this power point talks about the causes, impacts and management strategies of volcanoes. it describe about the types of lava flow and types of volcanoes also,

1. Volcanoes
For A- level
Mr. Yonas Gemeda
November 2019
Addis Ababa

2. Lesson outcomes
• At the end of this lesson, you should be
able to:
• Define the term volcano and related
terms.
• Explain about plate tectonic theory
• List and explain types of plate boundaries
• List and explain types of volcano

3. What does volcano mean?
 volcano is a hill or mountain formed
by the extrusion of lava or ejection of
rock fragments from a vent.
A volcano is a place on the Earth’s
surface where hot, molten rock (called
magma) breaks through.

4. Term related with volcanoes
• Magma is the molten rock which is
found below the surface.
• Lava the molten rock when on the
surface.
• Pyroclastic materials : very hot gases,
ash and volcanic bombs, pyroclastic
flows

5. Features of volcano

6. Causes of volcano
• Plate movement…......a theory which briefly
explain about plate movement and its
feature is a plate tectonic theory.
• Tectonic plates are a piece of lithosphere
that moves slowly on asthenosphere.
• There are seven major, eight minor and
numerous micro plates have been identified.

7. Processes of plate movement
• Heat from the core
creates convention
currents in the magma of
the mantle and these
cause plates to move.
• Convention current is the
transfer of heat from
place to place, denser
colder fluid sink in to
warmer areas

8. Plate boundaries
• Where two or more plates meet.
• There are three types of plate
boundaries
A. Constructive (divergent)
B. Destructive ( convergent)
C. Conservative ( transform)

9. Types of plate boundaries
Destructive Constructive Conservative

10. Types of volcano

11. Types of volcanoes
Cinder cones
It is also known as pyroclastic cone
• Cinder cones form when blobs of gas- charged
lava are thrown into the air and break into
fragments.
• Steep slopes – 33 degrees
• Small mostly less than 300 meters
• Composition.. Pyroclastic fragments of any
composition . Basalt is most common.

12. Cinder cone
• Cinder cone is form by pyro clastic
materials accumulating around the
vent.
• Most cinder cones are associated with
mafic or intermediate lava.

13. Types of volcano
• Shield volcano
• Shield volcanoes are broad, gently sloping
volcanoes constructed of solidifed lava flows.
• During lava spreads widely and thinly due to its
low viscosity.
• The slopes are usually between 2 degree and 10
degree.
• From the horizontal producing a volcano in the
shape of flattened dome or shield.

14. Shield volcano
• Shield volcano contains less than 50% silica.
• It is a fluid, flows long distances and
solidifies slowly.
• Shield volcanoes form mainly along
constructive plate margins.

15. Types of volcanoes
• Strato volcano or composite
• It is one cone structured of alternating
layers of pyroclastic fragments and
solidified lava flows.
• The slope is intermediate in steepness
compared with cinder cones and sheild
volcanoes.
• Pyroclastic layers build steep slopes as
debris collects near the vent.

16. Composite volcano
• Strato volcano forms at converging (
destructive ) plate boundaries wher the
magma gains added silica as it rises through
continental rocks.
• It is more viscous than that of a shield
volcano, resulting in steeper sides.strato
volcanoes are particularly dangerous
because they have long dormant periods.

17. Stratovolcano

18. Types of volcano
Lava domes
• These relatively small domes, with steep
sides and rounded tops, can form on the
slopes of, or on the crater of strato
volcanoes.
• They are composed of silicic lava( more
than 60%) which is too viscous to flow far.
So it solidify quickly, forming a thick crust.

19. Types of flow
• Volcanoes are classified in a number of
ways . These include the types of flow,
the type of eruption and the level of
activity.

20. Flow
• Lava flow is surficial outpouring of molten
rocks.
• Lava flows are the most commonvolcanic
feature on earth.
• The most commondivision of lava flow are:
1. pahoehoelava flow
2. Aa lava flow
3. Blocky lava flow
4. Pillow lava flow.
• Some times turbulent lava flow added

21. Pahoehoe lava flow
• Is a smooth and continous
lava crust
• Forms whent ht effusion rate
is low and
• Velocity of lava is slow.
• Lava flow that was originally
pahoehoe may transform into
Aa lava, but the reverse is
imposible.
• Best known examples of
pahoehoe lava flows are from
the big island of Hawaii

22. A a lava
• Aa lava is a rough rubbly
crust of a lava flow.
• It is a major lava flow
type.

23. Pillow lava
• Pillow lava is usually
basaltic or andesitic in
composition and
always associated with
water.
• Pillow lavas are
usually associated mid
ocean ridge volcanism.

24. Lava flows controlling..
• There are a number of ways of
reducing lava flows. These include:
• Spraying them with water
• Bombing them
• Seeding the lava with foreign nuclei.

25. Other types of volcanoes
• Active volcanoes are volcanoes that
continue to erupt or are at risk of erupting.
• Extinct volcanoes have stopped erupting
• Dormant volcanoes are ones that have not
erupted for a very long time but could still
erupt.
• The distinction between dormant and
extinct is difficult to define.

26. Volcanic hazards
• Volcanic hazards can be divided into six
main categories
• Lava flows
• Ballistics and tephra clouds
• Pyroclastic flows
• Gases and acid rain
• Lahars (mudflows)
• Glacier bursts

27. Primary hazards
• Pyroclastic flows
• Volcanic bombs
• Lava flows
• Ash fallout
• Volcanic gases
• Earthquakes

28. Secondary hazards
• Atmospheric ash fallout
• Landslides
• Tsunamis
• Acidic rainfall
• Lahar (mudflows)

29. Socio economic impacts
• Destruction of settlements
• Loss of life
• Loss of farm lands and forests
• Destruction of infrastructure-
roads, airstrips and port facilities
• Disruption of communications

30. Volcanic strength
• The strength of a volcano is measured by the
volcanic explosive index(VEI)
• This is based on:
• the amount of material ejected in the explosion,
• The height if the cloud
• The amount of damage caused
• Any explosion above level 5 is considered to be
very large and violent.
• A VEI 8 refers supper volcano.

31. Predicting volcanoes
• Volcanoes are easier to predict than
earthquakes because there are certain signs.
The main ways of predicting volcanoes include:
• Seismometers record swarm of tiny
earthquakes that occur as magma rises
• Chemical sensors to measure increased sulfur
levels

32. Predicting volcanoes
• Lasers to detect the physical swelling of the
volcano
• Ultrasound to monitor low frequency waves
in the magma, resulting from the surge of
gas and molten rock.
• Direct observation

33. Living with volcano
• People often choose to live in volcanic areas
because they are useful in variety ways.
• Some countries created by volcanic
activities
• Some volcanic soils are rich, deep and fertile
and allow intensive agriculture.
• Volcanic areas are important for tourism.
• Some volcanoes are culturally symbolic and
are part of the national identity

34. Thank you
!!! !!!
☺☼☺☹