Volcanoes and global climate

volcanoes

* How are they created?* Where are they located, and why?

* What does the inside of a volcano look like?

* How can we predict them?* What happened at Mt St Helens?

A destructive plate boundary (Convergent Boundary) is found where a continental plate meets an oceanic plate.

The oceanic plate descends under the continental plate because it is denser. As the plate descends it starts to melt due to the friction caused by the movement between the plates. This melted plate is now hot, liquid rock (magma). The magma rises through the gaps in the continental plate. If it reaches the surface, the liquid rock forms a volcano.

Why do they happen?

Destructive/Convergent plate boundary

At a constructive plate boundary (Divergent boundary), two plates move apart.

As the two plates move apart, magma rises up to fill the gap. This causes volcanoes. However, since the magma can escape easily at the surface, the volcano does not erupt with much force.

Why do they happen?

Constructive/Divergent plate boundary

Volcanic bombs, ash, lava, gases

Magma chamber

Parasitic cone

Crater

Main vent

Label this cross section of a volcano

CraterVolcanic bombs, ash and gases

Main vent

Parasitic cone

Magma chamber

Cross section of a volcano

Cross section of a volcano

Volcano shapes

Why do volcanoes have different shapes?

Volcano shapes

Hot spots

The Hawaiian islands are a chain of volcanoes in the Pacific Ocean.

Hawaii

Look at their location on the map below.

Why is this an unusual place for them to be located?

Hot spot volcanoes

In the animation above, why are the volcanoes to the left of the ‘hot spot’ extinct?

Active, extinct, dormant

• What do you think these three terms mean? Write a description of them

Predicting an eruption

Prediction

• How do you think volcanoes can be predicted? Take two minutes to consider how it’s done...

• There are three ways:– Measuring seismic activity– Measuring poison gasses– Satellite imagery

• Let’s look at these in turn

Prediction: Seismic activityYou should remember from when we studied earthquakes that when the ground starts to shake, seismic waves pass through the ground from the focus. Volcanoes are often accompanied by seismic disruption due to the rubbing of tectonic plates together.

If seismic activity increases near a volcano (if the ground starts to shake more), then this is a sign that an eruption is likely.

Prediction: poison gases

As magma nears the surface and its pressure decreases, gases escape. This process is much like what happens when you open a bottle of soda and carbon dioxide escapes.

Sulphur dioxide is one of the main components of volcanic gases, and increasing amounts of it herald the arrival of increasing amounts of magma near the surface.

Prediction: satellite imagery

Satellites can pick up subtle changes in the temperature of clouds near a volcano, as well as subtle changes in the ground temperature. Increasing heat is a likely indicator of an eruption.

If a volcano becomes deformed it is likely that changes inside the mountain are making it so. Mount St Helens bulged before it erupted in May 1980.

Pyroclastic Flow

Pyroclastic flow

Pyroclastic flow is the fast-moving current of hot gas and rock which travel away from the volcano at speeds as great as 450 mph.

The gas can reach temperatures of 1000c

The flow normally hugs the ground and travels downhill, destroying much in its path.

Case study: Mount St Helens

Mt St Helens is located on the ‘Ring of Fire’.

Mt St Helens eruption (May 1980)

Internet Linkshttp://volcano.und.nodak.edu/vwdocs/msh/msh.html

Mt St Helens is located on a destructive plate boundary where a continental plate (North American) meets an oceanic plate (Juan de Fuca).

Mt St Helens – causes of the eruption

Juan de Fuca plate North American plate

Which plate is denser?Describe what happens when the oceanic plate descends under the continental plate.

Mt St Helens – the eruption

The detail•Mount St Helens is in Washington State, USA.

•The volcano forms part of the Ring of Fire

•The volcano had lay dormant for 123 years

•The eruption was preceded by two months of seismic activity and steam venting

•On March 18th, an earthquake of magnitude 4.2 was experienced

•There were 8 earthquakes per day in the week building up to the eruption

The detail (2)• The side of the mountain bulged by 120m in the build-up

to the eruption• It erupted on May 18th 1980 at 8:32 am.• The eruption was so powerful that the mountain's summit

was blown off, reducing it from 2,950 m to 2,550 m• The eruption column rose 24,000m into the sky and fell

on 11 US states• Huge mudslides were created by the blast• Fifty-seven people were killed; 250 homes, 47 bridges,

15 miles of railways, and 185 miles of motorway were destroyed

• The damage cost over one billion dollars

This shows the landslide (green) and the directed blast (red) that occurred during

the first few minutes of the

eruption of Mount St.

Helens in 1980.

N

0 10km

Mt St Helens – consequences of the eruption

BEFORE

AFTERMt St Helens – consequences of the eruption

What damage did the eruption cause?

Short-term and long-term effects

• Short-term– 70mm of ash fell. 7000 students have an

early holiday– Mudflows blocked and diverted rivers– Railway and road bridges destroyed– Portland harbour was blocked– Hot mudflows raised the temperature of rivers

and lakes to 30C– Unemployment grew tenfold immediately after

the eruption

Short-term and long-term effects

• Long-term– Burrowing gophers increased the fertility of

the soil by mixing in the ash– Tourism increased– Deer mice, vole, chipmonk and gopher

populations increased due to the lack of predators

– The US Government spent $951million on disaster relief

Emergency planning

Imagine that you are part of the emergency planning team for an

impending volcanic eruption.

A (fake) volcano is found at grid reference 3505, with the crater located

at 347052.

Signs of an impending eruption have been growing. There are real concerns

for the people of Ambleside.

What will you do, where will you do it, and in which order is it best done?

!

!

!

What can you do?• Road blocks• Evacuation of people• Radio warnings• Leaflet drops• Moving animals• Dispatch search and rescue teams• Block rivers• Anything else?

Is there any crucial information you haven’t been told?

Remember:

Where?

When?

Why?

Prioritise the actions you will take and justify why you have done them

in that order.