Original subtitles

>> Earth, a four-and-a-half-

billion-year-old planet, still

evolving. As continents shift

and clash, volcanoes erupt and

glaciers grow and recede, the

earth's crust is carved in

numerous and fascinating ways,

leaving a trail of geological

mysteries behind.

In this episode, the 450-

million-year-old geological

history of New York City is

explored. A metropolis

pockmarked with strange rocks,

haunted by footprints of

ancient giant reptiles, and

lined with a vast curtain of

solidified lava. Scientists

investigate the evidence for

fiery volcanoes, massive

floods and ice sheets four

times as high as the Empire

State building. The clues to

understanding New York City's

geological past provides a

window into the formation of

the earth itself.

S01x05 New York Original Air Date on March 10, 2009

== sync, corrected by elderman == @elder_man

The investigation into New

York City's geological history

begins here, with Manhattan's

rocky outcrops. These rocks

are clues to how the land was

made and how its geology

helped it become a dense,

thriving, pulsating city.

They're scattered all over

Manhattan, poking through the

surface of parks and through

the concrete between the

buildings. Some, squashed

between two apartment blocks,

are the size of a whale.

They are the extraordinary

survivors of ancient times.

Most importantly, they are the

surface tips of the bedrock in

which Manhattan's buildings

are anchored. Gigantic

skyscrapers stand in two

clusters, in downtown and

midtown. In the section

between, the buildings are

lower. The clues to the shape

of Manhattan's familiar

skyline are the rocks beneath

the surface.

A leading expert

on the rocks in New York is

geologist Charles Merguerian.

>> The entire history of the

development of the earth's

crust is emblazoned in the

rocks beneath us. The rocks

here in New York City harbor

an ancestry that dates back

over a billion years of time.

>> Merguerian is searching for

evidence to show how the

city's bedrock was made.

At Inwood Hill Park in Upper

Manhattan, he's found an

extremely hard piece of the

bedrock known as Manhattan

schist. To the untrained eye,

it's just a piece of rock, but

to Merguerian, this is his

first clue.

>> The rocks that we're

looking at right here are

rocks of the Manhattan schist

formation and the--these rocks

are very severely deformed,

and the structures here in

this rock is a structure that

comes up like this, bends

around and comes back down on

itself as such, and in

three-dimensional view, it's a

structure that looks something

like this. A very, very tight

fold with a plunge towards the

south here. These are rocks

that were very, very strongly

deformed over protracted

periods of time. And it's the

same bedrock that occurs over

much of New York City.

>> This tight fold in the rock

suggests New York's

bedrock was formed under great

pressure. To confirm this

hunch, Merguerian takes a

sample to the lab for detailed

analysis. Radiometric dating

proves this rock is about 450

million years old. But the

rock has even greater secrets

to tell.

It contains a kaleidoscope of

minerals, which opens a window

into the ancient world.

>> To me, minerals are like

the instrument cluster in your

car, they tell you everything

about how your car is running.

>> Merguerian uses a

microscope with polarized

light to view the minerals.

>> The examination tells us

the former depth regime,

how deep the rocks were, they

tell you the age of the rocks,

they tell you everything you

want to know about the

development of the earth's

crust.

>> What's striking about these

samples is that the minerals

inside are elongated.

It is a clue that these rocks

must once have been crushed by

massive forces. And the colors

support this theory. Under the

polarized light, the sample

from Inwood Hill Park shows up

blue. This comes from a

mineral called kyanite, which

forms at great depths. It's

conclusive evidence that this

rock was compressed deep under

the surface. Rocks forged at

these depths are much harder,

ideal for a city's

foundations. But what gigantic

weight was on top?

Merguerian believes there is

only one answer.

The rock was once buried under

the crushing weight of a chain

of massive mountains.

>> The minerals that we find

in the bedrock units of New

York City tell us that the

rocks of New York City were

formerly buried when they were

formed, under very high

pressures, and that those

high pressures indicate that

these rocks formerly were

produced at depths of 20

to 25 miles, and probably the

mountains were as high as the

Alps are today.

