1. Chapter 3: Volcanoes

2. Chapter 3.1
Key Concepts:
Where are Earth’s volcanoes found?
How do hot spot volcanoes form?

3. Definitions:
Volcano: a weak spot in the Earth’s crust where molten material (magma) comes to the surface
Magma: a molten mixture of rock forming substances, gases and water from the earth’s mantle.
Lava: when magma reaches the Earth’s surface.

4. Volcanoes & Plate Boundaries
600 active volcanoes on land, many more under the sea.
Volcanoes occur in belts that extend across continents and oceans.
Ring of Fire - major volcanic belt formed by the many volcanoes that rim the Pacific Ocean.

5. Volcanic belts form along the boundaries of Earth’s plates

6. Volcanic belts form along the boundaries of the Earth’s plates
Diverging ( )and converging () occur.
Results in fractures in the Earth’s crust
Magma reaches the surface.

7. Most volcanoes occur at
Divergent Boundaries
Mid Ocean Ridge
Convergent boundary
Points of subduction
ex. Mount Etna – Eurasian and African plates

8. Volcanoes on Divergent Boundaries
Under ocean: point of Mid ocean ridges occurring ( long underwater mountain ranges)
Many have rift valleys down the center
Lava pours out of rift valley – creates new mountains.
Land - Great Rift Valley in East Africa

10. Volcanoes on Convergent Boundaries
Volcanoes form when:
Two oceanic plates collide
Oceanic and continental plates collide
In both situations, oceanic plates sink beneath a trench.
Rock above the plate melts to form magma.
Erupts to the surface as lava

11. Volcanoes on Convergent Boundaries

12. Volcanoes on Convergent Boundaries
Magma – less dense than the surrounding rock
Magma rises to the surface and breaks through the ocean floor creating volcanoes.
String of islands formed: Island arc
Examples: Japan, New Zealand, Indonesia, the Philippines

13. Hot Spot Volcanoes
Hot Spot – an area where material from deep within the mantle rises and melts forming magma
Volcanoes form above a hot spot when magma erupts through the crust and reaches the surface.

14. Hot Spot Volcanoes
Some hot spots lie in the middle of plates far from plate boundaries.
Others occur on or near plate boundaries.

15. Hot Spot Volcanoes
A hot spot in the ocean floor can gradually form a series of volcanic mountains
Ex. The Hawaiian islands

16. Hot Spot Volcanoes A hot spot can also form under continents
Ex. Yellowstone National Park, WY

18. 3.2 PROPERTIES OF MAGMA Vocabulary:
Element-a substance that cannot be broken down into other substances
Compound-a substance made of two or more elements that have been chemically combined
Physical Property-a characteristic of a substance that can be observed or measured without changing the composition of a substance
Chemical Property-any property that produces a change in the composition of matter.

19. Pahoehoe-fast moving, hot lava that has low viscosity
aa-higher viscosity, slower moving, cooler lava that Pahoehoe
Viscosity-the resistance of a liquid to flow
Silica—major ingredient in magma made of silicon and oxygen.

20. Magma Composition
Magma varies in composition and is classified according to the amount of silica it contains.
The graphs show the average composition of the two types of magma. Use the graphs to answer the questions.

22. What materials make up both types of magma?
Silica, oxides, and other solids
Which type of magma has more silica? About how much silica does this type of magma contain? Rhyolite, 70%
A third type of magma has a silica content that is halfway between that of the other two types. About how much silica does this type of magma contain? 60%
What type of magma would have a higher viscosity? Explain. The rhyolite forming would have higher viscosity because it contains more silica

23. Volcanic Eruptions 3.3 Objectives:
Explain what happens when a volcano erupts.
Describe 2 types of volcanic eruptions
Identify stages of volcanic activity
What comes out of volcanic explosions?
Ash, lava, steam, rock, gases, dirt

24. Volcanic Eruptions 3.3 Magma forms in the asthenosphere
Convection currents in the mantle bring magma towards the surface
Magma tries to flow into any open crack
When magma reaches a weak spot in the crust, a volcano forms
Lava is magma that has reached the surface

25. Magma Reaches Earth’s Surface
Volcanoes are systems of passage ways through which magma moves.
Inside a Volcano
Magma collects below the volcano in the magma chamber
Magma flows upward through a tube (pipe) that connects the magma chamber to the surface.

