>> Earth, a unique planet,
restless and dynamic.
Continents shift and clash,
volcanoes erupt,
glaciers grow and recede--
titanic forces that are
constantly at work,
leaving a trail
of geological mysteries behind.
And there is nowhere more
mysterious than Death Valley,
the hottest and driest desert
in the United States.
This is a place where even
700-pound rocks appear to move
by themselves.
It's the lowest point
in the U.S., and right here,
the earth's crust is thinner
than almost anywhere else
on the planet.
Death Valley is a dynamic
laboratory for investigators
who uniquely read rocks
like x-rays to reveal
the inner workings of the Earth
and its history...
adding to the continuing story
S02x09 Death Valley Original Air Date on January 26, 2010
-- Sync, corrected by elderman -- -- for addic7ed.com ---
Death Valley is the largest
National Park in the lower 48
states, more than 3 times
the size of Rhode Island,
straddling the border
of California and Nevada
and surrounded by towering
mountain peaks.
140 miles long
and up to 15 miles wide,
with temperatures reaching
a scorching 134 degrees
fahrenheit, this is one
of the most inhospitable places
on Earth.
[rattlesnake hissing]
But for geologists, Death Valley
has a unique attraction.
Here they can witness
the interplay of the Earth's
most titanic geological forces.
>> When you look at Death
Valley, really you're looking
at a battle, a battle between
processes that are occurring
on the earth's surface,
and we can see the record
of those forces of nature
locked into the rocks.
Death Valley has an archive
that is almost unrivaled
worldwide.
>> To uncover Death Valley's
earliest history, Prave is
hunting for its oldest rocks.
He is searching in one
of its most remote spots,
in the extreme south
of the valley in the isolated
Alexander hills.
>> This is one of the oldest
rocks in Death Valley.
It's 1.2 billion years old.
And given the color of this rock
and the fact that it's
quite soft--it can powder
when I scratch it--
These are all clues that tell me
that this is a limestone.
>> The limestone is a major clue
to revealing the way
this arid desert used to look.
>> If we think about the type
of environments that limestones
can be deposited in,
the first that comes to mind
is an underwater
and a marine setting.
>> There is only one way
to form limestone.
It is made from the tiny bones
and shells of sea creatures.
They die and sink to the sea
floor, where the weight
of further layers on top of them
crushes them slowly
into solid rock.
And Prave has discovered
other startling evidence
that Death Valley had
a watery past.
>> Fossils are a major clue.
They are vital in the type
of evidence that a geologist
will use. And these are
some very nice examples
of the type of fossils
that you can find
in these ancient rocks.
And you can see here
these curving surfaces
outlining what look to be
large cabbages that are
sliced in half.
These were algae
known as a stromatolite.
>> Ironically, these marine
fossils have survived
in the Death Valley desert
only because there is
so little water that might
otherwise have washed them away.
But they would have originally
looked like this
when they flourished
in the Death Valley waters
as the limestone formed
more than one billion years ago.
>> These tell us that
the environment when this rock
formed would have been
a shallow sea.
If I'd been here when these
rocks were first being formed,
I'd be sitting in my swimming
trunks about waist-deep
in water, very much
like the Bahamas today.
>> The stromatolites are
some of the earliest signs
of life on our planet.
To discover what happened
over the next one billion years,
Prave studies evidence
in the surrounding hills.
>> The different bands of colors
and the rock layers in the hills
represent ancient seas that
covered the Death Valley area.
The seas would deposit
a layer of limestone,
move back across the land.
Another layer of limestone
would be deposited.
And so we have a history
of the seas moving across
the Death Valley region from
the time of the stromatolites
to these rock layers now,
more than a billion years later.
>> Geologists wanted to
figure out what dramatic
geological upheaval could
have turned Death Valley
from a shallow sea to the
baking-hot desert of today.
And Prave has found clues
in a rock that is entirely
different from the marine
limestones he has studied
up until now.
>> This is a nice example
of a rock type called a granite.
And it forms those veins that
are in the hillside behind me.
You can think of these
like the fingers of my hand.
They're fed upward from
a much more larger, massive area
of granite sitting underneath.
>> The granite tells scientists
the reasons why Death Valley's
ancient seas vanished.
