Science
of the Earth
11 - 14
Magma Introducing igneous processes
Earth Science Teachers' Association:
Science of the Earth 11-14
A series of three-Unit packs:
Pack 5: Magma - introducing igneous processes
Ml: Lava in the lab - the treacle investigation -the factors affecting the viscosity of lava.
M2: Lava landscapes - viscosity of lava related to landscape development in the Puys
district of France.
M3: Crystallising magma - investigations into the main factors affecting the cooling rates
and textures of igneous rocks.
Intended use:
Science courses for Key Stage 3. Geography courses.
Aims and Requirements: These are given on the Teacher Sheets for each of the three
Units.
Suggested Approach:
Each Unit is intended to take 70 to 80 minutes with homework, with time allocated to
planning the investigation beforehand, for Ml: Lava in the lab. The Units follow a
progressive series from 1 to 3, but each may be used as a free-standing entity if required.
Resources:
The Units require the use of materials and equipment which are readily available in school.
Unit M2 will be greatly enhanced if the following item can be obtained:
Volcanologie de la chaine des puys, a 1:25000 map produced by the Dept.de Geologie et
Mineralogie, Universite de Clermont-Ferrand. This is a superb map in colour, with "hill
shading" showing all the Puys and lava flows in dramatic detail. It is a most valuable asset to
teaching this Unit and also looks good on the lab wall, long after the Unit is completed! The
map is available at £9 alone, or accompanied by an explanatory text in English for £14, (at
2002 prices), from ESTA Promotions, Dr David Williams, GEOU Dept. of Earth Science,
Open University, Milton Keynes, MK7 6AA. Email: [email protected]
Further Reading:
For pupils:
Understanding Geology, David Webster, Oliver and Boyd, 1987, ISBN 0050036645
For teachers:
Geoscience - Understanding Geological Processes, Dee Edwards & Chris King eds. Hodder
& Stoughton, 1999, ISBN 0340688432
Footnote: Experience in teaching "Lava in the lab", since this Pack first appeared. has led
to the follOWing suggestion from Ben Church, ~fMonmouth Comprehensive School. To
reduce mess in the lab, pupils can be encouraged to conduct their investigations by keeping
their treacle in boiling tubes. {f they insert a bung in each tube before inverting it, they can
still test the effects of temperature, solid content or even gas content, by timing the flow down
the tube for a given distance. Much of the treacle can even be recycled!
It is helpful if the technician has filled the boiling tubes (about a quarter full), the previous
day, by warming the treacle so that it flows readily, then allowing it to cool to room
temperature.
Magma - introducing igneous processes
M1: Lava in the lab - the treacle investigation
Notes on teaching the Unit.
1.
Thick or thin?
Pupils are likely to come up with the following ideas on changing the viscosity of treacle:
Changing the temperature (cf. syrup on porridge)
L-------------------------l--------------------------
M 1: Lava in the lab - the treacle investigation
Adding a runny liquid, e.g. water (cf. mixing milk with the syrup on porridge)
Adding a gas, e.g. air
Adding solid material, e.g. sand (cf. mixing the milk/syrup mixture into the porridge).
2.
Plant T (for treacle)
Pupils could devise investigations into anyone of the variables above. It is best if different groups are
encouraged to investigate different variables and all the results are 'pooled' at the end.
The most difficult investigation to do in a fair way that produces reasonable results is the addition of
air, even by using a syringe.
One of the better ways of carrying out the heat investigation is to have a number of water baths at
different temperatures into which test tubes containing measured amounts of treacle are put. The test
tubes are removed when the treacle has reached the water-bath temperature, quickly inverted and the
fall of the treacle to the bench from a fixed height is timed.
Pupils may devise a number of other methods to measure viscosity (e.g. as in Figure Tt).
-
Figure TI. Trickling treacle.
Some possibilities for measuring the viscosity of the treacle include:
a
a)
pouring treacle from a spoon/spatula at measured height and timing the fall of the first drop.
b)
placing some treacle on a sloping petri dish or tile and timing its flow downslope to the other
side (this does not work well for the heat investigation as the treacle soon cools as it flows
downslope, unless the slope can be heated in some way).
c)
one interesting way of doing the investigation using test tubes, is to attach three clamps to one
stand, each containing a test tube at the same height above the bench, then put treacle of different viscosities into the three test tubes and invert the whole stand.
L -_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
2------------------------------------
M 1: Lava in the lab - the treacle investigation
3.
Treacle trickle or treacle torrent?
When pupils have completed their investigations, plotted their results and cleared up the mess, it is
helpful if all the results are 'pooled' in a class discussion as preparation for the next section.
4.
From treacle to lava; from lava to volcanic eruptions
If you have specimens of lavas with gas holes (called vesicles), e.g. pumice, and/or specimens of
lavas containing obvious crystals, these can be used to show pupils that the evidence for different
lava viscosity can become 'fossilised' in the lava.
The most 'runny' lavas are hot (e.g. 1100 0c) with much dissolved fluid and few solid particles
(crystals). These often flow quickly (e.g. up to 100 km per hour has been measured, before the lava
cools). They can also flow for long distances (e.g. tens of kilometres) forming thin sheets. Lavas like
this produce relatively 'safe' (i.e. non-explosive) eruptions and volcanoes that are broad with shallow
slopes, like Volcano X in Figure 1.
The diagram of Volcano X is based onthe shape of the Hawaiian Island of Maui which is a shield
volcano formed of low viscosity lavas.
High viscosity lavas are the opposite. They may produce very explosive and dangerous eruptions
and the volcanic fragments they throw out (bombs, blocks and fine ash) produce steeper-sided volcanoes with slopes of the loose fragments of over 30", like Volcano Y in Figure 1.
The diagram of Volcano Y is based on the shape of Mayon, an explosive volcano in the Philippine
Islands with slopes of more than 35° . Avoid active volcanoes like these on your holidays!
The treacle investigation is based on an original idea of the science staff at Penglais School,
Aberystwyth.
This Unit devised by: Chris King, Altrincham Grammar School for Boys, Altrincham.
Margaret Fordham, Malory School, New Eltham, London.
Robert Smith, Sir George Monoux Sixth Form College, London.
3---------------------------------
M 1: Lava in the lab - the treacle investigation
1.