>> But even the most

impressive mountain chains

can't survive the ravages of

time. The Rocky Mountains, for

example. Millions of years

ago, they soared nearly six

miles into the sky. Today,

erosion has halved their size.

The same process happened in

New York. Rain, wind and ice

wore the ancient mountains

almost flat. But the

microscopic crystals found in

the rock in Manhattan testify

that they existed in the past.

How did the mountains form?

The answer lies in the way the

earth's crust moves.

A network of

interlocking individual

pieces makes up the earth's

surface. Geologists call them

tectonic plates. Over millions

of years, they collide and

break apart to form different

continents. 450 million years

ago, the earth's surface

looked completely different.

North America was much further

to the south.

>> MERGUERIAN: North America

was tilted 90 degrees clockwise

from its present orientation and

it was straddling the equator.

As such, the climate was

tropical, the east coast of

North America was really

experiencing Club Med

conditions.

>> The weather may have been

awesome, but the ancient East

Coast was heading for trouble.

The plate beneath it was

moving. The East Coast was on

a collision course with

ancient West Africa. 450

million years ago, they

collided. The impact unleashed

geological chaos. Under

intense compression, the land

was forced upwards to form a

soaring range of mountains.

>> The collision that took

place is the most fundamental

and impressive

mountain-building event to

affect the east coast of North

America.

>> Today, all that remains are

their stumps, stumps that form

the bedrock of modern-day New

York. The collision that built

up the ancient mountains also

folded the bedrock into dips

and rises. These folds are

responsible for the shape of

Manhattan's skyline.

The city boasts two clusters

of skyscrapers in downtown and

midtown. Here, the hard

bedrock that formed deep

underground was forced up.

It is now close to the surface

and provides solid anchorage

for the high-rise buildings.

In the dip in the middle the

rock was folded down.

The area is filled with loose

sediments, less suitable for

skyscrapers.

>> MERGUERIAN: When the bedrock

is at the earth's surface

where it's actually exposed,

then it's pretty easy

to build tall buildings 'cause

you can root them directly

into solid rock.

However, in areas where the

bedrock is deep and covered by

glacial sediment, in those

cases, it's very difficult to

build tall buildings because

you need to root those

buildings either into solid

rock or build concrete

abutments called caissons that

can support tall buildings.

>> New York's deep history is

beginning to take shape.

Building up from tiny crystals

in the rock, scientists

revealed how New York's

bedrock was formed under the

crushing weight of a massive

ancient mountain range.

The result was hard Manhattan

schist, a perfect foundation

for the city's skyscrapers.

But New York City still had a

long way to go.

The colliding plates created

an enormous landmass - the

last great supercontinent,

called Pangaea. New York was

now trapped in the center...

but somehow it made it back to

the coast. Hidden beyond the

city's streets is evidence of

huge volcanic eruptions, mass

extinctions and continents

torn into pieces. Clues that

could explain how New York

became one of the world's

great maritime cities.

[]Investigators are piecing

together how New York City's

unique geology was formed.

Much of its early success as a

trade and commerce center is

owed to its deep-water harbor

and its location at the coast.

But 450 million years ago,

things were different.

The area of New York City was

landlocked, embedded in the

heart of a huge

supercontinent. How did it get

to the coast? The

investigation fast-forwards

250 million years. In a quarry

in New Jersey, 25 miles

northeast of Manhattan,

paleontologist Paul Olson

unearths the first of a string

of clues that could explain

how New York City reached the

coast. A giant fossilized

footprint.

>> This is the footprint,

actually the mud that filled

in the footprint, of a

four-footed crocodile relative

that was the dominant

carnivore during the late

Triassic. You can see the toes

here have little pads on them

and here's the handprint, and

these animals would have been,

in this case, about the size

of a modest crocodile, but

some of them became much, much

larger, the size even of a T.

Rex.

[ROARS]

>> The footprints are from a

huge crocodile-like creature

called Postosuchus.

It first appeared on the earth

around 230 million years ago.

Then, some 30 million years

later, its footprints suddenly

vanished. But Postosuchus

wasn't alone. Half of all land

animals perished at the same

time. The fossil evidence

proves it to be one of the

biggest mass extinctions ever

recorded.