Today, it is solid rock.
But it was once hot molten magma
from deep underground.
Only one force of nature
has the awesome power
and 2,000-degree fahrenheit heat
to melt rock into magma
and fire it to the surface...
Volcanoes.
The seas here didn't
just drain away.
They were pushed back
by these mountains of fire.
It was only in the 1960s,
with the realization
that earth's continents
were drifting around the planet,
that scientists figured out
why the volcanoes erupted
under Death Valley.
The theory of plate tectonics
revealed that around
100 million years ago,
an ancient oceanic plate began
sinking under North America,
pushing up the land.
Heat from the collision powered
a coastal chain of volcanoes,
erupting on the land and finally
driving away the seas
submerging Death Valley.
>> This landscape would have
been very explosive, a hostile
type of setting.
And that then set the stage
for what was to become
Death Valley.
>> Still surviving in the valley
to this day is the ghost-town
evidence of another substance
far rarer than granite
that the volcanoes
grought to the surface...
gold.
Although gold occurs naturally
in more than 30 different
U.S. States, the gold
in Death Valley was concentrated
in veins in the rock, as magma
solidified near the surface.
It made it worth mining,
and millions of years
after its formation, it sparked
the Death Valley gold rush.
>> This is a wonderful example
of a gold mine shaft.
It's the Eureka mine, high up
in the Panamint Mountains,
associated with trying to find
gold in the granites that were
intruded into these rocks
100 to 200 million years ago.
The gold would have been
in veins, these fingers
that would have been injected
up into these rocks.
And the gold would have been
concentrated in these veins.
>> The gold rush here lasted
just a few years.
Miners often had to remove
a ton of rock to recover
only 1/10th of an ounce of gold,
enough to produce just a single
wedding ring.
Today, all that remains are
empty tunnels and ghost towns.
>> It's interesting to consider
that the frenzy of activity,
mining gold, was actually
a direct result of the kind
of volcanic activity
100 to 200 million years ago.
>> Geologists investigating
the battle that raged
in Death Valley between fiery
volcanoes and ancient seas
have found important evidence.
Stromatolite fossils are proof
that Death Valley was once
submerged by the waters
of a shallow sea.
Veins of granite could only
have formed in the fiery heat
of the volcanoes that burst
to the surface around
100 million years ago
and drove that sea away.
The volcanoes built up the land
that was to become Death Valley
into peaks as high
as the Cascades Mountain range.
But deep beneath the Earth's
surface, awesome geological
forces were about to destroy
those peaks, stretch the land
apart, and transform
the mountains of Death Valley
into the lowest point
in the U.S.
>> For a billion years,
Death Valley remained
a flat plain under the sea.
Around 100 million years ago,
erupting volcanoes formed
high mountain ranges.
But then the real geological
mystery began. The land here
must have undergone
an extraordinary transformation
because today in Death Valley,
those high mountain ranges
have vanished. Incredibly,
the one-time mountains
have sunk below sea level
to become the lowest point
in North America.
Yet all around the valley,
snow-capped peaks still soar
up to 11,000 feet into the air.
The investigation digs deep
under the landscape to discover
what vast geological forces
could have caused
that huge difference in height
between two places just
20 miles away from each other.
>> There are a lot of
mysterious aspects
about Death Valley.
It's a unique landscape,
because the valley floor itself
is very deep.
It's below sea level.
And the mountains rise up
very steeply on either side.
>> Clues to the power
of these underground forces
lie all over the valley...
If you know where to look.
many of the rock layers
were originally deposited
on the ancient flat sea bed.
they can still be seen
as horizontal layers.
But other nearby layers
aren't horizontal at all.
They tilt downwards
into the ground.
Miller finds a further clue
of earth's power in the unusual
shape of this cinder cone,
a mound of ash and debris
lying on Death Valley's floor.
>> It looks like it's
two cinder cones, but in fact
it's really just one
that's been pulled apart
along a big fault zone.
This has moved some 700 feet
in some 700,000 years.
So that's about a foot
per thousand years,
which sounds like it's
really, really slow, but if you
look at it over a great length
of geologic time, you get
quite a lot of slip.
And give it even longer time,
it will be offset even more.
