1. Chapter 9 Volcanoes

2. Section 1 Volcanic Eruptions
Volcano – a mountain that forms when molten rock, called magma, is forced to the Earth’s surface.

3. Nonexplosive Eruptions
Lava – magma that flows onto Earth’s surface.
Lava flows are associated with nonexplosive eruptions.

4. Explosive Eruptions
Clouds of hot debris and gases shoot out from the volcano
Volcano may actually
decrease in size.

5. Cross Section of a Volcano
Lava
Vent
Magma Chamber

6. Magma
The composition of the magma determines the explosiveness of the volcano.
Water content
More water = more explosion
Example: Soda Can
Silica Content
More silica = slow flowing magma (high viscosity)
Discovery: Volcano

7. What erupts from a Volcano?
Lava:
Blocky Lava
Pahoehoe Aa
Pillow Lava

8. What erupts from a Volcano?
Pyroclastic Material – the rock fragments created by a volcanic eruption.
Volcanic Blocks
Volcanic Bombs
Lapilli
Volcanic Ash

9. Section 2 Volcanoes’ Effects on Earth
An Explosive Impact –
Ashe – high into atmosphere – blocks sunlight
Makes it hard to breathe
Blocks roads

10. Flows and Fallout
Lahar – a mixture of mud, groundwater, flowing at a rapid speed down the mountain after an eruption.

11. Pyroclastic Flows
Rapidly flowing clouds of hot ash and volcanic glass rolling down the mountainside.
Can cut down houses, trees, block roads, and devastate river valleys.

12. Climatic Changes
Volcanic ash and sulfuric gases can reach the upper atmosphere.
These gases can affect the amount of sunlight reaching the ground.
Mount Pinatubo, 1991
Average global temperatures
dropped as much as 0.5 degrees
Celsius.

13. Three Types of Volcanoes
Shield – built by repeated nonexplosive eruptions where lavaflows slowly build the mountain.
Cinder Cone – small volcanoes made from pyroclastic materials of moderately explosive eruptions.
Composite (Stratovolcanoes) – explosive eruptions followed by outpourings of lava. Layered Volcano

14. Craters and Calderas Crater – funnel shaped pit at top of the volcano
Caldera – when a magma chamber empties and the roof collapses.

15. Lava Plateaus
Large layers of lava flowing from fissures in the ground. Columbia River Plateau

16. Section 3 - What Causes Volcanoes?
The Formation of Magma
In the lower crust / upper mantle large reservoirs of magma form.
Pressure / Temperature – affect magma formation
Density – magma rises because it is less dense than the surrounding rock.

17. Ring of Fire
Boundary around the Pacific Plate – 75% of the world’s active volcanoes.

18. Hot Spot Volcanoes
An isolated volcano not caused by movement at a plate boundary, but rather by the melting of a mantle plume.