NARRATOR: Alcatraz.
The Rock.
The most infamous prison on earth.
CANTWELL: I think Alcatraz was the perfect prison for the time.
It was 'The Big Stick' against crime.
NARRATOR: America's worst: Al Capone, Machine Guy Kelly and Whitey Bulger,
all called the "rock" home.
The island lies just over a mile off shore, but escape was almost impossible.
Prisoners who tried, faced icy waters, deadly currents, disorientating fog
and fearsome predators.
To understand these dangerous forces, a new investigation pulls a plug on the seafloor,
and drains the waters of San Francisco Bay.
It will reveal the secrets of the seabed with stunning computer graphics.
Can the underwater landscape explain the rock's reputation as an inescapable prison?
In 1962 three men did break out from Alcatraz.
Will draining the Bay throw new light on what happened to them?
-They entered the water at the North end and took off in a raft never to be seen again.
NARRATOR: Did they reach the mainland and freedom?
Or did the ferocious currents shaped by the seabed seal their fate?
And can this underwater landscape show why Alcatraz might be the safest place
when the next earthquake hits California?
Secrets are revealed, as we drain Alcatraz.
The island of Alcatraz sits alone in the middle of San Francisco Bay.
Within this dramatic landscape, Alcatraz and the remnants of the renowned
US Federal prison are just a mile from the heart of the city.
For 29 years, it held some of the most dangerous
and notorious criminals in history.
MARTINI: Alcatraz was the end of the line.
And that's what it was designed for.
It was the place where they could take and isolate the troublemakers,
the gang leaders, the most problematic.
The most troublesome prisoners, they sent them to Alcatraz.
NARRATOR: Officially, no one successfully escaped 'the rock'.
But why exactly was no inmate able to break out of Alcatraz?
To answer this, high resolution sonar scans plot
the hidden depths of San Francisco Bay.
For the first time cutting edge computer graphics transform the scans
into remarkable images of the seabed.
This is Alcatraz as never seen before.
Today, the Island is a museum run by the National Park Service.
Over a million people visit every year.
One man has watched it rise to become one of America's most visited attractions.
Ranger John Cantwell.
He's worked on the Island for over 25 years.
He knows its history.
-There's a term that we use on Alcatraz, layers of history, and the first layer of history
would be the Army's time on Alcatraz.
They arrive in 1853 and built a fortress to protect the harbor.
The Federal Bureau of Prisons take over in 1934 and they ran the island for 29 years
as a super max penitentiary.
NARRATOR: American justice reserved Alcatraz for the worst of the worst.
The prison was fortified to make sure they would stay put.
-Where I'm standing is on Broadway, this is the main corridor in the cell house.
Alcatraz being a super max penitentiary meant that you had high security,
one officer for every three convicts.
They were constantly being watched.
12 times a day they would have counted every convict in this penitentiary building.
NARRATOR: Prison breaks were suppressed with extreme force.
But escape was a constant temptation.
Freedom was just a short swim away.
-The punishment of Alcatraz was this, the view of what was going on across the Bay.
Everything is in plain view and these men that were incarcerated on Alcatraz
could see it.
-I think it's fair to say every guy that ever did time here considered
'how are you gonna escape?'
NARRATOR: Liberty seemed so close that for some it was irresistible.
-The official count is 14 different escape attempts of that number
five men are still unaccounted for.
NARRATOR: To make it off the island the convicts first had to escape
from the prison itself.
-Well probably one of the most famous escape attempts from the building
is the 1937 Roe and Cole escape attempt.
They cut through the windows and pop out into the San Francisco Bay.
And they sent boats out looking for those two guys and never found them.
The official on this is that they were swept out to sea.
NARRATOR: Powerful currents weren't the only dangers facing escapees.
Alcatraz folklore claimed that predatory sharks swam in the Bay area.
In 1959, a college student had been killed by a great white in these waters
and in 2015 the Alcatraz shark legend was confirmed on camera,
when tourists witnessed a great white attacking a seal at the island's dock.
But fear of shark attacks didn't stop the escape attempts.
