1. What caused Mt. St. Helen’s to erupt?
Volcanic Activity
What caused Mt. St. Helen’s to erupt?

2. Where do Volcanoes Occur?

3. Where do volcanoes occur?
Along convergent boundaries above subduction zones
Ring of Fire
Along divergent boundaries at mid-ocean ridges

4. Hot Spots
Hot Spots are unusually hot regions of Earth’s mantle where plumes of magma rise to surface
Located away from plate boundaries
Example: Hawaii

5. Volcano Status Active Erupts Regularly
Lifetime can span months to millions of years
Can be currently erupting or showing signs of unrest (earthquakes, emitting gas)
Ex: Mt. St. Helens

6. Extinct Dormant Unlikely to erupt again No magma/lava supply
Ex: Hawaiian Islands not over hot spot
Dormant
Erupted in past but is now quiet
*Difficult to determine status of volcanoes*

7. Effects of Volcanoes
Volcanoes emit water vapor, carbon dioxide, and sulfur dioxide into the air
Gases are suspended in atmosphere and block radiation from sun
Global temperatures can be affected
Health issues for humans (Respiratory)
Pyroclastic flows, tephra, lahars (hot mud flow)

8. Volcano Predictions?
Volcanologists study deposits left from previous eruptions
Warning Signs: earthquakes activity and gas emissions
Seismometers measure EQs and correlation spectrometers measure SO2 levels

9. Volcano Safety Structural support – walls, supportive buildings
Evacuation procedures
Communication between scientists and public

10. Volcanoes in our Solar System
Volcanoes may have been present in the history of other planets
Mars, Venus
Volcanoes are active on Jupiter's moon, Io