>> Miller's next challenge
is explaining what is making
the fault line move.
For that, she studies
other ancient rock formations
whose jagged outline has given
them the name turtlebacks.
>> The turtlebacks are crucial
to understanding Death Valley's
early origins. They have so much
of the record here, if you're
willing to spend time
to try to unravel it.
>> The real clue lies in
the rocks' distinctive texture.
>> If you just take a look
at this rock closely,
you can see that it's
very kind of strung out,
very stringy. It tends to be
pretty fine grained.
>> This texture tells Miller
where these rocks came from.
>> We see evidence that these
rocks were deformed,
just like if you'd take
a piece of plastic
and were to heat it up,
you could bend it.
It's the same thing with rock.
And so these rocks formed at
high temperatures and pressures
within the earth's crust
at depths of about 10 miles
or so, and they have since been
brought to the earth's surface.
>> Miller concluded that some
overwhelming underground force
must have raised the turtleback
rocks to the surface
and stretched them out
like warm toffee
as Death Valley formed.
The final explanation
of what happened here
once again came back to the way
continents drift around
the globe.
As the collision of the plates
that had forced ancient
volcanoes to the surface
slowed down and ceased,
the high mountains that once
dominated the land were slowly
pulled apart and tilted
downwards.
Gradually, as the underlying
crust grew thinner and thinner,
a deep basin formed
between the mountain ranges.
Death Valley is the most extreme
example of what such stretching
forces can do.
By measuring seismic waves,
scientists discovered that here
the continental crust
is just 16 miles thick.
This might sound like a lot,
but it is far thinner
than almost anywhere else
on the planet.
Around the globe,
the earth's continental crust
averages 25 miles thick.
It's strongest beneath
the Himalayas.
At 43 miles, thick enough
to support the weight
of massive mountains
such as Everest.
The turtleback rocks
also offer Miller evidence
as to when Death Valley's
stretching started.
Dating these rocks reveals that
the deformation started here
around 13 million years ago,
although Death Valley did not
take on its final shape
immediately.
>> Death Valley's really young
when you look at the whole
geologic time scale.
Modern Death Valley is probably
3 or 4 million years old
at the most. The stretching
started before that.
But Death Valley itself
is a very recent feature.
>> Scientists know that the
process is far from finished.
They've found irrefutable
evidence in the alien
Death Valley landscape
known as Badwater Basin.
>> I'm standing here
at Badwater, which is
the lowest point
in the western hemisphere.
It's 282 feet below sea level.
We're actually standing
below sea level about the depth
of a football field.
This floor has been sinking.
It's about a tenth of an inch
per year, which is about
half of the speed at which
your fingernail grows.
>> Continual stretching
of the earth's crust
has turned Badwater
into one of the lowest spots
on any continent on the planet.
Yet its true depth
is even lower still.
>> The surface that we see here
is the present-day surface.
But what one has to realize
is that beneath our feet,
we can go down through sediment
that represents ancient periods
of time, when Death Valley
was a surface that goes down
3 miles.
>> You would need to drill down
through the sediment
to a depth equivalent
to 11 Empire State buildings
end to end before you hit
the crustal bedrock.
The total volume of material
in this basin would bury
New York to the depth
of nearly a mile.
The valley floor is constantly
being covered with sediment
cascading from the surrounding
mountains, but it can never
fill up completely.
>> The sediment is coming in
at a rate that is less than
the rate of sinking
of Death Valley itself.
So that we're always maintaining
a surface here on the valley
that is sitting below sea level
and is continuing to sink
through time.
>> This constant movement
shows Earth's geological forces
at their most dynamic
and makes Death Valley unique.
>> The allure is that nowhere
on earth do we see continental
crusts being pulled apart
at this rate or this magnitude.
>> The investigation into
Death Valley's creation
has established how it sank
to become the lowest point
in North America.
The turtleback rocks were
deformed by the powerful
tectonic forces pulling
the mountains apart
to form a wide valley floor.
The still-sinking landscape
of Badwater, currently 282 feet
below sea level, is proof
that the crust here
is still being stretched today.
But the sinking of Death Valley
is just one part of the story.
