1. Igneous Rocks
Section 6.2

2. Rocks Overview
A rock is a group of one or more minerals that have been bound together.
Three Major Types:
Igneous rock
formed by the cooling and hardening of magma or lava
2. Sedimentary rock
formed by the compactions and cementations of sediment
3. Metamorphic rock
formed by the effects of heat and pressure on other rocks

3. Rocks Overview
The rock cycle is the repeated series of events by which rock gradually and continually change from one type to another.

4. Igneous Rock Formation: The Starting Material
Igneous rocks formed from underground magma are called intrusive igneous rocks. When formed at the Earth’s surface, they are called extrusive igneous rocks.
Felsic Magma
thick, slow moving magma
contains large amounts of silica
rocks are usually light in color
Mafic Magma
hotter, thinner magma
contains much smaller amounts of silica
rocks are usually dark in color

5. Igneous Rock Formation: Underground Magma
Igneous rocks are formed by the cooling and hardening of hot molten rock from inside the Earth.
The rate at which magma cools determines the size of the crystals that make up that particular rock.
Slow cooling crystals = large crystals
Fast cooling crystals = small crystals

6. Igneous Rock Descriptions
Igneous rocks are classified based on the mineral composition and texture.
Three main families of igneous rocks:
1. Granite family
Felsic rocks
Usually coarse grained texture
Usually light in color
2. Gabbro family
Mafic rocks
Dark in color more dense than the granite
Family
3. Diorite family
Have characteristics of both felsic and mafic rocks
Darker than the granite family, but not as dark as the gabbro family.
Rocks can be either coarse or fine grained.

7. Igneous Intrusions
An igneous intrusion is a rock mass that forms when magma cools inside Earth’s interior (may be called a pluton).
Laccolith
Volcanic neck
Volcano
Sill
Dike
Batholith

8. Section 9.1 How and Where Volcanoes Form

9. Volcano Characteristics
A volcano is a landform that develops around the opening in Earth’s crust through which molten rock, ash, and gasses can erupt.

10. Magma Formation Three ways to form magma: 1. Decrease in pressure
2. Increase in temperature
3. Increase in amount of water in the asthenosphere

11. Volcanic Activity at Different Boundaries
Observe an animation of volcanism at a subduction zone. Ex: The Cascade Range
Observe an animation of volcanism along a rift zone. Ex: Iceland
Observe an animation of volcanic islands forming over a hot spot. Ex: Hawaii

12. Where is the volcano being formed?

13. Section 9.2 Erupted materials

14. Types of Magma Ways that magma can differ: Silica content Gas content
principal ingredient in all magmas
Gas content
mainly water vapor and CO2 dissolved in magmas at depths where they form
Viscosity
resistance of a liquid to flow
Melting temperature

15. Explosive Eruption Conditions
Magmas high in silica content resist flow
Higher gas concentration
Lower melting point
Location

16. Flows on Earth’s Surface
Lava = hot molten rock that flows out on Earth’s surface
Pahoehoe
Basaltic lava high in temperature, smooth,
rope-like lava that flows very easily

17. Lava flows on land AA
basaltic lava moves slowly and cools quickly into rough jagged rock

18. Underwater Lava Flows Pillow lava
rounded lumps of lava that form underwater
crack and form pillow shapes because of the drastic temperature change in the ocean

19. Ash and Rock Fragments Pyroclastic flow
dense, superheated eruption of gases and pyroclastic material
rapid down hill movement at speeds over 100 kilometers per hour

20. Ash and Rock Fragments Pyroclastic material
gases and solid fragments of solid rock that is ejected from a volcano
Ex: ash (smallest), lapilli (intermediate), block (largest)

21. Volcanic Landforms Section 9.3

22. Types of Volcanoes Shield volcano Cinder Cone volcano
Lava flows out of the earth creating a broad base and gentle slopes
Composed of basaltic lava
Cinder Cone volcano
Forms when lava is thrown into the air from a vent and cools before reaching the ground
Fragments of molten rock pile up around the volcanic vent
Composite volcano
Layers of material accumulate around a vent
combination of hardened lava, ash, and/or pyroclastic material erupt

24. Cinder Cone

25. Composite Volcano

26. Other Formations Associated With Volcanic Activity
Lahar
hot ash mixed with snow and ice to form a fast moving mud flow

27. Other Formations Associated With Volcanic Activity
Caldera
Large crater-shaped basin at the top of a volcano
Usually caused by a collapse in the magma chamber

28. Other Formations Associated With Volcanic Activity
Lava Plateau
Large flat area where lava spills out onto the Earth’s surface.