Horizon (1964–…): Season 50, Episode 7 - Swallowed by a Sink Hole - full transcript
Seffner, Florida.
A place where the earth opened up...
..and killed a man.
Lazy Lanes, this place is called.
It just seems so ordinary,
so normal.
DOG BARKS
I mean, look at this,
"Beware of the dog."
And yet this whole estate sits above
a trap door into the hidden Florida.
'The bedroom floor just collapsed
'and my brother-in-law is
underneath the house.'
The trap door into that hidden
Florida opened here,
in February 2013...
..creating a sinkhole.
Without warning, it swallowed
everything in this bedroom,
and for those who saw it, it was
something they'll never forget.
It's like this thing was alive.
You know, it was turning,
moving around,
making noises, you know,
almost like a growl.
Sinkholes don't just
happen in Florida.
They're occurring
all over the world.
I want to find out why
sinkholes form...
..what this underworld
is really like.
You've not been down there?
Never been in there,
didn't even know it existed.
And why some are deadly.
Until last spring,
a house stood here.
A home lived in by two brothers,
Jeff and Jeremy Bush,
along with their families.
My bedroom was right here.
So, your bedroom was here?
Yeah, my bedroom was right
here in the front.
And you walked in through the front
door, and there was a living room.
Yeah, so, you went in and then
the living room was on the right?
Yeah, living room was on the right,
kitchen behind my bedroom,
and then the dining room
and then my brother's room.
That was... So it was on the far
right-hand side.
And then there was another bedroom,
it was Janell's... Oh, right.
It was Janell's bedroom.
It was a normal night, I guess?
It was, it was normal.
I had just got home from work,
come in about ten, 10.30,
and told everybody good night
and went to bed.
And then that's when it happened.
My wife turned the light on, and...
..as I was getting ready to walk
in the door,
she turned the light on and
all you could see was this big hole.
It sounded like a car hit the house,
but the house didn't move,
um, nothing moved.
The walls didn't move, nothing.
Pictures were still
hanging on the wall, everything.
It just was a loud crash.
That's a scream I'll never forget.
Um...
He just kept saying,
"Help me, somebody help me."
SIREN WAILS
That scream was the last anyone
heard of Jeff Bush.
No-one had any idea what was
happening,
just that he was in trouble.
It was a 911 call
and it said that a family member
had fallen underneath the house.
The first one there was
Deputy Duvall.
I guess my first idea
was it may have been, like,
an accident-type,
like, somebody was trying to
renovate their house
and something happened
with the floor,
it was rotten, you know,
something of that sort.
He rushed straight in.
He went straight in the house,
and he pulled a couple of people
out of the house,
made them get out of the house.
Everybody was screaming
and kind of running around.
As soon as I saw them,
I knew that it wasn't just somebody
that had fallen into the floor
by an accident, you know?
I knew just from their reactions
that it was something a lot
more significant.
I looked inside the room.
There was nothing.
All you could do was smell
fresh dirt.
It took his whole bedroom.
The only piece of concrete that was
left was by the door.
It took his bed, his dresser, his TV
and everything down in the hole.
The door was open
and when I went through the house,
everything looked like it
was normal.
You know, the floor was intact
and the lights were on,
the power was working.
Nothing out of the ordinary -
but I went to the bedroom,
and the door was open, and as soon
as I turned and looked in,
there was nothing in the bedroom.
It was just a giant hole.
Jeff had been pulled down into the
underworld by a sinkhole.
All I could see was
the tip of his box spring,
the tip of his bed frame
and his mattress, and that was it.
You didn't see Jeff at that point?
Couldn't see Jeff, I thought I...
I thought I could hear him
yelling for me to help him.
Yeah, and so you just...
I just jumped in there
and started digging.
You want to take a minute?
Jeremy was... If you're
walking into the actual bedroom,
he's pretty much right there between
the door and the centre of the hole.
I started digging by my hands,
and I was yelling and screaming
for him,
and yelling for my father-in-law
to get a shovel
and a flashlight, so I could see.
So I grabbed hold of his bed
and tried moving his bed,
and it wouldn't move
and I broke the bedframe in half
trying to get it out.
Then I started... He got me the
shovel and I started digging.
And they were real close. You've
seen Jeremy, you've seen Jeff.
And they worked together,
they did everything together.
They played video games together,
they...
They were... They were brothers,
they were tight brothers.
Jeff Bush had been swallowed alive,
and the sinkhole came close to
swallowing his brother, Jeremy, too.
The ground was still
falling as I was in the hole
and the concrete was moving
and breaking, still.
So, you were on your way down?
I was on my way down.
And you didn't even notice it? I
wasn't paying attention to it at all.
I was just trying to
get my brother out.
If you can imagine an hourglass,
the funnel inside of an hourglass,
you've got the deeper portion,
then you've got the out...
the outermost wall.
Jeremy was in the middle
and while it was sinking,
it was also expanding out
because everything on the outside
was filling in the void.
I know I didn't want to come out
the hole,
I wanted to pull the deputy in there
with me to help me dig him out,
because nobody was helping.
Of course.
Those who saw it forming
will never forget it.
When everybody asks me about it,
I tell them it's like this thing
was alive,
and when I say that it was eating,
it literally...
Things, the furniture,
it was still sinking,
it was still going into the ground.
And, you know, it was kind of,
kind of turning, moving around,
making noises, you know,
almost like a growl, and it just...
Like something was alive.
Jeremy was seconds from being
sucked down
to the same terrible fate
as his brother
when Deputy Duvall saved him.
He grabbed me by my arm
and snatched me out of the hole,
and that was the last time that
anybody went back in the house.
When the sun came up, everything
seemed normal from the outside.
All anyone knew was that
Jeff Bush was gone,
his body never to be discovered.
I found meeting Jeremy and hearing
what happened to his brother
deeply disturbing and unsettling.
Such a horrible thought, isn't it?
That idea of the ground opening up
and literally swallowing you alive,
it's just...
It's the stuff of nightmares.
My science, geology, tries to give
answers to why things happen
and hopefully save lives.
And one of the reasons I've become
so interested in sinkholes right now
is that I've noticed more of them
in the news.
In the last few years,
they have been captured
as far afield as China...
..and Guatemala.
They create the fear
that the ground beneath our feet
could open up into an unseen world
at any time.
Incredibly,
this young girl survived.
But it's in Florida
where the fear of dropping
into the underworld is greatest.
A few months after Jeff Bush died,
over 100 people
were saved from this resort complex
near Disney World
just before it collapsed.
The dubious honour of being called
the sinkhole capital of the world
costs the state of Florida hundreds
of millions of dollars a year.
So at least lawyers are getting
something out of it.
Look at that.
As soon as homeowners see some
kind of crack in their house,
they're encouraged to phone these
sinkhole attorneys.
And they ply their trade
up and down the highway here with
all their billboards.
I've never seen a sinkhole before,
not up close,
but to really understand them
you can't just look at the surface.
You have to see what's
happening underneath.
If you really want to know what
the Florida underworld is like,
you've got to descend into it.
On the rope!
There's one thing I could tell
straightaway -
the rock I'm descending through
is very familiar.
It's one of the most common rock
types in the world
and obviously one of the most useful
- it's a raw ingredient for cement.
But it's also the maker of these
fantastic subterranean worlds.
If you were walking above,
you'd never know this was here.
A great void, taking shape
beneath the surface of the earth.
Professor Jason Polk has been trying
to understand what it is that makes
them collapse.
He estimates that the caves started
forming millions of years ago.
That's the last kind of part of it,
breaching to the surface?
Eventually the rock becomes so thin
that a large collapse can
occur instantaneously.
And a lot of the sinkholes you see
in Florida where
you have those instant collapses are
where it's thin rock and thick soil.
So what's your best bet about how
old that collapse was,
when did daylight come in here?
Best guess is from work we've done
with the sediments where
we've done radiocarbon dating to
actually see how old these
sediments are,
and we know that they are at least
10,000 years old,
so that collapse is probably 10,000
years old at a minimum. Yeah.
It may look like the sinkhole's
dead, but it's anything but.
Ever since the roof fell in,
the cave has been filling
with sediment.
But then three years ago,
that sediment disappeared.
So 2010 then, it was up to there,
is that right?
You would have been under sediment.
And just within minutes,
hours - straight down?