Geologists still need
to investigate how one
of the hottest places on earth
was shaped by the power
of moving ice.
>> 1.2 billion years ago,
Death Valley was submerged
by ancient seas.
Around a billion years later,
volcanic mountains drove
the seas away.
13 million years ago,
the continental crust
started stretching apart here.
And by 3 million years ago,
Death Valley was one of the
lowest points on earth.
The clue that showed
investigators what happened next
was the discovery in the valley
of a little-known
but highly valued
white crystalline rock.
>> When one thinks
of prospectors
in the Death Valley region,
one often thinks of them
hunting for gold and for silver.
But there was one mineral
that was much less glamorous,
much less sexy and exciting,
and that was borax,
but it was actually known
as the white gold of the desert.
>> In 1880, borax was a rare
but in-demand mineral used
in antiseptics and detergents.
One impoverished couple
desperately trying to make
a living in Death Valley
was Aaron and Rosie Winters.
They heard from a passing
prospector that they could make
good money from borax
if they could find it.
They learned from their fellow
prospector the then-secret
method of testing rock
for borax.
Anxious to keep potential
profits for themselves,
the couple waited until
the dead of night to perform
the test in Death Valley.
>> You burn the mineral
to see if the powder
that we have in front of us here
contains any borax.
Now, what the Winters did
is to add sulfuric acid
to borax-bearing mineral.
We'll add some alcohol.
The Winters probably used
cheap whiskey back in 1880.
And the flame should burn
hopefully a green color
if borax is there.
And as we can see,
the flame is green in color.
And in 1880, the Winters knew
that they would become wealthy
because they had borax.
>> From these humble beginnings,
a whole industry grew
in Death Valley.
It made the Winters' fortune
and also gave scientists
a priceless clue in their quest
to understand the geological
history of Death Valley,
Because borax deposits
like these can only be found
in the beds of ancient
freshwater lakes.
The sea water that once covered
this valley had long gone
a billion or more years earlier.
But the presence of borax proves
that freshwater must have
flooded into the area
when ice-age glaciers started
to melt from the surrounding
mountains around 200,000
years ago.
As the glaciers melted,
rivers flowed towards
the lowest point--Death Valley.
Gradually a vast lake spread out
across the flooded valley floor.
The valley's catchment area
was huge. Its rivers drained
more than 9,000 square miles,
an area bigger than
New Hampshire.
The water pouring in
from the surrounding mountains
leached minerals such as borax
from the rocks and deposited
them on the lake bed.
>> In a lot of the lake beds,
this mineral, borax, would
appear as kind of a white
fuzzy mineral. It was actually
called cotton ball.
>> the borax proved
that a lake existed here.
Geologists called it
Lake Manley, after one
of the pioneers,
William L. Manley, who had
named Death Valley in 1849.
But they had no evidence
to tell them its depth
and its size.
A solution to this puzzle
is revealed in this small hill
with a road cut straight
through it near the valley's
edge at a spot called
Beatty Junction.
>> It's very fortunate to have
a road cut right through
this gravel deposit.
So, in the exposure, we can see
very well rounded pebbles.
We can also see some crude
layering in the gravels.
And they're stacked in
against each other.
And we call that shingling.
>> The shape and the smoothness
of the stones tells Caskey
exactly how these pebbles
got here.
>> Yhe way they're stacked
tells us that the direction
of water flow that laid
these pebbles down like this
was from the right to the left.
So we know that this had to be
wave action. That's strong
evidence that this is
a beach environment.
>> By looking at the height
of this pebble beach
above the valley floor,
Caskey calculates the dimensions
of the lake.
>> From this beach gravel bar
that we're standing on,
the waves would have been
crashing at our feet,
and as we look south,
it's hard to imagine
a lake sitting out there
across that vast salt pan.
But Lake Manley would have
covered about 600 square miles
and it would have been about
450 feet deep.
It's odd mapping shorelines
on a really hot day
in Death Valley.
You kind of long for
the ancient days of yore,
when there were big lakes
out here. You can imagine
this was a beautiful place
full of lush vegetation.
You know, it was quite
a different place
than it is today.
>> For Caskey, the next step
is discovering why Death Valley
no longer has a lake.