Thick or thin?
Some liquids are thick and so they flow slowly. Custard, thick
gravy and engine oil are like this.
Other liquids are thin and very runny so they flow quickly.
Water and petrol are like this.
Magma is rock which has been heated up so much underground
that it has melted and formed a liquid. When magma flows out
of the ground in volcanoes it is called lava. Lavas can be very
thick and slow-flowing or they can be thin and fast-flowing.
What makes some lavas runny and other lavas thick?
How is this linked to different sorts of volcanoes and different
sorts of eruptions?
We can find out by doing some experiments, but we can't bring
lava into your school lab because it is too hot (it may be hotter
than 1100 QC) and the nearest active volcano is too far away.
Treacle is a liquid like lava and the 'runniness' of both of these
liquids can be changed in similar ways. So we can do lab
experiments on treacle and then use these to understand how
lavas work.
1.1
On a copy of Data Sheet 1 ('Plan a Treacle Investigation'),
write your answers to these questions in section 1.1.
a)
How can treacle be made more runny? Try to think
of two or more different ways.
b)
How can treacle be made less runny? Think of at
least one way.
L -_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
4---------------------------------
M1: Lava in the lab - the treacle investigation
2.
Plan T (for treacle)
When you have worked out how the 'runniness' of treacle can
be changed, you can try out your ideas.
2.1
Choose one of the different ways of changing the
'runniness' of the treacle for your investigation.
Write the method you have chosen into the first part of
section 2.1 on Data Sheet 1. Then work through the rest
of the sheet, planning your investigation.
Compare your plan with the plans of other people in your
group or class to get the best possible plan for your investigation. Check this 'Master plan' with your teacher.
3.
Treacle trickle or
treacle torrent?
Now find out how treacle flows when its 'runniness' has been
changed.
3.1
Do the investigation by following your 'Master plan'.
Be sure to clean up afterwards.
Don't forget to record your results and to plot them on a
graph.
Then write down what your investigation showed.
Were your first ideas right or wrong?
3.2
Could your investigation have been done better? How?
Be ready to tell the rest of the class about your investigation
and your results.
L-------------------5-----------------~
M 1: Lava in the lab - the treacle investigation
4.
From treacle to lava;
from lava to volcanic
eruptions.
The investigations you have carried out have probably shown
that the runniness of treacle can be changed by:
a)
adding or removing heat, (Le. changing the temperature to
make it hotter or colder).
b)
adding water or air.
c)
adding solid material, like sand.
The runniness of lava changes naturally for similar reasons, i.e.
a)
Lavas can be hot or cool.
b)
Lavas can contain a lot of dissolved water and gas or very
little dissolved fluid.
c)
Lavas can contain many small crystals or no solid crystal
material.
4.1
a)
Which will be more runny, hot lava or cool lava?
b)
Which will be more runny,lava with much dissolved
water and gas or lava with very little water and gas?
c)
Which will be more runny, lava with many crystals
or lava with few crystals?
4.2
Write down these sentences correctly.
a)
Lavas that are hot, with a lot of dissolved water and gas
and no crystals flow
slowly for short distances/quickly for long distances.
b)
Lavas that flow quickly and for long distances form
thin sheets of lava/thick masses of lava
c)
Lavas that are cool, with little dissolved water and gas and many
crystals flow .....
d)
Lavas that flow slowly over short
distances form ....
e)
The runniness of liquids is also called
viscosity.
Liquids that are very viscous (have
high viscosity) are very thick,like
toothpaste. Liquids that are not very
viscous (have low viscosity) are ....
(complete this sentence)
L -_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
6--------------------------------
M 1: Lava in the lab - the treacle investigation
There are two different types of volcano shown in the pictures in
Figure 1.
____~==~~~~~F~~~~~i~~~~i~
Volcano X
o
km
5
o
km
5
VolcanoY
Figure 1. Drawings of two volcanoes, X and Y, in cross section.
4.3
Which volcano might have fonned:
a)
from hot, gas-filled, crystal-free lava,
b)
from cool, crystal-filled lava that lost its gas early in
the eruption? Why?
In volcanoes that have slow-flowing lava, the lava often be-
comes stuck in the mouth of the volcano and becomes a solid
volcanic plug. Under this plug, pressure from the magma
,--_____________--, builds up until eventually the volcano 'blows its top' in a
very E'xplosive and dangerous eruption (Figure 2).
vertical
blast
lateral
blast
In volcanoes like these, most of the cone is built of volcanic
ash and solid blocks blown out of the
volcano.
4.4
If you were going on holiday, would you like to go to
a place where active volcanoes just fonn sheets of lava
or a place where the volcanoes have very steep cones?
Why?
Figure 2. The Eruption of Ml Sl Helens in May 1980.
M 1: Lava in the lab - the treacle investigation
Plan a Treacle Investigation
Treacle is a liquid and liquids are runny.
1.1
Changing the 'Runniness' of Treacle
Different ways of changing the runniness of treacle are:
2.1
a)
to make it more runny (two or more ways) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __
b)
to make it less runny (at least one way)
-------------
My 'Runniness' Investigation
In my investigation, I am going to change the 'runniness' of the treacle by: ____________
I plan to change the 'runniness' in steps by: ________________________________
I plan to find out how runny the treacle is at each step by: _________________________
I will need the following apparatus and materials (use only the apparatus and materials available in the lab, or from your kitchen or workshop at home):
-------------------When the apparatus to
test the runniness of
the treacle is set up, it
will look like this
(drawing):
I will plot the results of my
investigation in a table like this:
I will use the results from the
table to plot a graph like this:
use the
back of this
sheet for
your table
and graph
ideas
I think my results will show that: ______________________________
8-------------------------------
Magma - Introducing Igneous Processes
M2: Lava Landscapes
Notes on teaching the Unit
The Unit is best used after pupils have gained some experience of the properties of lava, notably viscosity
(see Ml: "Lava in the Lab - The Treacle Investigation").
1.
Volcano Power
Start this Unit with a bang by either showing pupils a video of a volcanic eruption or simulating a
volcano in the lab using ammonium dichromate.
The ammonium dichromate 'eruption' is very effective and a wonderful stimulus for pupil
discussion. However, ammonium dichromate is a classified substance and this activity requires a
risk assessment.
