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Volcanoes
• Mountains
that
erupt lava
Lava
ACTIVE
Z
Zz
Rock
DORMANT
EXTINCT
Hawaii
vent
cone
Pipe
(Conduit)
magma
chamber
Crust
• A look at the
mantle and crust
Mantle
Cold air
Ocean
Hot Melt
Hot Mantle
Cooler
Mantle
How do volcanoes erupt?
There are two types of eruption:
Effusive: Hot magma rises to the surface and
flows over the sides
Explosive: The Magma has lots of gas in it. As
the pressure builds inside the volcano it eventually
has too much energy and erupts upwards
explosively.
We are going to demonstrate an eruption- which
type is it? Why?
• EXPLOSIVE
magma
Sticky
Lots of Bubbles
• EFFUSIVE
magma
Runny
Not many bubbles
Hawaii
Courtesy of www.swisseduc.ch
• ’a’a
• Pahoehoe
Rough
Lots of pieces
Smooth
or Ropy
Courtesy of A. Rust
What would you call them?
Courtesy of A. Rust
Where can we find volcanoes?
They form along special places called Tectonic Plate
boundaries
Where can we find volcanoes?
At Tectonic Plate boundaries
The tectonic plates are a bit like closely packed iceburgs that
move around.
Are there volcanoes in Britain?
There are no active volcanoes in Britain today –
we are not on a Tectonic Plate Boundary
BUT
Many millions of years ago (about 60 million) we
were on a Tectonic Plate boundary.
How do geologists know this?
How can we find out about volcanoes that existed in the
UK a long, long time ago?
Geologists are a bit like detectives:
They look for clues.
1. The types of rock
2.Rocks under the
microscope
3. The landscape
Activities
The types of
rock
Geologists have made maps showing
where different types of rocks can be
found in the UK
•Look at the Geological map and find where we live
•Where can we find the closest volcanic rock to our school?
•Have you visited any of the places marked on the map where volcanic rock
can be found?
•Now look at the rocks that we have brought from a collection at Bristol
University. What do they feel like? How heavy are they? Do they have air
bubbles inside them?- thinking back to the volcanic eruption what might have
made the bubbly rock? Fill out the table on the back of your Geological map
Geologists take a closer look at rocks by taking very thin slices to look at
under the microscope. We have brought some with us today so that you can
take a look too.
Volcanic rocks
What did you discover from looking at the rocks?
What rock had holes in it?
Which rocks had the biggest crystals?
Basalt-fine crystals
formed as lava cools
quickly above ground
Pumice
Gabbro- fine to
coarse crystalsformed underground
Volcanic
Bomb
Granite- magma cools
slowly underground and
produces large crystals
2.Rocks under
the
microscope
Rocks Under The Microscope
Notice the size and shape of the crystals.
Both are magnified 11 times
Rhyolite
Diorite
2.Rocks under
the
microscope
Rocks Under The Microscope
Notice the size and shape of the crystals.
Both are magnified 12 times
Andesite
Granite
What can the size of the crystals tell
us?
Small crystals form when the molten rock cools quickly- this happens
when the lava flows over the Earth’s surface
Larger crystals are formed when the molten rock cools slowly- this
happens when the magma is trapped underground.
From the rocks you have seen today, which do you think came from
underground and which were formed in lava flows above ground?
You can test this for yourself by growing your own crystals- some in a
warm/hot place and the other in a cool/cold place. We’ll help you set this
up as an experiment
Evidence of ancient volcanoes in UKlooking at geographical features
The
landscape
Edinburgh,
Scotland
Lava flow
Arthur’s Seat
Salisbury Crags
Evidence of ancient volcanoes in UKlooking at geographical features
The
landscape
Granite batholith
of Dartmoorwas part of a
huge
underground
chamber that
was filled with
magma.
Evidence of ancient volcanoes in UKlooking at geographical features
The landscape
Staffa's, an island off Scotland has spectacular columns
made of basalt formed from a lava flow 60 million years
ago. Huge amounts of magma rose up through the
cracks in the Earth's crust, erupting as lava and volcanic
ash onto the surface. This volcanic activity lasted many
hundreds of thousands of years and eventually created a
2.2 km plateau of lava and ash.
• Questions
V____
ent
What are volcanoes?Mountains that erupt l a v a.
Lava is very:
hot
A dormant volcano is:
Cone
cold
awake
Conduit
M
________
a g m a chamber
asleep
Why do volcanoes erupt? Hot magma wants to go:
How do volcanoes erupt? Two types: e x p l o s i v e
What helps make explosive volcanoes erupt?
How can we find signs of volcanoes in UK?
What does the size of the crystals tell us?
up
down
and effusive
b u b b l e. s
.