>> The evidence for this mass

extinction is that we have

lots and lots of fossils right

in this area. And what you see

is especially in the--in the

reptile footprints, you see

one group of forms, the forms

that are related to

crocodilians, disappear.

>> Whatever caused the mass

extinction must have been a

catastrophic event.

Olsen had a hunch that the

mass extinction was somehow

related to New York's return

to the coast.

The ancient area

of New York sat of a line of

great weakness, the plate

boundary where two continents

joined to form the

supercontinent Pangaea.

And it was unstable, prone to

earthquakes and volcanoes.

Olsen's quest - to find the

evidence for the natural

disaster that finished off

Postosuchus 200 million years

ago.

A band of dark rock above

the footprints in the New

Jersey quarry caught his eye.

It was basalt, the smoking gun

Olson was looking for.

Basalt is a volcanic rock.

It forms when hot lava erupts

onto the surface and cools.

Did the volcanoes that forged

this basalt trigger the mass

extinction and also rip

Pangaea apart? On its own, the

evidence at the quarry was

unconvincing. The layer of

basalt is only a few feet thick.

To prove mass lava

flows caused this global

catastrophe, scientists needed

corroborative evidence.

High above the Hudson River,

geologist Matt Gorring follows

another lead. He's studying

the Palisades, a dramatic

geologic feature that hugs the

Hudson River, beginning across

mid Manhattan and running into

northeast New Jersey.

They too are made of basaltic

rock, the same rock implicated

in the mass extinction of land

animals. But the Palisades are

on an altogether different

scale.

>> The Palisades are a sheet

of basaltic magma, about 1,000

feet thick, it's about 40

miles long, so it's a

very prominent set

of cliffs that run all the way

up the west side of the Hudson

River.

>> Here is proof of massive

volcanic activity. Hot lava

flooded out of ruptures in the

earth's crust and covered

ancient North America in a

mile-deep sheet. The lava

cracked as it cooled. The

vertical ruptures formed

regular pencil-shaped columns.

These distinctive rock

formations have been known to

geologists since the 19th

century.

Intriguingly, they

appear on both sides of the

Atlantic, in North and South

America, Europe and Africa.

Geologists suspected that

their presence pointed to the

spot where Africa and Europe

separated from America.

But that was just an unproven

theory, until the 1950s, when

scientists developed a

revolutionary technique called

paleomagnetism. Now, they

could study the magnetic

properties of rocks.

Many rocks, including basalt,

have a distinctive magnetic

signature, formed as the rock

is born. Tiny crystals inside

the rock act like compass

needles. When the magma that

forms the rock is fluid, the

crystals align to the earth's

magnetic field, pointing north.

As the rock solidifies,

the crystals freeze, forever

locked in that fixed magnetic

alignment. As continents move

and the rocks travel, the

crystals end up pointing in a

different direction than

north. Gorring and his team

investigate the magnetic

signature of the Palisades.

To get a sample, they bore

into the rock with a

water-cooled drill.

They measure the exact

orientation of the crystals

today with a compass.

When they offset this reading

with magnetic north, they can

calculate the original

location of the rock.

>> Uh...14.

One of the useful things

that you can do with this rock

is you can take it back in the

lab and measure its magnetic

orientation, and that magnetic

orientation will be

when this rock crystallized or

solidified 200 million years

ago. So this rock would

have minerals that would be

pointing in some other

direction other than north

today.

>> When scientists compared

the magnetic orientation of

the Palisades with the other

basalt outcrops around the

Atlantic, they discovered they

formed at approximately the

same latitude. Not only did

the rocks have the same age,

they were also born at the

same location. For example,

200 million years ago, New York

and Morocco were neighbors.

The geologists had all the

proof they needed. They

could now confidently piece

together what happened.

It began with a global

volcanic disaster.

>> About 200 million years

ago, North America and

Africa began to pull apart

from each other.

There were gigantic lava

outpourings. These lava flows

erupted along very long

cracks in the earth's crust,

that would have produced

fountains of lava extending

thousands and thousands of

feet into the atmosphere.