26. Magma Reaches Earth’s Surface
Inside a Volcano
Gas and magma leave through vents
Central vent is the opening at the top
Side vent anywhere along the side of the volcano
Lava pours out of the vents and creates a lava flow
A bowl shaped area called a crater may form around the central vent

28. Magma Reaches Earth’s Surface
A Volcanic Eruption
Dissolved gases are trapped
in magma under extreme
pressure (CO2 in a soda bottle)
as magma flows , pressure because there is less rock on top of it.
the dissolved gases expand and form bubbles
When a volcano erupts, the force of the expanding gas forces magma up the pipe until it explodes out the vent

29. Content checkpoint… think/pair share…take two minutes to answer these questions with a partner nearby…..
What common everyday occurrence can we relate to a volcanic eruption?
What happens to the pressure in the magma as it rises toward the surface?

30. Kinds of Volcanic Eruptions
Volcanic eruptions can be quiet or explosive.
Eruptions depend on the properties of magma
Silica content
Viscosity

31. Kinds of Volcanic Eruptions
Quiet Eruptions
Magma has low silica content = low viscosity
Magma flows easier so gases bubble out gently
Lava can flow many kilometers from the vent
Produce both pahoehoe and aa lava
Example: Hawaiian Islands – Mount Kilauea

32. Kinds of Volcanic Eruptions
Explosive Eruptions
Magma has high silica content = high viscosity
Magma doesn’t always flow out of vent and so it builds up (like a cork in a bottle)
Trapped gases build up pressure until they explode
Magma is pushed out of the vent with incredible force

33. Kinds of Volcanic Eruptions
Explosive Eruptions
Lava breaks into fragments that cool quickly and harden into different sizes
Ash – fine, dust sized particles of lava
Cinders – pebble sized particles
Bombs – baseball to car sized chunks of lava
Pyroclastic flow: when an explosive eruption hurls out gases, ash, cinders and bombs.
Pumice forms when lava cools quick and traps air bubbles inside
Obsidian forms when lava cools quick leaving the surface smooth and glass-like

34. Kinds of Volcanic Eruptions
Volcano Hazards
Quiet eruptions cause lava to flow far --- burning and burying everything in its path
Explosive eruptions can bury entire towns in ash, cause landslides, avalanches, cause damage from gases and cinders/bombs.

35. Content checkpoint… think-pair-share take two minutes to answer these questions with a partner nearby.
What is pyroclastic flow?
How does volcanic ash cause damage?
What is the main difference between a quiet eruption and an explosive eruption?

38. Stages of Volcanic Activity
Life Cycle of a Volcano
Scientists use historical records and monitor volcanoes to determine what stage of activity a volcano is in
A volcano can be active, dormant or extinct
An active volcano is erupting or showing signs of near future eruptions
A dormant (sleeping) volcano can awaken in the future and become active
An extinct (dead) volcano is unlikely to erupt ever again

39. Stages of Volcanic Activity
Monitoring Volcanoes
Geologists use tiltmeters to detect slight changes in surface elevation cause by magma moving underground
They monitor gases escaping from a volcano
Increase in temperature might mean magma is nearing the surface
The changes detected may give a short warning time BUT
We cannot be certain the type of eruption or how powerful it will be

40. Think and Discuss….
Which is more likely to be dangerous – a volcano that erupts frequently or a volcano that has been inactive for a hundred years? WHY?

