1. VOLCANOES

2. TYPES OF VOLCANOES Volcanoes are classified by appearance
Steep slopes = Strato/composite Volcanoes
Gentle slopes = Shield volcano
These are the three main types, but there are other types as well on next picture.
Appearance predicts type of eruption
Steep slopes → explosive (violent) eruptions
Gentle slopes → non-violent (quiet) eruptions

3. TYPES OF ERUPTIONS ERUPTIONS FALL INTO 2 CATEGORIES
Non-Violent (calm or quiet) eruptions build up the volcano
Violent(explosive) eruptions destroy the volcano

4. TYPES OF ERUPTIONS
VEI: Volcanic Explosivity Index

5. Strato/Composite Volcanoes Steep slopes – Explosive
Formed from viscous (thick) lava
Found in subduction zones & some hot spots
Ex/: Casades, Mt St Helens, 2, 3 T
The person who took these photos is Gary Lee Rosenquist. He barely made it. David Johston is the Volcanologist who died. He was pretty muc in front of the blast. That's why there is an observatory named after him. hese are the three main types, but there are other types as well on next picture.

6. Shield volcano Gentle slopes- Non-violent
Formed from fluid (thin) lava
Only found over a hot spots
Ex: Hawaiian islands
These are the three main types, but there are other types as well on next picture.

7. 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

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

9. 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

10. EXPLOSIVE HAZARDS VISCOUS LAVA (High Viscosity) Cool temperature
Compositon: 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→ strato volcanoes

11. 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

12. VISCOSITY→MAGMA/LAVA
Viscosity is resistance to flow
Viscosity determined by
Temperature HOT= thin, flows easily COOL= thick
Composition Silica(SiO2)=mineral in magma LOW SILICA (basalt) = thin HIGH SILICA (granite) = thick low gas = flows easily

13. 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

14. 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

15. 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”

16. PREDICTING ERUPTIONS: VOLCANO MONITORING
Predict Eruptions by
Study and comparison of past eruptions
Warning Signs-
Small quakes (seismicity)
Swelling of slopes
Changes in water pH
Changes in gases emitted

17. VOLCANO SUMMARY APPEARANCE → ERUPTIONS MAGMA VISCOSITY → ERUPTIONS
Steep slopes (Strato volcano) → explosive (violent)
Gentle slopes (Shield volcano)→ non-explosive (quiet)
MAGMA VISCOSITY → ERUPTIONS
Viscous (thick) magma → explosive (violent - Strato)
Fluid (thin) magma → non-explosive (quiet - Shield)
FORMATION →MAGMA/LAVA →ERUPTIONS
Subduction zones → explosive (violent - Strato)
Sea Floor spreading zones → non-explosive (quiet- shield)
Hot spot → usually non-explosive, but can be explosive
MONITORING→PREDICTION OF ERUPTIONS
Slope changes, quakes↑, water pH↓ , gases ↑