And these were becoming easier as the fabric of Alcatraz began to crumble.
-The complex was aging.
Concrete starts to crack and spall, steel rusts, barbed wire rusts,
it's almost impossible to make an escape-proof prison.
NARRATOR: In the last year before the prison closed
there were two remarkable escape attempts.
In December 1962, two men made it to the water.
-John Paul Scott and Darl Parker escape from the basement
of the penitentiary building.
And they cut through two bars in the basement window.
Pop out the window.
Shimmy up a set of pipes.
Scramble across the roof top of the cell house and basically,
came down off the west wall of Alcatraz island.
Scrambled down this road and hit the water.
They found Darl Parker standing on that rock,
Little Alcatraz island, about 50 yards off the north end waving to the officer
in the the guard tower yelling 'come get me'.
But they found John Paul Scott at the base of the Golden Gate Bridge.
NARRATOR: John Paul Scott was officially the only prisoner to successfully swim across
the bay, but he was so exhausted when they found him
that he was quickly returned to Alcatraz.
There was one other escape attempt in 1962,
the most famous in the prison's history.
Three convicts, Frank Morris, and brothers Clarence and John Anglin planned for months
to escape, and eventually got off the island on a home-made raft.
But they were never seen again.
-The case is still alive.
The official record is they're presumed drowned.
NARRATOR: It's one of the great Alcatraz mysteries.
Could Morris and the Anglin brothers have been the only ones to make it to freedom?
Alcatraz closed in the spring of 1963.
Officially no one escaped successfully.
But its true strength as a prison can't be explained just by the thickness of its walls.
Or the vigilance of its guards.
The waters around the rock were also a deadly barrier to escape.
Now science can explain just how and why the Bay was so dangerous.
Imagine you could pull the plug on the bottom of the bay
and drain the water from around Alcatraz.
For the first time we combine high definition sonar scans and cutting-edge computer images
to uncover the hidden world of the seabed and this remarkable landscape.
Finally, an unobstructed view of Alcatraz.
-It's a rock that rises from San Francisco Bay.
It's isolated but it's highly visible from the shore you can also you can reach out
and touch it but it's a mile and a half away.
NARRATOR: Draining the Bay reveals Alcatraz as a pinnacle of bedrock
emerging from the seafloor.
It's surrounded by mountain peaks.
All of them are ancient survivors from an age of earthquakes.
Tom Parsons is a geophysicist with the United States Geographical Survey.
He has studied this area for decades.
TOM: So we're standing at the Golden Gate and we're standing on mountains that were formed
100 million years ago.
Now we're sandwiched right between the San Andreas and the parallel Hayward Fault,
both of which are helping to accommodate plate motion here between
the Pacific and North American plates.
NARRATOR: San Francisco sits right on the edge of the North American Plate.
As the Pacific Plate grinds north past it, stress builds up along
the major fault lines in the area, the Hayward Fault and most notably the San Andreas.
-This region is very volatile it, it produces large earthquakes.
We've seen them in 1906, 1868, both were devastating earthquakes in San Francisco.
NARRATOR: The nightmarish effects of the 1906 earthquake,
7.9 on the Richter scale, are a reminder of how the area's violent geology threatens the
existence of a great city.
Over 100 million years ago, the landscape is entirely different.
There was a third plate between the two larger ones called the Farallon.
-The Farallon Plate used to sit between the Pacific and North American Plates.
It was shoved underneath the North American plate over all that time.
NARRATOR: The movement of the Farallon Plate was the catalyst that created
San Francisco Bay and Alcatraz as it ground under the North American Plate.
This process is called subduction.
As the Farallon Plate disappeared, fragments of the Earth's crust
were forced upwards, creating a valley and mountains.
-Alcatraz was part of the coast range belt that was uplifted by
the subduction of the Farallon Plate.
NARRATOR: The Bay area was then a long-forested valley with a number of rocky mountains.
One of these mountains was Alcatraz.
10,000 years ago, as the last ice-age came to an end the area was deluged
by billions of gallons of melt water.
