• Established 1981
• Provide for a safety zone around an active volcano
• Southwestern Washington
Mount St. Helens
• May 18, 1980
• Major eruption of a stratovolcano
• Not a typical eruption
Mount St. Helens
• The warning signs
• Steam and gasses
• Change in shape - bulge
• Numerous small earthquakes
Mount St. Helens
• Eruption - May 18, 1980
• Earthquake (5.2) - massive landslide
• Lateral blast - blowout
• Vertical eruption - ash fall, ash flow
Mount St. Helens
• The landslide - bulge = unstable slopes
• Largest in human history = eruption trigger
Mount St. Helens
• Lateral blast
• Superheated ash
• Blowout - trees flattened
Mount St. Helens
• Vertical eruption - tephra
• Ash flow
• Ash fall
Mount St. Helens
• Ash Fall
• Blanketed an area downwind
Mount St. Helens
• Lahars - mudflows - volcanic ash and water
• Don’t require and eruption
• Most dangerous volcanic event
Mount St. Helens
• The lava dome
• A rebuilding phase
Anatomy of an Eruption
• Question:
• Will the next eruption of Mt. St. Helens be as large as the one in 1980
- why or why not?
Recent Activity
• September 2004
• Oct. 1st - steam eruption
• Is a major eruption likely?
Monitoring the Volcano
• Predicting Eruptions =>
- Precursors
- Shape
- Seismic Activity
- Gasses
Volcanoes & Human History
• The loss of entire cities
• Climate change
– Ash
– gasses