And there is evidence about that
in one of its most unusual
landscapes--this twisted,
jagged field of white peaks
that's called
The Devil's Golf Course.
Even the sounds here
are mysterious.
In the silence of the desert,
there is a faint popping noise
as the relentless sun
sucks every drop of moisture
out of the parched surface.
[popping sounds]
>> The salt that we see here is
the remains of an ancient lake.
It's called Devil's Golf Course
because it's probably
the least likely surface
that you would ever want
to play golf on.
>> The surface is made up
of rough salt crystals,
popping when they expand and
contract in the searing heat,
but this salt did not
come from the sea.
Just like the borax, the salt
was leached from the rocks
when freshwater started flowing
into Death Valley
200,000 years ago.
The salt was originally
dissolved in the freshwater
Lake Manley, and Caskey
has a simple experiment to show
exactly how it ended up
on the floor of Death Valley.
>> I'll pour the water and salt
solution into this pan,
and as the water evaporates,
we should see salt forming.
And that's exactly how this
salt crust forms.
So...
it's hot enough out here today.
It should evaporate
pretty quickly.
In a fairly short amount
of time, there are some
beautiful salt crystals formed
along the edges.
That's essentially how
a salt pan forms.
When the rainwater comes in,
the salt goes into solution,
basically just like the water
that we have in this water
bottle, and from the moment
the water starts evaporating,
salt crystals start forming.
>> Today, Death Valley's
salt pans cover more
than 200 square miles,
An area 3 times the size
of Washington, D.C.
They are the remnants
of the ancient lake
that finally disappeared
2,000 years ago, when Earth's
climate began to warm up.
From then onwards,
Death Valley's temperatures
just kept on rising.
>> Death Valley is definitely
one of the hottest spots
in the world.
The record high
was 134 degrees fahrenheit,
recorded back in July 10, 1913.
And just to give you
perspective on that,
the caretaker of the Furnace
Creek Ranch, who actually
was the one doing the recordings
back then, he describes that day
as being so hot, he saw
the swallows falling dead
in flight.
>> Geologists today understand
how Death Valley's unusual
geology is responsible
for the punishing climate
that killed off its lake.
It stays so dry because there
are 3 distinct mountain ranges
between Death Valley
and the moisture carried
off of the Pacific Ocean,
over 200 miles away.
>> We have the Sierra Nevadas
to the west of us.
The storms come in from the west
laden with moisture.
As they rise up, they lose
most of that moisture
on the west side,
and each set of mountains
wicks a little more moisture
out of the clouds.
And here, with our 3 sets
of mountains in between us
and the ocean, by the time that
moisture gets to Death Valley,
there's either all gone, or we
just get a few drops of rain.
>> Almost all storms
from the coast are stopped
by the 3 mountain ranges,
each one in turn having
an effect the scientists call
a rain shadow.
>> So we are in the rain shadow
of a rain shadow
of a rain shadow and average
less than two inches a year.
>> And there is another way
that geology influences
the desert climate.
Air heated under
the cloudless sky is trapped
by the surrounding mountains.
In summer, Death Valley becomes
a deadly, dangerous furnace.
The local weather station
provides a graphic demonstration
of how quickly that heat
could have destroyed
Death Valley's lake.
Every day, Callagan checks
the rate of evaporation.
>> The summer months,
it may take 5 of these
containers here. So I'm going to
fill them up and dump them into
the pond until it brings the
water level up to the needle.
Now, our average rainfall
is barely 2 inches a year,
but the evaporation pond records
up to 150 inches of evaporation.
>> That huge discrepancy
between the amount of rainfall
and the speed of evaporation
means that a lake 12 feet deep
and 30 miles long would
evaporate in just a single year.
Lake Manley was bigger
than that, but over time,
it never stood a chance.
The scientists' studies
of Death Valley have
solved the mysteries
of its freshwater past.
Borax, discovered here
in the 1880s, proves
that Death Valley was once
filled with a freshwater lake.
Pebbles unearthed on an ancient
shoreline show the lake once
covered 600 square miles,
an area 3 times the size
of Chicago.
