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
All magma contains gases that expand and rise buoyantly as the magma rises to the surface (like bubbles in a soda)
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 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? Fluid lava Fluid lava Flows great distances
thin ; flows far;
allows gas to escape;
quiet(non-violent) eruptions
builds mountain
Fluid lava
Flows great distances
Viscous lava
thick (granitic – high silica content)
traps gas
violent eruptions
destroys mountains

28. FORMATION →ERUPTIONS Volcanoes are formed by
SUBDUCTION explosive eruptions
Sea Floor Spreading quiet eruptions
Hot Spots usually quiet eruptions
Subduction: if continental: oceanic crusts – continental -> Granitic magma -> explosive
Sea Floor: crusts are oceanic (basalt) -> quiet eruptions
Hot Spots depends upon crust

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”