This document summarizes information about volcanoes and earthquakes. It describes the different types of volcanic eruptions based on the viscosity of erupted rocks like basalt, andesite and rhyolite. The viscosity determines the resulting landform, from mild cinder cones to violent caldera eruptions. Dangers of eruptions include pyroclastic flows and lahars, but volcanism also provides fertile soils and geothermal energy. Earthquakes are caused by the elastic rebound of rock as stresses are released on faults; their damage potential increases exponentially with magnitude on the Richter scale.

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

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

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
Mt. Elden, N. AZ
Lava Dome developing
in Mount St. Helens
“Dacite - Rhyolite Landform”

15. Calderas -
Highly explosive eruptions that
lead to structural collapse from an
emptied magma chamber
“Andesite to Rhyolite Landform”
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

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. Pelée, 1902
Mt. St. Helens, 1980
Mt. St. Helens, 1980

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