This is John G B with all of us crumple.
This episode is the second of two of my conversation with
Martin giggling. In the first episode, we
discussed fluvial deposits in the geological record and we
trace the effect that the breakup of Pangaea around, 200
million years ago had on river systems In this episode, we
address the history of rivers of Europe and the Americas as well
as the impact of recent ice ages.
On today's Rivers, we end by considering how humans have
changed with us and their deposits throughout the history
of mankind. Martin gambling has spent a
lifetime studying rivers and river sediments around the
world. He's Emeritus professor in the
department of Earth and environmental Sciences at
Dalhousie University in Halifax, Nova Scotia in Canada.
What about the rivers of Europe? You've already touched on a few.
What is their history? The European story is dominated
by the Collision of Africa, along with micro continents
against southern Europe. And of course, this generates
the Alps in particular 30 million years ago, the
carpathians is a great bulge of the Alpine system.
Something like 15 million years ago and complications with the
Pyrenees as well in Iberia. The Alps in particular has
really dominated the scene. The would have been Rivers
flowing down across northern Europe into tethers, but once
the Alps began to rise, those were all effectively destroyed
or turned into tributaries of other systems.
So Europe, at least Western Europe is largely a story of
Three Rivers, the Rhone the Rhine and the Danube, the Rhone
may have been the original major river running around the
Western. Side of the Alps, which would
initially have just been an island in the toughest for
gradually became a dominating mountain chain and progressively
through time. After about say 10 15 million
years ago, it was the Danube that was dominating flowing
around Eastwood's, right? Brand The Fringe of the Alps as
they extended and then running down into the pannonian, Basin
in Hungary, through Vienna, and out into the Hungarian Plains
for quite a long time. Time is flowed into a very large
lake in the pannonian Basin but had Advanced with a major Delta
filled in the lake with alpine sediment, cut through ranges and
got down to the Black Sea about 4 million years ago.
What is the pannonian Basin? Yes, the pannonian Basin is the
very big horse Plains of Hungary where the Maggie has raised,
their horses, famous Horseman, and those are still present as
very big flat Plains but Underneath a lake deposits.
And this is part of what sometimes called the lag Amare
in European terms, very large lakes connected to tethers,
partly, brackish partly, fresh that ran all across this tract
of country. But what's been happening lately
is that the Rhine has started to come into its own, it occupies a
rift valley where there have been volcanics, quite recent
volcanic, sand places and for quite a long time the Mine was a
series of disconnected, drainages most, particularly the
Moselle coming in from Eastern France.
But by about 3 million years ago, these drainages are
connected up and Alpine sediment was now making its way right
through to the North Sea and because the Rhine is occupying a
rift valley at a lower elevation, it's beginning to
suck out the headwaters of the Danube and in places in the
swabian Alps, there are cave systems where water is draining.
Underground out of the Danube and into the headwaters of the
Rhine through a series of Springs.
It's a river capture in progress.
Moving, more or less underground.
It's incredible stuff. Can you talk about the history
of South American rivers and especially that of today's
largest river? The Amazon that is one of the
most fantastic River stories of all.
There's the Amazon, it's the world's largest river.
By a very large margin. It's bigger than something like
the eighth. Next Rivers all.
Lined and it is only about nine million years old in its present
position. What happened?
Was that South America began to drift away from Africa?
And were Rivers flowing into the Pacific on the far side.
One of which would have been a Proto Amazon it is sometimes
referred to as the sano-sama which is amazonas spelt
backwards if you wanted a name for River now flowing in the
opposite direction, that it now occupies But in the bias seen
about 25 million years ago, the and he's started to rise and
drainage began to flow eastwards.
And so, the Amazon went through a reversion and initially it
terminated as a series of major Wetlands on the South American
continent blocked off by a rock Arch.
So it didn't get to the Atlantic eventually, it broke through the
arch and then ran into a rift that runs along the lower line
of the Amazon and reach The Atlantic Ocean that was about 9
million years ago. And that's when Andean sediment
first begins to appear in the deep sea fan of the Amazon off,
the South American Coast. Meanwhile, the Amazon has picked
up a lot of the drainage from The Orinoco in the northern part
of the continent. And there's a very bizarre
circumstance called the Cassie Ciara Channel which is a place
which actually connects the two rivers and where the Amazon In
is draining off flow from the Orinoco, but they've not
separated into separate catchments as yet.
It's a river capture that actually in progress and
Alexander Von Humboldt took a canoe through it.