This created what we call San Francisco Bay.
Alcatraz island forms.
This 1853 photograph shows the tip of the drowned mountain as a featureless rock
in the middle of the Bay.
Alcatraz may look tranquil and isolated.
But it's surrounded by powerful natural forces.
By draining the Bay, we can explain why the island earned its deadly reputation,
and what may have happened during the 1962 escape from Alcatraz!
NARRATOR: We're pulling the plug on San Francisco Bay and draining the waters
to discover why escaping from Alcatraz was so dangerous.
(door slams).
Over three decades there were 14 daring escape attempts.
The story of one of these is legendary.
-Probably the most famous escape attempt is the 1962 breakout.
NARRATOR: Frank Lee Morris, and brothers Charles and John Anglin devised
an audacious bid for freedom.
-The escape attempt was incredibly ingenious.
It involved stealing an immense amount of material: dozens of rubber raincoats,
glue, electric motors to turn into drills.
The guys even made a periscope, they made a flashlight.
NARRATOR: And use homemade tools to breach the prison walls.
(inaudible)
-We're in one of the Anglin Brothers cells and they were ingenious to actually create
a portal at the back of their cell.
And they fashioned a drill made out of a vacuum cleaner engine,
put a diamond bit on the end of this thing and then poked holes through the concrete to
loosen up the concrete around the air vent.
Dummy heads were made out of concrete material, human hair glued onto the heads
and the faces painted on these heads and at night with the lights down
it looked like they were sleeping in their cells.
So in the cell house, the lights go out at 9:30.
That's basically when they make their break.
Once the lights are out the heads are in place they go up to the rooftop and they've got
from 9:30 to 6:30 the next morning to make it to the mainland.
NARRATOR: With over 50 rubber raincoats glued together, the escapees construct a makeshift
raft and life vests.
This is their lifeline to freedom.
They carry everything to the roof and drag it down to the water's edge.
-So this is the actual spot where they entered the water.
Frank Lee Morris and the Anglin Brothers came down this hillside.
They dragged their raft.
Inflated it at the seawall here, jumped in and took off into the night.
They searched the waters looking for these three men,
and the raft or the men were never found.
NARRATOR: The official FBI documents state the three men and their raft
were most likely swept out to sea.
Their bodies were never recovered.
But is this what really happened?
Were they lost at sea?
Or could they have made it to the mainland?
To understand the fate of the three escapees on their raft,
scientists are studying the geology of the bay itself.
Can the sea bed offer an answer?
First, Patrick Barnard from the United States Geological Survey
explores the underwater landscape at the mouth of San Francisco Bay.
He hopes analysis of the seabed will explain the powerful currents
that surge around Alcatraz, making escape attempts so dangerous.
-Today we're going to be mapping from the Golden Gate Bridge
west towards the outer coast.
So, it'd be very interesting to see what's on the seafloor in that area.
NARRATOR: It's the first time that high tech multi beam scanners have been used
to explore how the seabed itself may have shaped the prisoners' fate.
-The incredible thing about multi-beam, is it captures the seafloor in high resolution
so we get a sounding at least every one meter along the seafloor so we can see
in incredible detail what the seafloor looks like.
NARRATOR: This remarkable technology projects thousands of sound waves towards the seabed.
The waves reflect off the contours, giving the team
an unprecedented view of the bottom.
The investigation begins under the most iconic location in San Francisco.
-We're right underneath the Golden Gate Bridge at the narrowest part
of the Golden Gate strait.
The purple represents the deeper parts of the channel which are about 92 meters deep
in this location.
NARRATOR: After several passes over the deep channel,
the monitor shows a strange landscape below.
-We're seeing a largely featureless bottom.
This whole center portion of the swath is scoured clean to bedrock.
NARRATOR: Draining the water from under the Golden Gate Bridge reveals a huge gorge.
It's far deeper than the rest of the Bay.
Large enough to hide a 30-story building.
But what happens to the seabed when the multi-beam vessel heads west to the open ocean?
