VOLCANEOUS AND EARTHQUAKES: GEOLOGICAL PHENOMENA

VOLCANEOUS AND EARTHQUAKES

1. Volcanoes and EarthquakesVolcanoes and Earthquakes
GPH 111

2. Volcanoes and Earthquakes Volcanoes and Earthquakes
Game Plan: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. VolcanoesVolcanoes
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 EruptedTypes 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 Increase in
silica silica
content, content,
increase in increase in
viscosity.viscosity.
Activity Time

5. Rock Types Generate Rock Types Generate
Viscous to Non-viscous flows Viscous to Non-viscous flows
of lavaof 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 Rock class determines
landform type and eruption landform type and eruption
style: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 ConesCinder 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 VolcanoesShield Volcanoes - -
Basically really big, long
duration cinder cones
“Basalt Landform”
Olympus MonsMauna Loa

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

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

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

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

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

15. CalderasCalderas -
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 -
andesiticLong Valley Caldera, 15 miles wide,
rhyolitic, 760,000 years old
released 160 cubic miles of material

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

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

18. Positives associated with Positives associated with
Volcanism: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 If you knew this would
happen….happen….
What would you do… How sure do What would you do… How sure do
you need to be?you need to be?

20. EarthquakesEarthquakes
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 TheoryElastic-Rebound Theory
How do How do
earthquakes earthquakes
work?work?

22. 1989 Loma Prieta 1989 Loma Prieta
EarthquakeEarthquake
EpicenterEpicenter - location
at the surface
FocusFocus - actual
location of maximum
movement

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

24. Earthquake DamageEarthquake Damage
““Earthquakes Earthquakes
don’t kill don’t kill
people, people,
buildings do.”buildings do.”
Japanese sayingJapanese 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, Cinder cones, Shields, Composite Cones,
Lava Domes, CalderasLava 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-Elastic-
Rebound TheoryRebound Theory
Field evidence associated with earthquakes
Help: Chapter TL