First note that:
1.
Ammonium dichromate (VD, [i.e. (NH4)2Cr207) will explode if it is heated when confined.
2.
It is an oxidising agent which forms explosive mixtures with reducing agents.
3.
It is an irritant and should not be handled without the use of gloves and eye protection.
4.
It is poisonous.
L-____________________________________ 9 ------------------------------------
M2:
Lava Landscapes
5.
It is dangerous if mixed with powdered metals.
6.
During the 'eruption', chromium (Ill) oxide dust is produced which is also irritant and
poisonous.
The following method has been supplied by the CLEAPSS School Science Service. We would like to
thank them for their advice.
Place a conical heap of ammonium dichromate (no larger than would cover a lOp piece) on the central
ceramic portion of a wire gauze mat. Put the mat on a tripod in a fume cupboard, and heat from
below with a lighted bunsen. Lower the fume cupboard door and stand back to watch the 'ash eruption'.
1.1
Pupils' lists will vary, but may well include the following:
lava"', 'bombs"", pumice"', ash"', dust*, steam and other gases, noise, light, heat, etc.
1.2
Materials which might be expected to remain are shown by a "'.
2.
Volcano briefing
This is a short revision section, to reinforce the work covered in Unit M1.
2.1
Loose ash and volcanic bombs come to rest at the maximum angle for stability of loose materials, i.e.
around 30°. Ash-fall cones may be symmetrical, or they may be elongated in the direction of the
prevailing wind. A lateral blast also produces an asymmetrical cone.
3.
Expedition to the Puys
The Puys district of the Auvergne has long been regarded as a classic area for the study of volcanic
land forms, although the volcanoes are now extinct. The area featured in the fierce controversy between the 'Neptunists' and 'Vulcanists' of the 18th Century. The Vulcanists won a conclusive battle in
1763 when Desmarest traced a flow of black columnar basalt right back to the ash cone from which it
had originated.
Answers to the pupil exercise on Data Sheet 1 are shown in Figure T1.
DS1 forms the centre spread of this Pack and should be photocopied onto A3 paper.
4.
Expedition evidence explained
1.
The slopes of Le Puy de Pariou are about 30° from the horizontal.
2.
The cone is composed of volcanic ash, produced from lava of moderate viscosity (andesite).
3.
Translation of the labels of the Puy de Dome is as follows:
The birth of a dome of viscous (pasty) lava.
a) dome (rich in dissolved gas)
L -_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
10
------------------------------~~~
~~
g®m
~~"""-
~"co~
t-"-jermom.Ferran~
•
Br 'm
~,
14$ ~~/'\I
;:'I\~
Area P: Geological history 8,200 years ago, lava of moderate
viscosity was blasted into pieces by
gas action and shot into the air as
solid particles. The particles fell back
to earth, the large ones nearest to the
vent of the volcano, the smallest ones
further away.
Landform - A symmetrical
cone with a crater near its summit.
=
=;7
A
Area S: Geological history10,000 years ago, a lava of very high
viscosity was squeezed out of the
ground, like toothpaste. It built up a
high dome of lava. Later, gases at up
to 700 ·C burst out from the side of the
dome and rushed down the hillside at
500 km per hour. The hillside was
'rebuilt' from clouds of ash particles
carried by the hot gases. The ash
became 'welded together' by the heat.
Landform - A dome-shaped
hill several kilometres across, rising
500 metres above its surroundings.
1~'1(
~
.~
~:~"
\'v~'
,
4<,
N
t
~
~. .'
.
"",-
....•.......
[E]
:::.
... '
,.
~.
Map of part of the Puys district of the Auvergne, France.
(adapted from ''Vo1canologie de la Chaine des Puys",
ed. PNR V.A. with the permission of the authors)
Key
®
Cone, built mostly
of volcanic ash
'"4
~
~
~
~
Lava forming a dome
C
Lava flow
_~_:-~_-.-..:t-~~~ ~
Lake
~~~~-
Town
Direction of view for
drawings A to 0
km
o
Area R: Geological history3,400,000 years ago, a lava of very low
viscosity was erupted and flowed
down an old valley. The lava was
harder than the rocks around it. There
has been enough time for erosion to
remove the surrounding rocks. The
original volcanic vent has also been
eroded away.
Landform - A long ridge with
steep sides overlooking gentle valleys.
This is an example of 'inverted' relief,
where what was once in the bottom of
a valley now forms the higher land.
234
o
Area Q: Geological history8,500 years ago, a lava of very low
viscosity was erupted from an ash
cone and flowed for 30 km. The flow
followed an old valley and filled it
with lava.
Landform - A long line of low
hills with lakes on either side. The
lakes were formed where streams
were dammed up by the solid lava.
M2: Lava Landscapes
b) destruction of the dome, by violent release of gas.
'Nuee ardente' means 'incandescent gas cloud', but the French term is commonly used
verbatim by English-speaking geologists. The cloud may contain gas, ash, liquid droplets
and blocks of lava.
4.
Inverted relief. The original lava flow occupied a valley, but the lava proved more resistant to
erosion than the rocks of the valley sides. The valley sides have been worn away, leaving the
lava flow perched up as a ridge.
5.
Lava flows can some times divert or even dam up rivers, in this case forming permanent lakes.
6.
All the volcanic products form upstanding features of the landscape. Pupils will add a variety of
detail.
7.
The ash cone of the Puy de Pariou may be expected to be eroded more quickly, since it is composed of loosely compacted ash, which would be more easily weathered and washed away. The
Puy de Dome is mostly composed of lava which would have crystallised into a tight mosaic of
interlocking crystals, providing less access to the agents of weathering.
(The dates are derived from thermoluminescence techniques or by radioisotopic methods. The
younger lavas are dated by Carbon14 dating on charred wood or soil included in the lava: the
older lavas are mostly dated by the K/ Ar method).
8.
Eruptions in order of 'danger' would have been:
most dangerous
- Puy de Dome (viscous trachyte lava, liable to explode)
- Puy de Pariou (explosive ash eruptions, from andesite lava of moderate
viscosity)
least dangerous
- the long lava flows of the south eastern part of the map. These consist of
low viscosity basalts.