And showed in the early 1800s that these were actually
connected armchair observers in Europe, have claimed that it
couldn't possibly be true. Can you pick out a couple of
examples that represent the diverse histories of the rivers
of North America? Yes, I could talk forever about
this. There are so many The rivers.
They history is a so interesting.
We've talked a bit about the Mississippi and that goes back
to about 300 million years following the line of the Fallen
Basin along the western side of the Appalachians that was a
mountain chain of Andean scale. But once Pangea was assembled,
along that line then very big Rivers would have run out across
the continent and some of them ran out into the Boreal see in
north western Canada so you have It'll scale rivers that no
longer exist. Running out from the
Appalachians. The Mississippi continued to run
south and in the Cretaceous in particular, the Cordillera began
to rise in Western North America.
And then the entire drainage system of North, America was
altered the Gulf of Mexico had come into existence in the
Jurassic and you had Rivers running down off the chordal
error rivers, that we know today like the plat, the I saw the red
Canadian P cos rivers and so on and these all ran down to the
gulf where they competed, if you like with the Mississippi for
access to the Gulf Waters. So the Mississippi at times was
reduced to quite a small River But as time passed the Missouri
fed into it. And so the Mississippi has
regrown into a very major drainage that captures a lot of
what comes off the Western Plains.
So it's managed to maintain its place.
The river that you have to talk about though with North America
as the Colorado River. And I couldn't possibly talk to
you about this without getting into the issues of the Grand
Canyon and in the Cretaceous the Colorado headed eastwards into
the Western interior Seaway across the Midwest.
But then Dynamic topography came in as the continent drifted over
the Pacific, the Colorado Plateau Rose and the basement
Range Systems of rift. Valleys lowered the topography
in the very western part of the continent and all of this
resulted initially in rather disconnected drainage systems.
But eventually, a through flowing river system of the
Colorado that connected drainages ran into a series of
Lake basins and then about 4 million years ago or so in the
pliocene made its way down to the Pacific and cut right
through and the Grand Canyon. Most of it was cut apparently
within the past six million years.
It's incredibly big. Have you been there?
Yeah, I have. Yeah, absolutely.
An impressive thing to see and it's very young the lowered base
level when it got through to the ocean.
Meant that the river just cut a massive Gorge as other rivers
have done. The vulgar has done that.
The Nile has done that, and these will eventually fill up
with sediment probably as The other ones have done but at the
moment, it's standing. There is the most famous Canyon
on Earth. What about the ice ages?
Particularly the more recent ones, how they had a significant
impact on Rivers? They certainly have and I have
had an impact at a far more rapid rate than the plate
tectonic effects which are in the millions tens of millions of
years. The ice age has been operating
on scales really of thousands or hundreds of thousands of years
and the changes are absolutely radical, the ice.
Ice across North America and Eurasia came a long way down
down into as far as Nebraska in North America and this is ice 3
kilometers thick. It does extraordinary things it
erodes river, valleys it spreads, huge volumes of
glacial, debris everywhere it depresses the crust.
It does everything. And rivers, of course, cease to
exist when the ice that magnitude covers them.
So let me give you a few examples.
The Yukon. It was initially a relatively
small drainage that Rose NIV Pacific Ocean and ran down into
the Pacific but it's exit got blocked by a nice lobe and It
reversed and so at the present day it rises within 50
kilometers of the Pacific and then runs 3000 km round to the
Bering Strait quite incredible. And the McKenzie one of the big
rivers of North America occupied Is a glacially eroded trough
that didn't previously exist. There was no drainage along its
present course and the Mackenzie has originated only since the
Ice Age something like 12,000 years ago and it must be among
the youngest of all the big rivers of Earth entirely as a
result of glacial effects. Other things that happened in
particular in North America, the weight of the ice depressed, the
land and once the ice sheets melted back which they did,
Quickly enormous glacial lakes formed, including glacial Lake
Agassiz in North America as well as very big lakes and Siberia.
And these were held in place by lobes of ice.
That was belting as well as glacial debris natural dams
which failed and released a number of catastrophic Outburst
floods and meltwater that rahl down, rivers to the ocean down
the Mississippi system as far as the Gulf of Echo out through the
st. Lawrence and Hudson to the
Atlantic and out along the Columbia River to the Pacific.
And it's the Columbia river floods that really brought all
of this to light through the work of J Harlen Bretz.