When the last freshwater pools
dried up here 2,000 years ago,
Death Valley started its reign
as the driest place in the U.S.,
which makes it ironic that
the investigation's next phase,
examining the valley's most
recent geological upheavals,
involves scientists studying
the awesome power
of fast-flowing water.
>> Around 100 million years ago,
Death Valley's ancient seas
gave way to exploding volcanoes
whose peaks were then
wrenched apart to create
the lowest spot in America.
From around 200,000 years ago,
the valley filled
with a freshwater lake.
But the rain shadow
of surrounding mountains
dried up the water.
For the past 2,000 years,
Death Valley has been hotter
and drier than anywhere else
in North America...
which makes it all the more
mysterious to find
Mosaic Canyon, a deep chasm
seemingly cut by water,
in this parched and arid land,
especially when there is
evidence of massive boulders
having been pushed around
like pebbles.
>> Just look at the size
of that boulder and look at
how high above my feet it is.
It's about 3 feet in diameter,
and I can't even estimate what
the weight of that thing is.
>> She may be in a desert,
but Messina knows there is
only one force that could have
lifted the boulder up so high.
>> Water brought it here
and left it here.
The force of the water
that came through here
had to have been pretty severe
in order to get that boulder
up there plastered
against the wall.
This boulder gives us evidence
about the force of the water
that comes down these canyons
during flash floods.
>> A flash flood is one
of nature's most lethal weapons.
>> If there were a flash flood
coming down this canyon,
I wouldn't have enough time
to run out of its path
because the water flows down
at an incredible velocity.
Flash floods are among
the most violent processes
on the earth.
They can carry material
the size of an S.U.V.
without any problem at all.
>> In one of the driest places
in the world, the floodwater
comes from a surprising source--
rain.
On average, Death Valley
receives just two inches of rain
a year. This is less than half
the rain that falls on New York
in a single month.
But violent summer storms
mean it can all fall
in just a single day.
The floods transform
the desert landscape
in a number of ways.
One is known as the desert
bloom, where seeds and plants
that may have lain dormant
for up to 10 years burst into
flower after a sudden rainfall.
This phenomenon might be
beautiful, but there is
another, deadlier side
to these floods,
with a human cost.
>> In 2004, there was
a flash flood that came
down Furnace Creek.
It was just this muddy slurry
that was dense enough
to pick up a vehicle
and carry it downhill,
and several people died in it.
The 2004 flash flood is small
in compason to some of
the events that we see preserved
here in the rocks.
>> Flash floods happen
all over the world,
but there's evidence here
of their particular and rare
geological effect
in Death Valley.
>> This marble is
very highly polished.
It's not scratched.
It's not gouged.
It's been polished
by very fine grained material
that comes down as part
of a flash flood.
So it's really smooth,
and it's fluted.
It's really unique.
>> To uncover how these unusual
polished walls were formed,
Messina takes a closer look
at what geologists term
the badlands.
>> I think it's called bad
because nothing will grow on it.
There's just this very loose
material out here,
and it erodes so readily that
plants can't even take root.
So this is "bad land."
>> The rock that makes up
the badlands is the dried-up
remains of the 2,000-year-old
lake bed that once submerged
Death Valley.
>> This is nothing more
than desiccated mud.
It's called mudstone because
it's slightly lithified,
meaning it's turned into rock.
>> The mudstone's minerals
are arranged in tightly packed,
flat sheets.
>> The rain can't penetrate
the mudstone, and therefore,
the rain picks up a lot of the
particles and carries
them downhill.
>> These particles are the key
to the canyon's smooth,
polished walls.
>> It flows through here
so laden with sediment
that it causes a lot
of polishing and incision.
So every time a flash flood
comes through, this canyon
gets deeper, the walls
get higher, and the rock
gets more polished.
>> The sediment-laden floods
can carve into Death Valley's
rocks with tremendous
speed and force.
These canyons have been
gouged out where the rocks here
have been fractured
and weakened by the continuous
stretching the valley
is undergoing.
>> This is up-front,
in-your-face geology
happening right here.
Death Valley is dynamic.
This is a place where things are
happening in a human lifespan.
>> In this arid desert,
yhe investigation has identified
water as the latest factor
in Death Valley's continuing
geological evolution.
The giant boulders plastered
high on the canyon walls
illustrate the power
of flash flooding in the desert.