Although basalts may flow at at up t0100 km per hour, they do not usually erupt without warning. They may destroy property but it is normally possible for people to get out of the way in
time. (Note that the lava flow dated at 3,400,000 years pre-dates Homo sapiens by 3 million
years or so!)
9.
Fissure eruptions are a digression from the main story, but pupils should realise that most of the
world's lavas (basalts) are produced from fissures rather than from central volcanoes. This
includes submarine eruptions.
Fissure eruptions on land generally produce 1ava plateaus', which weather to form a series of
flat-lying steps, known as 'trap topography'. The lavas are called plateau basalts, and are
characteristic of Antrim, the Deccan Plateau of India, the Columbia/Snake River Plateau of the
U.S.A. and many others. Stepped hillsides are also developed on some of the lavas of West
Scotland (60 million years old) and even in the Lake District (450 m.y. old)
This Unit devised by: Peter Kennett, High Storrs School, Sheffield.
L-----------------------------------12
M2:
1.
Lava Landscapes
Volcano power
Volcanic eruptions
can either be very
explosive or fairly
quiet, and many
different things
come out of the
mouths (or vents
of volcanoes).
1.1
Think about any volcanic eruptions you have seen (e.g. on
television) and write a list of as many things as you can
that come out of volcanoes.
1.2
Go through your list again and mark a .. against those
things which you might expect to find many years later,
long after the eruptions had ceased and the volcano had
become 'extinct'.
The volcanic products you have marked (..) help to build a
very distinctive landscape, which remains for many years
after the eruptions have stopped. After a very long time,
volcanic rocks may still be found, although the landscape
itself is so eroded that the original volcanoes cannot be
recognised.
For example,
A)
Active volcanoes can be found in parts of Italy.
B)
Extinct, but still recognisable volcanoes occur in the
Auvergne region of France.
L -_________________________________
13
------------------------------~
M2: Lava Landscapes
C)
There were volcanoes in Britain, but they stopped
erupting about 40 million years ago. There are no
'volcano-looking' cones in this country now, although there are many areas where ancient lavas
make up much of the landscape, such as in the Lake
District, Wales and Scotland.
We shall study the French examples, to help you to see
how volcanic landscapes form.
2.
We know the following about volcanoes:
Volcano Briefing
2.1
a)
Molten rock which erupts through volcanic vents
and fissures is called lava.
b)
Some lavas are more runny than others (i.e. they
have different viscosities).
c)
The viscosity of a lava depends upon several things,
including: its temperature, its gas content, its
chemical composition and the proportion of solid
material which it is carrying.
d)
A lava of low viscosity flows easily and may flow a
long way from the volcanic vent.
e)
A lava of high viscosity is very pasty and does not
flow very far. Volcanoes with pasty lava have
explosive eruptions, blasting volcanic bombs, blocks
and ash up into the air. The fragments fall to earth to
form volcanic cones.
Why do falling ash, blocks and bombs form cone-shapes?
L -_____________________________________
14 ------------------------------
Clermont-Ferrand
N
t
Map of part of the Puys district of the Auvergne, France.
(adapted from ''Volcanologie de la Chaine des Puys",
ed. P .N.R.V.A. with the pennission of the authors)
Key
,
®
Cone, built mostly
of volcanic ash
Lava forming a dome
c
~
~
Lava flow
, Lake
Town
Direction of view for
drawings A to D
km
o
1
D
234
16
17
M2:
3.
Lava Landscapes
Expedition to the Puys
Figure 1 shows the location of the Puys district in France.
Data Sheet 1 has a detailed map of the area,
showing some of the volcanic rocks. Drawings of some of the volcanic landscapes are
shown beside the map.
N
1
Paris
•
I
.I
I
FRANCE
Clermont-Ferrand
"
"I
200 km
Most of the volcanic eruptions took place
between 4,000 and 60,000 years ago. This is
not very long ago in terms of geological
time and the landscape still looks very
'volcanic'. In places, however, there are
some much older rocks, dating back several
million years. There has been a lot more
time for these rocks to be eroded, so their
landscape is quite different.
Look at the drawings on Data Sheet l.
Write a description of each landscape on a
6 cm square piece of paper. Don't worry
yet about explaining how the landscapes
formed.
3.1
When you have finished, pass your descriptions to your partner to see if he or she can match up
each description to the correct drawing. Rewrite any
deSCriptions which are not good enough and stick them
into position in Column 2 beside the right drawings.
L -_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _- - - - '
Figure 1. The location of the Puys
district in France.
3.2
The arrows on the map show the directions from which
each drawing was made, but do not show which drawing
belongs to which arrow. Match them up and connect each
drawing to its most likely location on the map (using a
pencil line). Check your answers with your teacher before
going any further.
3.3
Data Sheet 2 contains some more sketches of the area.
These have been drawn by French geologists who have
tried to show the history of the volcanic activity there.
The original French labels may help you.
Cut out the sketches and try to match each one up to the
correct picture on the map sheet (DS1). Stick them into the
right positions in Column 3.
3.4
Data Sheet 2 also contains some written descriptions of the
geological history and the resulting landscapes of the
features shown in each picture in DSl. Read these carefully, then cut them out and stick them into the correct
spaces in Column 4.
L-------------------------------19------------------------------
M2: Lava Landscapes
4.
Expedition evidence
explained
Check your work from section 3 with your teacher and then
answer the following questions:
1.
Estimate the angle of the slopes of the cone of Le Puy de
Pariou. (Drawing A)
2.
What kind of material probably makes up the cone of Le
Puy de Pariou? (Drawing A)
3.
.Try to translate the meaning of the French caption above
the sketches showing the history of Le Puy de Dome
(Hint: you can do this from your knowledge of the viscosity of the lava, even if you do not know much French!)
(Drawing B). Try translating some of the other captions
too.
4.
Explain the meaning of the term 'inverted relief' in
DrawingC.
5.
How can lava flows affect the river flow in an area?
(Drawing D)
6.
How does the resistance of volcanic products to erosion
affect the ways in which the landscape may develop after
the eruptions have all ceased? (all the drawings).
7.
The Puy de DOme and the Puy de Pariou are of similar
age. (Drawings A and B). Which one would you expect
to be more recognisable 500,000 years from now? Explain
your answer.
