1. Volcanoes and Earthquakes
GPH 111

2. Volcanoes and Earthquakes Game Plan:
Types of eruptions and the importance of viscosity
Rock class and landform type
Dangers associated with volcanic eruptions
How earthquakes work
Earthquake danger

3. Volcanoes Stem from the release of magma on to earth’s surface
At least 1,500 active volcanoes on the planet (1 eruption in recorded history)
50 volcanic eruptions every year
Mt. Pinatubo, 1990

4. Types of Rock Erupted (igneous extrusive)
Basalt - silica content between 48% and 55%
Andesite - silica content between 55% and 60%
Dacite - silica content between 60% and 70%
Rhyolite - silica content between 70% and 77%
Increase in silica content, increase in viscosity.
Activity Time

5. Rock Types Generate Viscous to Non-viscous flows of lava
Basalt - low silica, low viscosity (like……), trapped gasses released easily
Andesite - medium silica, higher viscosity (like……), trapped gasses release much less easily
Dacite and Rhyolite - high silica, high viscosity (like…….), trapped gasses have a hard time escaping, but if they do…

6. Rock class determines landform type and eruption style:
Cinder Cones - (basalt) mildly explosive
Shield Volcanoes - (basalt) mildly explosive
Composite Volcanoes - (andesite to dacite) mild to highly explosive
Lava Domes - (dacite to ryholite) non-explosive
Calderas - (andesite to ryholite) extremely violent and explosive

7. Constructed from fountains of lava that rain around the vent.
Cinder Cones -
They can also issue low volatile flows, quietly oozing from the vent.
SP Crater, N. AZ
Hawaii - Cinder Cone in Action
“Basalt Landform”

8. Shield Volcanoes - Basically really big, long duration cinder cones
Mauna Loa
Olympus Mons
“Basalt Landform”

9. Composite Volcanoes -
Build up over time with alternating ash fallouts and lava flows, tendency to generate extremely violent events mixed with more moderate events.
Mt. Fuji - classic composite cone
“Andesite - Dacite Landform”

10. Composite Volcanoes -
Mt. Saint Helens
“Andesite - Dacite Landform”

11. Composite Volcanoes -
Mt. Saint Helens
“Andesite - Dacite Landform”

12. Composite Volcanoes -
Mt. Pinatubo
“Andesite - Dacite Landform”

13. Composite Volcanoes -
Marianas Trench
“Andesite - Dacite Landform”

14. Lava Domes -
Highly viscous eruptions that build internally and externally
Lava Dome developing in Mount St. Helens
Mt. Elden, N. AZ
“Dacite - Rhyolite Landform”

15. Highly explosive eruptions that lead to structural collapse from an emptied magma chamber
Calderas -
Show Movie - Crater Lake, 6 miles wide, 7,700 years ago - andesitic
Long Valley Caldera, 15 miles wide, rhyolitic, 760,000 years old released 160 cubic miles of material
“Andesite to Rhyolite Landform”

16. Dangers associated with eruptions:
Lahars
a hot or cold mixture of water and rock fragments flowing (70 mph) down the slopes of a volcano and into river valleys
Pyroclastic flows
fluidized masses of rock fragments and gases that move rapidly in response to gravity
(can travel over 400 miles per hour, and reach temperatures approaching 2,000° F)
Mt. St. Helens, 1980
Mt. St. Helens, 1980
Mt. Pelée, 1902

17. Dangers associated with eruptions:
CO2 Emissions - Release of CO2 from buried magma into the atmosphere through faults, fissures, and lakes.
Mammoth, CA – 1,300 tons of sulphur dioxide released every day.
“What might some positives be?”

18. Positives associated with Volcanism:
Fertile Soils
Enriched soils from mineral rich volcanic ashfalls
Geothermal Energy
Magma in the earth heats groundwater and the steam is used to power generators
New Land
Lava flows from continents into oceans can generate new land for development

19. If you knew this would happen….
What would you do… How sure do you need to be?

20. Earthquakes Detected with Seismographs (movie)
Rated based on the Richter Scale
Elastic Rebound theory (Demonstration)
Evidence and Damage from an Earthquake
3.0 on the Richter Scale represents 31.5 times more energy than a 2.0, and 992 times more than a 1.0

21. Elastic-Rebound Theory
How do earthquakes work?

22. 1989 Loma Prieta Earthquake
Epicenter - location at the surface
Focus - actual location of maximum movement

23. Field Evidence of an Earthquake…
Fault Scarps – Steplike linear landform coincident with a fault trace and caused by geologically recent slip on the fault
Fissures – Cracks or ruptures on earth’s surface from earthquakes, but without offset

24. Earthquake Damage “Earthquakes don’t kill people, buildings do.”
Japanese saying

25. Things to Know:
Basic volcanic rock breakdown based on silica and their viscosity
Basics associated with volcanic forms linked to the different rock types - Cinder cones, Shields, Composite Cones,
Lava Domes, Calderas
That low viscosity eruptions tend to be much less violent than high viscosity eruptions and why
Dangers associated with volcanism
Positives associated with volcanism
Problems with volcanic or earthquake prediction
How Earthquakes are generated with regard to the Elastic-Rebound Theory
Field evidence associated with earthquakes
Help: Chapter TL