-We're located a little over a kilometer from the Golden Gate Bridge now to the west,
but the bottom is still clean, it's still bedrock lined.
NARRATOR: As the boat moves further from the bridge, the water grows much shallower.
The sonar readings suggest a dramatic transformation in the seascape below.
-The bottom is changing, we're seeing a lot more sediment on the seafloor now.
NARRATOR: Draining the water reveals an incredible sight.
-We're starting to see some very large sand waves here that are emerging
from the depths of the Golden Gate strait.
NARRATOR: These formations on the seabed are huge.
-So the largest sand waves are about 200 meters long, six meters high,
the biggest ones ten meters high are about three stories.
NARRATOR: And they're sitting just yards away from the harbor entrance.
-They look like probably what the Sahara would look like if you were walking through it.
NARRATOR: These giant sand waves are caused by the huge tidal rush
through the Golden Gate Strait.
The fast-moving water picks up sand and dumps it as it slows down.
-The sand waves at the mouth of San Francisco Bay are there because you have
this very large estuary and all the tidal flow associated with it,
roughly two trillion liters of water being forced through on every tide.
NARRATOR: Huge tidal forces push water through the narrow channel.
The solid bedrock of the gorge does not erode.
So, the strait acts like a fire hose as the water rushes through it.
And the flow is 160 times greater than the volume of water
cascading over Niagara Falls.
-You have all this sand and gravel being carried along and forced through
this narrow opening and then as the opening widens further and further all this material
gets deposited in these bed forms.
NARRATOR: The drained landscape shows how the geology of the seabed shapes
the powerful tidal currents in San Francisco Bay.
First there's the deep gorge that funnels the water into a jet stream.
Moving west, beyond the Bridge the seabed rises from
over 300 feet deep to just 130 feet.
The 'drain' shows how the racing current dumps thousands of tons of sand,
creating these giant sand waves up to 30 feet high.
But what does this underwater landscape of the Golden Gate have to do
with escaping from Alcatraz?
These racing tides are what the inmates had to contend with when fleeing the rock.
Is it possible that Frank Morris and the Anglin brothers got caught
in these wicked currents?
The records from the 1962 FBI investigation show the tide charts on June 11th.
From 9:00 pm to 3:00 am there was a strong outgoing tide.
Which peaked at exactly 11:46 pm.
So, when did the three escapees hit the water in their home-made raft?
-From the moment lights out happened, which I think was 9:30,
as soon as they could've they would have gotten out of their cells, give it an hour,
hour and a half to have gotten everything that they needed to through that vent on the roof,
across the cell house, down the other side, hit the water.
I think that they started paddling as soon as they got to the water.
Let's say 11:00.
NARRATOR: The three convicts would have been in the water at peak tidal flow during an
ebbing, outgoing tide.
What were their chances if their flimsy raft made of raincoats broke up,
leaving them to swim in the powerful currents?
-If you tried to escape off the north end of the island especially during ebbing tide
like they did in 1962 where the currents are extremely strong
and moving straight out to sea.
It would have been very difficult to swim out of that current within
an hour and a half you could have been at the open coast.
NARRATOR: So Morris and the Anglin brothers had to struggle with the fastest
and deadliest current flow in the bay.
And these currents show no mercy.
Known to destroy vessels far larger than a raft.
San Francisco Bay is a ships' graveyard.
cisco Bay reveals a deep ominous gorge under
the Golden Gate Bridge and giant sand waves rising from the seabed.
Evidence of massive water flow through the mouth of the Bay.
Two and a half miles to the east of the Golden Gate lies Alcatraz.
CANTWELL: This is a great example of the tidal movement around Alcatraz island.
I'd gauge this at about a five-knot tide.
NARRATOR: It is possible to swim from Alcatraz to the mainland.
But only during the brief period when the tides are turning
and the currents slow down.
-I've done this swim on a slack tide and there's no way that you'd catch me in this
water trying to make it to San Francisco.
NARRATOR: Fierce currents
were just one of the challenges inmates faced when they tried to escape.
There were other deadly hazards.
Bill Baker is one of the few surviving inmates from Alcatraz.
