Behind the News Specials
The content in these specials will support students from Years 5 - 8 to achieve a range of
understandings within an Essential Learnings curriculum. The stories emphasise investigation,
communication and participation, encouraging students to be reflective thinkers about a range of
issues taught in schools.
State / Territory
Victoria
SA
WA
NT
Qld
NSW
Tasmania
ACT
Outcomes
Level 4 & 5
Standard 4
Level 4
Band 4
Level 4
Stage 4 & 5
Band B – Grade 5/6
Band C - Junior Secondary
Upper Prim
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NATURES FURY
Curriculum Links
Science: structures and systems
This week’s program helps students to gain knowledge and understanding of structures and
systems in relation to natural events such as:
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CYCLONES
TSUNAMIS
EARTHQUAKES
KYOTO – GREENHOUSE GAS
Transcript:
Behind the News on Nature's Fury - the science behind cyclones, tsunamis and earthquakes.
CYCLONES
Hi and welcome to our special look at our violent earth... I'm Krista Eleftheriou.
First today, cyclones.
They can be very dangerous, and very unpredictable, so we thought we'd better find out more
about them.
It was Christmas eve 1974 when a powerful cyclone called Tracy did this to Darwin. Sixtyfive people died and many more were injured and as you can see there wasn't much left
standing afterwards. Cyclone Tracy was a category four.
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So was Ingrid, when it crossed the far north Queensland coast, but it caused little
damage.
Australia's cyclone season is between November and April, when the ocean's
temperature is above 26.5 degrees, but they can occur at other times too. On average
about ten cyclones hit northern Australia a year.
The word Cyclone actually means turning wind with one eye. As you can see by the photo
taken from above the clouds look like they are turning in a circle.
Cyclones form over warm oceans when air, heated by the sun and ocean, quickly rises.
The air is loaded with water from the ocean and as it cools it creates huge thunderclouds.
The rising air spirals upwards creating very windy conditions.
Although these winds swirl around at very high speeds it can actually be quite calm in the
centre of the cyclone, which is called the eye. But either side of the eye, well that’s where
the cyclone's wind is strongest. Once the cyclone is over land it quickly loses power.
Similar severe tropical storms are found in equatorial regions across the world, all of them
rotate in a circle. In Asia they're called Typhoons and in the Americas, hurricanes. In the
northern hemisphere they rotate in an anti-clockwise direction. Cyclones in the southern
hemisphere rotate in a clockwise direction.
This is another storm you may be familiar with, a Tornado. Although it may look similar it
is not a tropical storm, Tornados usually form over land and are most common in northern
America and Africa.
But back to cyclones. There are five categories of cyclones, depending on their wind
speed. Winds in a category one cyclone reach about 125 kilometres an hour.
That's the weakest cyclone, they get a lot more powerful. Category two has winds of
between 125 and 169 km/h. Category three up to 224 km/h. When tropical cyclone Ingrid
hit land it was a category 4, which can have wind speeds of up to 279 km/h. Cyclones can
strengthn and weaken and Ingrid reached a category 5 with winds of more than 280 km/h.
That's about three times faster than this.
It's not just wind that causes damage. This isn't normal flooding. It's a storm surge and
they often occur with a cyclone. The strong winds whip up waves and push the water onto
land. The ocean rises over several hours as a cyclone moves closer to the coast.
As for naming a cyclone, well, it prevents confusion when there's more than one cyclone
in an area. There are set lists of names for Cyclones. You can check out the BTN website
to find out the name of the next one.
And it's not just wind that can be destructive.
TSUNAMI
You've probably heard a lot about the Boxing Day tsunami that killed thousands of people and
left many more homeless. But how do they start? And why do they happen?
Only a few months after the earthquake that caused the tsunami another one rocked Indonesia.
An earthquake on land can do this! An earthquake under the ocean can do this! To
understand how it works you need a jigsaw. Yep that's right.
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The earth's crust the bit below the surface, is a bit like a jigsaw. The Earth is actually
made up of 16 big pieces, called tectonic plates, but unlike a jigsaw they don't fit perfectly
together and the pieces are always moving. And when they crash into each other, like
this, or this, they cause an earthquake.
Not just any earthquake can cause a tsunami. It firstly has to happen under the ocean.
The ocean floor has to suddenly rise or fall and only really big earthquakes have enough
power to start a tsunami.
The recent Asian earthquake had more power than 9000 atomic bombs exploding all at
once. It happened here, just off the coast of Indonesia and cause 1000 kilometres of the
ocean floor to move. The earthquake caused underwater landslides and pushed up the
ocean floor by as much as 100 metres. That movement sent out a tsunami thousands of
kilometres across the ocean.
A Tsunami isn't just one wave but a series of waves. Volcanic eruptions or a meteorite
can also trigger a Tsunami.
Tsunamis are common in Japan and that's where the word comes from. It means 'harbour
wave'.
