What will I learn? After taking this course you will have an understanding of Arctic landscapes, how they were formed and how they are changing. You will also learn how scientists from countries around the North are working together to understand how these changes will affect the People of the North and the global community. You will experience a range of scientific topics, up-to-date-methods for understanding our environment, and the current consensus views on the future of the Arctic environment. Do I need prior knowledge? No prior knowledge is needed for this course; participants should only come equipped with natural curiosity and a willingness to invest time in understanding an environmental issue of global concern. The terms and concepts are targeted at an educated public, not specialists, but resources will be provided so those who are motivated can explore some issues in more depth.
Lecture 2. Landscapes and land-forming processes
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來自 National Research Tomsk State University 的課程
The Changing Arctic
100 個評分
從本節課中
Changing landforms: the legacy of glaciers and permafrost
In this module we will talk about glacial erosion, moraines, ice dams and tsunamis.
與講師見面
Terry V. CallaghanProfessor of Botany, Honorary Doctor
[MUSIC]
Which is true?
A, effects of climate on snow and ice are as expected and
similar to effects on ecosystems.
B, Effects on snow and ice are not as expected and
similar to those on ecosystems.
C, Effects on snow and ice are as expected but
often contrasted with effects on ecosystems.
D, Effects on snow and ice are not as expected,
but effects on ecosystems not as expected.
The correct answer is C.
>> This section of the course will deal with landscapes and
land-forming processes.
The very beautiful extensive mountain and
lowland landscapes of the arctic contain textbook examples of processes
which we call geomorphological processes that have formed northern landscapes and
even landscapes further south that were once likely arctic.
The landforms and the processes of forming land in the Arctic
is much easier to study there than elsewhere because the Arctic lands have
not been changed dramatically by human land use or by extensive vegetation.
So we can learn from the Arctic about processes that happened here,
further south, many thousands of years ago.
Also some of the processes are unique in the Arctic, although they may have
happened further south during the last ice age or just afterwards.
These processes are associated with pattern ground processes
resulting from permafrost in the ground.
It's important that we learn about the process in the Arctic in the past and
now in order to predict what will happen in the future and to understand what our
landscapes for the south in Europe, for example, experienced 10,000 years ago.
The landscapes of the North have been changing continually over time.
Over periods of about 100,000 years, 40,000 years, and 20,000 years.
If we look at the map here which shows what the North was like about 18,000 years
ago then we see that the ice sheets were massive compared with what we see today.
For example, ice sheets covered areas from in the north, all the way
through to the Scandinavian coastline and the Russian western coastline.
The sea level there was about 120 meters lower than it is today.
And what that means is that we have land exposed 18,000 years ago that
is now covered by water.
So 18,000 years ago it was possible to walk from Siberia,
eastern most Siberia to Alaska.
And of course that's what people did and
that's what a lot of animals did like mammals.
Not all land was covered by ice though.
So, we can see that particularly in Eastern Siberia where it was
relatively dry 18,000 years ago and then some places in Alaska and
a few small pockets of Arctic Canada there were no ice sheets so
these areas have remained free of ice for about 20,000 years, or even more.
The ice sheets have outlets.
These outlets are flowing glaciers.
They accumulate snow from the ice sheets in the interior or
the higher areas in the mountains, and they flow down,
here under gravity to the coast sometimes or they terminate inland.
We will hear in another section, section two, a lot more about glaciers.
But here in this section I want to deal with the land forms
that the glaciers create, not the glaciers themselves.
So the headlands of where the glaciers form, where most snowfall is,
right up in the top of the mountains, and the process of carving out the rock
around that headland of ice, creates something we call cirques.
These are hollow, semicircular hollows or
basins where they place his form and flow out of.
As they flow out, they carry with them the debris, the rocks and
the gravel that have fallen through erosion in those areas.
And these are transported down with the glacier.
Sometimes they go through the glacier and melt the glacier and go through, and
are transported under or at the sides, and they form the reigns.
On these moraines you can see the front of the glacier, it's a retreating glacier,
you can see almost half circles of terminal moraines.
And besides there will be lateral moraines too.
You can just see one on the right hand side.
Sometimes these moraines act as dams holding back and
the water that comes off in summer from the fine glacier.
In another section, we will look at the very dramatic release of water from
a glacier which creates a massive flood, well that's for another lecture.
When the glaciers move you can see then the results of their carving of
the landscape.
And they leave very classic, what we call U-shaped valleys.
Smooth sides with a smooth curve to the valley bottom.
These are classical phenomena where we know that ice was present before.
And we see these landscapes further south than the Arctic,
and we know if we say a U-shaped valley, for example, in north of England,
it tells us there were glaciers there in the past.
When the glaciers thaw, the water is released in a series of streams.
But these streams are very complex compared with most streams.
They change every year, they change according to the rate of thaw, and they
connect and form into connections and they carve the landscape out in front of them.