A convict, he was sent to the rock for three years in 1957 after attempting to break out
from other prisons.
But escaping Alcatraz was another matter.
-I thought about it a lot but I couldn't figure out how to beat the water.
Because the water kills ya because it's cold.
That water is the wall that kept us here and it killed a lot of people trying to escape
and so that becomes very ugly, you know,
after you look at it a while.
NARRATOR: The frigid water that frightened Bill Baker is caused by the upwelling
of cold currents from the deep ocean.
These replace the warmer surface waters relentlessly churned up by the strong winds
of San Francisco Bay.
Average temperatures range from a bone chilling 51 to 60 degrees Fahrenheit.
In these conditions hypothermia will quickly overwhelm any swimmer.
But when this cold water is mixed with warm air, it creates
another killer that silently invades the bay.
Fog.
Thick fog could be a prisoner's friend, concealing a break-out from Alcatraz.
-In 1937 two men escape from the industries building into the fog.
They basically timed it between the head counts; they had about a 45-minute jump
on the officers before they realized that they were missing.
NARRATOR: For Ralph Roe and Ted Cole, the fog offered cover once
they were off the island.
But the white-out also posed a threat.
JAN: If someone were to escape into the foggy bay it would be almost an impossible
type of situation, it'd be very dangerous, it'd be disorienting.
So that would be almost a worst-case type of scenario for someone to try and escape in.
NARRATOR: Jan Null knows all about fog.
He has been a local San Francisco meteorologist for years.
But why is fog so prevalent in this part of the world?
-The mechanism that creates the classic fog for San Francisco is, you know,
a sea breeze circulation.
As that air flows over the very cold water along the California coast
it condenses out, forms the marine layer, fog and then that spreads inland.
NARRATOR: There is only one place for fog to reach San Francisco.
-The only sea level gap for that fog to get through is the Golden Gate so that's the area
that's going to get the most fog.
It's focused, you know, from the Gate right toward Alcatraz and then on toward Berkley.
NARRATOR: When Roe and Cole escaped they quickly vanished into the white-out.
MARTINI: It was December, it was cold.
One eyewitness, he saw them.
He claims to have seen them in the water being swept out.
99.9% sure they didn't make it.
NARRATOR: The thick fog made rescue impossible.
Roe and Cole were never seen again.
The FBI speculated they had died in the icy water.
The San Francisco Bay fog mixed with the wicked fast-moving currents
is a recipe for disaster.
By draining the water, we can see the results of this deadly combination.
There are ghostly, large artifacts scattered on the seabed.
Dozens of shipwrecks.
San Francisco Bay is a graveyard of lost ships.
And there is one, just east of the Golden Gate Bridge, deep down
on the side of the gorge that has a tragic tale to tell.
The shipwreck is the City of Chester.
But how did it get here?
August 1888.
The City of Chester moves towards the Golden Gate Strait.
STEPHEN: August is a time when you get heavy fogs around here.
And it was foggy, she's heading out the Golden Gate, at the time when a great ocean
liner is heading in.
It was far larger.
Far faster.
NARRATOR: Now, 130 years later, National Park historian Steve Haller
and archaeologist Peter Gavette are searching for the lost vessel.
-The City of Chester went down rapidly and she sank in 200 or so feet of water.
We're over the spot where she lays.
NARRATOR: Multi beam sonar gives a tantalizing glimpse of the sunken ship.
-You can see the super structure.
That's the stern there.
-The fact that the City of Chester hasn't been covered with sediment is great.
With the multi-beam data, we can look at the City of Chester wreck as it happened.
NARRATOR: Using the data from the scan, we can now drain the wreck of the City of Chester.
Does it offer any evidence of how the disaster unfolded?
-You can see exactly where the fatal damage to the ship occurred and you can see
how that bow section is off kilter with the rest of the ship so it broke her keel.
NARRATOR: The drained ship is the crime scene, giving clear evidence of its fate.
-We can actually see where it was struck just aft of the port side just aft of the bow
and almost split it in two.
