes
another step

for mapping the route
of the divers

and this particular cave system.

It looks like the system misses
nearby businesses.

But the divers discovered
a branch

that heads straight
for a big box store

and goes right underneath it.

BRETT HEMPHILL:
There have been several times

when we've been exploring
cave systems in Florida

where we actually realize
after we create a map

or we do a radio location

that the conduit indeed runs
under a house

or an actual
commercial property.

First thing they'll ask you is,

"Is there a chance that my house
could fall into a sinkhole?"

NARRATOR:
Although some cave systems
are close to the surface

and can pose a threat,
most are well below ground

and, like this one,
are not a cause for concern.

But in Florida, many people do
live on dangerous ground

and are worried about their
property and personal safety.

JIMMY FERRARO:
All we do is think about,

"Is the house going
to collapse today?

"When is that going to happen?

"Is it going to collapse
while we're sleeping,

like the house
in Seffner, Florida?"

It's a constant weight
on our shoulders.

NARRATOR:
Prospective homeowners can check
public records to see

if a given neighborhood is prone
to sinkholes before moving in.

And the state is compiling
a comprehensive sinkhole map

showing the most active regions.

There is also technology that
can detect sinkhole activity

before houses are even built.

So why are developers building
in dangerous areas?

And why are people
moving into them?

If you're a land owner
and you own a tract of land

that, let's say, is 50 acres,

well, you don't want
to test that land

because once you find sinkholes,

your land isn't worth
anything anymore.

NARRATOR:
And if the land gets sold?

ANDERSON:
If you're the developer and
you find sinkhole activity,

then all the money
that you've sunk

into the development is lost.

NARRATOR:
What about local government
protection?

ANDERSON:
If the county finds that
there is sinkhole activity

on that 50-acre tract,

they will never get the tax
revenue associated with it.

NARRATOR:
And the result?

Left the homeowners
to bear the burden of dealing

with these sinkhole conditions.

NARRATOR:
But perhaps the biggest problem
is Florida's booming population.

As people flock to the Sunshine
State, more houses, roads

and businesses will
surely bring more sinkholes

and perhaps
more fatalities as well.

So the efforts
of researchers and geologists

to better understand
the precise conditions

for sinkhole formation

and the tipping points
for their collapse

may one day give us the data
to help save lives.

The only question is,
"Will we use it?"

This NOVA program
is available on DVD.

To order, visit shopPBS.org,
or call 1-800-PLAY-PBS.

NOVA is also available
for download on iTunes.