8.
Which of the four eruptions shown in the pictures would
have been the most dangerous and which the least dangerous? Put the eruptions into order of 'danger'.
L--------------------------------------20--------------------------------
M2:
Lava Landscapes
9.
Most of the volcanic rocks of the Puy district have
erupted from separate vents, known as 'central volcanoes'. Many of the world's lavas, however, have erupted
from fissures, which are cracks in the earth's crust, many
tens of kilometres in length.
The lavas from fissures are usually of very low viscosity
and flow in broad sheets for many kilometres. The Antrim Plateau in Northern Ireland is a good example,
which was built up from many lava flows, about 60
million years ago.
Study the block diagram of the fissure eruptions of the
Antrim Plateau (Figure 2). How is the landscape of the
area different from that of the Puys district of France?
Lava erupting
from fissure
'Steps' in lava, formed
by later erosion
Fissure
. ...
. .
. .. . .. Older
rocks'. : • • '.' • •
.. : .. ' . .. . .. :.•••
..... . ....... .. .
. ... .
"
r
Magma
Figure 2. Block diagram of the Antrim Plateau, showing lavas produced by fissure
eruptions, 60 million years ago.
10.
If you ever go on holiday to a volcanic area, ancient or
modem, try to work out for yourself what happened.
How did the volcanic activity affect the landscape? Use
your eyes, a sketch book and a camera. Bring back the
results for your school, plus a few loose rock specimens,
if the airline will let you!
L -_________________________________
21--------------------------------~
M2: Lava Landscapes
How French geologists think the volcanic features
were formed (not in order).
Croissance d'un dome
de lave pateuse
The geological histories of the areas shown in the
drawings in DSl (not in the right order).
Area P: Geological history 8,200 years ago, lava of moderate
viscosity was blasted into pieces by
gas action and shot into the air as
solid particles. The particles fell back
to earth, the large ones nearest to the
vent of the volcano, the smallest ones
further away.
Landfonn - A symmetrical
cone with a crater near its summit.
Dome
(riche en
gaz dissous)
Destruction du
dome par
liberation
brutale
des gazAiflMijIM:'
Area Q: Geological history 8,500 years ago, a lava of very iow
viscosity was erupted from an ash
cone and flowed for 30 km. The flow
followed an old valley and filled it
with lava.
Landfonn - A long line of low
hills with lakes on either side. The
lakes were formed where streams
were dammed up by the solid lava.
Gaz
Area R: Geological history 3,400,000 years ago, a lava of very low
viscosity was erupted and flowed
down an old valley. The lava was
harder than the rocks around it. There
has been enough time for erosion to
remove the surrounding rocks. The
original volcanic vent has also been
eroded away.
Landform - A long ridge with
steep sides overlooking gentle valleys.
This is an example of 'inverted' relief,
where what was once in the bottom of
a valley now forms the higher land.
Area S: Geological history 10,000 years ago, a lava of very high
viscosity was squeezed out of the
ground, like toothpaste. It built up a
high dome of lava. Later, gases at up
to 700°C burst out from the side of the
dome and rushed down the hillside at
500 km per hour. The hillside was
'rebuilt' from clouds of ash particles
carried by the hot gases. The ash
became 'welded together' by the heat.
Landfonn - A dome-shaped
hill several kilometres across, rising
500 metres above its surroundings.
qu'e11e recouvre
22----------------------------~
Magma - introducing igneous processes
M3: Crystallising magma
~---------------23---------------
M3: Crystallising magma
Notes on teaching the Unit
A day or more before the Unit is taught one of the crystallisations for 'Crystal chaos' should be prepared (see
the preparation method on TS4). At that time, microscope slides should also be put in the deep-freeze.
Just before the start of the lesson, a second crystallisation for 'Crystal chaos' should be begun.
1.
How big can they grow?
1.1
Most granites contain just three visible types of crystal (mineral) randomly scattered through the rock
and interlocking (ie no gaps between the crystals). These are:
feldspar -
white; crystal shapes may look approximately rectangular; flat surfaces glint in the
light (these are cleavage or flat breakage surfaces); cannot be scratched by a steel point
(eg the needle of a pair of compasses);
biotite mica - black; plate-shaped crystals (flat but thin); flat cleavage surfaces glint, sometimes with
a yellowish colour; soft enough to be scratched with a copper coin;
quartz grey and glassy; poor crystal shapes; irregular breakage surfaces; harder than a steel
point.
1.2
Common igneous rocks that you may have available are those listed in Table Tt on TS4. The most
common ones are shown in bold.
2.
Home grown crystals
There are various ways in which this investigation can be carried out. In the method used in the Pupil
Sheets, the pupils carry out one crystallisation, then make predictions based on their findings, before
testing their ideas. This has the advantage that the pupils are able to make and test predictions, they
can observe the crystallisation twice and also, if the first crystallisation does not work (due to the
supercooling described below) then there is a second chance for the pupils to see the correct result. The
most straightforward way of conducting the crystallisations is as follows:
1.
Show the pupils the crystalline Salol in the jar, before putting some into the boiling tube and
melting it in the water bath. When it has melted, remove the Bunsen so that the temperature of
the Salol increases no further. Put some slides in the water bath to be warming.
2.
While the Salol is melting, pupils label a piece of paper and place a microscope slide at room
temperature in the correct place on the paper.
L-____________________________________ 24 -------------------------------
M3: Crystallising magma
3.
When all is ready, give out the slides from the deep-freeze and, as soon as possible, go round the
groups with a pipette of molten Salol and put a few drops (enough to cover a new 5p piece) onto
each slide. Touch each drop of Salol with the pipette to start the crystallisation.
4.
Check soon afterwards that the crystallisation has begun, since the Salol may supercool and not
crystallise at all, unless the liquid is seeded by touching with the pipette. If, by the time the
liquid is seeded, the pools of Salol on the different slides have reached the same temperature,
there will be little difference in their crystallisation.
The pupils should find, in this first part of the investigation, (2.1d) that:
i)
ii)
iii)
crystallisation began first on the slide from the deep-freeze;
the crystals grew fastest on the deep-freeze slide;
since many crystals form on the deep-freeze slide, and these interfere with one another as the
Salol cools, the room temperature slide has the largest crystals.
