1. Presentation
Presented By:
Tayyaba Hanif 28005
Kashef Ali 28006
Safdar Abbas 28007
Department of Geography
Govt College University Faisalabad
Subject: Geography of Natural Hazards and Disasters
Topic: Volcanoes
2. Volcanoes
Introduction:
Volcanism is the process where deep magma erupts onto the surface or
emplaces near the surface through a volcanic conduit, thereby forming various
types of volcanic debris.
Volcanoes refer to eruption of hot molten material known as magma from
the earth crust.
As plates move away from each other, at certain places, the surface might
get stretched and thinner.
In such a situation, the hot molten lava and gaseous substances below this
thinned surface could open up a fissure and come out.
All eruptions (gaseous or liquid) from a volcano is at high temperature, and,
the mouth of a volcano might look like, as if it’s ejecting fire.
3. Characteristics of volcanoes
A volcano is formed by eruptions of lava and ash.
Volcanoes are usually cone shaped mountains or hills.
When magma reaches the Earth's surface it is called lava. When the lava
cools, it forms rock.
Volcanic eruptions can happen at destructive and constructive
boundaries, but not at conservative boundaries or collision zones.
Some volcanoes happen underwater, along the seabed or ocean floor.
magma rises through cracks or weaknesses in the Earth's crust.
Pressure builds up inside the Earth.
The lava from the eruption cools to form new crust.
Over time, after several eruptions, the rock builds up and a volcano
forms.
4. Cross section of a volcano
The diagram below shows how magma pushes up between the two plates:
5. The magma chamber is a collection of magma inside the Earth, below the
volcano.
The main vent is the main outlet for the magma to escape.
Secondary vents are smaller outlets through which magma escapes.
The crater is created after an eruption blows the top off the volcano.
An eruption occurs when pressure in the magma chamber forces magma up
the main vent, towards the crater at the top of the volcano.
Some magma will also be forced out of the secondary vent at the side of the
volcano.
7. Shield volcanoes
Shield volcanoes are found on constructive plate margins, where two plates
move away from one another. Shield volcanoes have the following
characteristics:
basic lava, which is non-acidic and very runny
gentle sides as the lava flows for long distances before it solidifies
no layers, as the volcano just consists of lava
less violent eruptions
shorter periods between eruptions
They are low, with gently sloping sides.
They are formed by eruptions of thin, runny lava.
Eruptions tend to be frequent but relatively gentle.
Example: Mauna Kea in Hawaii, USA or the Galapagos islands
9. Composite volcanoes are found on destructive plate margins, where the oceanic
crust sinks beneath the continental crust. Composite volcanoes have the
following characteristics:
Acidic lava, which is very viscous (sticky).
Steep sides as the lava doesn't flow very far before it solidifies.
Alternate layers of ash and lava. For this reason, they're also known
as stratovolcanoes.Strato means layers.
Violent eruptions.
Longer periods between eruptions.
Composite volcanoes are made up of alternating layers of lava and ash (other
volcanoes just consist of lava).
They are usually found at destructive boundaries.
The eruptions from these volcanoes may be a pyroclastic flow rather than a lava
flow. A pyroclastic flow is a mixture of hot steam, ash, rock and dust.
A pyroclastic flow can roll down the sides of a volcano at very high speeds and
with temperatures of over 400°C.
Example: Hekla in Iceland, Mt St Helens in the USA and Mt Kilimanjaro in
Tanzania.
Compacts Volcanoes
11. Super volcano
A super volcano is a volcano on a massive scale. It is different from a volcano
because:
it erupts at least 1,000 km3 of material (a large volcano erupts around 1
km3);
it forms a depression, called a caldera (a volcano forms a cone shape);
often has a ridge of higher land around it;
erupts less frequently - eruptions are hundreds of thousands of years
apart.
Yellowstone is one example of a super volcano.
12. Classification of Volcanoes
Active volcanoes are those with volcanic activities in the present
Dormant volcanoes; those which are not active presently but could show
activity any time.
Extinct volcanoes are those which were “active” some time, but, have
ceased volcanic eruptions now.
Active volcanoes Dormant volcanoes Extinct volcanoes
13. Causes of Volcanoes Eruption
The Earth's crust is made up of huge slabs called plates, which fit together
like a jigsaw puzzle. These plates sometimes move.
Between the Earth's crust and the mantle is a substance called magma
which is made of rock and gases.
When two plates collide, one section slides on top of the other, the one
beneath is pushed down. Magma is squeezed up between two plates.
Did you know? Volcanoes are like giant safety valves that release the
pressure that builds up inside the Earth.
14. Wear are a large number volcanoes
What is the Ring of Fire?
Over half of the world’s volcanoes arise in a belt around the
Pacific Ocean called the Ring of Fire.
Which is the largest volcanic mountain?
Mauna Kea which is also worlds tallest mountain is the largest
volcanic mountain.
15. The positive and negative effects
of volcano eruptions
Volcanoes have a large effect on their locality. They produce
ash, lava, volcanic bombs, pyroclastic flows and lahars. Ash from large
volcanoes has been known to affect global climates.
The effects of volcanoes can be both positive and negative.
Positive effects:
Geothermal energy is where heat from within the Earth is used to generate
electricity. Geothermal energy can be generated in areas where magma lies
close to the surface. This is good for increasing our renewable energy use.
Ash ejected by the volcano acts as a good fertilizer for soils.
Volcanoes attract many tourists, who enjoy the dramatic scenery that they
produce
16. Negative effects
Volcanoes are dangerous. They can kill people and damage
property.
Economic activity can suffer as it is hard for businesses to
operate after an eruption.
Habitats and landscapes are damaged by lava flows
Flooding start
Landslides start
Food/ water supply interrupted.
Homelessness
Unemployment
Long term issue with tourism industry
17.
18.
19. Monitoring volcanoes - popular
techniques
Volcanic eruptions are unpredictable. However,
scientists can monitor volcanoes to estimate
when they are likely to erupt. Scientists can use a
variety of techniques to do this, such as:
seismometers - used to measure earthquakes
occurring near an eruption
Tilt meters and GPS satellites – these devices
monitor any changes in landscape. Volcanoes
tend to swell near an eruption
seismometers
20. Benefits of living by a volcano
People choose to live in volcanic areas
despite the risks of an eruption. Volcanoes
can provide people with many benefits such
as:
volcanic rock and ash provide fertile
land which results in a higher crop yield for
farmers
tourists are attracted to the volcano, which
increases money to the local economy
geothermal energy can be harnessed, which
provides cheaper electricity for locals
minerals are contained in lava, eg diamonds -
these can be mined to make money