They covered an almost

inconceivably large area,

roughly four million square

miles, from southwestern

France to southwestern Brazil,

from New York to central Mali

in Africa. This area was

covered in ponded lava flows

that in some places ended up

being nearly a mile thick.

>> Volcanic eruptions led to

soaring temperatures.

Half of the plants and animals

died. Postosuchus didn't stand

a chance.

As enormous forces

tore Pangaea apart, a giant

sea formed between the

separating land masses - the

Atlantic Ocean. The city of

New York was now at the coast.

200-million-year-old

footprints beneath a layer of

basalt and the Palisades

towering above the Hudson

provide evidence that Pangaea

split apart to create the east

coast of North America.

But the story of New York City

was far from over. After being

built by fire, the region was

about to be overcome by

another destructive force.

[]Scientists are piecing

together the story of New

York's violent geological

past.

250 million years ago,

the Atlantic Ocean opened up,

leaving the area of New York

on the coast. But the maritime

city still had a long way to go.

There was no deep Hudson

River channel. It was nothing

but a small stream. What

forces transformed it into the

wide river capable of carrying

heavy freighters far inland?

A clue to how the Hudson

Valley was created is the

strange boulders that are

scattered throughout

Manhattan's Central Park.

Some of them weigh several

tons. But they're strangers to

these parts, totally unlike

the surrounding rocks.

Geologist Charles Merguerian

investigates where they came

from.

>> This boulder is a boulder

from the Palisade sheet on

the other side of the Hudson

in New Jersey. You can see

it's very nicely polished.

Compositionally, it is totally

different than the surrounding

bedrock, which is Manhattan

schist, and the Manhattan

schist here is very rich in

mica. This rock has no

light-colored mica in it

whatsoever. The Palisade sheet

is located to the west and

north of us.

>> The Palisades run for 40

miles along the Hudson River.

Something immensely powerful

must have moved the boulders

such a great distance.

Merguerian knows the answer

is ice.

Scientists have

noticed a similar phenomenon

4,000 miles away in

the Swiss Alps. As huge

glaciers grind their way

across the landscape, they

gouge out lumps of rock and

carry them along in the base

of the ice. These rocks act

like sandpaper and carve out

deep scratches. When the ice

melts, it leaves the boulders

behind. Merguerian is

convinced the same thing

happened in Central Park.

Ice moved the Palisade

boulders and carved out

grooves in the bedrock

underneath.

>> This bedrock exposure in

Central Park shows the

profound effects of glaciation

in the form of these

spectacular glacial grooves

that move up the outcrop and

show this pattern where

glaciers grabbed huge boulders

and those huge boulders acted

like tools to produce these

scratches.

>> To Merguerian, the rocks in

Central Park are compelling

evidence that New York once

was covered in ice.

Over millions of years,

growing and receding ice has

repeatedly turned North

America into a frozen

wilderness.

But the grooves on the rocks

in New York don't tell the

full story. The destruction

caused by the ice points to a

gigantic glacial event that

would dwarf the future

metropolis.

To find out the

extent of the ice, Merguerian

traveled to Bear Mountain,

some 50 miles north of New

York City.

Once again, the

clue was in the rocks. He

found glacial marks similar

to those in Central Park.

>> What we're looking at here

are chatter marks. Chatter

marks are very diagnostic

features of glacial erosion,

they're produced by boulders

embedded in the base of a

thick sheet of glacial ice.

Those boulders impinged on

this bedrock surface,

polishing it, smoothing it off

and then plucking pieces of

rock off as the glacial ice

moved over with the boulders

embedded in the base.

>> T gouges in the rocks

could mean just one thing.

The glacier must have been

thousands of feet thick.

>> In this case, although

we're standing at an elevation

of about 1280 feet above sea

level, the glacial ice sheet

covered Bear Mountain as if it

weren't even there.

>> Scientists have found

identical chatter marks on

nearby peaks up to a mile

above sea level. It was

unmistakable proof.

A glacier at least one mile

thick ground its way across

these mountains.

Did this same ice sheet also

plow through Central Park?

Another nearby rock face

provided the answer.