NARRATOR: In the thick fog the City of Chester and the White Star Liner Oceanic
are on a collision course.
They do not see each other until it's too late.
Powerful currents drive them together.
-The city of Chester heals off to port, the Oceanic hits her in the side,
far heavier vessel, splits her hull.
NARRATOR: The smaller ship is fatally wounded.
The City of Chester sinks in only six minutes, killing 16 people on board.
She is just one of many shipwrecks that lie on the bottom of San Francisco Bay.
The deadly result of extreme natural forces that make this bay so dangerous.
These are the same forces that escapees from Alcatraz had to contend with.
Most notably Frank Morris and the Anglin brothers who escaped the island prison
on June 11th, 1962.
What would their chances have been in these conditions?
-If you consider the two ocean-going steamers can get tossed around to the point
where one cuts the other one in half, what are the odds of three guys in a rapidly
deflating homemade rubber raft gonna have?
NARRATOR: But could the powerful currents in the Bay have instead helped the escapees?
Could they have been pushed to shore, and to freedom?
in a home-made raft.
Ever since, there have been wildly different rumors about their fate.
Some claim to have seen them on the mainland.
But that conflicts with the official FBI report, which states
that their objective was Angel Island, a two-mile paddle north of Alcatraz.
-They did what nobody else ever did, they got off the island with a head start and,
and were never seen again.
CANTWELL: The official Bureau of Prisons report on these three men in the raft is
that the raft took on water, the men were in the San Francisco Bay,
they became hypothermic and the currents took them out to the Pacific.
NARRATOR: But this was never proved.
And when the story broke around the world,
there was excitement and intrigue.
MAN (over newsreel): It appears to be the first successful escape in the history
of the maximum-security prison.
NARRATOR: For weeks, the FBI searched the bay.
Their goal was to find them dead or alive.
MAN (over newsreel): The escape triggered the greatest man hunt in San Francisco's history.
NARRATOR: Though they never discovered any trace of the bodies,
the FBI did find evidence of the escape.
-They recovered two of the inflatable life vests.
They recovered two of the plywood paddles found floating in different places in the bay.
Another one of the life vests was recovered outside the Golden Gate
at a beach north of the Golden Gate.
There was no lack of evidence that they escaped.
NARRATOR: This evidence was scattered all over the Bay area,
with no signs of the men.
How did this happen?
Could the three fugitives have made it?
Is there a possibility that the strong currents worked in the escapees' favor
by pushing them to the shore?
Patrick Barnard and his USGS colleague Josh Logan
explore this intriguing theory.
They use high-tech buoys with GPS sensors to track the currents.
PATRICK: The conditions are very similar to what they would have been during
the escape in 1962.
We're at peak ebb flow.
The water is moving about a meter and a half a second,
or about five and a half kilometers per hour.
JOSH: The GPS will be recording its position every five seconds.
We'll be able to pick that up on our laptop and be able track it in real time.
And that'll let us know the direction and the speed that the water's moving.
Okay, so we are tracking now.
I'm going to deploy the drifter.
NARRATOR: The buoy is dropped at the north end of Alcatraz on the escapees' route
to Angel Island.
At first the buoy's path seems to confirm the theory that the men were swept out to sea.
-It's drifting about, averaging about six kilometers an hour right now.
In 15 minutes we've drifted about half the distance between Alcatraz
and the Golden Gate.
It looks like it is going right down the middle of the Golden Gate Strait.
NARRATOR: Even in a strong headwind, the fast-moving current
pushes the buoy further out.
But then, the unexpected happens.
-It was going about six kilometers an hour until it hit that that seam
and then it slowed down to one kilometer an hour.
NARRATOR: The buoy stops
just before the Golden Gate Bridge.
It's not what the team predicted.
-Alright it looks like it just sort of slowed down because it got into an eddy.
That's pretty interesting.
So you can see it was travelling south west in a straight line until
it hit that eddy and then it slowed down and changed directions.
NARRATOR: An eddy is created by water moving in a circular motion,
almost like a slow-moving whirlpool.
