-
All right, let's get up
our picture of the earth.
-
The earth is pretty awesome.
-
I'm a geologist, so I get
pretty psyched about this,
-
but the earth is great.
-
It's powerful, it's dynamic,
it's constantly changing.
-
It's a pretty exciting place to live.
-
But I want to share with you guys today
my perspective as a geologist
-
in how understanding earth's past
-
can help inform and guide
decisions that we make today
-
about how to sustainably live
on earth's surface.
-
So there's a lot of exciting things
that go on on the surface of the earth.
-
If we zoom in here a little bit,
-
I want to talk to you guys a little bit
about one of the things that happens.
-
Material get shuffled around
earth's surface all the time,
-
and one of the big thing that happens
is material from high mountains
-
gets eroded and transported
and deposited in the sea.
-
And this process is ongoing all the time,
-
and it has huge effects
on how the landscape works.
-
So this example here in south India --
-
we have some of the biggest
mountains in the world,
-
and you can see in this satellite photo
-
rivers transporting material
from those mountains out to the sea.
-
You can think of these rivers
like bulldozers.
-
They're basically taking these mountains
and pushing them down towards the sea.
-
We'll give you guys an example here.
-
So we zoom in a little bit.
-
I want to talk to you guys
specifically about a river.
-
We can see these beautiful patterns
that the rivers make
-
as they're pushing material
down to the sea,
-
but these patterns aren't static.
-
These rivers are wiggling
and jumping around quite a bit,
-
and it can have big impacts on our lives.
-
So an example of this
is this is the Kosi River.
-
So the Kosi River
has this nice c-shaped pathway,
-
and it exits the big mountains of Nepal
-
carrying with it a ton of material,
-
a lot of sediments that's being
eroded from the high mountains,
-
and it spreads out across India
-
and moves this material.
-
So we're going to zoom in to this area
-
and I'm going to tell you a little bit
about what happened with the Kosi.
-
It's an example of how dynamic
these systems can be.
-
So this is a satellite image
from August of 2008,
-
and this satellite image is colored
-
so that vegetations or plants
show up as green
-
and water shows up as blue.
-
So here again you can see
that c-shaped pathway
-
that this river takes as it exits Nepal.
-
And now this is monsoon season.
-
August is monsoon season
in this region of the world,
-
and anyone that lives near a river
is no stranger to flooding
-
and the hazards and inconveniences
at minimum that are associated with that.
-
But something interesting
happened in 2008,
-
and this river moved in a way
that's very different.
-
It flooded in a way that's very
different than it normally does.
-
So the Kosi River is flowing down here,
-
but sometimes as these rivers
are bulldozing sediment,
-
they kind of get clogged,
-
and these clogs can
actually cause the rivers
-
to shift their course dramatically.
-
So this satellite image
is from just two weeks later.
-
Here's the previous pathway,
-
that c-shaped pathway,
-
and you notice it's not blue anymore.
-
But now what we have is this blue pathway
-
that cuts down the middle
of the field of view here.
-
What happened is
the Kosi River jumped its banks,
-
and for reference,
the scale bar here is 40 miles.
-
This river moved
over 30 miles very abruptly.
-
So this river got clogged
and it jumped its banks.
-
Here's an image from about a week later,
-
and you can see
these are the previous pathways,
-
and you can see this process
of river-jumping continues
-
as this river moves farther away
from its major course.
-
So you can imagine
in landscapes like this,
-
where rivers move around frequently,
-
it's really important to understand when,
where and how they're going to jump.
-
But these kinds of processes
also happen a lot closer to home as well.
-
So in the United States,
-
we have the Mississippi River
that drains most of the continental US.
-
It pushes material
from the Rocky Mountains
-
and from the Great Plains.
-
It drains it and moves it
all the way across America
-
and dumps it out in the Gulf of Mexico.
-
So this is the course of the Mississippi
that we're familiar with today,
-
but it didn't always flow
in this direction.
-
If we use the geologic record,
-
we can reconstruct
where it went in the past.
-
So for example, this red area here
-
is where we know the Mississippi River
flowed and deposited material
-
about 4,600 years ago.
-
Then about 3,500 years ago it moved
-
to follow the course
outlined here in orange.
-
And it kept moving and it keeps moving.
-
So here's about 2,000 years ago,
-
a thousand years ago,
-
700 years ago.
-
And it was only
as recently as 500 years ago
-
that it occupied the pathway
that we're familiar with today.
-
So these processes are really important,
-
and especially here, this delta area,
-
where these river-jumping events
in the Mississippi
-
are building land at the interface
of the land and the sea.
-
This is really valuable real estate,
-
and deltas like this are some of the most
densely populated areas on our planet.
-
So understanding the dynamics
of these landscapes,
-
how they formed and how they will
continue to change in the future
-
is really important
for the people that live there.
-
So rivers also wiggle.
-
These are sort of bigger jumps
that we've been talking about.
-
I want to show you guys
some river wiggles here.
-
So we're going to fly down
to the Amazon River basin,
-
and here again we have a big river system
-
that is draining and moving and plowing
material from the Andean Mountains,
-
transporting it across South America
-
and dumping it out
into the Atlantic Ocean.
-
So if we zoom in here, you guys
can see these nice, curvy river pathways.
-
Again, they're really beautiful,
but again, they're not static.
