There are three main types of volcanoes: shield volcanoes, composite volcanoes, and cinder cone volcanoes. Shield volcanoes have low viscosity lava that flows great distances, building wide mountains. Composite volcanoes have more viscous lava and explosive eruptions due to trapped gases, forming steep cones. Cinder cone volcanoes are short-lived and formed from violent eruptions of gas-rich lava that falls as cinders around the vent. Volcanoes form at plate boundaries due to subduction and spreading, or at hot spots from fixed magma plumes.

1. Three Types of
Volcanoes

2.  1. List and describe the three types of
volcanoes.

3. EXPLOSIVE HAZARDS
VISCOUS LAVA (High Viscosity)
 Cool temperature
 Composition:
silica-rich (granitic)
 Thick & gooey → Erupt violently; scattering
ash and fragments
widely
 Does not flow very far;
builds steep-sides;
often destroys volcanoes
Ex. rhyolithic & andesitic
lava→ stratovolcanoes

4. NON-EXPLOSIVE HAZARD
FLUID LAVA (Low viscosity)
 Higher temperatures
 Composition: Low silica
(basaltic)
 Thin → Erupt “quietly”
 Great flows of lava that
build mountains
Ex. Basaltic lava→ shield volcanoes

5. MAGMA/LAVA →ERUPTIONS
Non-Explosive Eruptions:
Fluid lava flows easily
allows gases to bubble
away
Explosive Eruptions:
Viscous lava traps the gases
until large pressures build
up & the system explodes
Pyroclastic flow (ash, rock
fragments) flow out of vent

6. EXPLOSIVE HAZARDS
PYROCLASTIC FLOW
Travels over 200 mph
Tephra = all ash & rock
fragments
– ash: pieces smaller than 2 mm;
travel farthest
– lapelli: small pieces between 2-66
mm
– volcanic bomb: pieces larger than
64 mm
Burns EVERYTHING in its path

7. ERUPTION HAZARDS
LAHAR
Water, mud &
ash that flow
like a river

8. Shield Volcanoes
• The magma inside a shield volcano is rich in iron
and magnesium and is very fluid.
• Since the magma is very fluid, the lava coming
out of the volcano tends to flow great distances.
• When shield volcanoes erupt, the flowing lava
gives the volcano the shape of a gently sloping
mountain.

9. Shield Volcanoes
 Eruptions of shield volcanoes are mild and
can occur several times.
 Mauna Loa in Hawaii is an example of a
shield volcano.

10. Shield Volcanoes
 Low silica level
 Low viscosity Lava
 High or low levels of gas
 Low to medium explosivity
 Flattened mound
 Resembles a warrior’s shield

11. Mauna Loa, Hawaii

12. Piton de la Fournaise

13. Surtsey, Finland

14. Composite Volcanoes
• The magma inside a composite volcano is rich in
silica and much thicker than magma from a
shield volcano.
• Gases get trapped inside this thicker magma.
• Eruptions from composite volcanoes can be
flowing lava or explosions. The explosive
eruptions come from the trapped gases and
produce cinders and ash.

15. Composite Volcanoes
• These different types of eruptions are what give
composite volcanoes their alternating layers of
lava and cinders.
• Composite volcanoes have much steeper slopes
than shield volcanoes.
• Mount Fuji in Japan and Mount St. Helens in the
USA are examples of composite volcanoes.

16. Composite Volcanoes
 High in silica
 High viscosity magma
 High levels of gas
 Highly explosive
 Cone shaped
 Formed by layers of lava flow and ash
buildup

17. Mt. Rainier, Washington

18. Mt. Fuji, Japan

19. Mt. St. Helens, Washington

20. Cinder Cone Volcanoes
• The magma inside a cinder cone volcano has
large amounts of gas trapped in it.
• Eruptions from cinder cone volcanoes are
violent and explosive because of all the gas
trapped in the magma.
• The large amounts of hot ash and lava thrown
out of the vent fall to the ground forming the
cone shape that these volcanoes have.

21. Cinder Cone Volcanoes
• Cinder cone volcanoes are usually only
active for a short time and then become
dormant (inactive).
• Paricutin in Mexico is an example of a
cinder cone volcano.

22. Cinder cones
 Low silica lava
 High levels of gas
 “Fire-fountain” eruptions
 Commonly found on the flanks of shield
volcanoes
 Made from a pile of rock pieces
 Structurally weak

23. Pu'u ka Pele, Hawaii
(on the flanks of Mauna Loa)

24. Floreana Island, Galapagos

25. Puu OO, Hawaii

26.  2. Explain how volcanoes relate to plate
tectonics.

27. WHAT KIND OF LAVA FLOW?
Viscous lava
• thick (granitic – high silica
content)
• traps gas
• violent eruptions
• destroys mountains
Fluid lava
• thin ; flows far;
• allows gas to escape;
• quiet(non-violent) eruptions
• builds mountain
Fluid lava
Flows
great
distances

28. FORMATION →ERUPTIONS
Volcanoes are formed by
1.SUBDUCTION
explosive eruptions
2.Sea Floor Spreading
quiet eruptions
3.Hot Spots
usually quiet eruptions

29. VOLCANO FORMATION:
HOT SPOTS
 A fixed source of magma
rising beneath a plate
forming volcanic islands
 Magma can be basaltic or
granitic –so eruptions can
be explosive or “quiet”