1. Chapter 6- Volcanoes

2. Which statement concerning volcanoes is accurate?
All volcanoes erupt explosively.
Lava is the most deadly thing about volcanoes.
Volcanic eruptions can influence the climate of Earth.
Volcanoes occur in random locations on the surface of Earth.

3. Volcanoes • expulsion of molten rock (Lava), gases and
water vapor onto the surface of the Earth.
sometimes violently, sometimes not -
1500 active volcanoes
>
Active = erupted in recorded history -
e.g. Mauna Loa and Kilauea (Hawaii) -
Mt. St. Helens (Washington) -
Mt. Pinatubo (Philippines) -
Mt. Fujiyama (Japan) -
Mont Serrat (Caribbean)
Mt. Fujiyama, Japan

4. Extinct or inactive volcanoes
Dormant
Extinct Volcanoes vs
Dormant volcanoes
Dormant volcanoes • • - -
have not erupted recently, but may do
have not erupted recently, but may do so again.
>
>
Mt. Vesuvius (Italy)
Mt. Vesuvius (Italy)
Extinct volcanoes • •
Extinct or inactive volcanoes - -
have not recently erupted
nor do they give indications
of erupting in the future.
Thousands of these
>
>
types of volcanoes exist.
Mt. Kilamanjaro (Tanzania,Africa)

5. Types of Volcanoes

6. A small shield volcano in Iceland

7. What materials are not commonly associated with volcanic eruptions?
Lava
Steam
Gasses
All of the above are associated with volcanic eruptions

8. more water = more explosive Magma composition
Discussion: Why do some volcanoes erupt explosively, whereas others erupt in a more subdued fashion that is not explosive?
Water in magma
more water = more explosive
Magma composition
high silica content = high viscosity (flow resistance)
high viscosity = more explosive
Magma Temperature
cooler = higher viscosity (see above)
Gas content
more gas = more explosive
All factors are related to tectonic location

9. Composite Volcanoes a.k.a.- stratovolcanoes • -
interbedded pyroclastics and lavas.
typically andesitic to rhyolitic lava
>
intermediate to felsic magma composition
Found on continents and island arcs
mostly associated with convergent plate
boundaries (subductive)
examples of composite
Mt. St. Helens, Mt. Vesuvius, Mt. Pinatubo,
Mt. Fujiyama, Mt. Kilamanjaro., Mt. Rainier (photo)

10. Stratovolcano formation

11. Composite or Stratovolcanoes
Mayon volcano, Philippines, is a
Mayon volcano, Philippines, is a
View of Mount St. Helens,
View of Mount St. Helens,
nearly symmetrical composite
nearly symmetrical composite
Washington in 1978.
Washington in 1978.
volcano.
volcano.

12. Cinder Cones Primarily cinder-sized (0.25-1.0 mm) material.
but may have other sizes too.
Cinders fall to Earth and collect around the vent.
have steep slopes up to 33 degrees
smaller than shield volcanoes, usually less than
400 m tall
Form on the flanks of larger volcanoes.

13. Cinders and volcanic ash

14. Lava Types Lower viscosity lava Higher viscosity lava
Pahoehoe lava (smooth & ropey) in
Hawaii.
Lower viscosity lava
Aa lava (rough and blocky) also
in Hawaii.
Higher viscosity lava

15. Pillow Lavas 1 meter 1 meter These bulbous masses of pillow
lava formed when lava erupted &
lava formed when lava erupted &
cooled under water.
cooled under water.
1 meter
1 meter

16. Lava Fountain
Lava Fountain

17. It is possible to drive faster than lava flows to escape it?
True
False

18. It is possible to outrun a pyroclastic flow in a car.
True
False

19. Pyroclastic Ash Flow aka Nuee Ardentes
Pyroclastic ash- lava blown up into the air •
smaller stuff is ash, larger stuff are
called "bombs"
extremely fast (100's m/sec)
extremely hot -
sometimes glowing redhot
extremely lethal
many deaths associated with volcanic
eruptions are related to these events
>
e.g., Pompeii and Herculanum
aka Nuee Ardentes '

20. Ash plume from a stratovolcano eruption

21. Pyroclastic flow ,
Nuee Ardente

23. , Lahars & Nuee Ardentes , •
Lahars are mud flows that often occur after eruptions. •
Nuée ardentes are mobile dense clouds of incandescent ash that can move downhill at
speeds up to 100 km/hr. ,
Mt Pelee destroyed St. Pierre on the island of Martinique, West Indies in 1902

24. The effects of explosive volcanic activity
Casts of people from Pompeii, killed by ash from Mt. Vesuvius, Italy

25. Gases and Magma • Volcanic gases Felsic magmas Mafic magmas -
water vapor
- carbon dioxide
nitrogen
- sulfur oxides
hydrogen sulfide
- chlorine
Felsic magmas
highly viscous : Si-rich
inhibits the expansion of gases
pressure builds up
explosive eruptions, like Mt. St. Helens.
Mafic magmas
lower viscosity
lower gas pressure
erupt rather quietly, like Hawaiian Volcanoes.

26. Lake Nyos, a volcanic lake in Cameroon, Africa
CO2 emitted from the acidic lake killed 1700 villagers near the lake in 1986

27. Mt. St. Helens- May 18, 1980

28. Yellowstone Caldera

30. Bathymetry map of Crater lake, Oregon

31. Volcanoes are randomly distributed around the world with no discernable pattern?
True
False

32. Distribution of volcanoes is not random•
related to plate tectonics •
commonly found along plate boundaries

33. Effects of Volcanoes and their activity•
builds up mountains and new land or destroys old
(geosphere) - •
kills many living things
(biosphere) - •
ejects ash and gases into the air
Changing weather and climate patterns for several •
months to a year
(atmosphere) -
Causes changes in drainage patterns, and pollutes •
many water sources
(hydrosphere) -
Ash blocks incoming sunlight from space
(exosphere)