1. Volcanoes

2. Anatomy of a Volcano
Magma Chamber – the source of the volcano’s magma.
Conduit – A tubelike structure connecting the magma chamber to the vent.
Vent – the opening at the top

3. Crater vs. Caldera Small Explosion outward Large
Collapse of the chamber inward

4. Types of Volcanoes Composite Cones
Steep Slopes due to vertical eruptions
Composed of alternating layers of ash and lava
Explosive eruptions
Generally found at subduction zones where oceanic crust is pulled under continental crust
Andesitic magma

5. Types (continued) Shield Cones Hawaiian Dangers
Flat, broad slopes due to passive oozing lava
Composed of layered lava flows
Passive eruptions
Found at rift valleys and hot spots in the ocean
Basaltic magma
Hawaiian Dangers
Pa’hoe’hoe flows
A’a’ flows

6. Pa’hoe’hoe
Fluid
Oozing

7. A’a’
Rocky
Jagged

8. Types (continued) Cinder Cones Small cones Steep slopes
Small, explosive eruptions
Found on the flanks of composite and shield cones
Composed of tephra (ash)

9. Warning Signs of a Composite Cone Eruption
Strange Animal Behavior
Presence of sulfur gas
Increased earthquake activity
Increased avalanches and landslides
Swelling of the mountain
Minor small eruptions

10. Dangers of a Composite Cone Eruption
Pyroclastic flow – dense, fast moving currents of ash and rock
450 mph
1800 degrees farenheit

11. Dangers (continued) Lahar – a mudflow mixture of ash and water
Can be 400 feet deep
Can cover 100 square miles

12. Dangers (continued)
Tephra – Fragments of volcanic rock blasted from an eruption
As small as ash
As large as boulders

14. Intrusive Volcanism

16. Formation of Magma Comes from the Upper Mantle when it melts
Forms in 3 general areas
Subduction Zones
Spreading Centers
Mantle Plumes

17. Subduction Zone
The friction of the plate subducting adds heat that melts the rock
The seawater lowers the melting point allowing it to melt compared to the rock around it
A decrease in pressure also helps rock melt

18. Spreading Center
When the plates split apart, the asthenosphere moves upwards and the loss of pressure helps melt the rock

19. Mantle Plumes
Mantle rock rises beneath the lithosphere and the loss of pressure helps melt the rock.

20. Factors that affect the magma
Amount of silica present
Silicates form in long chains and cause the magma to slow
High Viscosity (resistance to flow)
Amount of water present
Magma cools when it rises helping it solidify but the decreasing pressure also helps keep it liquid.
Dropping pressure tends to override the cooling effect unless there is a lot of water present.
In this case the water is lost as steam and helps the magma solidify faster

21. Igneous Rocks
Igneous rocks are rocks that have formed from the direct cooling and crystallizing of magma.
They can be classified based upon two things:
The type of magma
The rate of cooling
There are 2 types of magma that form most igneous rock

22. Andesitic Magma The type of magma that is explosive High silica
Is sticky and doesn’t flow well.
Creates lighter colored rocks
Has more water content because it is trapped by the thicker magma

23. Basaltic Magma Magma that is very fluid Low silica Flows very well
Produces darker colored rocks
Low water content because it escapes as steam

24. Cooling Rates
Igneous rocks that are formed at or near the Earth’s surface cool very quickly.
These are called extrusive rocks
Igneous rocks that are formed deep below Earth’s surface cool very slowly.
These are called intrusive rocks

25. Extrusive Rocks
These rocks cool so quickly that the minerals do not have the time to develop
Small crystal size

26. Intrusive Rocks
These rocks cool so slowly that the minerals take a long time to develop
Large crystal size

27. Other Properties Some igneous rocks have holes in the surface
This is from the escape of gases as the rock cools
This rock is considered vesicular when this occurs.