The pupil should, therefore, predict that, on a warm slide (2.1e) the crystals will:
i)
ii)
iii)
take some time to begin forming;
grow slowly;
form large crystals.
5.
When they have made their observations and predictions, give out the warmed slides and distribute more molten Salol as described above. Pupils should record their results and conclusions.
This final crystallisation can be done instead on a microscope slide on an overhead projector. The slow
crystallisation on the warm OHP surface is then projected onto the wall for all the pupils to see.
2.2
Lavas that cool quickly at the surface are fine-grained, (ie they are composed of small crystals) whereas
& 2.3 magmas that crystallise deep beneath the surface produce coarse-grained igneous rocks.
(Note: Some igneous rocks have large crystals set in a fine-grained crystal ground mass because they
began crystallising at depth before rising up to complete their crystallisation on or near the surface.)
3.
Crystal chaos
This must be a demonstration because the safety regulations do not allow lower school pupils to use
potassium nitrate (or potassium dichromate) in crystallisation investigations.
The crystallisations begin quite fast, but take several hours to complete; this is why it is suggested
above that one crystallisation is prepared a day or more previously and one is begun at the start of the
lesson. The third crystallisation should be begun now.
L------------------------------------25 -------------------------------
M3: Crystallising magma
Method
Mix a spatula full of copper sulphate crystals with an equal amount of potassium nitrate crystals in a test
tube. Cover them with a similar quantity of dilute sulphuric acid and warm, while stirring, until the crystals
dissolve. Hold the test tube under a running cold tap for a minute or so to cool the solution, then pour it into
a watch glass. Nicely-shaped blue copper sulphate crystals form first in a random pattern. The gaps are later
filled in by the white, needle-shaped potassium nitrate crystals.
The ratios of the salts can be varied to change the results and orange potassium dichromate can be used
instead of the white potassium nitrate. The results can be 'thrown onto the wall' using an overhead projector.
This method was first described by K. C. Murfitt and M. J. Bradshaw in Geology Vol. 1, 1969, pub.
Association of Teachers of Geology.
At the end of this section, it is useful to point out to pupils that nearly all igneous rocks are classified according to their crystal sizes and the different types of crystals (minerals) they contain. Common dark minerals
found in rocks contain iron and magnesium whereas the common pale rock-forming minerals do not. This
results in the scheme shown below.
Table Tt. A Common Classification Scheme for Igneous Rocks (for teacher reference).
Grain size
Dark crystals
scattered
Dark crystals
common
Dark crystals
abundant
Dark crystals
only
Coarse
granite
diorite
gabbro
periodotite
Medium
microgranite
microdiorite
dolerite
rare
Fine
rhyolite
andesite
basalt
rare
Glassy and
dark colour
volcanic glass or obsidian
The most common igneous rocks are shown in bold.
Please note: Pupils should be able to classify some rocks according to a scheme they have been given but, it
will not be necessary for pupils to learn rock names like those in the table above as part of their
National Curriculum studies.
4.
How and where?
4.1
The coarsest igneous rocks form when magmas cool very slowly at the greatest depths, ie near level E.
The slow cooling occurs because of the many layers of insulating rock above. The finest-grained rocks
form by cooling quickly at the surface (at A). Some become chilled so quickly that there is no time for
crystals to grow, so that volcanic glass is formed. Medium-grained rocks form at depths D, C and B,
with their grain sizes reflecting rate of cooling and thus the depth of burial.
L-------------------------------~----26------------------------------
M3: Crystallising magma
4.2
Granite forms in large igneous masses called batholiths deep within the crust.
4.3
Basalt forms lavas at the surface while dolerite is found in dykes and sills at moderate depths.
4.4
Granite contains much less iron and magnesium (eg 1%) than basalt and dolerite (eg 10% Mg/Fe).
4.5
The map in Figure 3 is based on the postcard geological map sold with the 'Science of the Earth, 11-14'
three-Unit pack called 'Hidden Changes'. This is a better source of information for pupils if you have a
class set available. The coloured postcards can be purchased from: The Sales Desk, British Geological
Survey, Keyworth, Nottingham NG12 5GG.
The granite was most probably intruded into the roots of mountains, 10 to 20 km below the surface, as
part of a mountain building episode. Mountain building episodes occur when two of the Earth's plates
collide.
4.6
Granites are exposed by steady erosion of the mountains and overlying rocks as the areas were uplifted
in the geological past. Much uplift is caused by movement of the Earth's plates.
4.7
When the volcanoes were erupting, they were spectacular at best and very dangerous at the worst.
The geological evidence shows that landscapes in Britain were very different in the past. This is illustrated in
many other 'Science of the Earth' Units as well.
This Unit was devised by: Adrian Marks, Cornwall College, Redruth.
L----------------------------------27 -----------------------------
M3: Crystallising magma
1.
How big can they
grow?
Some of the biggest crystals ever found were discovered in
South Dakota, USA. One of these giant crystals was 14 metres
long, more than a metre thick and weighed 65 tonnes.
All crystals form by growing and the crystals in South Dakota
became so big because they grew and grew for a very long time.
Magma is hot liquid rock. When magma cools down crystals
grow in it until all the liquid rock has become solid crystals.
Rocks made from crystalling magmas are called igneous rocks.
Some igneous rocks have tiny crystals and some have large
crystals (the large crystals are usually a few mm across, not as
big as those in South Dakota!). Why do some igneous rocks
have small crystals and some have large ones?
We can get some clues by looking at a piece of the igneous rock
called granite. When you turn a piece of granite in the light,
many of the crystals sparkle. The crystals give the clues as to
how the granite formed, so we must look at them carefully.
1.1
How many different things can you write down about the
crystals in the granite? This list may help you;
different types, or all the same?:
different colours, or all the same?:
clustered together?;
white, black, grey, other colours?:
different sizes, or all the same?:
average size?:
different shapes?:
scattered, or clustered together?:
gaps, or crystals fit together well?:
dull or shiny?:
scratched easily, or hard to scratch?:
Granite is a coarse-grained igneous rock with
crystals that you can easily see. The crystals in
granite look like this.
Medium-grained igneous rocks like dolerite
have smaller crystals, like this.
