teacher’s notes
student’s notes
Amazing Earth: facts that
fascinate – teacher's notes
The following facts and anecdotes are offered to teachers
as suggestions for enhancing their lessons. All have been
checked for accuracy and sources have been given where
available.
Earthquakes
The Earth rings like a bell after a large earthquake – the
lowest ring tone is E flat in the 20th octave below middle C
(Source: F Press and R Siever, Earth, New York: Freeman,
1986, p 467).
Sound from the eruption of Krakatau (Krakatoa) in 1883
travelled nearly 5000 km (3000 miles). (Source: P Francis,
Volcanoes: a planetary perspective, Oxford: OUP, 1993, p
80).
The ash cloud from Krakatau (Krakatoa) travelled round
the Earth several times and caused amazing sunsets. The
Earth cooled down by 0.25 oC because the ash reduced
the energy received from the Sun. (Source: P Francis,
Volcanoes: a planetary perspective, Oxford: OUP, 1993, p
377).
Earthquakes in Wales in 1984 and 1990 were due to
Atlantic floor spreading, crushing Britain towards Asia.
European plate movement is largely eastwards – so the
crushing movement is towards Asia.
To create a mountain system requires several million
earthquakes over tens of millions of years.
Northridge Mountains in the USA rose in height by 70
cm due to a magnitude 6.9 earthquake on the Richter
scale releasing energy equivalent to 2 billion kg of high
explosive - equivalent to 100 of the atomic bombs used at
Hiroshima.
Small (magnitude 2) earthquakes happen several times
per day; the Earth moves, yet we can't feel them - they can
only be detected by instruments.
Scientists are still investigating whether dogs do howl
before an earthquake strikes. There have been so many
reports of this and of chickens roosting before an
earthquake that it is no longer dismissed as a myth.
Some people have tried to lubricate fault planes with
water and mud to avert earthquakes. More recently
people have suggested forcing the faults apart using high
pressure steam.
There is no chance of outrunning an earthquake - P
waves travel at several kilometres per second.
The deepest recorded earthquake started 730 km (450
miles) below ground. The ones that do the most damage
tend to originate 0 – 65 km (0 - 40 miles) below ground.
Chinese scientists claim that they can predict an
earthquake by monitoring the water level in wells and
boreholes. Others say that levels of radon gas in the
ground may increase before an earthquake because of
the increased pressure underground releasing the gas.
Changes in electrical resistance of the ground may also
hold clues.
The Kobe earthquake in Japan in 1990 caused a loss of
$200 billion – the most expensive natural disaster of all
time (Source: B. McGuire. A guide to the end of the world,
Oxford: OUP, 2002, p 20).
Around 1400 earthquakes rock the planet every day.
(Source: B. McGuire. A guide to the end of the world,
Oxford: OUP, 2002, p 30).
In 1556, a single earthquake in China is estimated to
have killed 800 000 people. (Source: B. McGuire. A guide
to the end of the world, Oxford: OUP, 2002, p 30).
Volcanoes
In the 1960s, a Royal Navy patrol ship (ironically called
HMS Protector) became stuck in floating pumice from a
new volcanic eruption in the South Sandwich Islands in
the Pacific Ocean.
Nine of the world's most expert vulcanologists were
killed when a volcano blew up in their faces, whilst they
were on a field trip. It happened on Galeras Volcano, in
Columbia, South America, in 1991. Some of them thought
that they could tell when the volcano would erupt, by
studying the gases which were being given off. Another
was hoping to use variations in the Earth's gravity field to
tell if molten magma was getting near to the surface.
Thinking that it was safe for a few more days, they went
down into the crater. The gravity meter seemed to be
broken. However, it now seems more likely that, as the
pressure built up in the volcano, the changes in gravity
were so great, that the instrument had gone off scale. The
volcano suddenly erupted, not with runny lava, but with
solid blocks of rock as big as fridges. These flew up into
the air and fell on the scientists, killing nine of them and
badly injuring several more. (Source: Horizon, BBC TV,
17/1/02).
In 1783, the Laki fissure volcano in Iceland erupted over
a period of eight months. The eruption produced acid rain
and ash, which fell across much of Northern Europe. It
also reduced the average temperature of Northern
Europe by about 1 oC. A widespread famine affected
many people. Even the cows in the fields starved, because
the grass was so coated with abrasive ash that their teeth
were worn down and they couldn't eat.
Mont Pelée is a volcano in the West Indies. In 1902 it
began to show signs of eruption, and one man told
everyone to get out of the nearby town of St Pierre. There
was an election coming up and everybody thought he was
saying it for political reasons, so they ignored him.
