1. Volcanoes

2. Structure of a Volcano

3. What is a volcano?
a landform produced by magma emerges via an opening in the crust as lava flow
Lava cools and solidifies to form a layer of volcanic material
with each eruption, layer upon layer built up to form a volcano
Lava continues to rise through a passageway – pipe. Lava ejected at a top opening – crater
Crater when blown off  caldera
Caldera eventually filled with water  crater lake

4. Explosive or Quiet Eruptions?
Basic lava
Low in silica
Non-sticky
Less viscous, more fluid
Temp usually higher
Gas and steam escape easily
Acidic lava
High in silica
Sticky, more viscous, less fluid
Temp usually lower
Thick sticky lava does not allow gas and steam to escape easily
Explosive eruptions!
Quiet eruptions…

5. Shape of volcano? Basic Lava Volcano
Fluid lava flow covers larger areas  gently-sloping volcano shield volcano
E.g. Island of Hawaii, regarded as a single shield volcano with 3 active peaks maua Kea, Mauna Loa, Kilauea
Acidic Lava Volcano
Less fluid lava, moves very slowly solidifies quickly  a steep-coned volcano
Most common composite volcano (alternate layers of hardened lava, ash & cinder)
E.g. Mt Mayon, Mt Merapi, Mt Fuji, Mt Etna, Vesuvius

6. A Volcano formed by acidic Lava Most common type – composite volcano

7. Mauna Loa
Mauna Kea
A Shield Volcano

8. Lava Plateau
Lava Plateau – formed when huge volumes of magma erupted from several cracks in the earth’s crust rather than from a single pipe

9. Distribution of volcanoes (Map)

10. Distribution of volcanoes
Along convergent plate boundary where subduction takes place
Produce chain of volcanic islands
e.g. Pacific Ring of Fire
Along divergent plate boundary where new sea floor materials
produce submarine volcanoes
e.g. Mid-Atlantic oceanic ridge
Away from plate boundary, a plate moving over fixed ‘hot spots’
Which are localised heat sources in the mantle
to produce groups of volcanoes
e.g. the Hawaiian Islands

11. Hot Spots

13. Impacts of Volcanic eruptions
Volcanic eruption affects the environment thorough:
Emission of toxic gas
Lava flows
Mudflows of rocks and ash
Pyroclastic materials of ash and
cinder bombs
Disturbances on ocean floor may trigger off tsunamis

14. Impacts of Volcanic eruptions
Destroy property – farmlands, buildings, infrastructure
Cause injury and loss of lives
Disrupt economic activities
Brings about misery and aggravates poverty e.g. in 3rd World countries

15. Why do people still live near Volcanoes?
Cultural Rootedness
Sense of belonging
Generations live there
Economic Reason
Fertile soils for agriculture
Economic Reason
Energy Resource
Harnessing of geothermal
power for development
Economic Reason
Tourism
e.g.geysers & hot
Springs
Economic Reason
Mining of minerals, sulphur
Employment opportunity
Economic Reason
Poverty- no means to relocate