Just almost immediately.
And where, down...down here?
Straight down here in this hole,
which is the pathway to some
unknown void below where all of this
sediment is washed down
and continues to wash down.
You've not been down there? Never
been in there, didn't even know
it existed. God!
So do you reckon it's...? I mean,
are you slightly freaked out
that underneath we know there's
a big hole?
It feels solid but we know that
if we'd have been here a few years
ago when this happened, we'd be...
We'd be down there.
We'd be down below in the unknown.
Wow, that's a bit scary.
We should go.
I don't like that, actually.
That gaping hole showed how alive
this sinkhole still is.
I was very glad to leave.
I've been told that if I want to
get a sense of just what
a problem sinkholes really are
here, there's somewhere I should go.
This estate is just north of Tampa.
In many ways, it's a pretty
unremarkable place.
Full of retirees chasing
the dream of all year round sun.
It all looks so perfect, doesn't it?
I mean, look at it.
But behind the facade, virtually
all of these houses have got
structural problems and cracks
and got people going to
bed at night really not sure
if those sounds that they're
hearing is going to be another hole
appearing underneath them.
So instead of spending their time
making extensions and patios...
..the builders round here
are pouring hundreds of tonnes of
cement beneath
the foundations of these houses
in an attempt to stabilise them.
'I went to visit one of
the long-standing residents,
Darlene Denaro.'
So how many of these houses would
you say have had problems
or are getting problems now?
Erm...well, she has one, and in one
down there on that side...
By the white car?
By the white car,
and then across the street there's
one that was fixed. Right.
Yeah, then this one and this one,
and then she suspects she has
a sinkhole.
Which one, which one,
the one with the green car?
No, on the other side.
Other side of that?
Yeah, and then around the corner,
where Louis lives,
he lives on this side right here
and he had, they had...
It's one, two, three and then one
down here, he had a humungous one.
I think he had pretty close to
70 truck loads.
So you're kind of in the centre,
really, of this... Sorry, well,
yeah, I was thinking,
I mean, that...
I feel like I'm in...
Yeah, I'm in the centre.
For decades, new housing has been
springing up all across Florida.
Built on what was once rough
farmland,
they seemed to offer a golden
future for their new inhabitants.
But now I get the sense
that many of them
are gripped by a collective
fear of what might lie beneath.
When you moved here, was anything
mentioned about sinkholes
here? Nothing.
What was it before?
Farmland, wet farmland, swampland.
Everybody who's... The old Florida
people that had been
here for years, it was a very wet,
soggy, swamp piece of property.
We would have never moved
here, never.
If you'd known. No.
What's happening on this estate
is not that unusual -
sinkholes ruining
the American Dream.
Look at this. Here we've got one.
For a lot of people,
this is reality now,
trying to fill in this huge void
underneath their houses.
I detected a real
fear on this estate.
After all, Jeff Bush lived just
an hour down the road.
But how justified are those fears?
It's very hard to get a sense of how
many sinkholes there are in
this state.
And just what a threat they are
to the people living here.
So I'm going to try and get a rather
higher perspective on the problem.
RADIO CHATTER
It's going to be so good to get up
top because, I mean, to be
honest, on the ground,
it's quite a tedious landscape.
It's very flat, there's lots
of trees and tarmac that obscure
the views, but I think that from
here, everything will become clear.
So we're going to go up about
500 feet, is that right?
Above sea level. Right.
What I'm looking for is evidence
of ancient sinkholes,
depressions in the land that have
formed into lakes.
You can start to see some now.
You see that over there?
Just a pockmark, a series of
little lakes.
Like the whole place now is just
lake land, everywhere you can see.
It's just little pockets,
like just here.
Looks like the whole place is
a giant golf course with
kind of water hazards.
This is pretty much Florida,
I guess.
Each one of those lakes beneath us
started as a hole into a limestone
cavern beneath.
It's quite interesting, there's this
intricate anatomy to them.
Some of them are just,
just perfect circles,
and that's just one sinkhole,
but others you can see,
it's like four or five have all
joined together.
So the whole thing is just
pockmarked as far as you can see,
filled with water, so you get these
ornamental water features
that people build their houses
and jetties around.
They're really sought-after.
But the thing is, potentially,
they're lethal. I mean, these things
can open up
and you're left with
a hole in the ground.
It's reckoned there are several
thousand of these sinkhole
lakes across the state of Florida,
several thousand of them!
And that's just a part of it.
I tried to get a figure on just
how many sinkholes
there are in the state.
One county claims to have over
6,000 of them,
but the truth is,
no-one really knows.
They've literally stopped counting.
To understand why,
you have to travel back to the very
origins of the state itself.
Head a couple of miles out to sea
and you can observe the whole
process beginning.
Tens of millions of years ago,
modern Florida emerged as shallow
seas just like this receded.
Warm seas that once teemed with
marine life.
Quite nice, nice temperature.
No need for a snorkel and flippers.
It's amazingly shallow,
even two miles off the shore.
For a wee walk
in the Florida Keys.
What I'm standing on is the remains
of the marine life that
inhabited this
warm shallow coastline.
And the remains of those creatures
form a mud made from carbonates.
When those creatures
die and decompose,
they turn into this, carbonate mud.
It's amazing to think this stuff
is just the smashed-up
hard parts of millions
of sea creatures.
And yet this is
Florida in the making.
Over hundreds of thousands
of years it gets compressed
into limestone, the rock that
virtually all of Florida is made of.
An entire peninsula, around
500 miles north to south
and over 160 east to west.
And almost every inch of that
is made of marine organisms.
And that's the key
to sinkholes, really,
because what can be created
can also be destroyed.
This is the bedrock of
Florida stripped bare -
an old quarry at Windley Key.
If this looks solid
and unchanging, it isn't.
CREAKING
Something has been eating
it away and still is.
The thing is, everywhere you look,
this rock is being destroyed.
I mean, look at this bit here.
It's been eroded away.
These are kind of miniature
sinkholes, really.
And what's created them
is just rain.
The rain is falling down
and dissolving them away.
But to eat away the limestone,
that rain has to change.
Pure water has a pH
of around about seven,
but as it falls through
the atmosphere it picks up
carbon dioxide molecules that turns
it into a very weak acid,
carbonic acid.
And the other thing is
that if it hits, here,
rotting vegetation and soil,
then that pH drops even more.
So, look at this. This is a pH meter
and it's reading seven.
Now, if I stick it
into this soil here,
it's gone down - 6.6, 5.3.
So that is really quite
dramatically more acidic.
It's that acidity over thousands,
tens of thousands of years,
that basically eats out
those huge caves.
And if you don't believe me
that acid can dissolve away rock,
I've got a little bit of acid.
It's hydrochloric acid,
but it's quite dilute.
Look, if I pour it on my skin,
it does nothing.
But if I pour it on this
fossil coral...
look at that.
It's just going crazy.
One moment you've got
calcium carbonate,
next moment it's all fizzed
back to carbon dioxide.
And it's this process that's very
slowly dissolving the whole state.
One of the things that drew me
to geology is how it makes
you see the certainties
of the world we've created, the
human planet, rather differently.
There are almost 20 million
people living in Florida
and the population's
growing rapidly.
Driving along the streets of
somewhere like Miami, you feel
as if you're in one of the safest,
most modern places in the world.
It's all built on rocks that
are being dissolved by water.
Every drop that falls from the sky,
every drop that sinks through
the ground, is turning to acid,
and that acid is very slowly
dissolving the whole state.
To witness it in action, you
have to leave the urban sprawl
and head out into the old Florida,
the Florida that existed before
people ever set foot here.
Step just a few feet
from the freeway
and you're into this primeval land
of swamp and alligator.
It's a world I'm entering in
search of something rather special.
I'm off to meet up with a
remarkable team of explorers
who will really be able to show me
why there are so many
sinkholes in Florida.
This is Peacock Springs.
It's an alien place.
It's a part of Florida
that most tourists,
even most residents, never see.
It's like a lost world.
The water is just so clear.
And so it should be, really,
because this is
Florida's lifeblood.
Something like 95% of the state's
ground water comes through
springs like this.
And what's so special about
this place is that beneath me
is a massive flooded cave complex,
the so-called Floridan aquifer,
through which all
this water's flowed.
And it's home to some of the most
intriguing sinkholes in the state.
