Types of Volcanoes

1. Volcanoes

2. What is a volcano?
• A point on the earth’s crust where magma
forces its way to the surface
• Ash and gases may also escape

3. Where do they occur?
• On subduction zones
• On constructive plate boundaries
• On hot spots

5. What types of volcanoes are there?
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
* Continental hotspots are basaltic but
potentially highly explosive

6. Acid (rhyolitic) volcanoes
Lava domes
• Formed of layers of lava
high in silica
• Lava is viscous and does
not run 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. Example – lava dome
• Mount St Helens - Washington state, USA
before
during
after

8. Example - stratovolcano
• Mount Pinatubo, Luzon, Philipines
before
During…
after

9. Other famous stratovolcanoes
Fuji,
dormant
Krakatoa,
active
Vesuvius,
active
Kilamanjaro,
dormant

10. Location of stratovolcanoes
• Along
subduction
zones
• Often found in
volcanic arcs*
• E.g. Cascade
range, USA
*not to be confused with Island chains formed over hotspots

11. Basic (basaltic) volcanoes
• Also known as shield volcanoes
• Formed of widespread layers of lava low in
silica – low viscsity, lava travels very far
• Low form spread over a great distance

12. Example – basic volcano
• Eyjafjallajökull, Iceland

13. Example 2
• Kilauea, Hawaii

14. Calderas
• 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”

15. Caldera - Santorini
• Destroyed the Minoan civilization
due to tsunamis circa 1600BC
• May have given rise to the Atlantis
myth

16. Yellowstone national park

17. Yellowstone is a hotspot

18. Hotspots
• Tectonic plate
moves over a
magma ”plume”
• Occasionally
erupts, creating a
volcano
• Hawaii – basic
• Yellowstone - acid

19. Major hotspots

20. Volcanic Explosivity index (VEI)
• 1 – Hawaiian gentle (Kilauea)
• 2 – Strombolian explosive (Stromboli)
• 3 – Vulcanian severe
• 4 – Peléan cataclysmic (Mt.Pelée)
• 5 – Plinian paroxysmal (St.Helens)
• 6 – plinian/ultra-plinian colossal (Krakatoa)
• 7 – ultra-plinian super-colossal (Tamb.)
• 8 – supervolcanic mega-colossal (Y.st)
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

21. Volcanic hazards
• Most hazards during
eruptions are caused
by what comes out of
a volcano
• In worst case scenarios
then a volcano may
violently explode

22. Volcanic hazards – lava flows
• Mostly associated
with basic volcanos
• Slow moving 1 – 5
kmh
• Low risk to human
life
• Cover large areas
and destroy large
amounts of
infrastructure

23. Hazards – pyroclastic flows
• Hot clouds of ash and gas
• Move downhill, close to the ground,
following valleys
• High speed – up to 500 kmh
• As far as 30 km
• Up to 7000 C
• Highly dangerous

24. 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

25. 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

26. Hazards – lava bombs
• Molten rocks thrown out of volcano
• Pummice – smaller rocks
• Travel short distances
• Can start fires

27. The Decade Volcanoes
• 16 volcanoes identified as potentially
highly hazardous to humankind

28. So why live near a volcano?
• Aesthetic beauty
e.g. Mount Fuji,
Japan
• Mining of
minerals and
diamonds
• Geothermal
energy and hot
springs

29. So why live near a volcano?
• Highly fertile soils – soft rocks and high
mineral content

30. So why live near a volcano?
• Poverty – cheap
marginal land
• Overcrowding
and population
pressure –
nowhere else to
live
• Common
problems in
LEDCs

31. So why live near a volcano?
• Complacency or naivete
– ”nothing will happen”
• Confidence
– ”we will be warned and have time to get away”
• Tradition/family
– ”we have always lived here”

32. Predicting volcanic eruptions
• Monitoring seismic disturbances (tremors)
• Changes in volcano profile (shape)
• Chemical changes in groundwater
• Emissions of gases
• Thermal monitoring (temperature)

33. Vesuvius

34. Mount Vesuvius
Mount Vesuvius is an active volcano in Italy
It is the only volcano on the European
mainland to have erupted in the last 100
years
It is not currently erupting
It is dormant, not extinct

35. • Vesuvius is
in southern
Italy near
Naples
• Location:
40°49′N
14°26′E

36. Naples
Vesuvius

37. Vesuvius is a composite volcano
(strato-volcano)

38. Vesuvius - data
• Height (elevation)
1,281 metres
(4,203 ft) above
sea level
• Has a collapsed
caldera from a
previous eruption

39. Formed at the collision of two
tectonic plates – the African and
the Eurasian
• A converging,
destructive
boundary, with
very little
movement
• Several volcanoes
nearby, none
active

40. An acid volcano
• Potential for
violent eruptions
• Slow moving lava
• Explosions
• Hot ash/cinders
• Pyroclastic flows
• Real danger!

41. 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

42. Pompeii Ad79

43. Pompeii AD79
• Massive eruption of Vesuvius buries the
towns of Pompeii under a thick layer of
burning ashes and pumice up to 2.8
metres deep and Herculaneum under 23
metres of ash and pumice
• Eruption lasted for two days
• Deaths unknown – estimates from 5000 to
25000

44. Causes of deaths
• Burial under ash and pumice
• Killed by pyroclastic flows
• Collapsing building
• Rain of lava bombs
• Starvation
• Disease
• Drowning (many fled to the sea for rescue)

45. Buried alive!

46. The population of Naples is 960,000
(as of 2012)
The centre of Naples is 15km from
Vesuvius
the population of the Naples suburban
region is nearer 3 million

47. Reducing the risks
• Round-the-clock monitoring of the volcano
– Tremors, gasses, changes in water
• Identifying hazard areas
– Weak spots, secondary vents, predicting
routes of pyroclastic flows
• Creating an evacuation plan
– Zoning, warning systems, public education

48. Evacuation plans?
• Red zone – immediate risk from pyroclastics
• Blue zone – secondary zone of floods and lahars
• Yellow zone – mostly ash and other debris

49. Useful links
• 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