1. Sudden Earth Events
VOLCANOES

2. Where are Volcanos Found?
What is a Volcano?
Opening in Earth’s crust that releases solid rock, magma, steam & ash
May be active (erupting) or dormant (no occurring eruption) or extinct
Ring of Fire
Formed by edges of Pacific plate
Where are Volcanos Found?

3. Reasons Volcanoes Form
SUBDUCTION ZONES
Result of converging plates
One plate is pushed downward & melts
Magma is eventually forced through an opening

4. Mount Vesuvius

10. PLUMES
Result of diverging plates
Rising magma leaks into the crust
Can form new islands on the surface

11. Types of Volcanoes
Based on
Thickness of magma
Amount of gas

12. Types of Volcanoes Strato Steep sides & high peaks Thick magma
Strato
Steep sides & high peaks
Thick magma
Large amounts of gas (usually)
Violent eruptions
Ex. Mount Vesuvius (Italy) Mount St. Helens (US)

13. 2. Cinder cone
Steep sides, shorter peaks
Cylindrical shape
Magma is less thick
High amounts of gas
Generally harmless eruptions
Ex. Stromboli (Italy), Paricutin (Mexico)

14. Shield volcano
Largest volcanoes
Broad, gentle sloping sides
Usually build up from the sea floor
Runny magma
High or low amounts of gas
Ex. Mauna Loa (Hawaii)

15. Effects of Volcanos Lava Ash Fragments of rock less than 2mm in size
Lahars
Mudflows formed from ash, debris and water

16. Avalanches & landslides
Pyroclastic flows
Mixture of hot gas, ash, and other rocks travelling very quickly down the slopes

17. Mount St. Helens Back from the Dead

18. Monitoring a Volcano 1. Shape of Volcano Tilt Crack openings
2. Seismicity
The frequency, magnitude, location, and type of earthquakes

19. 3. Gas Geochemistry
Gas samples are collected from active vents
Gases include carbon dioxide and sulfur dioxide
Composition of the gas
Rate of gas emission

20. 4. Geology 5. Hydrologic Regime Lava & rock samples
Changes in ground water
Temperature
Level
Rates of streamflow
Stream & ice accumulation