Can draining the water from San Francisco Bay reveal anything
that would cause such a giant eddy?
Just east of the bridge there is a strange feature on the seabed.
-Right toward the Golden Gate there's some very shallow depths from a large bedrock outcrop,
known as a sill, in this location, and so this causes an uprush
of a lot of water and eventually some flow separation causing this eddy.
NARRATOR: The deep-water currents run directly into this bedrock sill,
forcing the fast-flowing water to the surface.
This creates the giant eddy which stops the buoy dead in its track.
Draining San Francisco Bay is revealing how powerful currents on the surface
that swept men to their deaths are shaped by the contours below.
Other strange features on the seabed help to explain the deadly outcome
of an earlier escape attempt.
Convicted burglar Aaron Burgett made a break for freedom in September 1958.
His friend, Bill Baker, was an inmate at the time.
-Well he was a young man he was like I say he was strong and he was, you know,
strong as a mule.
NARRATOR: While on garbage detail, Burgett overcame a guard and then
jumped into the waters off the west side of Alcatraz.
-They didn't know what happened to Burgett and they locked us all down.
There was boats circling the island all day and night, you know,
with searchlights and everything and every day that passed
we were more optimistic that he was gone.
NARRATOR: Though the prisoners hoped he made it,
two weeks later the authorities found Burgett.
-But then one day his body washed up and then that was the end of that.
I was very sad about that because I hoped that like heck that he made it.
NARRATOR: Strangely, Burgett's body was found just yards off the shores of Alcatraz.
So why wasn't he washed out to sea by the powerful currents in the Bay?
The clues may lie in the shallow waters around Alcatraz.
They've never been accurately mapped before.
Now Professor Rikk Kvitek, from California State University Monterey,
uses a one-of-a-kind surveying vessel to explore the terrain.
-It's designed to work in all the places a conventional vessel can't go.
It can work in shallow water around rocks and it's outfitted with all
the sonar systems found on a normal hydrographic vessel except it's all operated by one.
NARRATOR: After a day of scanning the shallows, back and forth along the western cliffs,
Professor Kvitek's survey helps explain what happened to Aaron Burgett's body.
The drained seabed around Alcatraz shows dozens of large rocks and crevices.
When Burgett drowned, his body probably sank to the bottom and became trapped in these rocks.
Later, as it decomposed, gases forming in the corpse would have lifted it to the surface.
The 1962 escapees didn't try to swim to freedom.
They used a home-made raft.
But where they ended up, lost out at sea, or safe on the mainland, is the real mystery.
NARRATOR: Patrick Barnard and Josh Logan hope to confirm how the seabed in San Francisco Bay
influences the water currents above.
They want to determine the course the escaping prisoners took in 1962.
The first test buoy stopped dead in a giant eddy.
Now they deploy two other buoys in different locations
along the route to Angel Island.
-Ah, we're going to release it a little bit further north
from where we released the last drifter.
NARRATOR: The two buoys begin their journey towards the Golden Gate.
The second moves down into the same eddy as the first, but the third buoy
heads directly towards the Bridge.
-This one seems to be heading out the gate instead of getting caught in that eddy
that we saw further to the south.
NARRATOR: Moments later it's past the Bridge.
-So that third buoy is basically gone straight out the main channel and has sped up.
NARRATOR: The drained seabed shows exactly why this buoy is moving southwest.
As it floats slightly further north it moves past the bedrock sill,
and misses the eddy.
Then powerful currents sweep it through the gorge and under the Golden Gate Bridge.
Soon the buoy is in the open ocean.
-We deployed it for about an hour and it went 6.8 kilometers
at a maximum speed of ten kilometers an hour.
-It's about in line with the predictions of the model.
I was surprised the first two didn't make it out.
But they got caught in these eddies and this one was going pretty much right
as the model predicted peaking at ten kilometers per hour, which is far faster
than anybody can swim.
NARRATOR: Getting caught in the eddies may not have saved the escapees.
They had to fight against powerful currents to get to the mainland.
