The document provides an overview of volcanoes, explaining their characteristics, types, and the hazards they pose, such as lava flows and pyroclastic flows. Different types of volcanoes are discussed, including acid, basaltic, and stratovolcanoes, along with their eruption patterns and geological formations. Additionally, it highlights the benefits of living near volcanic regions and methods for predicting eruptions to reduce risks.

1. VOLCANOES
Presented by:
Abinash Acharya

2. • It is point on the earth’s crust where magma
forces its way to the surface due to pressure.
• Ash and gases may also escape during a
typical volcanic eruption.
What is a volcano?

3. Location Of Volcanoes

4. Layout Of A Volcano

5. Types Of Volcanoes
Acid Volcanoes
• Highly explosive
• Magma/lava is viscous
(thick)
• Found where oceanic crust
is subducted under
continental crust
Basaltic Volcanoes
• Less explosive*
• Magma/lava less viscous
(runny)
• Found at rift zones
(constructive boundaries)
and hotspots

6. Acid Volcanoes
Lava Domes
• Formed of layers of lava
high in silica
• Lava is viscous and does not
flow very far
• Rounded Form
• Composed completely of
lava
Stratovolcanoes
• Also called composite
volcanoes
• Formed of layers of lava and
ashes
• Lava is viscous
• Distinct cone shape

7. LAVA DOMES-EXAMPLE
Mount Chaiten, Chile

8. STRATOVOLCANO-EXAMPLE
Mount St. Helen, US (Before and after)

9. Basaltic Volcanoes
• Also known as shield volcanoes
• Consists of widespread layers of lava and
have low viscosity
• Silica content is low
• Low form spread over a great distance

10. Basaltic Volcano-Example
Eyjafjallajökull, Iceland

11. Calderas Volcanoes
• Collapsed Volcanoes
• Magma chamber has emptied and the ground
has sunk
• Often becomes a lake
• New volcanoes can form, or pressure can build
from below, lifting the ground
• If acidic, this can cause a catastrophic eruption
in the form of a ’Super Volcano’

12. Calderas-Example
Mount Pinatubo, Phillipines

13. Hotspots
• Tectonic plate moves over a magma plume
• Occasionally erupts, creating a volcano

14. Major Hotspots

15. Volcanic Explosivity Index (VEI)
TYPE DESCRIPTION EXAMPLE
Hawaiian Gentle Kilauea
Strombolian Explosive Stromboli
Vulcanian Severe Nabro
Peléan Cataclysmic Mt.Pelée
Plinian Paroxysmal St.Helens
Plinian/Ultra-Plinian Colossal Krakatoa
Ultra-Plinian Super-Colossal Tambora
Supervolcanic Mega-Colossal Yellow Stone
Number 8 has never been experienced in human history
The list has been simplified. See correct details here:
http://www.unc.edu/~rowlett/units/scales/VEI.html

16. Volcanic Activity Index

17. Volcanic Hazards
Most hazards during eruptions are caused by
what comes out of a volcano. In the next few
slides, we’ll be seeing the different types of
volcanic hazards.

18. Volcanic Hazards – Lava Flows
• Mostly associated with basic volcanos
• Slow moving 1 – 5 km/h
• Low risk to human life
• Cover large areas and destroy large amounts of
infrastructure

19. Hazards – Pyroclastic Flows
• Hot clouds of ash and gas
• Move downhill, close to the ground, following
valleys
• High speed – up to 500 km/h
• As far as 30 km
• Up to 7000 C
• Highly dangerous

20. Hazards - Lahars
• Occur on high volcanos covered in snow and
ice, or wet mud/soil
• Eruption causes snow to melt, or lava mixes
with mud
• Flows downhill like wet concrete

21. Hazards – Ash Clouds
• Slow moving
• Weight of ash can collapse buildings
• Destroys crops, pollutes water
• Affects air traffic
• Can enter high atmosphere and cause cooling – disrupting
climate

22. Hazards – Lava Bombs
• Molten rocks thrown out of volcano
• Pummice – smaller rocks
• Travel short Distances
• Can Start Fires

23. Benefits Of Living Near a
Volcanic Region
• Aesthetic beauty eg. Mount Fuji, Japan
• Mining of minerals and diamonds
• Geothermal energy and hot springs
• Highly fertile soils – soft rocks and high
mineral content

24. Predicting Volcanic Eruptions
• Monitoring seismic
disturbances (tremors)
• Changes in volcano profile
(shape)
• Chemical changes in
groundwater
• Emissions of gases
• Thermal monitoring
(temperature)

25. History Of Eruptions
• 1800 BC – destruction of Bronze age
settlements – then several more times
• 79 AD – destruction of Pompeii
• At least 40 times until the last eruption in 1944
– witnessed by allied troops towards the end of
WWII
• = once every 40-50 years

26. Reducing The Risks
• Round-the-clock monitoring of the volcano:
Tremors, gases, changes in water
• Identifying hazard areas: Weak spots,
secondary vents, predicting routes of
pyroclastic flows
• Creating an evacuation plan: Zoning, warning
systems, public education

27. References
• http://greenfieldgeography.wikispaces.com/IG
CSE+Plate+Tectonics+and+GCSE+Plate+Te
ctonics
• http://volcano.oregonstate.edu/
• http://www.physicalgeography.net/fundament
als/chapter10.html
• http://volcanoes.usgs.gov/hazards/index.php