Hey! Hi! How's it going?
You have picked the
most beautiful spot.
Yeah, it's a remarkable area.
Fantastic.
'Jarrod Jablonski and his team
are among the most experienced
'cave divers in the world,
and they've been exploring
'cave systems like these
for decades.'
Ah! That's better. Dry land.
It's quite deep in there, though.
I hadn't realised.
Yeah, the water's actually
a pretty good level.
It varies a lot, depending
on the drought conditions,
how much rain we're getting.
'What most people would
find terrifying,
'these divers find magical.'
You've got this hidden
world that no-one else
but a few of you guys know about.
Yeah, very much. We kind of enjoy
that every now and then.
You go down and you're looking
around and it's just you
and you start thinking about how
few people in the world get that
really special experience.
'Even though Jarrod and his
team are really experienced,
'what they're about to do is
still incredibly dangerous.'
How many people have been killed,
do you think, in these caves diving?
Probably somewhere in the
neighbourhood of 500 people
have lost their lives
exploring Florida caves.
Most of those, certainly by a great
majority, especially in the early
years, were untrained open water
divers, so really a very bad recipe.
So they thought it was the
same environment as the sea?
Yeah, didn't know. Swim around
in a beautiful place like this -
as you said, it's beautiful
and very benign looking.
Then you go into the cave,
which also looks at first benign,
and then, if you don't know what
you're doing, you can kick up the
bottom conditions and you don't have
a guideline, get lost pretty easily.
'The entrance to this hidden,
deadly Florida was just below us
'and, whilst cave diving
is a step too far for me,
'I was keen just to
look into its jaws.'
So where's the entrance then?
We're going to go down right here
and we're going to go right in this
way, which is going to descend down.
We'll have about
6m deep and then we'll
descend down to depth which
will be about 20m deep.
And you're going to
head in that direction?
In this direction towards
a sinkhole called Pothole
and then the next sinkhole, Olsen.
There's a series of sinkholes that
you can access through this conduit.
All right, well, I'll see
you off the premises, then.
All right. Excuse me!
I'll see how long
I can hold my breath.
I like it. Don't take me with you.
All set? Good stuff!
Well, they've gone.
I can just see the last of them
disappearing into the entrance.
But, to be honest, it's not for me,
so I'm going to follow them
on dry land.
As I headed ashore,
Jarrod and team swam into the
very throat of the underworld.
For all their beauty,
these labyrinths are lethal.
All a diver has to do is kick up
the sediment with a careless
flick of a fin and the visibility
will reduce to zero.
That's how most people
lose their lives down here.
What I find amazing about these
caves is how extensive they are.
Divers have explored
over 10km of them,
but the caves' conduits and
pore spaces of this aquifer
stretch from one end of
the state to the other.
It's weird to think that they're
right beneath my feet.
Apparently, the first little
bit's really tortuous,
so if they manage to squeeze their
way through that, then, according
to this map, we should get the first
indication of progress just up here.
What I'm looking for
is a small sinkhole -
a place where the expanding cave
has reached the point where
its roof has failed, allowing
the soils to fall down,
creating a link between
the worlds above and below.
It's a sobering thought
that those caves
are expanding in all directions.
And that's because all it takes
to make the limestone dissolve
is water,
and there's plenty of that.
So this is it.
So this is Pothole sink, then.
We've come from just about
two minutes' walk away,
from this Peacock Spring
where the guys went in.
And, at one point, the limestone
would have been across, like this,
but then what's happened is this
bit's been dissolved down and then
the wear of the soil at some point -
maybe, I don't know, 10,000 years,
20,000 years ago - the whole
thing's just caved in on itself,
collapsed, creating this hole,
and you've got this.
This is essentially a conduit.
It's maybe 40, 50 foot down below.
So, somewhere down there the guys
are swimming past and supposedly
what happens is you're going to
see the bubbles as they go past.
That's what we're waiting for.
This is a nursery ground
for sinkholes,
the rock dissolving at a rate of
around 4cm every thousand years.
The void's getting bigger
and ultimately the soil
above falling into them,
creating yet another sinkhole.
There, there we go!
So that means they're
now right beneath us.
The air's coming up, so that means
they're safe so far.
So, the thing is, they've got
another hour to go before they can
actually surface properly
and have proper fresh air.
At least they're safe.
So far, so good.
Now, onto the next bit.
Dissolving limestone
like this is known as karst,
and it's not just
confined to Florida.
Limestone is common
all over the world.
There are pockets of it in the UK,
but here sinkholes
rarely make the news.
What's special about Florida
is the extent of the limestone
and just how big the sinkholes are.
You know, it's the kind of
place that makes you contemplate
Florida in a whole different way.
If I hadn't have known there was
a team of divers down there,
this would just be another pond
and another little patch of wood,
but actually it's a
gateway to the underworld,
an underworld that stretches
the length and breadth of Florida
and an underworld that's killed
and will kill again.
So, at any point, I'm hoping
to see this burst of bubbles
and that'll be them, safe.
Oh, yes!
That must be them, look.
Look at this. Yeah, here they come.
Here they come.
What a beautiful spot
to come out, as well.
There's something
quite elegant about it.
Really big sinkholes
happen only rarely,
but when they do,
they make quite an impact.
On the 8th of May 1981,
the residents of Winter Park,
close to Orlando, witnessed this.
What started as a small hole
soon developed into
a 13m deep monster,
some hundred metres wide.
We watched a house slide in,
we watched eight or nine cars
slide in, we watched the
swimming pool slide in.
And you just sit there and watch it
and you're powerless to help.
Any thoughts about making it a lake?
It will be a lake. We've already
found that out yesterday.
The engineers and that sort of
people said it will be a lake and
there's nothing
we can do about that,
so we just have a new lake
in the city.
When you're confronted with
footage as dramatic as this,
you have to ask, what triggered it?
Why did it happen now?
The ancient geology of this state,
the limestone, isn't enough.
First glance, it must seem
as if nowhere's safe in Florida,
but actually some places
are more at risk than others.
This map shows the locations of
all the verified sinkholes
and you can see how widespread
they are across the state.
But there's a real cluster of them
here in West Central Florida -
a sinkhole sweet spot, if you like.
And Jeff Bush's place
is just in there,
right on the southern edge
of that sweet spot.
On the face of it,
this clustering of sinkholes
doesn't make much sense.
Why are some parts of
the state relatively safe
and others much more prone
to sinkholes...
..even though they're all underlain
by the same rock, limestone?
So far, this search to
understand what sinkholes
are all about has focused
on one material, rock.
The thing is, voids in limestone
open up ridiculously slowly,
I mean, over thousands of years.
So there's another material
that we should consider,
one that's far more mobile -
soil.
Geological mysteries seldom
have just one culprit,
and the material that covers this
vast, unstable slab of limestone
is rather more interesting than
you might initially think.
In fact, it determines
how deadly sinkholes are.
To understand why, you
have to take a very close look
at the soils around here.
And the best way
to do that is to take
a trip down the Hillsborough River.
The only problem with that is
that the Hillsborough River
is infested with alligators.
I can't believe I'm risking
my life for soil.
There's one, there's one!
There's one just there.
Four, five-footer.
Look at that.
It's off, doesn't like me!
I think it's more scared of me.
The reason I'm out here
on the Hillsborough River
is that this area is
almost sinkhole-free.
But just downstream,
it's a very different story.
Look at this, a map of
all the sinkholes in Florida.
All these red squares here are
crammed into West Central Florida.
And then look, you get this kind of
sinkhole-free area in here.
To see that in more detail,
we have to go to a different map.
Look at this one here.
This is the Hillsborough River,
drifting in the
Hillsborough River,
just probably up here.
We're just on that bend there.
So, the thing is, in this area round
here, there's just no sinkholes.
But actually, to the west and
to the east, it's sinkhole city.
But to understand why
there's no sinkholes here,
we have to get to the shore.
The limestone beneath me is the
same as anywhere else in Florida
and is riddled with
caves and fissures.
But it's the earth above
that's different here.
So what makes this place so safe?
Time for a bit of
old school geology.
This is the instrument of
a soil scientist, the auger.
What you do is you clear
a bit of ground
and then you stick it in.
Kind of just drill your way down
through the vegetation.
Can you hear the vegetation ripping?
