unit 2 relief and water on earth wiki

Geography and History 1º ESO Unit 2 Relief and water on Earth

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Unit 2 Relief and water on Earth

Contents:

I- Relief

1- Structure of the Earth and relief formation

2- Shaping of relief

3- Types of relief

II- Water

1- Water on Earth

2- Oceans and seas / continental waters

3- Uses, risks and problems of water

Unit 2- Relief and water on Earth

Now you all know what Geography is and what its purposes are, we can start the study

of our planet. To start with, we are going to analyse the Geosphere, that is to say the

relief and landforms of the Earth. In the second part of this unit, we will investigate the

Hidrosphere, in other words, the water of our planet in all its forms. As a result, we will

have a whole description of two of the three main parts of the Earth, and it will only

leave the study of the Atmosphere to complete this issue (unit 3).

However, it is also time to face one of your more awful nightmares concerned with

Geography: studying the physical maps. But don´t worry, we are going to begin with an

easy one, the World map, only for remind what you already know. The other maps will

be studied in unit 4.

I- Relief

1- Structure of the Earth and relief formation

Do you know what the theory of tectonic drift1 is? Probably not, but if I say to you that

350 million years ago there was only a big continent called Pangaea (literally “all the

Earth), you would tell me that you already knew it. A scientist named Alfred Wegener

was the author of this theory one century ago, claiming that in the past there was just a

huge continent (Pangaea) surrounded by one big ocean (Panthalassa). The internal

forces of the Earth broke this continent and so during the past 150 million years our

world has been changing until its present distribution. That is the reason why if you

1 Deriva continental


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stare at a world map you may say it is like an enormous jigsaw puzzle.

In order to understand this process we have to remember how the internal structure of

the Earth is. In other words, we must know how the Geosphere is divided:

As you can see, the Earth is divided into three different layers:


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- The inner one is the core or endosphere;

- The second layer is the mantle, the biggest one and composed of magma (molten

rocks) which can be ejected by volcanoes (lava);

- The outermost layer is the crust, which is divided between the continental crust

and the oceanic crust.

Moreover, the lithosphere (the rigid crust and upper mantle) is divided in tectonic plates

which are floating on molten rocks in a very slowly movement. Both oceanic and

continental plates are constantly producing movements of collision and separation, and

that is the reason why the continents have been “travelling” during the past, and still go

on.

Watch this video and figure out

how

the Earth is thought to be in the

future:

https://youtu.be/uGcDed4xVD4

But, how is it possible that these tectonic plates could be moving constantly? Stare at

this picture:

As you can see, magma is coming up to the surface from inside the Earth through a

fissure called oceanic dorsal, which actually is the separation between two oceanic

plates. This way, the Earth is creating new land constantly and moving the plates.

However, some of these plates are colliding, and that is the place where the crust

disappears, creating deep ocean basins and forming the great mountains of the world.

https://youtu.be/uGcDed4xVD4


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These collision and separation movements also create faults where earthquakes and

volcanoes are usual, and it is the reason why some places are constantly affected by

these phenomenons.

Let´s watch these video: https://youtu.be/KDrDLAzYhGo

The subduction movement is the origin of some of the biggest earthquakes we have

known, even reaching the nine points in the Richter scale!

And now, why don´t we watch this video to summarize all this information?

https://youtu.be/6Z4as_imJfM

2- Shaping of relief

Now we know one important thing: the relief of the Earth is constantly changing,

although we may don´t notice it. Actually, the relief is made up by internal forces

(plates tectonic, earthquakes, volcanoes, etc.) and by external forces which shape the

natural forms.

We have learnt something about the first

ones, although we can say something else.

For example, the process which creates

mountain ranges and landforms is called

orogenesis, and it is the origin of the big

mountains of the world (folding the

Earth´s surface), the volcanoes and the

fault- block where earthquakes are usual. You only have to take a look at the world map

and you can realize that the biggest mountains have been

lifted by the collision of two tectonic plates. Fault block diagram

Watch carefully this video and try to understand how an earthquake is formed.

https://youtu.be/hlePrsXTGxQ

As you can see, these enormous forces have been shaping our planet since the beginning

of time, but there are other agents which are transforming the shape of our planet, the

external agents. We can find three external agents which are water, wind and living

beings (leaving apart the human action over the Earth´s surface). All these agents

https://youtu.be/KDrDLAzYhGo

https://youtu.be/6Z4as_imJfM

https://youtu.be/hlePrsXTGxQ


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produce erosion, transportation and deposition which constantly are creating new

landscapes, sometimes in a very particular way (just think about the Pedriza).

Water is a fundamental agent in these processes, sometimes eroding itself the land

(rivers, seashores or glaciers) or combined with others agents (freezing or oxidizing the

rocks). Moreover, it is necessary for the plants and animals which create the biological

erosion (roots, dens, etc.).

