What rivers can tell us about the earth's history | Liz Hajek | TEDxPSU

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[ Applause ]

>> Alright.

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 and 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 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 is material gets shuffled

around earth's surface all the time,

and one of the big things 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.

If we zoom in a little bit, we can see that,

I'll give you guys an example here, right?

So if we zoom in a little bit,

I want to talk to you guys specifically about a river.

You can see these beautiful patterns that the rivers make

as they're pushing material down to the sea,

but these patterns are not static.

These rivers are wiggling and jumping around quite a bit,

and it can have big impacts on, 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 sediment 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, 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 is satellite image is colored so that vegetation

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,

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, this 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 an, 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 father 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 U.S. It pushes material

from the Rocky Mountains and from the Great Plains,

it drains and it 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 know the Mississippi 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, 1,000 years, 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 they're some of the most, 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 Andes 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, right?

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 changed.

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 cutoff.

It's almost like a whip cracking and snaps off the pathway

of the river at a certain spot.

So, just for reference, again, so in this location,

that river changed its course over 4 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 mountains

and transported to 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.

Alright, we don't have a lot of observations, we only hear,

only have 30, you know,

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, 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 look

like in the past.

We can do this to help reconstruct and understand how,

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 the first, just the first 600 million years

of earth's history, so, just a little bit of time here.

So as, 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 environment 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,

I'm going to 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,

and pretty extreme global warming event, and,

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 is 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 we reconstruct how the landscape changed in response

to this warming event.

So, here, yay, rocks! So [laughter], here,

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

of the yellow blob here is a, 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 flood plains.

So we can look in detail and we can reconstruct with some,

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 did so, they looked maybe similar

to what we, what I showed you in the Amazon River basin,

but right at the onset of this climate change event,

the rivers changed 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 that change,

or the reasons that rivers change their pattern and their,

and their movements, is because of things

like with extra water falling on the land's surface, when,

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.

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