>> The feature that we're

looking at here are a series

of sub-parallel glacial

scratches and grooves and

these are, again, are

produced by the glacial ice

sheet dragging boulders across

this very durable granite

surface, it's kind of polished

the surface. And, in addition,

it's produced these rather

subtle but--but--but obvious,

when the lighting is right,

striae or grooves in the

bedrock. Now if we measure the

orientation of these,

these--these come out about

north 20 degrees west, just

about identical in orientation

to the striae that we measured

at Central Park.

>> It's significant evidence

that the ice sheet that

covered Bear Mountain also

flowed over the surface of

Central Park. Proof that New

York City was covered by a

glacier four times higher than

the Empire State Building.

>> MERGUERIAN: Just imagine

glacial ice, a huge thick ice

sheet over a mile thick,

exerting tremendous pressure

on the surface and sculpting

the surface into the landscape

that we see today.

>> The ice sheet's crushing

weight bulldozed everything in

its path and cut through the

remains of the ancient

mountains. Before the ice

arrived, the waters of the

Hudson River had gently cut

down through the landscape to

form a V-shaped valley. But a

mile-thick glacier takes no

prisoners. It gouged out the

sides and the bottom of the

river valley and turned it

into a U-shaped riverbed.

The Hudson River was now

navigable for big ships.

The picture of modern-day New

York was almost complete.

Long grooves in the rocks in

Central Park showed scientists

that a vast ice sheet flowed

over the eroded remains of

these mountains. And marks and

glacial striations on Bear

Mountain proved this ice sheet

was at least four times higher

than the Empire State Building.

When the ice melted,

it left a vast ridge of debris

blocking the Hudson River from

the Atlantic. The final

challenge for geologists was

to find out how the ridge was

destroyed and how New York's

harbor opened to the oceans.

[]New York today boasts one of

the largest natural harbors in

the world. But it wasn't

always that way. Towards the

end of the last Ice Age, the

port's wide entrance was

blocked. 16,000 years ago, the

melting glaciers left behind a

220-foot-high wall of debris.

The ridge stretched from Long

Island to Staten Island and

forced the Hudson River

through a narrow, more

westerly course to the ocean.

What powerful forces destroyed

this rock jam? The prime

suspect was a flash flood.

But scientists needed evidence

to prove that such a flood had

happened. In the 1960s,

fishermen made an unexpected

find at the mouth of the

Hudson River. They dredged up

a giant mammoth tusk from the

depths of the sea floor.

[TRUMPETS]

Herds of these giant beasts

roamed the plains of North

America before they became

extinct at the end of the

last Ice Age.

Finding the odd

mammoth tusk here and there's

not so surprising. But since

the initial discovery,

scientists have found hundreds

more tusks and bones in the

mouth of the Hudson River.

It was as though a violent

torrent swept the mammoths

away and dumped their remains

off the coast. And there were

more clues nearby.

Huge boulders resting on the

sandy sea floor, some of them

as big as cars. The boulders

must have been part of the

ancient moraine that once ran

between Long Island and Staten

Island. Geologist David Franzi

knows that only a raging

torrent could have shifted them.

>> Based on the size of the

boulders that we see here, we

know that that flood must have

discharged on the order of 1.5

million cubic feet per second.

That's three times larger than

the largest Mississippi River

flood ever recorded.

>> And all that water had to

come from somewhere.

Scientists began looking for

the source of this flood, a

flood powerful enough to

transport huge boulders all

the way to the sea.

>> Rocks to a geologist are

like pages in a history book.

For us, erosion oftentimes

rips some of the pages out of

our history book, so it's the

job of the geologist to put

together a fragmentary record

into a coherent history of the

events that happened in the

past.

>> 300 miles north of the

city, in upstate New York,

Franzi tracked what might have

been the flood's path to an

unusual grove of trees on

Covey Hill in the Adirondack

Mountains.

The trees are jack pines.

They are rare in this area,

where the soil is usually

fertile and deep. But on Covey

Hill, their presence shows

that there is no more than a

few inches of soil on top of

the bedrock.

>> The jack pine is

essentially rooted right

out on the top of a rock's

surface here. This is a bare

sandstone surface, very little

mineral soil, and it's subject

to prolonged periods of

dryness during the summertime.

