Download volcanoes 1 - Earth Science Teachers` Association

Issue 63
VOLCANOES 1
What are volcanoes?
Registered Charity No. 1005331
Introduction
Children are usually fascinated by the awesome power of volcanic eruptions. This PEST looks
at ideas that link to the Science curriculum (Sc1) and aids more able KS1 and lower KS2
children to:


observe, explore and ask questions about the phenomena
use reference materials to find out more about scientific ideas
share their ideas and communicate them using scientific language.
There are also links to Sc3 (how materials change when they are heated or cooled) and
Geography (how places have become the way they are and how they are changing).
Background Information
When anyone is asked what a volcano is, they tend to describe one as a cone shaped mountain
with red-hot lava running down the slopes. This is not a bad description but it only goes a small
way in explaining what a volcano really is.
So what are volcanoes?
To understand what a volcano is, it is necessary to understand what the Earth is like under our
feet. The Earth is a little bit like a peach or nectarine, which has a tough skin on the outside
with a virtually solid area under that and a hard stone in the middle. The Earth has a hard skin
called a crust, the land we stand on and the ocean floor. Underneath that is a large, deep area
of very hot rock, the mantle. The mantle’s rock is so hot that it can move around by flowing in
circulating or convecting thermal currents. Below the mantle is an extremely hot liquid layer,
called the outer core. This surrounds the solid inner core which is made mainly of iron. Cutting
a peach or nectarine in half to show the pupils rather than just describing it will give them a very
good 3D illustration of the interior of the Earth and the crust-mantle-core proportions are almost
perfect too. A volcano forms when hot molten rock (magma) breaks through the Earth’s crust.
Earth’s hard crust
(land and ocean floor)
Diagram of a slice
through the Earth
Mantle of
hot, slowly flowing rock
Liquid outer core
Solid inner
core
Issue 63 – Volcanoes 1
What is magma?
Magma is a basically a very deep layer of molten rock produced either at the top of the mantle
or from partly melted crust. Minerals are the basic ingredients of solid rocks. The hottest mantle
rock from deep under the Earth’s crust rises up to the top because it is lighter (less dense). The
whole mantle moves around very slowly, in thermal currents. As the hot mantle rises it begins
to melt. The crust is solid and hard so it usually stops the molten rock or magma leaking out.
Where the crust is very thin, like some areas of the ocean floor, the magma can push its way
through and erupt onto the surface to form new rocks and land. It seeps through weaknesses in
the crust and as it does so it forms into larger blobs and travels upwards towards the surface of
the crust. The magma from under the crust is called lava once it is erupted onto the surface.
Which minerals does lava contain?
Quartz, mica and feldspar are the most common minerals in lava. When the lava cools down
and hardens, such minerals form crystals of various sizes from very small and barely visible to
larger and easily visible ones. They form rocks called basalt or andesite, depending on the
amount of each mineral present at the time the rocks form.
What else does magma contain?
Within the magma there are gases as well as the molten minerals. If, while the magma moves
towards the surface the gases are able to escape through the cracks in the rocks then the
eruption of the magma onto the surface will be slow and steady forming a stream of red hot lava
like Hawaiian volcanoes. If, however, the gases cannot escape and they are trapped in the
magma when it reaches the surface then the eruption will be explosive shooting ash high into
the air and spreading clouds of gas and ash over a large area like Mount St Helens in the USA.
Which of these eruptions are most dangerous to humans and animals?
The explosive ones are more dangerous because they are more sudden, are much faster and
spread much further than the streams of lava. These explosive eruptions are so fast that people
and animals cannot get out of the way quickly enough. With the lava stream everyone can see
where it is and they can move out of the way. It will cause damage to buildings and land but it
is more unlikely that anyone would be hurt.
Volcanoes can erupt under the sea as well as on land. In fact most of the volcanoes are under
the sea but we cannot see them. The volcanoes under the sea erupt lava into very cold water
which cools the lava down very quickly, forming into a dark dense rock consisting of very small
crystals (basalt). Whereas, the lava from volcanoes erupting onto the land tends to cool more
slowly which allows larger crystals to form (grow) within the new rocks. These rocks (andesites)
are also less dense than the basalts erupted from the ocean crust.
The first volcanic eruptions lay out a relatively flat surface which begins to cool and harden into
solid rocks. The subsequent eruptions build up on top and may result in the cone shaped
volcanoes we all are familiar with.