And then you get down
into the soil, the topsoil,
and as you get below that,
it gets a little bit easier.
In fact, it's easy now.
So we can see what's
underneath the topsoil.
And what we see is,
this is all soil but then this here,
this is just sand. Look at that.
Really coarse, loose sand.
You can tell how coarse is it,
cos when you chew it,
it's quite gritty
between your teeth.
It's the sand that's
key to there being
so few sinkholes in this area.
So the point is you've got this
really loose, incohesive sand,
and as the rainwater falls on it,
to be honest, it just drains
straight through.
Straight through
to the limestone below.
This means that the
soils never build up.
The sands just fall into
the voids as they form,
so the closest thing you'll get
to a big sinkhole round here
is this rather innocuous puddle.
The limestone underneath here
would have started out
something like that and then it's
just been kind of dissolved down.
And what you've had is you had the
sand just kind of dripping, draining
through it, and it just captures
this, just a little patch of water.
The limestone here is only
a few feet beneath the
thin sandy soil, which is constantly
being washed down into it.
Now, the thing is, these really
aren't dangerous at all.
There's hardly any chance
of something like this collapsing.
But a few miles down the river,
you enter sinkhole alley.
This is where the big sinkholes
happen
and the first thing you notice is
the landscape's changed.
We're out of the swamps and into an
area rich in agriculture.
During the winter, the fields around
here are full of strawberries,
making good use of the deep fertile
soils and warm weather,
so creating the fruit
bowl of America.
But I'm here in the off season
and there's not a strawberry
in sight, but that doesn't matter,
as I'm only interested in the soil.
You can see that's gone down much,
much easier here.
Now if I just pull that up now,
let's see what we've got.
OK, look, you can see it's much
darker and it's still sandy,
still pretty sandy but look, it's
got some kind of strength to it,
so that means there's some
clay in there.
Now if I went down another few
metres or so,
if I could be bothered going all the
way down,
I'd find something completely
different.
I'd find something like this.
This is a clay
and you can roll that.
It's got some kind of strength.
Look at that.
Just not going to do anything.
And it's that clay that turns out
to be really important
because that clay is really sticky.
It's got its own strength
and because of that,
rather than as the water
comes through,
rather than it just washing the clay
down into the sinkholes below,
it stays there and it builds up,
so you get a much thicker sequence
of sediment and not just that,
sediment with some strength to it.
It's strong enough to bridge
the holes in the limestone...
..but not for ever.
Sooner or later,
the clay will give way,
and that's what happened
at Winter Park 30 years ago.
Back then, no-one knew there was
a void beneath this part of town...
but the whole place stood on a clay
trap door, just waiting to spring.
It's a strange idea that
a layer of clay could be
the cause for a potentially
deadly sinkhole.
Let me show you how,
in a rather homespun way.
What happens is this...
Above the voids in the limestone,
a layer of sand can form with
a muddy clay above it
and more soil on top of that.
So you get this layer cake of sand,
mud and sand.
And then this is the tricky part.
OK.
And it creates a void
in the sub-surface. Look at that.
And it's the clay layer that's
really important.
It's forming a strong bridge that's
holding the rest of that sand
up and not letting it collapse.
But if the clay loses its strength,
the bridge it created
fails...suddenly.
The whole thing just caves in.
It's kind of like a trap door
that's been pulled
and that is called
a collapse sinkhole,
and it's absolutely deadly.
But what triggers that failure?
This might seem like an urban
paradise,
but appearances can be deceptive.
Many people here wonder if they're
sitting on top of a fragile
clay bridge into the underworld.
So, alongside the cement mixers
trying to stabilise the foundations,
this is a pretty typical scene.
Geologists drilling.
What they're looking for is
clay beneath the sands,
a potential bridge which could fail
at any moment.
And if that clay were to fail,
the cause will be something we're
very familiar with.
Water.
The state of Florida is
greedy for water
to keep the lawns looking green,
to fill swimming pools...
..and, most importantly of all, they
need millions of gallons of water
to grow the famous Florida
strawberries and tomatoes.
And the demand for all this water
means the water table close
to those fields can drop by over
50 feet in just a few days.
And when the clay dries out, that
lack of water can be the trigger.
But that's just half the story.
Water can also cause clay to fail
because it becomes too wet.
Florida famously is hurricane
country.
And when they hit, they can
drop around a metre of water
on the land in a matter of hours.
Pretty bad out here now.
The sheer wear of all that
water on those fragile clay
bridges can be enough to cause
catastrophe...
..so, ultimately, water,
too much or too little, can be the
trigger for a sinkhole collapse.
But if water can be the trigger,
then there's another reason why
Florida's so prone to sinkholes.
And when you've spent a bit of time
here, it starts to become obvious.
It's something to do with us.
You know, the sinkholes,
sinkholes have always been here.
They're part of Florida's
constantly evolving geology.
But what's changed is us.
I mean, our fondness for the sun,
our expanding numbers,
we're taking over more
and more of the land.
As the population of Florida grows,
people need somewhere to live
and that means we inevitably end up
building on more
sinkhole-prone land.
It's easy to get the impression
here that this is a state
collapsing in on itself.
There are almost 6,700
sinkhole-related claims each year,
and the numbers are rising.
But incredibly, they've only killed
three people in the last
40 years as few collapse
without warning.
What's far more typical is what
happened at this restaurant.
Just a few weeks back, the staff
came in in the morning to find
that cracks had appeared overnight,
so they called in the engineers
and basically they - look at it -
condemned the whole building.
30-odd people used to work here.
But the thing is, because of those
warning signs, there was no tragedy.
Sinkholes may
seem as old as the Earth itself,
but for millions of years those deep
voids have been forming
incredibly slowly,
collapsing down only rarely.
In a sense, sinkhole-related damage
comes from what we're doing...
how we use our resources like water,
and especially the fact that
we're building on deep clay
soils above voids like this.
What happened to
Jeff on the 28th of February, 2013,
when a sinkhole opened up
under his bedroom,
sucking him deep into the earth,
is mercifully rare.
The bedroom floor just collapsed
and my brother-in-law is in there.
He's underneath the house.
It was a freak combination
of factors...
..shaped by the geology of where he
lived, certainly,
but also due to tragic bad luck.
What's clear is that Jeff's house
lay in sinkhole alley.
With its clay soil,
it's prone to sudden sinkholes.
A structural engineer who worked
with the emergency workers
that night was Bill Bracken.
The sinkhole was centred
exactly on the bedroom,
and was contained completely within
the footprint of the building,
so it was not visible from the air,
from outside.
The only way to see that hole was to
look in the window or
be inside the structure.
When they poked a remote
camera through,
they saw a neat hole in the concrete
slab of Jeff's bedroom
and a near vertical shaft over
20 feet deep.
The sinkhole formed
and the soil began to drop.
Because you had the entire structure
over the top of this,
because it was completely
contained inside the footprint
of the building,
when those soils began to drop,
it was almost a flushing action that
created a suction force,
so it wasn't as though a hole opened
up and things fell into it.
It was almost as though,
as the soil began to pull
away from the underside
and a void was being created,
a suction force was being
created as well.
Just tugged at the bottom
of the concrete base of the bedroom?
So, it effectively pulled
that slab down into the hole.
When fire crews placed a listening
device at the bottom,
they were in for a shock -
the sinkhole was still alive.
By the time that they had deployed
that, set that in there,
placed that on,
on the ground surface,
walked back to the box, connected it
and began receiving signals,
they began to sense a tugging,
if you will, on the cable.
When they went to check,
the listening device had already
been pulled down into the ground,
so over the next three days there
was about 30 feet of cable that
was draped out of the window and on
the ground, and we watched that
30 feet of cable reduce down to
about six-to-eight feet of cable.
So we knew that that sand
was still in an excited state.
It was still pulling down.
Everything that landed on it was
immediately pulled down in,
so we knew that whatever had
gone into that was down at least
30, 35 feet.
SIREN BLARES
The one certainty is that
when the emergency services
sent down a probe to look for signs
of life, they found none.
All that's left now is a family
trying to come to terms with
the freak tragic
events of that night.
They told us that they were
not for sure how far down he was
and that the ground
around everything was just too...
..too unsafe, too unstable for them
to do anything.
They could not risk
anybody else's life.
It makes me sick,
just the way it looks.