In the 1920s who interpreted the landscape of the channeled
scablands in Washington state has due to catastrophic floods
geomorphologist didn't like this, this was catastrophism
this smacked of old creation. I thought and they laid into
him, it couldn't be right. There must be other
explanations, but in the course of time Brett's was proved to be
correct. And the estimates now are the
for short periods of time, the outbursts that ran down the
Columbia. Rated at 20 million cubic meters
per second, and that's equivalent of 50 River.
Amazon's at Peak flow. Absolutely stunning.
They generated water falls on the scale of Niagara Era which
are now completely Drive. You've ever been across that
extraordinary landscape. And They Carried sediment out
for 1,000 kilometers down into the Pacific and something like
200 meters of sand it. Deep water off the Pacific.
That resulted from all of this, did the ice ages also affect the
courses of European rivers. Yes.
This the channel river which initially connected the Rhine,
the Thames, the saying of the psalm into one large river, The
drained, most of Western Europe ran right down to the Bay of
Biscay. And when the ice sheets melted
the sea level rise, simply drowned out the lowest 800
kilometres of the channel river system, and the rivers were all
left, is disconnected. Remnants, the Rhine, the Thames,
the psalm, and of course, in terms of human geography, this
is affected everything running right through from the Stone Age
right through to modern-day brexit.
It's an ongoing story of how River and glacial Dynamics have
affected human political history.
Speaking of recent effects, humans are now having a massive
impact on Rivers. What with all the dams we've
constructed and the confines we've placed on Rivers for
agricultural purposes and to protect cities from flooding,
how far back can the impact of humans be seen in the record of
fluvial deposits. that's a really very fundamental question
with a lot of importance that the present-day hominins arise
something like 7 million years ago in Africa and I asked Gail
Ashley who'd worked at Olduvai Gorge whether she could document
any trace of what early humans did we're talking perhaps two or
three million years ago and her response which I've always
remembered is that the early hominins trod likely on the
earth leaving only stone tools and Footprints.
And so there's nothing that she could see where you could make a
link between River Dynamics. And humans once fire was used,
which goes back about a million and a half years in Africa, the
must have been some effect on alluvial Landscapes with the
burning of forests release of sediments and so on, but so far
I haven't come across anything that really links early fire
records. Two Rivers.
At least not as far back as that.
When humans really began to have an effect is once they start to
domesticate plants and animals. And that is, as recently as
about, 11,000 years ago, prior to that the Fisher is along
rivers. There was food processing by
Rivers, but settlements were only transient and people were
hunter-gatherers moving through the landscape and as people say,
in Northern Canada, following the wealth of the land, their
livelihood, depended on their Mobility, But once plants were
domesticated, wheat. Barley, beans onions, Etc.
In the near East and animals cattle sheep goats Pigs by about
10,000 years ago. Then things began to change
something like nearly 10,000 years ago, people recognize
agriculture as an organized system.
And within a few thousand years of that, it's reckoned that
virtually everyone in the near East was a farmer probably
within little more than three thousand years at around the
same time, you're getting rice. Domesticated in China just
Inland from Hong, Kong something like 9,000 years ago and all
sorts of Water. Systems, irrigation goes along
with that you get Staples like Maize and squash in Central
America domesticated nine to ten thousand years ago and oddly
bananas in New Guinea going back.
Something like I think seven Thousand years or thereabouts,
the Amazon basin, long thought to have been a kind of human
Backwater by people who probably never went there as emerged as
being a major Centre for plant, domestication of all kinds.
As a lot of research going on into what happened there.
And we know about these things because you can document the
changes in animal bone structure size and so on, and in plant
genetics that go along with humans, too.
Deliberately engineering plants and animals for their own
purposes and over the next few thousand years.
You have donkeys domesticated in Egypt horses on the Russian
steppe Yaks, in eastern, Asia water, buffalo, probably in
India, or China, and then camels in Arabia.
And all of these were domesticated over a period of
three or four thousand years. And why was this important for
Rivers? Well, if you're going to have
cropped, Ends. You have to Deforest the land.
Make way, for the arable products you need pasture for
grazing animals, and these all affect the stability of river
systems and the sediment Supply coming down to the river's but
very importantly in places like Mesopotamia.
You have got to have irrigation if you're going to have crops
and this goes along with the rise of permanent settlements in
places particularly like Jericho some and years ago in the rift
valley of the Jordan and then the cities of Mesopotamia along
the Euphrates and the Tigris in Egypt, along the Nile and with
the Indus Valley Civilization along the Indus and its
tributaries. And if you've got cities with
big numbers of people, you need water supply, you need sewage
systems. You need infrastructure along
the rivers wharfs Bridges Pathways.
You generate large Depressions. Which have been documented by
archaeology on floodplains to make bricks.