Make a Model Volcano
Introduction
Show the class a globe making sure they understand that this represents the Earth they live on.
Explain briefly that, although the surface is made of cool, solid rock the earth is very hot inside –
so hot that parts of it melt to form liquid rock – magma. Sometimes very hot molten rock pushes
up through a crack in the solid rock and either flows out as lava or erupts explosively, shooting
lava, dust and gases into the air (atmosphere).
Issue 63 – Volcanoes 1
Activity
Work in small groups to look at illustrations in reference books to understand how a volcano is
built up.
Use plasticine or other modelling material to create a thick layer to represent earth’s surface.
Introduce red plasticine to illustrate a magma chamber welling up from within the earth.
Diagram 1
Earth’s surface
Magma
chamber
Insert a small plastic pot (e.g. film canister or plastic herb/spice drum) into the ‘magma
chamber’.
Diagram 2
Half fill the pot with bicarbonate of soda (at least 6 heaped teaspoons) mixed with red colouring
quickly pour in the vinegar (8 tsp all at once) to simulate an eruption (squirting the vinegar in
produces the best effect). Make sure the children understand that this only represents magma
coming up to the surface and isn’t what really happens.
Add a thin layer of plasticine to represent cooled down lava becoming solid rock.
Diagram 3
Repeat the ‘eruption’ several times, each time adding an extra layer of ‘lava’.
Diagram 4
Issue 63 – Volcanoes 1
Optional Activities
Comparing volcanoes
Older pupils may want to do this volcano building activity to complement their study of the
location of volcanoes (Issue 64). They could even adapt it to model a particular volcano.
Alternatively several groups could do the activity with each group producing a different shaped
volcano such as a steep cone, a broad shield volcano, a caldera (large crater-like basin at the
top). They could also add features such as woodland, river valleys or houses onto the slopes of
the volcanoes or close by to see which areas may be most affected in the event of an eruption.
Investigate the Different Types of Eruption
KS2 pupils may like to investigate some different types of volcanic eruptions. Violent and
explosive eruptions, such as the eruption of Mount St Helens, eject millions of tons of extremely
hot boulders and fine ash rather than lava into the atmosphere. This ash then falls out of the
sky like snow and covers everything beneath. Thick layers of ash cause buildings to collapse
and can cause severe breathing difficulties. Such large volumes of ash can also flow like
flooded rivers and rush down the flanks of the volcano at very high speeds – such surges are
called pyroclastic flows and they destroy and bury everything in their path, for example the
burial of the capital of Montserrat (Caribbean) when the Soufriere Hills volcano erupted.
PEST issue number 35 also contains excellent information about volcanoes which also
considers some bad and good aspects of them which are worth investigating.
Useful Web links:
http://www.pbs.org/wnet/savageearth/animations/
This is a good, labelled animation of a volcanic eruption with clear explanatory text.
http://www.sci.sdsu.edu/volcano/
Quite a good animation but the text uses more advanced language.
Forthcoming Events Full information is available from the respective web sites.
ESTA Primary Team Members will be providing practical workshops, resources and useful information at:The ASE Conference 8th - 10th January 2009 at Reading www.ase.org.uk
Saturday 10th January 2009, Primary Workshop: Sort minerals by devising and discussing criteria. Use this
knowledge to work through rock identification at different levels with the ESTA rock kit. Test rock porosity and make
your own well. Consider rock erosion and soil formation. Observe differences in porosity/permeability, colour, texture
and composition of various soils and link this to their origins. (QCA Unit 3D – Rocks and Soils). TAKE AWAY YOUR
OWN ROCK KIT AND TEACHING PACKS.
th
th
Geographical Association Conference, Manchester 17 – 18 April 2009. www.geography.org.uk
Rivers and Coasts in Action. Hands on workshop on rivers and coasts, their formation, erosion and evolution.
Participants build their own rivers or coasts and watch them evolve through time. Ideas will be provided to help transfer
this to individual classroom situations, using unusual everyday items and how to acquire and adapt resources.
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Primary group via Peter York, at the address right.
This issue was devised and written by Geoff Selby
Sly, National Stone Centre, Diane Payne, ESTA
Primary Team and Tracy Atkinson, ESTA Primary
Team. Edited by Niki Whitburn, Bishop Grosseteste
University College Lincoln.
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