3- Types of relief

Therefore, we have seen the main internal and external agents which create the different

types of relief of our planet. Now it is time to learn something else about them, and we

are going to begin with the continental and costal reliefs. You probably already know

that emerged land is only a quarter of the whole crust of the Earth, but you must know

that even under the sea we can find the continental shelf, so the border between land and

sea is not so clear; in fact the continental land reaches some kilometers offshore until

the continental slope.

In this picture you can see the main land and costal forms:

All these relief forms are so common that you probably know examples of all of them,

so you have to add these words to your geographical vocabulary! As you can see, these

forms are produced by the combination of internal and external forces, being the

erosion, transportation and deposition the origin of many of them.

On the other hand, we can find the ocean relief quite boring because the lack of

diversity in its forms. The reason is that the ocean ridges are constantly creating new

soil which is barely modified. In fact, the bottoms of the oceans basins are large plains

(abyssal plains) at a depth between 3 and 6 kilometers. The ocean trenches are located

in the subduction zones between two tectonic plates, reaching the deepest areas of the

world. In the areas where this relief touches with a continent, we can find the


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continental slopes (a big and steep precipice of several kilometers) and the continental

shelves, flat areas of 300 meters depth that reach the cost and very rich in living beings).

II- Water on Earth

1- Water on Earth

Look carefully at this graphic and think

about it. As you probably know, planet

Earth is also known as “the blue

planet” because 75% of its surface is

water. But, does it mean that mankind

can use this resource with no limits at

all? Actually, the access to water is a

big problem for several hundred of

millions people every day, and it is considered to be one of the main causes for future

wars.

If we only consider the fresh water (3% of water on Earth), we can notice that the

accessible water is so scarce that we must keep it unpolluted and use it responsibly.

However, if we take a look at the main rivers, lakes and aquifers we realized that it is

not always a reality.

Therefore, we are going to separate the study of water on Earth in two main topics. First

of all, you are going to learn about the oceans and seas and the continental waters.

After that, we will discuss about the risks and problems that affect this issue.

2- Oceans and seas / continental waters

Now we know that only a few water on Earth is fresh. However, salt water is hugely

important for humankind. For example, ocean currents can determinate the climate of

our planet (Do you know something about “El Niño”?). And don´t forget that cold

currents are essential for fishermen all around the world.


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The main characteristics of sea water are salinity, density and temperature, and this

produces the differences between the seas on Earth. Moreover, sea water has different

movements. On the one hand, there are waves produced by wind that erode the seashore

constantly, modifying the landscape. On the other hand, there are periodic high and low

tides produced by the gravitational pull of the Moon and Sun, which can be used to

obtain energy. In the end, there are ocean currents with different salinity and

temperature that move around the seas like rivers (Do you remember Nemo?). Cold

currents born in the poles and produce dry weather (West coast deserts) and low

temperatures. Hot currents cause higher temperatures and wet weather because of the

evaporation, and are originated in the equatorial zone. To sum up, we can say that sea

currents are the heating of the Earth, and if the climate change modifies these currents

(as it seems to be happened), weather disasters would be more usual.

Continental waters

Although continental waters are only the 3% of the whole water on Earth we must study

its multiple forms and the multiple ways we need them for (drinking water, irrigation,

fluvial travelling, etc.).

The first kind of inland water we can find are

rivers, with enormous diversity of flow rate and

length, but vital for human societies. Rivers can

be tributaries if they flow into other rivers, and

sometimes they can disappear in dry seasons, but

usually all of them have the following parts:

- Upper course, where we can find the

source of the river, with a little flow rate

but big erosion.


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- Middle course, where tributaries join the

main course. The stream transports

sediments that create rich valleys for

agriculture.

- Lower course, where we can find the

wider channel and the water moves slowly

so it deposits sediments that can create

deltas in the river mouth.

In any case, big rivers always produce the creation of big cities and civilisations, such as

the Egyptian, because of the possibilities of irrigated agriculture and travelling through

the river. Something similar happens with lakes and ponds all over the world, very

important for the economy of societies that live nearby.

Other forms we can find inland waters are underground water, which can be found in

aquifers all around the world and it can be extracted through wells, and glaciers, today

disappearing of many mountains of the

world because of the climate change.

As you can see in this diagram, a

glacier is just a river of ice that create a

big cirque basin in the summit of the

mountain; the tongue goes down the

mountain eroding the rocks and

creating a valley that forms a “U”, as

the rivers create “V” valleys.

3- Uses, risks and problems of water

Throughout this unit we have seen some of the uses that humanity has made of water.

Do you remember any of them? Nowadays agriculture, fishing, merchandise and many

other activities use the rivers and seas, and even the UNESCO calculates that 75% of

people will live near the costs in 2025. Even mining and energy industries are looking

to the oceans as a new source once the inland ones are running out. This increasing

pressure over the water sources of the planet is producing both flood disasters and water

scarcity, as long as the climate change is affecting the weather in the Earth. Moreover,

pollution is hugely affecting to rivers, lakes, aquifers and seas, so some of them cannot

be used for fishing or irrigating crops.


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