1. Chapter 18
Volcanic Activity

2. Lesson 5
Volcanoes: The Basics

3. What happens when you shake a can of soda and then open it?
Think About It…
What happens when you shake a can of soda and then open it?

4. How does the composition of magma affect its explosiveness?
Focus Question…
How does the composition of magma affect its explosiveness?

5. Nyiragongo Volcano East African Rift Valley
What is magma?
A mixture of molten rock, suspended mineral grains, and dissolved gases deep beneath Earth’s surface
Nyiragongo Volcano East African Rift Valley

6. 2. Types of Magma: Basaltic…
2. Types of Magma: Basaltic…
Gas Content
1 – 2 %
Silica Content
50%
Viscosity
low
Explosiveness
least
Origin/Location of Magma/Lava
oceanic/continental crust
Example
Mt. Kilauea in Hawaii
Mt. Kilauea A Hot Spot Volcano

7. Types of Magma: Andesitic…
Gas Content
3 - 4 %
Silica Content
60%
Viscosity
intermediate
Explosiveness
Origin/Location of Magma/Lava
continental margins
Examples…
Mt. St. Helens and Mt. Rainier (Washington)

8. Mt. St. Helens – From the Summit of Mt. Rainier

9. Types of Magma: Rhyolitic (Granitic)
Gas Content
4 - 6 %
Silica Content
70%
Viscosity
high
Explosiveness
greatest
Origin or Location of Magma/Lava
continental crust
Example
Yellowstone Supervolcano in Wyoming
Yellowstone Volcano

10. Yellowstone…

11. Types of Magma… 3. The higher the silica content…
Types of Magma…
3. The higher the silica content…
the higher the viscosity (resistance to flowing)…
the greater the explosiveness!
Krakatoa – Highly viscous and explosive!

12. Intrusive Activity… What is a pluton? An intrusive igneous rock body
Intrusive Activity…
What is a pluton?
An intrusive igneous rock body
Pluto –
god of the underworld

13.
Batholiths
2. A batholith is the largest of plutons common in the interiors of major mountain chains.
Yosemite – Part of the Sierra Nevada Batholith

14. El Capitan and Half-Dome, Yosemite National Park – Examples of Batholiths

15. Intrusive Activity… At subduction zones, a plate subducts, melts,
Where did all the magma come from?
Scientists hypothesize that…
At subduction zones, a plate subducts,
melts,
cools into a pluton.

16. Melting at an ocean/continental boundary formed the batholiths of Yosemite National Park, CA.:

17. Volcanoes… What is lava? What is a volcano?
Volcanoes…
What is lava?
molten rock that has reached Earth’s surface
What is a volcano?
A mountain or opening in Earth’s crust from which lava erupts
Paricutin in Mexico, 1943

18. 3. The Anatomy of a Volcano…
Vent – the opening in the crust through which lava erupts
Crater – bowl-shaped depression around the vent
Caldera – larger depressions around a vent where the volcano has collapsed into the magma chamber
d. Magma chamber – area under the volcano which holds the magma

19. Slides of Crater, Caldera…
Crater Lake
Yellowstone Caldera

20. 4. Label the Volcano…

21. Types of Volcanoes… Shield Basaltic lava builds up (Quiet eruptions)
IN THE NEWS…
Type of Volcano
Shield
How It Forms
Basaltic lava builds up (Quiet eruptions)
Description
Wide with gently-sloping sides
Example
Kilauea in Hawaii (hot spot)
Iceland (divergent)

22. Types of Volcanoes… Type of Volcano How It Forms Description Example
Cinder cone
How It Forms
Ejected tephra falls back to earth and piles up (Explosive)
Description
Small but steep
Example
Paricutin in Mexico
Convergent boundary
Paricutin, Mexico

23. Types of Volcanoes… Type of Volcano Composite How It Forms
Tephra eruptions alternate with lava flows
Description
Large & steep
Example
Krakatoa
Mt. St. Helens
Convergent
Mt. St. Helens -Before and After!

24. Mt. St. Helens… as seen from the crater of Mt. Rainier!

25. Mt. Rainier: Cascade Range
Hiking in the crater!
July 12, 2013

26. A Composite Volcano…

27. Volcanoes: Effects on the Lithosphere
Lesson 6
Volcanoes: Effects on the Lithosphere

28. Tephra… 1. What is tephra? Tephra classified by size…
Rock fragments thrown into the air during a volcanic eruption
Tephra classified by size…
dust  ash  lapilli  bombs  blocks
2. A pyroclastic flow is…
an eruption of gas, ash, and other tephra
These types of eruptions can be extremely violent and deadly because… the PC flow moves very fast and is very hot.
3. Ash and dust from a pyroclastic flow blocks sunlight and lowers global temperatures.

29. Effects of a Volcanic Eruption… Lahars
A lahar is a mixture of mud & debris created when…
heat from an eruption melts snow OR
rain forms around dust or ash in the atmosphere.

30. Earthquakes, Landslides and Tsunamis…
Earthquakes are caused when…
Magma breaks rocks as it makes its way to the surface.
Landslides are caused in two ways…
… a volcanic earthquake (EQ) or the eruption itself causes land to slide
Tsunamis are caused when…
… the volcanic landslide “bulldozes” water ahead of it

31. Earthquakes, Landslides and Tsunamis…

32. Earthquakes, Landslides and Tsunamis…

33. 5. Hawaii and Yellowstone…
… are formed at hot spots (very hot places in the mantle/crust)
… away from plate boundaries

34. 6. Kilauea: Effects on Land…
Basaltic lava…
burns vegetation and buildings
creates new land (16 acres a year!)

35. 7. Krakatoa: Effects on Land…
The eruption of Krakatoa…
Created a caldera when it blew the island apart
Caused a pyroclastic flow and tsunami (1883)

36. 8. Iceland: Effects on Land…
Iceland’s volcanoes in the rift valley are causing it to grow bigger – with older rocks on the east and west sides of the island.

37. Convergent Boundary Volcanoes
Ocean plates subduct under other plates and melt to form magma
Location – the Pacific Ring of Fire, the Mediterranean Belt
Mt. Vesuvius and Pompeii Victims

38. The Ring of Fire…

39. Divergent Boundary Volcanoes
As plates move apart, magma is forced upward into fractures and faults
Location – East Africa Rift Valley, mid-ocean ridges, Iceland

40. Divergent Boundary Volcanoes… Iceland
Divergent Boundary Volcanoes… Iceland
Surtsey Volcano

41. Pluton Slides…
The following slides depict different types of plutons. I cut these slides from the notes but left the slides on the ppt for future reference!

42. A Plethora of Plutons… Stocks
Stocks are irregularly-shaped plutons similar to batholiths but smaller.

43. A Plethora of Plutons… Laccoliths
Laccoliths are mushroom-shaped plutons with a round top and a flat bottom.

44. A Plethora of Plutons… Sills
A Plethora of Plutons… Sills
A sill is a pluton that forms when magma intrudes parallel to layers of rock.
The Palisades Sill, NY

45. A Plethora of Plutons… Dikes
A dike is a pluton that cuts across preexisting rocks.
Iron Dike Intrusion, Ironclads, Colorado

46. The Great Dike of Zimbabwe…