Fine-grained igneous rocks like basalt have
very small crystals that look like this.
1.2
Are the igneous rocks you have been given coarsegrained, medium-grained or fine-grained? If some have
no grains at all, they are called glassy.
L-------------------------------------28 ---------------------------------
M3: Crystallising magma
2.
Home grown crystals
We can find out how the crystals in igneous rocks form by growing crystals in a similar way in the lab.
2.1
Find out why the crystals in igneous rocks have different
sizes by following this recipe.
a) Read this through first so that you know exactly what
to do before you begin.
b) Take a piece of paper and label it as shown in Figure 1.
Put a microscope slide on the 'room temperature' part
of the paper.
R.OOM
TE.iII1PERATUR.E
FREEZE.R
WAR.M
Figure 1. Microscope slides labelled using a piece of paper.
c)
Ask for a microscope slide from the deep-freeze and
put it on the paper. As soon as you can, get a pipette
with some melted Salol from the water bath and put a
few drops on each slide. Then touch each drop of
liquid with the pipette. Watch what happens.
On which slide did crystals form first?
iD On which slide did crystals grow fastest?
iii) On which slide did the largest crystals form?
d) i)
e) If you had a warm slide, would you expect the
crystals:
i)
to form straight away or after some time?
ti) to grow quickly or slowly?
tii) to be large crystals or small crystals?
Write down these ideas (your predictions).
f)
L -________________________________
Test your ideas by asking for a warm slide. Put it on
the paper; add liquid Salol as soon as you can; touch it
with the pipette and watch carefully. Were you right?
29 ------------------------------
M3: Crystallising magma
The Salol helps us to find out how igneous rocks fonn because
they start off as liquid too. Magma is fonned when parts of the
Earth under the surface become so hot that the rocks there melt.
Then the molten rock usually rises up towards the surface and
begins to cool, fonning crystals as it cools.
2.2
Magmas that reach the surface are called lavas. They cool
quickly at the surface. Would you expect lavas to have
large crystals or small crystals? Why?
2.3
Some magmas stay deep under the surface and cool
slowly. Would you expect these to fonn coarse-grained
or fine-grained igneous rocks? Why?
Igneous rocks have crystals of different sizes because the
magmas cooled at different rates.
The Salol shows how the crystals in igneous rock fonn, but they
don't look much like the crystals in your piece of granite because the granite has crystals of different colours. But, we can
make a coloured 'igneous rock' in the lab too.
3.
Crystal chaos
The white crystals and the blue crystals both dissolve in wann
dilute acid, but then ...
3.1
Watch how the crystals fonn as the liquid cools down and
the water evaporates. Which crystals fonn first? Which
crystals have the best shapes?
3.2
How 'real' is the crystal chaos 'igneous rock' that you
have seen growing in the lab? Compare it with your
granite specimen to find out. Use the list in question 1.1
to help you.
3.3 How could you make an 'igneous rock' in the lab with
\ - -_ _ _ _ _ _ _ _ _ _~c~ry~s:t:al~s of other colours?
Different sorts of igneous rocks have crystals
with different colours because the chemistry
of their magmas was different at the beginning. For example, igneous rocks with
mostly dark crystals usually contain a lot of
iron and magnesium. Rocks with mostly
pale crystals do not contain so much of these
elements.
Igneous rocks have crystals of different
colours because their original magmas
contained different materials.
L---------------------------------------30 -----------------------------
M3: Crystallising magma
4.
How and where?
Volcano
Level'" "
A
0
The cartoon shows some early ideas about how igneous rocks are
formed. Now you can use your own lab investigations to see
how different sorts of igneous rocks can be formed in the Earth.
----
--
--
1
----
----
2
--
Level
B
3
4
"-
5
"-..
--
/'
/'
6
"-
"-..
"-
'-
"-
----
4.1
Figure 2 shows where in the Earth's crust different igneous
rocks crystallise and become solid. Different levels in the
crust are shown by letters.
i) At which level would you expect the coarsest-grained
igneous rocks to form? Why?
ii) Where do the finest-grained igneous rocks form? Why?
lii) Where would you expect medium-grained igneous
rocks to form?
4.2
At what level in the Earth's crust do you think your piece
of granite formed?
4.3
At what levels in the Earth's crust do you think basalt and
dolerite form? (Look at Section 1 for help).
"-
/
7
/"
Level
"'"
8
+
+
i-
+
9
"-
"-
"-.....
of
"
-t
t
t
"
-t
f
10
Depth
+
+
Batholith
/km
Figure 2. Drawing of a slice through the
Earth's crust showing where different
sorts of igneous rocks form.
L-________________________________
31
M3: Crystallising magma
.~
Key
E2J Granites
-
Lavas
4.4
Granite is made
mostly of pale crystals
because it contains
little iron and magnesium. Basalt and
dolerite are dark coloured igneous rocks.
Why?
4.5
Rocks seen at
the surface of the Earth
are called exposures.
How far away is your
nearest exposure of
granite? What do you
think the area was like
when the granite
formed?
4.6
If the granite
formed where you
think it did, how is it
that specimens of
granite can be broken
off and studied at the
surface of the Earth
today?
4.7
Where is your
nearest exposure of
lava. What do you
think the area was like
when the lava formed?
(Think of films of volcanoes you have seen
or work you may have
done on lava landscapes in the Puy area
of France).
• 100 km.•
....
Figure 3. The main igneous rocks found at the surface in Britain.
You have been looking at some of the effects of igneous activity in Britain long ago. There have been many great igneous,
sedimentary and metamorphic changes in Britain's geological
past. If you had been here long ago (well before people appeared on Earth), you would not have recognised the landscape where you are now sitting because it would have been
so totally different.
L-------------------------------------32-------------------------------
Earth Science Teachers' Association: Science of the Earth 11-14
Coverage of the National Curriculum:
The Units cover parts of the National Curriculum for Science (2000) as follows:
Sc3 Materials and their properties
Geological changes
Pupils should be taught:
2e about the formation of rocks by processes that take place over different time scales, and
that the mode of formation determines their texture and the minerals they contain.
2f how igneous rocks are formed by the cooling of magma ...
The Units assist in teaching to the Scheme of Work (QCA 2000):
Unit 8H The rock cycle
- Where do igneous rocks come from? and
- What is the rock cycle?