However, he was right. On 8th May 1902, a cloud of white
hot ash particles and gases shot out of the crater, and
rushed down the slopes of the volcano, burning and
suffocating everything in its path. Over 30 000 people
were killed, the harbour water boiled and ships were
overturned. There were only two survivors. One was the
man who gave the warning, who acted on his own advice.
The other was a condemned murderer in an underground
cell. When he was finally discovered, he was reprieved,
and went on to earn a living travelling the world on lecture
tours.
Mount St Helens is a volcano in the western USA.
Before it erupted in 1980, scientists had been studying it
and thought they knew what was going to happen. The
authorities evacuated people from what were though to
be the dangerous spots. However when the volcano
erupted, a cloud of hot ash rolled rapidly down one side
of it. Two people in a car got away, driving along a forest
road at 160 km per hour (100 mph). They overtook a car
going at about 110 km per hour (70 mph), whose driver
was later found dead, having been caught up by the
moving ash cloud, and suffocated.
Lava flowed at 60 km per hour (40 mph) during the
eruption of Nyiragongo, Africa in January 2002 and
engulfed the Congolese town of Goma, so quickly that
people were trapped between lava flows. (Source:
Geological Society website, www.geolsoc.org.uk, accessed
February 2003).
The amount of heat flowing from the Earth amounts to
40 million MW.
The total electricity generating capacity of the USA is, by
contrast, 400 000 MW - or only 1% of the Earth's heat flow.
The Earth loses 2 million MW through volcanic eruptions
(2% of the global heat flux). The hot springs area of
Yellowstone National Park (Wyoming, USA) produces 4200
MW. (1 MW is 1 million joules per second).
Tectonic plates and the structure of the Earth
Tectonic plate movement is around 3.5 cm (1.4 in) per
year on average, about the same as the rate that
fingernails grow.
South America and Africa were once joined – the
evidence is seen in the continuity of rock types and many
types of land fossils.
The deepest hole ever drilled has a depth of 12 km (8
miles), so far, 2003. Progress is slow because the drill tip
quickly gets blunt and lifting 12 km of drill out to replace it
takes ages. This is only 0.2% of the radius of the Earth
(6361 km, 3953 miles) – so a ‘Journey to the Centre of the
Earth’ is not feasible.
The Earth's crust’s average thickness is 35 km (22 miles)
under continents and 6 km (4 miles) under oceans. A
rough analogy to this is a postage stamp stuck on a
football.
The Earth’s magnetic field has flipped over many times;
every 500 000 years on average. Flipping over may take
about 10 000 years. The last major period of reversal was
over 500 000 years ago, so we are overdue for another
flip. Recent measurements of the magnetic field in the
South Atlantic indicate that a reversal may be starting now
(2003).
Atmosphere and ocean
70% of the oxygen added to the atmosphere each year
comes from plankton in the sea, only 30% from land
plants (Source: W. Heathcote, Whale Nation, London:
Jonathan Cape, 1988, p 131).
One cubic kilometre of seawater contains 4 kg of
dissolved gold (Source: B Mason, Principles of
Geochemistry, New York: Wiley, 1966, p 196).
In 1970, nearly 4 cm (about 1.5 inches) of rain fell in 60
seconds on the island of Guadeloupe in the West Indies
(Source: B. McGuire. A guide to the end of the world,
Oxford: OUP, 2002, p 16).
Nearly 4 metres of rain in 24 hours was dropped on the
island of Réunion in the Indian Ocean by a passing
cyclone in 1952. (Source: B. McGuire. A guide to the end of
the world, Oxford: OUP, 2002, p 16).
Tornadoes have windspeeds up to 500 km per hour
(300 mph). (Source: B. McGuire. A guide to the end of the
world, Oxford: OUP, 2002, p 20).
When, in 1998, Hurricane Mitch dropped over 30 cm (12
in) of rain on Central America, it triggered more than a
million landslides in the country of Honduras alone.
(Source: B. McGuire. A guide to the end of the world,
Oxford: OUP, 2002, p 20).
If the Greenland Ice Sheet melts, all the world’s coastal
cities will be drowned, from New York to London to
Sydney. (Source: B. McGuire. A guide to the end of the
world, Oxford: OUP, 2002, p 63).
Sea levels have risen by over 120 m since the ice started
to retreat around 18 000 years ago. (Source: B. McGuire. A
guide to the end of the world, Oxford: OUP, 2002, p 91).