Overgrown with grass, nobody taking
care of anything. And there's a...
My brother's down there still.
A place where the earth opened up...
..and killed a man.
Lazy Lanes, this place is called.
It just seems so ordinary,
so normal.
DOG BARKS
I mean, look at this,
"Beware of the dog."
And yet this whole estate sits above
a trap door into the hidden Florida.
'The bedroom floor just collapsed
'and my brother-in-law is
underneath the house.'
The trap door into that hidden
Florida opened here,
in February 2013...
..creating a sinkhole.
Without warning, it swallowed
everything in this bedroom,
and for those who saw it, it was
something they'll never forget.
It's like this thing was alive.
You know, it was turning,
moving around,
making noises, you know,
almost like a growl.
Sinkholes don't just
happen in Florida.
They're occurring
all over the world.
I want to find out why
sinkholes form...
..what this underworld
is really like.
You've not been down there?
Never been in there,
didn't even know it existed.
And why some are deadly.
Until last spring,
a house stood here.
A home lived in by two brothers,
Jeff and Jeremy Bush,
along with their families.
My bedroom was right here.
So, your bedroom was here?
Yeah, my bedroom was right
here in the front.
And you walked in through the front
door, and there was a living room.
Yeah, so, you went in and then
the living room was on the right?
Yeah, living room was on the right,
kitchen behind my bedroom,
and then the dining room
and then my brother's room.
That was... So it was on the far
right-hand side.
And then there was another bedroom,
it was Janell's... Oh, right.
It was Janell's bedroom.
It was a normal night, I guess?
It was, it was normal.
I had just got home from work,
come in about ten, 10.30,
and told everybody good night
and went to bed.
And then that's when it happened.
My wife turned the light on, and...
..as I was getting ready to walk
in the door,
she turned the light on and
all you could see was this big hole.
It sounded like a car hit the house,
but the house didn't move,
um, nothing moved.
The walls didn't move, nothing.
Pictures were still
hanging on the wall, everything.
It just was a loud crash.
That's a scream I'll never forget.
Um...
He just kept saying,
"Help me, somebody help me."
SIREN WAILS
That scream was the last anyone
heard of Jeff Bush.
No-one had any idea what was
happening,
just that he was in trouble.
It was a 911 call
and it said that a family member
had fallen underneath the house.
The first one there was
Deputy Duvall.
I guess my first idea
was it may have been, like,
an accident-type,
like, somebody was trying to
renovate their house
and something happened
with the floor,
it was rotten, you know,
something of that sort.
He rushed straight in.
He went straight in the house,
and he pulled a couple of people
out of the house,
made them get out of the house.
Everybody was screaming
and kind of running around.
As soon as I saw them,
I knew that it wasn't just somebody
that had fallen into the floor
by an accident, you know?
I knew just from their reactions
that it was something a lot
more significant.
I looked inside the room.
There was nothing.
All you could do was smell
fresh dirt.
It took his whole bedroom.
The only piece of concrete that was
left was by the door.
It took his bed, his dresser, his TV
and everything down in the hole.
The door was open
and when I went through the house,
everything looked like it
was normal.
You know, the floor was intact
and the lights were on,
the power was working.
Nothing out of the ordinary -
but I went to the bedroom,
and the door was open, and as soon
as I turned and looked in,
there was nothing in the bedroom.
It was just a giant hole.
Jeff had been pulled down into the
underworld by a sinkhole.
All I could see was
the tip of his box spring,
the tip of his bed frame
and his mattress, and that was it.
You didn't see Jeff at that point?
Couldn't see Jeff, I thought I...
I thought I could hear him
yelling for me to help him.
Yeah, and so you just...
I just jumped in there
and started digging.
You want to take a minute?
Jeremy was... If you're
walking into the actual bedroom,
he's pretty much right there between
the door and the centre of the hole.
I started digging by my hands,
and I was yelling and screaming
for him,
and yelling for my father-in-law
to get a shovel
and a flashlight, so I could see.
So I grabbed hold of his bed
and tried moving his bed,
and it wouldn't move
and I broke the bedframe in half
trying to get it out.
Then I started... He got me the
shovel and I started digging.
And they were real close. You've
seen Jeremy, you've seen Jeff.
And they worked together,
they did everything together.
They played video games together,
they...
They were... They were brothers,
they were tight brothers.
Jeff Bush had been swallowed alive,
and the sinkhole came close to
swallowing his brother, Jeremy, too.
The ground was still
falling as I was in the hole
and the concrete was moving
and breaking, still.
So, you were on your way down?
I was on my way down.
And you didn't even notice it? I
wasn't paying attention to it at all.
I was just trying to
get my brother out.
If you can imagine an hourglass,
the funnel inside of an hourglass,
you've got the deeper portion,
then you've got the out...
the outermost wall.
Jeremy was in the middle
and while it was sinking,
it was also expanding out
because everything on the outside
was filling in the void.
I know I didn't want to come out
the hole,
I wanted to pull the deputy in there
with me to help me dig him out,
because nobody was helping.
Of course.
Those who saw it forming
will never forget it.
When everybody asks me about it,
I tell them it's like this thing
was alive,
and when I say that it was eating,
it literally...
Things, the furniture,
it was still sinking,
it was still going into the ground.
And, you know, it was kind of,
kind of turning, moving around,
making noises, you know,
almost like a growl, and it just...
Like something was alive.
Jeremy was seconds from being
sucked down
to the same terrible fate
as his brother
when Deputy Duvall saved him.
He grabbed me by my arm
and snatched me out of the hole,
and that was the last time that
anybody went back in the house.
When the sun came up, everything
seemed normal from the outside.
All anyone knew was that
Jeff Bush was gone,
his body never to be discovered.
I found meeting Jeremy and hearing
what happened to his brother
deeply disturbing and unsettling.
Such a horrible thought, isn't it?
That idea of the ground opening up
and literally swallowing you alive,
it's just...
It's the stuff of nightmares.
My science, geology, tries to give
answers to why things happen
and hopefully save lives.
And one of the reasons I've become
so interested in sinkholes right now
is that I've noticed more of them
in the news.
In the last few years,
they have been captured
as far afield as China...
..and Guatemala.
They create the fear
that the ground beneath our feet
could open up into an unseen world
at any time.
Incredibly,
this young girl survived.
But it's in Florida
where the fear of dropping
into the underworld is greatest.
A few months after Jeff Bush died,
over 100 people
were saved from this resort complex
near Disney World
just before it collapsed.
The dubious honour of being called
the sinkhole capital of the world
costs the state of Florida hundreds
of millions of dollars a year.
So at least lawyers are getting
something out of it.
Look at that.
As soon as homeowners see some
kind of crack in their house,
they're encouraged to phone these
sinkhole attorneys.
And they ply their trade
up and down the highway here with
all their billboards.
I've never seen a sinkhole before,
not up close,
but to really understand them
you can't just look at the surface.
You have to see what's
happening underneath.
If you really want to know what
the Florida underworld is like,
you've got to descend into it.
On the rope!
There's one thing I could tell
straightaway -
the rock I'm descending through
is very familiar.
It's one of the most common rock
types in the world
and obviously one of the most useful
- it's a raw ingredient for cement.
But it's also the maker of these
fantastic subterranean worlds.
If you were walking above,
you'd never know this was here.
A great void, taking shape
beneath the surface of the earth.
Professor Jason Polk has been trying
to understand what it is that makes
them collapse.
He estimates that the caves started
forming millions of years ago.
That's the last kind of part of it,
breaching to the surface?
Eventually the rock becomes so thin
that a large collapse can
occur instantaneously.
And a lot of the sinkholes you see
in Florida where
you have those instant collapses are
where it's thin rock and thick soil.
So what's your best bet about how
old that collapse was,
when did daylight come in here?
Best guess is from work we've done
with the sediments where
we've done radiocarbon dating to
actually see how old these
sediments are,
and we know that they are at least
10,000 years old,
so that collapse is probably 10,000
years old at a minimum. Yeah.
It may look like the sinkhole's
dead, but it's anything but.
Ever since the roof fell in,
the cave has been filling
with sediment.
But then three years ago,
that sediment disappeared.
So 2010 then, it was up to there,
is that right?
You would have been under sediment.
And just within minutes,
hours - straight down?
Just almost immediately.
And where, down...down here?