The smooth walls of mosaic
canyon show how the dried mud
from an ancient lake still
affects how Death Valley
is being shaped to this day.
And yet some mysteries
remain unsolved, including one
of the world's most intriguing
geological riddles--the rocks
that seem to walk by themselves,
moving thousands of feet across
the floor of Death Valley.
>> Over 1.2 billion years,
Death Valley has been
transformed from a watery
landscape to a barren desert.
But even though geologists
now understand the processes
that have shaped this
extraordinary region, there are
still mysteries to be solved.
And there is no part
of Death Valley more mysterious
than an area known
as the Racetrack.
This parched, cracked lake basin
just 2 1/2 miles long
and a mile wide
is the setting for one
of Death Valley's most
intriguing geological puzzles--
its sliding stones.
>> I love this place
because it's odd.
I could come here
a hundred more times,
and every time there will be
something different,
something I didn't see.
>> Stretching behind these rocks
are long grooved trails
in the earth.
It is clear that they are tracks
left behind as the rocks move
across the valley floor.
The puzzle is to work out
how the rocks can slide uphill
against this slightly tilted
surface.
These are no mere pebbles.
Some of these rocks
are over 700 pounds.
And some of the trails
are nearly 3,000 feet long.
The phenomenon was first
recorded here by scientists
some 100 years ago, and yet,
in this remote location,
no one has ever seen
the rocks moving.
Messina has been tracking
the movement of each
individual rock on the Racetrack
since 1996. Her gps readings
are accurate to within
a single inch.
>> Geology is really nothing
more than detective work.
And rather than looking
for evidence of things
that took place a long time ago,
what I really like about
working on the Racetrack
is you are looking at things
that are happening right now.
It's an ongoing process.
>> Her first clue is the surface
on which the rocks slide.
>> If I try to move my hand
over it, I could probably
file my nails right now.
However, after it rains,
there's so much clay
in the lake-bed sediments
that it gets slick.
It's almost like teflon.
You wouldn't need very much
force to set even a very large
rock into motion, just because
the friction on the surface
is almost nil.
>> But water alone isn't enough
to make these rocks move.
Messina has identified
a second factor at work.
>> You can have rain,
but if you don't have wind
a couple of days later,
I don't think these rocks
are going anywhere.
>> The Racetrack is
a natural wind tunnel.
The wind funnels into the valley
from the south.
Close to the ground,
the winds can exceed hurricane
strength, reaching speeds
of over 90 miles per hour,
enough to push the rocks
into action.
>> If you have wind
and there is no friction,
all you'd need to do
is hit a rock with your finger
like that, and it would go
into motion.
>> When all these elements
are in place, the rocks can
Begin their mysterious journey.
[thunder]
>> Since no one has ever seen
the rocks in motion, we can
only guess how fast they go.
But based on some of
the evidence that I've seen,
these rocks aren't
inching along, by any means.
And the best estimate we have
is about 3 to 4 miles an hour.
So a nice, brisk walk.
>> But until this phenomenon
is witnessed, the mystery
of Death Valley's sliding rocks
will remain.
>> I hope that this mystery
isn't solved. It's what
keeps me interested, and I think
it's what keeps a lot
of people interested.
>> Geologists studying
Death Valley have figured out
its extraordinary geological
evolution.
Stromatolite fossils show
that this area was once
covered by seas.
Turtleback rocks prove that
the land was stretched apart
by tectonic forces,
dropping the valley floor down
to the lowest point in America.
Pebbles at Beatty Junction
prove that Death Valley was once
covered with a freshwater lake.
And the smooth, polished walls
of Mosaic Canyon show that water
is still at the heart of
Death Valley's modern evolution.
Death Valley remains
one of the most extreme
geological wonders on earth,
and it's still evolving.
Its valley floor is being
constantly pushed apart
by forces deep within the earth.
This means that the crust here
will continue to stretch
and thin. One day,
tens of millions of years
into the future,
Death Valley could be
separated by the sea
from the rest of the U.S.
Today, Death Valley continues
to sink at a steady rate
of 1/10th of an inch a year,
while its surface continues
to be sculpted by water,
living proof that the Earth
is never at rest.