Jack pine's adaptations make

it able to survive here where

no other tree species can.

>> What happened to the soil?

The jack pines continue to

grow at the entrance of a long

gorge over 300 feet wide.

Usually, gorges like this are

cut down over thousands of

years, but in this case, the

missing topsoil points to a

sudden flood event. A raging

torrent must have ripped away

the soil and cut deep into the

rock.

>> In a helicopter, Franzi

follows the gorge west.

Eventually, it opens into a

vast, empty basin located

next to one of the Great

Lakes, Lake Ontario.

>> It doesn't take much of a

stretch of the imagination

here to imagine this valley

filled with water and then

with these hills poking up

through as islands.

>> 16,000 years ago, this

basin was filled with two

billion cubic miles of water -

a huge lake geologists call

Lake Iroquois. It formed at

the end of the last Ice Age.

As glaciers receded, the melt

waters slowly filled up the

lake. The ice dams holding the

waters weakened. Eventually,

the dams collapsed, causing

sudden and devastating

flash floods.

>> Lake level dropped on the

order of 70 feet and about 160

cubic miles of water were

released into the Champlain

Valley, catastrophically.

That floodwater would have

coursed down the Champlain

Valley, through the Hudson

Valley and ultimately out into

the Atlantic Ocean.

>> The torrent raced towards

New York City, 300 miles to

the south, then took the

straightest course to the sea.

The floodwaters smashed into

the ancient moraine, the huge

pile of debris blocking the

direct exit of the Hudson

River.

>> The bridge we see behind me

spans the channel that was cut

by the flood event. When the

flood wave came through, it

was of sufficient intensity to

over-top the dam and very

rapidly cut the channel.

>> The gap that was created by

the flood still exists. It's

now a tidal strait called

the Narrows. Today, the gap is

spanned by the Verrazano

Bridge. The channel is deep

enough for even the biggest

ocean-going ships. It's the

most important entrance to New

York City's harbor.

Mammoth tusks and huge

boulders at the mouth of the

river showed scientists that

there was a torrent big enough

to blast a hole through the

ancient moraine. And a channel

leading towards the Great

Lakes revealed the source of

the flood. It was this flood

that created the Narrows and

gave New York a wide entrance

to its port. A unique geology

laid down the foundations for

New York City.

But the same forces that

constructed it may

also have sown the seeds for

New York's destruction.

[]Scientists have pieced

together the half-billion-year

history of New York City.

Huge mountains, volcanic

eruptions and glacial ice

shaped the area. But New

York's story doesn't end here.

The geology that created one

of the greatest cities on

earth also has the potential

to destroy it.

Experts have been studying the

potential threat to the city.

>> We're standing here in

Lower Manhattan on one of our

major thoroughfares, Canal

Street. And it's important,

because in 1821, a Category 2

hurricane raised the water

level at the Battery 13 feet

in one hour and, literally,

the Hudson River met the East

River and Canal Street was

covered by water and Manhattan

was actually two islands for

three hours, until the water

receded.

>> New York City is vulnerable

because of its position on the

coast.

Long Island stretches

northeast at a right angle

from the New Jersey shore.

New York City is nestled

behind the western end of Long

Island. Normally, the island

protects the city from the

sea, but when hurricanes

threaten, the opposite is

true. Long Island becomes a

dangerous liability.

Hurricanes racing north along

the beaches of the Atlantic

coast pile up huge bulges

of water in front of them.

They're called storm surges.

Hitting the right-angled

junction at Long Island,

the winds funnel the storm

surge in through the Narrows,

the gap between Long Island

and New Jersey.

>> This is the place, at the

actual apex of the right angle

in New York where all the

water being pushed by a

hurricane would be

concentrated. And in the

distance is the Verrazano

Bridge, and all that water

is gonna go through the

passage we call the Narrows

and it's gonna be accelerated

towards New York City, where

it will rise to abnormal

heights.

>> Experts believe that in the

United States, New York is

the third most vulnerable city

after Miami and New Orleans

to a hurricane disaster. If it

was hit today, the

consequences would be serious.

>> New York City is hit by

hurricanes only infrequently.