So could a tsunami hit Australia? Well actually yes. On average two tsunamis hit
Australia's coast every year? Usually they are too small to do any damage. Even the
Asian tsunami hit Australia. As you can see from this image, the waves travelled to almost
every coastline in the world. But in many places they were too small and hardly noticed.
The good news is Australia has a few natural barriers against tsunamis. Such as our off
shore reefs or this underwater step called a continental shelf, both cause a tsunami to
slow down and lose power long before they reach the coast.
Also Australia is in the middle of a tectonic plate, a long way from where the big
earthquakes happen.
If a big tsunami was to head our way a special warning system would give Australia plenty
of time to evacuate coastal areas.
And according to most scientists Australia hasn't been hit by a big tsunami for thousands
of years. So I think it's still pretty safe to continue hanging out at the beach.
Only a few months after the earthquake that caused the tsunami, another one hit Indonesia.
EARTHQUAKE
Was it a coincidence or do earthquakes often happen in the same places?
Another earthquake off Indonesia. So why has it happened again and in the same area?
The earth isn't just a big solid piece of rock. While on the surface it may seem quite solid,
the Earth's crust is actually made up of 16 big pieces and other smaller pieces, called
tectonic plates. A bit like these pieces floating in a pool, the tectonic plates float on top of
hot liquid, called magma, the same stuff that comes out of volcanoes.
The magma is continually swirling around and in some areas it pulls the tectonic plates
apart. This is happening to the plate Australia sits on. It's constantly moving northwards,
but not very fast, only about seven and a half centimeters a year. As it does, it crashes
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into the plate, which Indonesia sits on, causing earthquakes, off Sumatra.
If we check out where the world's powerful earthquakes have occurred over the past 40
years, we can see almost all of them have happened where the tectonic plates meet and
sometimes collide.
These collisions cause the Earth's crust to buckle like this, or one plate to rise over
another, like this, although sometimes two plates just grind against each other.
The recent Indonesian earthquake lifted this reef out of the ocean, forming one of a
number of new islands. People fled fearing another large tsunami, but it didn't happen
because the ocean floor didn't move as much as the quake three months earlier.
We often hear how powerful an earthquake has been. The one off Indonesia was 8.7 on
the Richter scale. A number one on the Richter scale is like a light truck traveling past
your home, you probably wouldn't feel it. But a number two shakes things up 10 times as
much. An earthquake measuring 8 is actually 10 million times more powerful than a one.
Big earthquakes can cause lots of damage. But it's not just the strength of an earthquake
that determines the amount of damage. The design and materials used in buildings also
make a difference, but so does what's underneath them.
Notice how this model of a building hardly moves, that's what happens to buildings on
solid rock. The earthquake vibrations don't have much effect. But check out this building
on a block of jelly. The vibrations easily travel through it. That's what it's like for buildings
on deep wet soil, like those found along Indonesia's coast. And as you can see the
damage is far worse.
That explains why there's more damage in some places than others.
KYOTO
Finally today, you might have heard of the term ‘Kyoto protocol’... it's seen as the first step
towards saving the earth. It's an agreement about cutting pollution - but not everyone is taking
part.
Greenhouse gases are produced by burning things like petrol to run our cars and coal to run our
power stations. Animals and humans also breathe out greenhouse gases, and emit them in other
ways too!
Greenhouse gases do play an important role because they help keep the Earth warm. They
allow sunlight to come into our atmosphere, but don't allow all the heat generated from the sun's
light to escape back into space. So a bit like clothes, the greenhouse gases form a layer that
keeps the Earth warm. But if that layer gets too thick, the Earth gets too warm.
That could cause the ocean to rise and droughts and storms to become more frequent.
So what can be done to stop these things happening? Well, more than 140 countries have made
an agreement. They’ve set themselves a target. These countries are aiming to reduce
greenhouse gas pollution. The agreement is called the Kyoto protocol.
So, why the name Kyoto Protocol? Because it was in the Japanese city of Kyoto where world
leaders reached the agreement.
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Over the next 7 years, the countries taking part will try to cut their greenhouse gas output by
about five percent, compared to 1990 levels.
So, how do they do it? By replacing some coal electricity plants with wind and solar power,
replacing petrol cars with electric cars, and good old fashioned trees, The oldest and one of the
best way of cutting greenhouse gases. Trees use a greenhouse gas called carbon dioxide to
grow and actually produce oxygen.
There's an international system of trying to even things out. It's called carbon trading.
And if one country cuts their greenhouse gas emissions by more then they need to, that country
can then sell off their greenhouse gas savings, called carbon credits, to a country making too
much pollution. So a country causing global warming can pay someone else for some global
cooling. But only countries that sign the Kyoto Protocol can be involved in carbon trading.
All these countries have put their hand up to cut greenhouse gases. But notice how the worlds
biggest greenhouse gas producer, the United States isn't involved, and neither is Australia.
Our Government says it won't take part because the world's larger polluters aren't involved.
But Australia is expected to reach the target anyway, because we've reduced our amount of land
clearing in recent years.
And that's it for our Behind the News special looking at nature's fury.
I'm Krista Eleftheriou, see ya next time.
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