41. 3.4 Volcanic Landforms Objectives:
List the landforms that lava and ash create
Explain how magma that hardens beneath earth’s crust creates landforms
Identify other distinct features that occur in volcanic areas
Volcanic activity on and beneath the surface has built up Earth’s land areas.

42. Landforms from Lava and Ash
Volcanic eruptions create landforms made of lava, ash and other materials
Shield volcanoes
Cinder cone volcanoes
Composite volcanoes
Lava plateaus
Another landform results from the collapse of a volcanic mountain
caldera

43. Shield volcanoes Gently sloping mountains
Thin layers of low viscosity lava build up over time
Ex) the Hawaiian Islands
CSAV Hawaii: Pele's Hair (Volcanic Glass) - YouTube
Kilauea Lava Flows on May 6, YouTube
Shield Volcano in Iceland l

44. Cinder cone volcanoes
High viscosity lava produces ash, cinders and bombs
Those materials build up around the vent in a steep cone shaped hill/mountain.
Ex) Sunset Crater in Arizona

45. Composite Volcanoes
Form when volcanoes alternate between quiet lava flows and explosive eruptions of ash, cinders and bombs
Tall, cone shaped mountain with alternating layers of ash and lava
Ex) Mt St. Helens, Washington and Mt. Fuji, Japan

46. Composite Volcanoes
Form when volcanoes alternate between quiet lava flows and explosive eruptions of ash, cinders and bombs
Tall, cone shaped mountain with alternating layers of ash and lava
Ex) Mt St. Helens, Washington and Mt. Fuji, Japan

47. Lava Plateaus
Low viscosity lava flows out of several long cracks and travels far before cooling
After millions of years a high plateau forms
Ex) Columbia Plateau in Washington, Oregon and Idaho

49. Calderas
Huge hole left by the collapse of composite volcanic mountains
Filled with fallen pieces of the volcano, ash and lava
Enormous eruptions may empty the pipe and the magma chamber
there is only hollow space left that can’t support the weight and it collapses on itself
Overtime water from rain and snow may fill the caldera
Ex) Crater Lake, Oregon

52. Soil from lava and ash
People settle near volcanoes because of the rich, fertile soil
At first, after volcanic eruptions the land is empty and barren
Overtime the ash breaks down and provides:
Potassium
Phosphorus
Other substances that plants need

53. Landforms from Magma
Sometimes magma forces its way through cracks in the crust but never reaches the surface
The magma cools and hardens within the rock layers
Overtime ice, wind, or rain erode away the surrounding rock and expose the hardened magma

54. Volcanic Necks Forms when magma hardens in the pipe
Overtime the outer rock is weathered away
Looks like a giant tooth
Ex) Ship Rock, New Mexico

55. Dikes and Sills
Dike: when magma forces its way across multiple rock layers and hardens
Sill: when magma squeezes between horizontal layers of rock and hardens
Ex) Palisades, NY & NJ

56. dike
sill

57. Batholiths
Large masses of rock that are formed when a huge mass of magma cools inside the Earth’s crust
The outer layers of rock erode away leaving the hardened magma exposed
Ex) Sierra Nevada Batholith

59. Dome Mountains Created by smaller bodies of magma
The hardened magma uplifts the surrounding rock and causes it to bend into a dome shape
Ex) Black Hills, South Dakota

60. Geothermal Activity Geo = Earth, therme = heat
Geothermal activity – when magma a few km beneath the surface heats underground water.
Ex) hot springs and geysers found near past and present volcanic activity

61. Hot Springs
Forms when underground water is heated by magma or hot rock
The heated water rises and collects in pools

63. Geysers Fountains of water and steam that erupt from the ground
The heated water and steam build up pressure until finally it erupts
Ex) Old Faithful, Yellowstone National Park

64. Geothermal Energy Heated water can provide an energy source
Heated water can be used to power turbines and create electricity
A panoramic view of the Geysers geothermal power plant in Geysers, Calif. The site, located above Santa Rosa, is the largest geothermal development in the world.