Straight down here in this hole,
which is the pathway to some
unknown void below where all of this
sediment is washed down
and continues to wash down.
You've not been down there? Never
been in there, didn't even know
it existed. God!
So do you reckon it's...? I mean,
are you slightly freaked out
that underneath we know there's
a big hole?
It feels solid but we know that
if we'd have been here a few years
ago when this happened, we'd be...
We'd be down there.
We'd be down below in the unknown.
Wow, that's a bit scary.
We should go.
I don't like that, actually.
That gaping hole showed how alive
this sinkhole still is.
I was very glad to leave.
I've been told that if I want to
get a sense of just what
a problem sinkholes really are
here, there's somewhere I should go.
This estate is just north of Tampa.
In many ways, it's a pretty
unremarkable place.
Full of retirees chasing
the dream of all year round sun.
It all looks so perfect, doesn't it?
I mean, look at it.
But behind the facade, virtually
all of these houses have got
structural problems and cracks
and got people going to
bed at night really not sure
if those sounds that they're
hearing is going to be another hole
appearing underneath them.
So instead of spending their time
making extensions and patios...
..the builders round here
are pouring hundreds of tonnes of
cement beneath
the foundations of these houses
in an attempt to stabilise them.
'I went to visit one of
the long-standing residents,
Darlene Denaro.'
So how many of these houses would
you say have had problems
or are getting problems now?
Erm...well, she has one, and in one
down there on that side...
By the white car?
By the white car,
and then across the street there's
one that was fixed. Right.
Yeah, then this one and this one,
and then she suspects she has
a sinkhole.
Which one, which one,
the one with the green car?
No, on the other side.
Other side of that?
Yeah, and then around the corner,
where Louis lives,
he lives on this side right here
and he had, they had...
It's one, two, three and then one
down here, he had a humungous one.
I think he had pretty close to
70 truck loads.
So you're kind of in the centre,
really, of this... Sorry, well,
yeah, I was thinking,
I mean, that...
I feel like I'm in...
Yeah, I'm in the centre.
For decades, new housing has been
springing up all across Florida.
Built on what was once rough
farmland,
they seemed to offer a golden
future for their new inhabitants.
But now I get the sense
that many of them
are gripped by a collective
fear of what might lie beneath.
When you moved here, was anything
mentioned about sinkholes
here? Nothing.
What was it before?
Farmland, wet farmland, swampland.
Everybody who's... The old Florida
people that had been
here for years, it was a very wet,
soggy, swamp piece of property.
We would have never moved
here, never.
If you'd known. No.
What's happening on this estate
is not that unusual -
sinkholes ruining
the American Dream.
Look at this. Here we've got one.
For a lot of people,
this is reality now,
trying to fill in this huge void
underneath their houses.
I detected a real
fear on this estate.
After all, Jeff Bush lived just
an hour down the road.
But how justified are those fears?
It's very hard to get a sense of how
many sinkholes there are in
this state.
And just what a threat they are
to the people living here.
So I'm going to try and get a rather
higher perspective on the problem.
RADIO CHATTER
It's going to be so good to get up
top because, I mean, to be
honest, on the ground,
it's quite a tedious landscape.
It's very flat, there's lots
of trees and tarmac that obscure
the views, but I think that from
here, everything will become clear.
So we're going to go up about
500 feet, is that right?
Above sea level. Right.
What I'm looking for is evidence
of ancient sinkholes,
depressions in the land that have
formed into lakes.
You can start to see some now.
You see that over there?
Just a pockmark, a series of
little lakes.
Like the whole place now is just
lake land, everywhere you can see.
It's just little pockets,
like just here.
Looks like the whole place is
a giant golf course with
kind of water hazards.
This is pretty much Florida,
I guess.
Each one of those lakes beneath us
started as a hole into a limestone
cavern beneath.
It's quite interesting, there's this
intricate anatomy to them.
Some of them are just,
just perfect circles,
and that's just one sinkhole,
but others you can see,
it's like four or five have all
joined together.
So the whole thing is just
pockmarked as far as you can see,
filled with water, so you get these
ornamental water features
that people build their houses
and jetties around.
They're really sought-after.
But the thing is, potentially,
they're lethal. I mean, these things
can open up
and you're left with
a hole in the ground.
It's reckoned there are several
thousand of these sinkhole
lakes across the state of Florida,
several thousand of them!
And that's just a part of it.
I tried to get a figure on just
how many sinkholes
there are in the state.
One county claims to have over
6,000 of them,
but the truth is,
no-one really knows.
They've literally stopped counting.
To understand why,
you have to travel back to the very
origins of the state itself.
Head a couple of miles out to sea
and you can observe the whole
process beginning.
Tens of millions of years ago,
modern Florida emerged as shallow
seas just like this receded.
Warm seas that once teemed with
marine life.
Quite nice, nice temperature.
No need for a snorkel and flippers.
It's amazingly shallow,
even two miles off the shore.
For a wee walk
in the Florida Keys.
What I'm standing on is the remains
of the marine life that
inhabited this
warm shallow coastline.
And the remains of those creatures
form a mud made from carbonates.
When those creatures
die and decompose,
they turn into this, carbonate mud.
It's amazing to think this stuff
is just the smashed-up
hard parts of millions
of sea creatures.
And yet this is
Florida in the making.
Over hundreds of thousands
of years it gets compressed
into limestone, the rock that
virtually all of Florida is made of.
An entire peninsula, around
500 miles north to south
and over 160 east to west.
And almost every inch of that
is made of marine organisms.
And that's the key
to sinkholes, really,
because what can be created
can also be destroyed.
This is the bedrock of
Florida stripped bare -
an old quarry at Windley Key.
If this looks solid
and unchanging, it isn't.
CREAKING
Something has been eating
it away and still is.
The thing is, everywhere you look,
this rock is being destroyed.
I mean, look at this bit here.
It's been eroded away.
These are kind of miniature
sinkholes, really.
And what's created them
is just rain.
The rain is falling down
and dissolving them away.
But to eat away the limestone,
that rain has to change.
Pure water has a pH
of around about seven,
but as it falls through
the atmosphere it picks up
carbon dioxide molecules that turns
it into a very weak acid,
carbonic acid.
And the other thing is
that if it hits, here,
rotting vegetation and soil,
then that pH drops even more.
So, look at this. This is a pH meter
and it's reading seven.
Now, if I stick it
into this soil here,
it's gone down - 6.6, 5.3.
So that is really quite
dramatically more acidic.
It's that acidity over thousands,
tens of thousands of years,
that basically eats out
those huge caves.
And if you don't believe me
that acid can dissolve away rock,
I've got a little bit of acid.
It's hydrochloric acid,
but it's quite dilute.
Look, if I pour it on my skin,
it does nothing.
But if I pour it on this
fossil coral...
look at that.
It's just going crazy.
One moment you've got
calcium carbonate,
next moment it's all fizzed
back to carbon dioxide.
And it's this process that's very
slowly dissolving the whole state.
One of the things that drew me
to geology is how it makes
you see the certainties
of the world we've created, the
human planet, rather differently.
There are almost 20 million
people living in Florida
and the population's
growing rapidly.
Driving along the streets of
somewhere like Miami, you feel
as if you're in one of the safest,
most modern places in the world.
It's all built on rocks that
are being dissolved by water.
Every drop that falls from the sky,
every drop that sinks through
the ground, is turning to acid,
and that acid is very slowly
dissolving the whole state.
To witness it in action, you
have to leave the urban sprawl
and head out into the old Florida,
the Florida that existed before
people ever set foot here.
Step just a few feet
from the freeway
and you're into this primeval land
of swamp and alligator.
It's a world I'm entering in
search of something rather special.
I'm off to meet up with a
remarkable team of explorers
who will really be able to show me
why there are so many
sinkholes in Florida.
This is Peacock Springs.
It's an alien place.
It's a part of Florida
that most tourists,
even most residents, never see.
It's like a lost world.
The water is just so clear.
And so it should be, really,
because this is
Florida's lifeblood.
Something like 95% of the state's
ground water comes through
springs like this.
And what's so special about
this place is that beneath me
is a massive flooded cave complex,
the so-called Floridan aquifer,
through which all
this water's flowed.
And it's home to some of the most
intriguing sinkholes in the state.
Hey! Hi! How's it going?
You have picked the
most beautiful spot.