Analysis of skills
Designing & planning an
investigation
Practical investigation
Ml
Experimental investigation
-V
~
Data collecting & recording
M2
M3
Analysis of skills
Decision making exercise
Ml
M2
M3
~
Solving problems by applying
results
Compiling a report
~
~
~
-V
-V
~
~
-V
-V
Calculation
Data plotting exercise
Date manipulation exercise
Three-dimensional thinking
-V
Thinking in the time
dimension
-V
Acknowledgements:
Thanks are due to Alan Birchall, Oominic Greenall, Lewis Jones and Helen Busteed for
artwork and cartoons, and to Or Reg Bradshaw for his help and advice in the preparation of
the text of the Units.
We are most grateful to the French authors of the original map and poster of the Puys district,
for allowing the use of adaptations of their work, namely: G. Camus et ai, Oept.de Geologie
et Mineralogie, Universite de Clermont-Ferrand, and P. Lavina and H. Monestier, Editions
Artisinales, Cormede.
Copyright:
There is no copyright on original material published in these Units, if it is
required for use within the laboratory or classroom. Copyright material reproduced by
permission of other publishers rests with the originating publishers.
"Science of the Earth 11-14" Units are published by The Earth Science Teachers'
Association.
Magma was originally typeset and printed in 1990, by Geo Supplies Ltd.
This reprint includes amendments to the information on the inside pages of the covers.
ISBN 0 9501031 3 6 2002
Printed by: TRADEPRINT, 515, Abbeydale Road,
Sheffield, S7 IFU TEL: 01142583434
British Coal has been so impressed by your work in the lab that they have offered you a job as an
assistant. You have been sent to an old mining area to find out if there is enough coal in the waste tips
to be worth separating out.
BE.ST
VoRTe.)<.
sePA'fI..Po'TOR
From one tip, you have taken samples of the spoil and used your school apparatus to discover that there
is 25% coal to 75% waste rock.
The waste tip is cone shaped, 50m high with a 200m diameter at the base (Figure 5).
-·----------------------------200m--------------------------~~~
Figure 5. Diagram showing the size and shape of the waste tip.
5.1
Using all the information available, set to work on the following problems:
a) Calculate the total volume of the waste tip, knowing that the volume of a cone =1/3wh
(h is the height of the waste tip and r is its radius, i.e. half the diameter)
b) Calculate the total volume of coal in the tip.
c) Calculate the mass of coal in the tip, given that the density of coal is 1.3 tonnes per m3.
(Density =
~~e
so, Mass = Density x volume)
d) Assume that 90% of the coal in the tip can be separated on a commercial scale. What would
be the value of the coal recovered, assuming that it is worth £45 per tonne?
e) Every tonne of coal recovered costs British Coal £25 to recover. (This is spent on the
separation process, transport and landscaping). Calculate the profit made by British Coal from
the whole waste tip.
Using these methods, not only can British Coal 'unspoil' the countryside, but it can often be done at a
profit too!
PS6
Coverage of Attainment Targets:
The Units cover parts of the following Programmes of Study (PoS, Key Stage 3) and Attainment Targets (AT) in
National Curriculum Science:
UNIT
PPl PP2 PP3
Attainment Target
ATl.
Exploration of Science: A) PoS, Key Stage 3:
Systematic investigations which -
~
~
'encourage systematic recording using methods appropriate to the data ... '
~
~
~
'encourage interpretation & evaluation of collected data .... against the demands of the problem... '
~
~
~
'encourage the search for patterns in data and ability to make simple predictions based on findings'
~
~
~
'encourage use of... technical vocabulary when reporting findings & conclusions.'
~
~
~
Statements of attainment:
Level 4 - 'follow written instructions & diagrams .... '
~
~
~
~
~
~
Level 5 - 'make written statements of patterns derived from data obtained from various sources'.
~
~
~
Level 6 - '... collaborative exercise: use experience & knowledge to make predictions in new contexts.'
'produce reports ... '
~
~
~
~
~
'are set within the every day experience of pupils & in wider contexts ... '
'require that pupils plan & carry through investigations in which they may have to identify, describe
and vary more than one key variable ... '
8)
'draw conclusions from experimental results'
AT2.
~
~
The variety of life. B) Statements of attainment:
Level 4 - 'understand that plants and animals can be preserved as fossils in different ways'.
AT5.
Human influences on the Earth. A)PoS, Key Stage 3:
' .. should investigate ways of improving the local environment through project work'.
~
8)
Statements of attainment:
Level 3 - 'know that human activity may produce local changes in the Earth's surface, air & water".
~
~
'.. give an account of a project to help improve the local environment'
Level 4 - ' know that some waste materials can be recycled'.
~
Level 5 - ' be able to argue for & against particular planning proposals in the locality, which may
have an environmental impact
~
Level 7 - 'understand the balance of advantages & disadvantages in the way human activity affects
the environment'.
~
AT6.
Types and uses of materials. PaS, Key Stage 3 and Attainment Level 5:
'Pupils should investigate various techniques for separating and purifying mixtures'.
~
AT9.
Earth & Atmosphere. A) PoS, Key stage 3:
'Pupils should investigate, by observation, experimentation and fieldwork, the properties and
formation of...sedimentary rocks and link these to major features and changes on the Earth's surface'.
~
~
'They should be aware of the time scales involved in the operation of geological processes ... "
~
~
8)
Statements of attainment:
Level 6 - 'be able to explain the processes by which ..... sedimentary rocks were formed ... '
~
~
ATl3.
Energy. POS, Key Stage 3: 'pupils should consider the importance of energy from the Sun .. the origin
and accumulation of fossil fuels .. '.
~
~
Level 6 - 'understand that the Sun is ultimately the major energy source for the Earth'.
~
~
Analysis of skills
Designing & planning an investigation
Practical investigation
Data plotting exercise
Data manipulation exercise
PPl PP2 PP3
~
~
~
~
Calculation
~
~
Three-dimensional thinking
~
~
Decision making exercise
~
~
~ Solving problems by applying results
Experimental investigation
Data collecting & recording
Analysis of skills
PPl PP2 PP3
~
~
Compiling a report
~
~
~
Thinking in the time dimension
~
~