Volcanoes

Hawaii

Z zZ

vent

cone

magma chamber

Pipe

(Conduit)

• A look at the mantle and crust

Cold Crust

Ocean

Hot Melt

Hot Mantle

CoolerMantle

How do volcanoes erupt?

There are two types of eruption:Effusive: Hot magma rises to the surface and flows over the sidesExplosive: 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?

magma magma

Hawaii

Courtesy of www.swisseduc.ch

RoughLots of pieces

Smooth or Ropy

Courtesy of A. Rust

Courtesy of A. Rust

What would you call them?

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.

3. The landscape

2.Rocks under the microscope

1. The types of rock

The types of rock

Geologists have made maps showing where different types of rocks can be found in the UK

Activities

•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?

Granite- magma cools slowly underground and produces large crystals

Basalt-fine crystals formed as lava cools quickly above ground

Gabbro- fine to coarse crystals- formed underground

Pumice

VolcanicBomb

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

2.Rocks under the

microscope

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 UK- looking at geographical features

Lava flow

Salisbury Crags

Arthur’s Seat

Edinburgh,Scotland

The landscape

The landscape

Granite batholith of Dartmoor- was part of a huge underground chamber that was filled with magma.

Evidence of ancient volcanoes in UK- looking at geographical features

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.

Evidence of ancient volcanoes in UK- looking at geographical features

The landscape

What are volcanoes?Mountains that erupt .

A dormant volcano is: awake asleep ________ chamber

V____

Conduit

Cone

Why do volcanoes erupt? Hot magma wants to go: up down

How do volcanoes erupt? Two types: e and effusive .

What helps make explosive volcanoes erupt? .

l a v a

x p l o s i v e

b u b b l e s

e n t

M a g m a

How can we find signs of volcanoes in UK?

What does the size of the crystals tell us?