Yeah, it's a remarkable area.
Fantastic.
'Jarrod Jablonski and his team
are among the most experienced
'cave divers in the world,
and they've been exploring
'cave systems like these
for decades.'
Ah! That's better. Dry land.
It's quite deep in there, though.
I hadn't realised.
Yeah, the water's actually
a pretty good level.
It varies a lot, depending
on the drought conditions,
how much rain we're getting.
'What most people would
find terrifying,
'these divers find magical.'
You've got this hidden
world that no-one else
but a few of you guys know about.
Yeah, very much. We kind of enjoy
that every now and then.
You go down and you're looking
around and it's just you
and you start thinking about how
few people in the world get that
really special experience.
'Even though Jarrod and his
team are really experienced,
'what they're about to do is
still incredibly dangerous.'
How many people have been killed,
do you think, in these caves diving?
Probably somewhere in the
neighbourhood of 500 people
have lost their lives
exploring Florida caves.
Most of those, certainly by a great
majority, especially in the early
years, were untrained open water
divers, so really a very bad recipe.
So they thought it was the
same environment as the sea?
Yeah, didn't know. Swim around
in a beautiful place like this -
as you said, it's beautiful
and very benign looking.
Then you go into the cave,
which also looks at first benign,
and then, if you don't know what
you're doing, you can kick up the
bottom conditions and you don't have
a guideline, get lost pretty easily.
'The entrance to this hidden,
deadly Florida was just below us
'and, whilst cave diving
is a step too far for me,
'I was keen just to
look into its jaws.'
So where's the entrance then?
We're going to go down right here
and we're going to go right in this
way, which is going to descend down.
We'll have about
6m deep and then we'll
descend down to depth which
will be about 20m deep.
And you're going to
head in that direction?
In this direction towards
a sinkhole called Pothole
and then the next sinkhole, Olsen.
There's a series of sinkholes that
you can access through this conduit.
All right, well, I'll see
you off the premises, then.
All right. Excuse me!
I'll see how long
I can hold my breath.
I like it. Don't take me with you.
All set? Good stuff!
Well, they've gone.
I can just see the last of them
disappearing into the entrance.
But, to be honest, it's not for me,
so I'm going to follow them
on dry land.
As I headed ashore,
Jarrod and team swam into the
very throat of the underworld.
For all their beauty,
these labyrinths are lethal.
All a diver has to do is kick up
the sediment with a careless
flick of a fin and the visibility
will reduce to zero.
That's how most people
lose their lives down here.
What I find amazing about these
caves is how extensive they are.
Divers have explored
over 10km of them,
but the caves' conduits and
pore spaces of this aquifer
stretch from one end of
the state to the other.
It's weird to think that they're
right beneath my feet.
Apparently, the first little
bit's really tortuous,
so if they manage to squeeze their
way through that, then, according
to this map, we should get the first
indication of progress just up here.
What I'm looking for
is a small sinkhole -
a place where the expanding cave
has reached the point where
its roof has failed, allowing
the soils to fall down,
creating a link between
the worlds above and below.
It's a sobering thought
that those caves
are expanding in all directions.
And that's because all it takes
to make the limestone dissolve
is water,
and there's plenty of that.
So this is it.
So this is Pothole sink, then.
We've come from just about
two minutes' walk away,
from this Peacock Spring
where the guys went in.
And, at one point, the limestone
would have been across, like this,
but then what's happened is this
bit's been dissolved down and then
the wear of the soil at some point -
maybe, I don't know, 10,000 years,
20,000 years ago - the whole
thing's just caved in on itself,
collapsed, creating this hole,
and you've got this.
This is essentially a conduit.
It's maybe 40, 50 foot down below.
So, somewhere down there the guys
are swimming past and supposedly
what happens is you're going to
see the bubbles as they go past.
That's what we're waiting for.
This is a nursery ground
for sinkholes,
the rock dissolving at a rate of
around 4cm every thousand years.
The void's getting bigger
and ultimately the soil
above falling into them,
creating yet another sinkhole.
There, there we go!
So that means they're
now right beneath us.
The air's coming up, so that means
they're safe so far.
So, the thing is, they've got
another hour to go before they can
actually surface properly
and have proper fresh air.
At least they're safe.
So far, so good.
Now, onto the next bit.
Dissolving limestone
like this is known as karst,
and it's not just
confined to Florida.
Limestone is common
all over the world.
There are pockets of it in the UK,
but here sinkholes
rarely make the news.
What's special about Florida
is the extent of the limestone
and just how big the sinkholes are.
You know, it's the kind of
place that makes you contemplate
Florida in a whole different way.
If I hadn't have known there was
a team of divers down there,
this would just be another pond
and another little patch of wood,
but actually it's a
gateway to the underworld,
an underworld that stretches
the length and breadth of Florida
and an underworld that's killed
and will kill again.
So, at any point, I'm hoping
to see this burst of bubbles
and that'll be them, safe.
Oh, yes!
That must be them, look.
Look at this. Yeah, here they come.
Here they come.
What a beautiful spot
to come out, as well.
There's something
quite elegant about it.
Really big sinkholes
happen only rarely,
but when they do,
they make quite an impact.
On the 8th of May 1981,
the residents of Winter Park,
close to Orlando, witnessed this.
What started as a small hole
soon developed into
a 13m deep monster,
some hundred metres wide.
We watched a house slide in,
we watched eight or nine cars
slide in, we watched the
swimming pool slide in.
And you just sit there and watch it
and you're powerless to help.
Any thoughts about making it a lake?
It will be a lake. We've already
found that out yesterday.
The engineers and that sort of
people said it will be a lake and
there's nothing
we can do about that,
so we just have a new lake
in the city.
When you're confronted with
footage as dramatic as this,
you have to ask, what triggered it?
Why did it happen now?
The ancient geology of this state,
the limestone, isn't enough.
First glance, it must seem
as if nowhere's safe in Florida,
but actually some places
are more at risk than others.
This map shows the locations of
all the verified sinkholes
and you can see how widespread
they are across the state.
But there's a real cluster of them
here in West Central Florida -
a sinkhole sweet spot, if you like.
And Jeff Bush's place
is just in there,
right on the southern edge
of that sweet spot.
On the face of it,
this clustering of sinkholes
doesn't make much sense.
Why are some parts of
the state relatively safe
and others much more prone
to sinkholes...
..even though they're all underlain
by the same rock, limestone?
So far, this search to
understand what sinkholes
are all about has focused
on one material, rock.
The thing is, voids in limestone
open up ridiculously slowly,
I mean, over thousands of years.
So there's another material
that we should consider,
one that's far more mobile -
soil.
Geological mysteries seldom
have just one culprit,
and the material that covers this
vast, unstable slab of limestone
is rather more interesting than
you might initially think.
In fact, it determines
how deadly sinkholes are.
To understand why, you
have to take a very close look
at the soils around here.
And the best way
to do that is to take
a trip down the Hillsborough River.
The only problem with that is
that the Hillsborough River
is infested with alligators.
I can't believe I'm risking
my life for soil.
There's one, there's one!
There's one just there.
Four, five-footer.
Look at that.
It's off, doesn't like me!
I think it's more scared of me.
The reason I'm out here
on the Hillsborough River
is that this area is
almost sinkhole-free.
But just downstream,
it's a very different story.
Look at this, a map of
all the sinkholes in Florida.
All these red squares here are
crammed into West Central Florida.
And then look, you get this kind of
sinkhole-free area in here.
To see that in more detail,
we have to go to a different map.
Look at this one here.
This is the Hillsborough River,
drifting in the
Hillsborough River,
just probably up here.
We're just on that bend there.
So, the thing is, in this area round
here, there's just no sinkholes.
But actually, to the west and
to the east, it's sinkhole city.
But to understand why
there's no sinkholes here,
we have to get to the shore.
The limestone beneath me is the
same as anywhere else in Florida
and is riddled with
caves and fissures.
But it's the earth above
that's different here.
So what makes this place so safe?
Time for a bit of
old school geology.
This is the instrument of
a soil scientist, the auger.
What you do is you clear
a bit of ground
and then you stick it in.
Kind of just drill your way down
through the vegetation.
Can you hear the vegetation ripping?
And then you get down
into the soil, the topsoil,
and as you get below that,
it gets a little bit easier.