-Anybody that's trying to paddle to shore they'd be heading southwest
and they'd probably be going sideways.
NARRATOR: The buoy test sheds fascinating new light on the 1962 FBI report.
The two buoys caught in the eddy moved in different directions
including one that amazingly floated back towards Alcatraz.
This could explain why debris from the prisoners' raft
was found near the island after the escape.
The path of the third buoy shows that if the prisoners drowned as the FBI believed,
their heavy bodies could have been swept out to sea by the ferocious currents.
But the test truly shows one thing, San Francisco Bay is unpredictable.
-The current field is so complex that you could literally just been
just a few meters on either side of the main part of the channel and you could have ended up
in completely different places.
You could end up ten kilometers out to sea or almost right back at Alcatraz.
NARRATOR: But for the three inmates, if they did reach the open ocean
there was one more deadly challenge.
Because of its high population of great white sharks,
this area is known as the Red Triangle.
-In June of '62, it would have also been during up-welling
season like it is now.
So, you have lots of nutrients in the water column.
Lots of fish and lots of bigger predators, so it's likely there could have been
more great whites in the area than there are during the rest of the year.
NARRATOR: So if they made it this far out, dead or alive, they may have become prey
for the great whites.
The bodies of the three inmates were never found.
But now science shows that it is unlikely that they could have survived.
The infamous prison closed its doors in 1963 with a perfect record.
Officially there were no successful escapes from Alcatraz, though many tried.
-The conditions surrounding this island is what really made it
an escape-proof prison.
MARTINI: The bay was the most formidable of the prison's walls.
You could say that the bay has really created Alcatraz' reputation.
NARRATOR: The 'perfect prison' was the result of extraordinary geology.
Deep gorges, giant underwater sand dunes, hard bedrock pillars at the Golden Gate Strait,
powerful currents and even great predators that roam the waters outside the Bay.
All-natural phenomena that made the rock 'inescapable'.
But there is another mighty natural force at work in San Francisco Bay that dwarfs
even the power of the ocean currents.
A drained Pacific Ocean reveals the first clue.
Deep under the waters off the coast of San Francisco lies the infamous San Andreas Fault.
The shifting tectonic plates are the trigger of major earthquakes in the past.
The most-deadly in 1906.
Over 3000 people lost their lives.
But could an even deadlier earthquake hit the area?
The so called 'big one'.
-So in our forecast we actually consider an earthquake that could start
at the southernmost part of the San Andreas Fault, run all the way along through the Bay Area
up north, involves the entire San Andreas Fault zone.
That earthquake would be on the scale of 8.2 to 8.4 in magnitude.
NARRATOR: The devastation would be far greater than the destruction
caused by the 1989 quake.
-If we were to see an earthquake of that scale in San Francisco that would cause,
unfortunately a lot of casualties, many buildings would collapse, freeways
and infrastructure type things would be in danger.
If it did happen I think we would see significant destruction in the city
and throughout the Bay Area and throughout California.
NARRATOR: The massive earthquake could cause parts of the city
to topple into the sea.
Much of the downtown core destroyed.
The Golden Gate Bridge pushed to its engineering limits.
But when the fire and smoke clears, 'one' place will still be standing.
-During a big earthquake Alcatraz would be a safe haven because it is built
out of very strong rock.
It's not going to collapse under strong shaking like soft soil would.
It's been there for 100 million years, it's hung in there,
so it's going to do well under an earthquake.
-If the geologists are correct and when the San Andreas lets go, Alcatraz
is the safest place to be, that is the ultimate irony.
The island that so many men wanted to get away from is the place
that's gonna offer the refuge.
NARRATOR: By draining Alcatraz and exposing the secrets hidden on the seabed,
a different picture of the island emerges.
The explanations behind its most legendary mysteries involve more
than just the prison itself.
The geography of San Francisco Bay: the waters, the rocks, the wind and the fog,
a tightly woven net making Alcatraz an inescapable place.
Unless the 'big one' hits.
By draining the waters around Alcatraz, the secrets of 'the rock' are revealed.
Captioned by Cotter Captioning Services.