-
These rivers wiggle around.
-
We can use satellite imagery
over the last 30 or so years
-
to actually monitor how these change.
-
So take a minute and just watch
any bend or curve in this river,
-
and you'll see it doesn't stay
in the same place for very long.
-
It changes and evolves
and warps its pattern.
-
If you look in this area in particular,
-
I want you guys to notice
there's a sort of a loop in the river
-
that gets completely cut off.
-
It's almost like a whip cracking
-
and snaps off the pathway
of the river at a certain spot.
-
So just for reference, again,
-
in this location, that river
changed its course over four miles
-
over the course of a season or two.
-
So the landscapes
that we live in on earth,
-
as this material
is being eroded from the mountains
-
and transported to the sea,
-
are wiggling around all the time.
-
They're changing all the time,
-
and we need to be able
to understand these processes
-
so we can manage and live
sustainably on these landscapes.
-
But it's hard to do
if the only information we have
-
is what's going on today
at earth's surface.
-
Right? We don't have
a lot of observations.
-
We only have 30 years' worth
of satellite photos, for example.
-
We need more observations
to understand these processes more.
-
And additionally, we need to know
-
how these landscapes are going
to respond to changing climate
-
and to changing land use
-
as we continue to occupy
and modify earth's surface.
-
So this is where the rocks come in.
-
So as rivers flow,
-
as they're bulldozing material
from the mountains to the sea,
-
sometimes bits of sand and clay
and rock get stuck in the ground.
-
And that stuff that gets stuck
in the ground gets buried,
-
and through time, we get
big, thick accumulations of sediments
-
that eventually turn into rocks.
-
What this means is that we can
go to places like this,
-
where we see big, thick stacks
of sedimentary rocks,
-
and go back in time
-
and see what the landscapes
looked like in the past.
-
We can do this to help reconstruct
-
and understand
how earth landscapes evolve.
-
This is pretty convenient, too,
-
because the earth has had
sort of an epic history. Right?
-
So this video here
is a reconstruction of paleogeography
-
for just the first
600 million years of earth's history.
-
So just a little bit of time here.
-
So as the plates move around,
-
we know climate has changed,
sea level has changed,
-
we have a lot of different
types of landscapes
-
and different types of environments
that we can go back --
-
if we have a time machine --
-
we can go back and look at,
-
and we do indeed have a time machine
-
because we can look at the rocks
that were deposited at these times.
-
So I'm going to give you
an example of this
-
and take you to a special
time in earth's past.
-
About 55 million years ago,
there was a really abrupt warming event,
-
and what happened was
a whole bunch of carbon dioxide
-
was released into earth's atmosphere,
-
and it caused a rapid
and pretty extreme global warming event.
-
And when I say warm, I mean pretty warm,
-
that there were things
like crocodiles and palm trees
-
as far north as Canada
and as far south as Patagonia.
-
So this was a pretty warm time
and it happened really abruptly.
-
So what we can do
-
is we can go back and find rocks
that were deposited at this time
-
and reconstruct how the landscape changed
in response to this warming event.
-
So here, yay, rocks.
-
(Laughter)
-
Here's a pile of rocks.
-
This yellow blob here,
-
this is actually a fossil river,
-
so just like this cartoon I showed,
-
these are deposits that were
laid down 55 million years ago.
-
As geologists, we can go
and look at these up close
-
and reconstruct the landscape.
-
So here's another example.
-
The yellow blob here is a fossil river.
-
Here's another one above it.
-
We can go and look in detail
and make measurements and observations,
-
and we can measure features.
-
For example, the features
I just highlighted there
-
tell us that this particular river
was probably about three feet deep.
-
You could wade
across this cute little stream
-
if you were walking around
55 million years ago.
-
The reddish stuff that's above
and below those channels,
-
those are ancient soil deposits.
-
So we can look at those to tell us
what lived and grew on the landscape
-
and to understand how these rivers
were interacting with their floodplains.
-
So we can look in detail
and reconstruct with some specificity
-
how these rivers flowed
and what the landscapes looked like.
-
So when we do this
for this particular place
-
at this time,
-
if we look what happened
before this abrupt warming event,
-
the rivers kind of carved their way
down from the mountains to the sea,
-
and they looked maybe similar to what
I showed you in the Amazon River basin.
-
But right at the onset
of this climate change event,
-
the rivers change dramatically.
-
All of a sudden they got much broader,
-
and they started to slide back and forth
across the landscape more readily.
-
Eventually, the rivers reverted
back to a state that was more similar
-
to what they would have looked like
before this climate event,
-
but it took a long, long time.
-
So we can go back in earth's time
and do these kinds of reconstructions
-
and understand how
earth's landscape has changed
-
in response to a climate event like this
or a land use event.
-
So some of the ways that rivers change
-
or the reasons that rivers change
their pattern and their movements
-
is because of things like with extra water
falling on the land's surface
-
when climate is hotter,
-
we can move more sediment
and erode more sediment,
-
and that changes how rivers behave.
-
So ultimately,
-
as long as earth's surface is our home,
-
we need to carefully manage
the resources and risks
-
associated with living
in dynamic environments.
-
And I think the only way
we can really do that sustainably
-
is if we include information
-
about how landscapes evolved
and behaved in earth's past.
-
Thank you.
-
(Applause)