In fact, it's easy now.
So we can see what's
underneath the topsoil.
And what we see is,
this is all soil but then this here,
this is just sand. Look at that.
Really coarse, loose sand.
You can tell how coarse is it,
cos when you chew it,
it's quite gritty
between your teeth.
It's the sand that's
key to there being
so few sinkholes in this area.
So the point is you've got this
really loose, incohesive sand,
and as the rainwater falls on it,
to be honest, it just drains
straight through.
Straight through
to the limestone below.
This means that the
soils never build up.
The sands just fall into
the voids as they form,
so the closest thing you'll get
to a big sinkhole round here
is this rather innocuous puddle.
The limestone underneath here
would have started out
something like that and then it's
just been kind of dissolved down.
And what you've had is you had the
sand just kind of dripping, draining
through it, and it just captures
this, just a little patch of water.
The limestone here is only
a few feet beneath the
thin sandy soil, which is constantly
being washed down into it.
Now, the thing is, these really
aren't dangerous at all.
There's hardly any chance
of something like this collapsing.
But a few miles down the river,
you enter sinkhole alley.
This is where the big sinkholes
happen
and the first thing you notice is
the landscape's changed.
We're out of the swamps and into an
area rich in agriculture.
During the winter, the fields around
here are full of strawberries,
making good use of the deep fertile
soils and warm weather,
so creating the fruit
bowl of America.
But I'm here in the off season
and there's not a strawberry
in sight, but that doesn't matter,
as I'm only interested in the soil.
You can see that's gone down much,
much easier here.
Now if I just pull that up now,
let's see what we've got.
OK, look, you can see it's much
darker and it's still sandy,
still pretty sandy but look, it's
got some kind of strength to it,
so that means there's some
clay in there.
Now if I went down another few
metres or so,
if I could be bothered going all the
way down,
I'd find something completely
different.
I'd find something like this.
This is a clay
and you can roll that.
It's got some kind of strength.
Look at that.
Just not going to do anything.
And it's that clay that turns out
to be really important
because that clay is really sticky.
It's got its own strength
and because of that,
rather than as the water
comes through,
rather than it just washing the clay
down into the sinkholes below,
it stays there and it builds up,
so you get a much thicker sequence
of sediment and not just that,
sediment with some strength to it.
It's strong enough to bridge
the holes in the limestone...
..but not for ever.
Sooner or later,
the clay will give way,
and that's what happened
at Winter Park 30 years ago.
Back then, no-one knew there was
a void beneath this part of town...
but the whole place stood on a clay
trap door, just waiting to spring.
It's a strange idea that
a layer of clay could be
the cause for a potentially
deadly sinkhole.
Let me show you how,
in a rather homespun way.
What happens is this...
Above the voids in the limestone,
a layer of sand can form with
a muddy clay above it
and more soil on top of that.
So you get this layer cake of sand,
mud and sand.
And then this is the tricky part.
OK.
And it creates a void
in the sub-surface. Look at that.
And it's the clay layer that's
really important.
It's forming a strong bridge that's
holding the rest of that sand
up and not letting it collapse.
But if the clay loses its strength,
the bridge it created
fails...suddenly.
The whole thing just caves in.
It's kind of like a trap door
that's been pulled
and that is called
a collapse sinkhole,
and it's absolutely deadly.
But what triggers that failure?
This might seem like an urban
paradise,
but appearances can be deceptive.
Many people here wonder if they're
sitting on top of a fragile
clay bridge into the underworld.
So, alongside the cement mixers
trying to stabilise the foundations,
this is a pretty typical scene.
Geologists drilling.
What they're looking for is
clay beneath the sands,
a potential bridge which could fail
at any moment.
And if that clay were to fail,
the cause will be something we're
very familiar with.
Water.
The state of Florida is
greedy for water
to keep the lawns looking green,
to fill swimming pools...
..and, most importantly of all, they
need millions of gallons of water
to grow the famous Florida
strawberries and tomatoes.
And the demand for all this water
means the water table close
to those fields can drop by over
50 feet in just a few days.
And when the clay dries out, that
lack of water can be the trigger.
But that's just half the story.
Water can also cause clay to fail
because it becomes too wet.
Florida famously is hurricane
country.
And when they hit, they can
drop around a metre of water
on the land in a matter of hours.
Pretty bad out here now.
The sheer wear of all that
water on those fragile clay
bridges can be enough to cause
catastrophe...
..so, ultimately, water,
too much or too little, can be the
trigger for a sinkhole collapse.
But if water can be the trigger,
then there's another reason why
Florida's so prone to sinkholes.
And when you've spent a bit of time
here, it starts to become obvious.
It's something to do with us.
You know, the sinkholes,
sinkholes have always been here.
They're part of Florida's
constantly evolving geology.
But what's changed is us.
I mean, our fondness for the sun,
our expanding numbers,
we're taking over more
and more of the land.
As the population of Florida grows,
people need somewhere to live
and that means we inevitably end up
building on more
sinkhole-prone land.
It's easy to get the impression
here that this is a state
collapsing in on itself.
There are almost 6,700
sinkhole-related claims each year,
and the numbers are rising.
But incredibly, they've only killed
three people in the last
40 years as few collapse
without warning.
What's far more typical is what
happened at this restaurant.
Just a few weeks back, the staff
came in in the morning to find
that cracks had appeared overnight,
so they called in the engineers
and basically they - look at it -
condemned the whole building.
30-odd people used to work here.
But the thing is, because of those
warning signs, there was no tragedy.
Sinkholes may
seem as old as the Earth itself,
but for millions of years those deep
voids have been forming
incredibly slowly,
collapsing down only rarely.
In a sense, sinkhole-related damage
comes from what we're doing...
how we use our resources like water,
and especially the fact that
we're building on deep clay
soils above voids like this.
What happened to
Jeff on the 28th of February, 2013,
when a sinkhole opened up
under his bedroom,
sucking him deep into the earth,
is mercifully rare.
The bedroom floor just collapsed
and my brother-in-law is in there.
He's underneath the house.
It was a freak combination
of factors...
..shaped by the geology of where he
lived, certainly,
but also due to tragic bad luck.
What's clear is that Jeff's house
lay in sinkhole alley.
With its clay soil,
it's prone to sudden sinkholes.
A structural engineer who worked
with the emergency workers
that night was Bill Bracken.
The sinkhole was centred
exactly on the bedroom,
and was contained completely within
the footprint of the building,
so it was not visible from the air,
from outside.
The only way to see that hole was to
look in the window or
be inside the structure.
When they poked a remote
camera through,
they saw a neat hole in the concrete
slab of Jeff's bedroom
and a near vertical shaft over
20 feet deep.
The sinkhole formed
and the soil began to drop.
Because you had the entire structure
over the top of this,
because it was completely
contained inside the footprint
of the building,
when those soils began to drop,
it was almost a flushing action that
created a suction force,
so it wasn't as though a hole opened
up and things fell into it.
It was almost as though,
as the soil began to pull
away from the underside
and a void was being created,
a suction force was being
created as well.
Just tugged at the bottom
of the concrete base of the bedroom?
So, it effectively pulled
that slab down into the hole.
When fire crews placed a listening
device at the bottom,
they were in for a shock -
the sinkhole was still alive.
By the time that they had deployed
that, set that in there,
placed that on,
on the ground surface,
walked back to the box, connected it
and began receiving signals,
they began to sense a tugging,
if you will, on the cable.
When they went to check,
the listening device had already
been pulled down into the ground,
so over the next three days there
was about 30 feet of cable that
was draped out of the window and on
the ground, and we watched that
30 feet of cable reduce down to
about six-to-eight feet of cable.
So we knew that that sand
was still in an excited state.
It was still pulling down.
Everything that landed on it was
immediately pulled down in,
so we knew that whatever had
gone into that was down at least
30, 35 feet.
SIREN BLARES
The one certainty is that
when the emergency services
sent down a probe to look for signs
of life, they found none.
All that's left now is a family
trying to come to terms with
the freak tragic
events of that night.
They told us that they were
not for sure how far down he was
and that the ground
around everything was just too...
..too unsafe, too unstable for them
to do anything.
They could not risk
anybody else's life.
It makes me sick,
just the way it looks.
Overgrown with grass, nobody taking
care of anything. And there's a...
My brother's down there still.