They move the gravel along, and they create this complex network,
interconnected network of streams, we call them braided streams.
The area they flow over, we call it Glacier Forefield and eventually over time
as it gets warmer those forefields will be covered by vegetation.
But even when glaciers have gone still the mountains are moving.
And we are losing material from them, and
the gravity of those materials come down the mountain slopes, and
accumulate in the valleys, and then are moved down along the valleys by rivers.
And this movement can be represented in a range of different landforms.
These include valleys and ridges, and
you can see them here on the slopes of the mountain.
I'm not talking about the big valley between mountains,
but the small valleys that you can see in the small ridges.
We have things called talus slopes, the slopes are not stable,
they're made of quite big coarse materials, small rocks,
gravel that can be very mobile and this we call talus.
So you can see talus there, we also have creep, sometimes we have permafrost and
we have soil creep called solifluction lobes.
And you can see them on the right hand side.
These dark bands are where the soil and the vegetation is creeping down the slope.
Sometimes we have stones that are moving in lines down the mountain called stone
stripes.
In the past when I was a student, we thought that these land forming processes
on the mountain side were going on all the time, but gradually and eventually you
would have a build up of material in the form of what we call alluvial fans.
Fan shaped accumulations of material between the mountain slope and
the valley bottom.
But recent research tells us that a lot of material is actually moved
very quickly in extreme events, and the events may only last one or
two minutes, and they may be infrequent, only once every 50 years.
But if you put all those two minutes together for
10,000 years then you have a big process of movement of material.
If we now move to areas further south where glaciers when
many thousands of years ago, for example, in the Faroe Islands.
There, we can still see the remains of glacial activity.
So this mound that you see, almost like a snake coming into the foreground,
a ridge is thought to be a moraine that is about eleven and a half
thousands years old from a peak cold period called the Younger Dryas period.
And researchers have determined the age of that moraine from the isotopes and
rock crystals that are exposed or have been exposed to cosmic rays.
That was information about the basic process in the mountains.
Of course, we have very vast lowlands in the Canadian Arctic and
particularly in the Russian far north.
These areas are special because they're formed by large rivers,
large river systems but the connections between rivers are not and
streams and their drainage networks are rather poor because of permafrost.
And permafrost is not far under the surface and impedes drainage.
And we'll learn a lot more about permafrost in section two.
The permafrost impedes drainage that means areas are wet.
Peat forms, and light forms.
But the lights undergo a cycle.
The one connections between, drainage connections establish between lakes and
neighboring lakes.
Lakes can drain, and you can see a big drained lake in the foreground.
And when the lakes have drained then, there's some areas dry and
then permafrost starts to accumulate, and
the land is lifted up by the accumulation of permafrost below.
And eventually, those areas get bigger and
bigger forming the plateau that we see in the fall ground,
which is rich in permafrost is raised, and but eventually cracks open.
There is a thaw and these small areas of water
expand creating what we call Thermokarst Lake and the cycle starts all over again.
Other areas of movement caused by freeze thaw.
The stone circles that we find in the polar semi-deserts,
where stones are moved and
the biggest stones are moved furthest, and we find nice circles in the stone nest.
The patterned ground of the coastal tundra,
where we have polygonal, or square-shaped patterning in the ground.
And another important characteristic of these areas
is that they are extremely rich in carbon.
Not the polar deserts, but the tundra.
And the reason for that is because the process of photosynthesis
is rather slow that takes up carbon from the atmosphere.
It takes the greenhouse gas out of the atmosphere and
stores it safely where it can't act as a greenhouse gas in the soil, but
the release of that greenhouse gas back to the atmosphere, over historical time,
has been even slower than photosynthesis, and that has led to an accumulation.
Over the past, when we've had cold periods the accumulation is so
great that part of that carbon is included in the permafrost, and then becomes
inaccessible to climate warming and to mobilization as a greenhouse gas.
And of course, section four we'll discuss why we're worried now
about the current warming and what will happen to that carbon.
In this session we're interested in land and land forming processes.
The importance of carbon in this session is that it leads to these vast
accumulations of carbon and landscapes which are a very dense in carbon.
In this particular slide we're looking at something called the yedoma,
in the Russian far north.
And this is an accumulation of soil, which is blown in during drier,
cold periods when this part of Russia was not covered in ice.
But it led to big accumulations of soil.
Then at the southern-most border of the Arctic tundra,
we come across the treeline.
The border, we call it an ecotone, between the northern tundra and
the big boreal forest, or taiga forest systems.
This is a boundary for our current section but in the next section,
we will learn about the permanently frozen ground.
And see what happens to it when it falls.
>> What is a cirque?
Is it A, Circles in polar deserts formed by stones of different sizes?
B, Moraines at the end of glaciers that are curved?
Or is it C, Depressions in mountain sides where snow accumulates to form glaciers.
