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


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)

55 thoughts on “What rivers can tell us about the earth’s history | Liz Hajek

  1. The Kosi river has a sad history of frequent floods and disrupting lives of thousands.

  2. Hey I have a question, I wonder if anyone could help and refernce me to some material on the subjec.

    At around 8:30 minutes in she speaks about a time when the earth's poles had palm trees. And that's everything anyone ever mentions about this period – The tropical poles. My question is how did the rest of the earth look at that time? Was the equator and everything north and south of it for thosands of kms a huge desert? Did anything manage to live there? What were the conditions there? Etc…

    Thanks ahead to anyone that could help I've been thinking about this for a long time now and it would really help me progress with some project I'm working on ☺

  3. As far as I can remember , kosi river flooding and changing of directions was due to break in some kind of dam in Nepal due to heavy rains ! Had there been no dam , it wouldnt have changed direction ! You ought to put man made things into your observations too

  4. This is all common sense. Nothing on this earth is Static. If you didn't know any of this before this video then you didn't pay attention in school.

  5. This was nicely done, though it only scratches the surface. For example some rivers have built their beds above surrounding ground level. When rivers meander and cut a new path, they can leave the loop behind, entrapped in what some call an Oxbow lake. Most people know the Nile floods to fertilize the surrounding land. But how many know that a major source of forest food is salmon who die, decompose and get distributed by flooding. You might thank salmon for your house!

  6. This subject is hugely important for those of us who live along rivers, in the shadow of levees. The Mississippi is a beast that almost changed course by hundreds of miles as recently as 1973 & 2011.

  7. I just love how Liz didn't infuse politics into her science. Fascinating talk, Liz!

  8. No feminism ==> interesting Ted Talk…

    How odd! I would have never imagined that! xDD

  9. Been awhile since I saw a good TED talk. ? Love that time lapse of the ?. ?

  10. I liked this talk was pure science but the talk itself was pretty badly constructed.
    Liz makes points like: "It's important we know how these landscapes will change." But nowhere in the video she actually explains why.

    I feel this talk had little structure where there is no real direction.

  11. We don't know,,, is the real honest answer.

    But a good story will make a believe that its just like another honest lie.

  12. stupid archologist it's not changing it patern it's just dry winter or wet winter

  13. now the captilist will follow the trail of the river go back to Africa God help those poor guys

  14. I am from Bangladesh and I can relate to the video. Thanks TED for arranging the talk and special thanks to Liz Hajek for the detailed information. (y)

  15. PSU, nice! I highly regret not going to any of the Ted Talks they hosted, while I was a student. Definitely makes sense that they have this subject material at Penn State, as it's earth sciences/geology department is one of the greatest in the world. I actually took my W course (writing intensive) for experimental designs/methods in the primary earth sciences building there, it was a psychology course, however, strangely enough held in the main Geology floor of that building.. annuyywayyy, great video!

  16. When she said she´s a geologist, have you also thought about that episode with Sheldon Cooper and the Geology?

  17. The only disappointing part of this was how short it was. Super interesting topic about our home!

  18. very good information. Just one question.. Did we had more rivers earlier than what we have today ? Just wanted to understand if we are moving towards draughts

  19. everyone is talking about politics and feminism well i just like seeing someone so passionate about rocks stand up there and nervously talk about their passion for rocks

  20. wait did she say an abrupt warming that happened 55 milions years ago that there were crocodiles in Canada…could it be the same thing happening now…?

  21. Yeah, I'm not going to buy this land, because in 4000 years it will be flooded and will lose some value…4:40

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