Like, in 1821 and in 1893 and

in 1938. However, the point is

that the hurricane that will

eventually hit New York City

again will be catastrophic,

and what is going to happen

when the utilities are knocked

out? What is going to happen

when salt water reaches into

the subways and ruins the

electrical system? We're

talking about unbelievable

amounts of money to restore

the infrastructure. We're

talking about setbacks and

delays in commerce and

banking and transportation,

a catastrophe that's never

been seen.

>> Storm surges are not the

only threat to New York's

future.

Earthquakes are also part of

the vast geological forces

that shape this area.

They are still at work today.

Some could change the city

in an instant.

November 4th 1884. New York

City was shaken by an

earthquake that lasted ten

seconds. The Brooklyn Bridge

swayed and people panicked.

The earthquake showed 5.5

on the Richter scale.

January 17th 2001, New York

City was struck again.

This time the quake was

relatively small, only 2.4,

but it struck right under

125th Street.

>> The earthquake in 2001 is

the first earthquake that we

could confidently locate in

Manhattan, that's its claim to

fame, it was felt widely.

>> It's impossible to study

the cause of the quakes at the

surface.

The evidence is

buried beneath the city.

Deep within New York's

bedrock, seismologist Leonardo

Seeber studies the cause of

these quakes.

[HORN BLARES]

In a subway tunnel 100 feet

beneath the bedrock under the

East River, there is a

ready-made laboratory. Here,

Seeber can study the rocks up

close and personal.

It is the same bedrock

Manhattan is built on.

But Seeber fears it isn't as

solid as once was thought.

>> New York area is considered

a seismic zone, meaning there

is a cluster of known

earthquakes that have occurred

in this area. So we are, as

geologists, very eager to

discover which faults

are responsible for these

earthquakes.

>> The majority of earthquakes

occur at the boundaries

between separate sections of

the earth's crust, the

tectonic plates on which the

continents sit. But New York's

earthquakes are different.

The city is firmly in the

middle of a tectonic plate,

halfway between the

mid-Atlantic ridge to the east

and the San Andreas Fault to

the west.

Seeber is anxious to

discover what's going on.

As he examines the walls of

the tunnel, he comes across a

possible clue. The long

fractures in the rock are

fault lines that formed when

pressure built up. As the

tension was released, the rock

cracked and shifted. This is

felt on the surface as an

earthquake.

>> SEEBER: This is an example

of a very small fault, but

it's a fault that probably did

generate some small

earthquakes. When one of these

faults generates an

earthquake, we think that

perhaps other faults of the

same family can generate

earthquakes.

>> These faults in New York's

bedrock are evidence that the

area was hit by earthquakes in

the past. But Seeber has no

way of knowing if the faults

are still active and

dangerous.

If a large earthquake hit New

York today, the consequences

would be catastrophic.

>> A large proportion of New

York City buildings are simply

not built to withstand

earthquake shaking.

We worry about transportation

tunnels, in particular,

tunnels that traverse rivers

where parts of the tunnels are

rooted in solid rock and other

parts are resting on soft

sediment. The oscillation

of these two different

materials could cause severe

cracking and fracturing.

The infrastructure

would be severely damaged, it

would take tens of years to

repair the damage caused by

such a large event.

>> With the evidence

geologists have collected, the

story of the creation of New

York City can now be told.

The city's bedrock was formed

under a chain of mountains

over a mile high. Volcanoes

and lava fields over millions

of square miles split up the

ancient supercontinent and

created the east coast of

North America. Glacial ice,

four times as high as the

Empire State building, carved

out the deep Hudson River.

A catastrophic flash flood

broke through the moraine to

form the Narrows and opened up

New York City's harbor to the

oceans.

Looking ahead to the

distant future, geologists see

more challenging times for the

city. In 40,000 years,

they predict this region will

be engulfed by another ice

sheet. And in 250 million

years, the Atlantic will start

to shrink again. Europe and

Africa will eventually crash

back into the American coast.

The fossilized remains of the

once great city of New York

will become just another layer

of rock in a vast new mountain

range. A footnote in the

immense, ever-changing story

of planet earth.

== sync, corrected by elderman == @elder_man