These cities were brick mud brick manufacture and all that
came out of the floodplain plays.
And so, I 6,500 years ago, you had the rise of irrigation
systems in Mesopotamia and the first Big Dam in Egypt, the
damn, of the pagans nearly 5,000 years ago.
We're 14 meters high with a facing of stone blocks.
And so, people are really Really beginning to modify the river
systems and I have to mention the Yellow River in China, where
Emperor's going back. Several thousand years,
constructed enormous embankments relief channels and kept the
river in its place for the benefits of Agriculture and of
navigation. And finally, the Romans masters
of water management as they were a pretty much anything else in
the engineering line aqueducts, 100 km long and Large dams built
in the near East to supply. The Roman Legions with water and
food. So humans over the past 10,000
years have really been affecting river systems in an earlier
podcast. I talked with Phil gabbard about
whether and how we might establish a new geological
period called the anthropocene defined by human impact on the
planet. If we do, establish such a
period, we would need to Mark the start of it.
With something laid down in the occurred that happened, more or
less simultaneously around the globe.
Can our impact on Rivers? Help us out here.
I think you can help us out quite a lot.
I've liked the approach of Phil gabbard, and his colleagues that
you need to consider the anthropocene to be a very
broad-based event. Going back a very long way in
human history. And I've moved away from
thinking of a narrowly defined Global spike in what we've been
talking about with human effects on Rivers means.
They go back about ten thousand years with domestication of
animals and plants. And you can pick that up with
what people call Legacy sediments.
The enormous runoffs of sediments into rivers, along
with serial pollen, the bones of domesticated animals, techno
fossils, such as pottery and bits of masonry, and you can
show that humans were affecting the Landscapes very prominently
far back in time. And once you get Ting, say,
5,000 years ago, you begin to get written records of
irrigation development Mesopotamia.
And the documentation is in China in particular associated
with the attempts of The Emperor's to control the Yellow
River. So there's no question at all
that human effects. Go back a long way.
The attempt to put a golden spike in to Mark the base of the
anthropocene is focusing on about 1950 linked to nuclear
fallout from Bombs and bomb tests, I'm uncomfortable with
using nuclear fallout in this way.
These are destructive systems. They caused huge deaths of All
Sorts. But really my line of thought is
more that we need a broad all-encompassing term that takes
us a long way back in Earth history to understand what we've
done and our widespread impact on Rivers.
Where would you put that then? Would it be the rise of the
modern engineer? Damn, we're pretty much every
major river on the planet has been significantly.
Damn door. Would you put it further back in
Antiquity? There's no question that the
rise of the big dams has hugely affected virtually, all modern
Rivers, but it doesn't just begin there, for example, by the
time of the domesday book in 1087 or thereabouts when William
the Conqueror invaded Britain, he recorded a water mill for
every 250 inhabitants of Britain.
And those water Mills Had small Weir's.
They had little dams. They had Mill, ponds and
Records. Particularly out of monasteries
show that the stocks of salmon and other.
Migrating fish were cut back through the medieval period.
We've been doing this for hundreds of years, even in that
kind of setting. And by the 1840s in the
northeastern us alone, there were sixty five thousand small,
dams and Mill, ponds, all the rivers have been retooled long
long. For the era of the big dance, we
have to understand the human impact on the land as being very
long ranging, you've studied just about every major river on
the planet. Do you have a favorite River?
I wish I had studied every major river.
All the black that has. I've got a long way to go, but
of all the rivers that I think about, I would have to place the
channel country of Australia at the top of my list.
I spent a long time with an Australian colleagues out there
in the red Centre of Australia. We drove along.
On the old, droving roads through Queensland, rivers of
the channel country, like the diamantina Cooper Creek, the
Georgina. And these run down through the
sand dunes down to Lake are with the salt flats and they are
absolutely fascinating. It's very hot work often into
the 40 Celsius range. But you find that life has found
a way to quote Jurassic Park and there are kangaroos and emus,
crayfish Burrows, eucalyptus trees growing along the side
phlox. Of herod's budgies.
And these are multi Channel and anastomose in rivers, dry for
many months of the year, and then, flooding down to Lake
Eyre, and it's absolutely fascinating walking through the
Creeks, these are about as near to a pristine Rivers.
You're likely to get there just wonderful places, Martin
giggling. Thank you very much.
Oliver. Thank you very much for talking
with me. I'm delighted to talk about
rivers anytime. For more about geology b, as
well as pictures and illustrations, that support this
podcast, go to geology B.com.