1. Chapter 8: Earthquakes and Volcanoes
Section 2: Volcanoes

2. A. Volcanoes -
cone-shaped hills
or mountains
formed by magma
eruptions

3. 1. When magma flows onto Earth’s surface through a vent, it is called lava.

4. 2. Tephra – bits of rock or solidified lava dropped from the air after an explosive eruption

5. 3. Some volcanoes form where Earth’s plates collide.
One plate subducts, or is forced underneath,
the other.
b. Part of the plate that is forced underneath melts, forming magma chambers.

6. Avalanches of
hot, glowing molten rock that flow on cushions of hot gases down a side of a volcano are called pyroclastic flows.
Montserrat, 1996

7. 5. How forceful an eruption is depends on the composition of the magma
More silica makes magma thicker and more
resistant to flow.
High viscosity

8. b. More iron and
magnesium
make magma
flow more
easily.

9. Water vapor trapped in the
magma becomes steam and
creates pressure.

10. 6. The type of lava and gases contained in the lava determine the type of volcano that forms

11. B. Four types of volcanoes:

12. 1. Shield volcanoes – basaltic lava, which flows easily
a. Forms a broad
volcano with
gently sloping
sides
b. Largest type of
volcano
Mauna Loa, Hawaii

13. c. Form where Earth’s plates are separating and magma is forced upward between the plates

14. 2. Cinder cone volcanoes - high gas content in the magma
Explosive, but
short-lived,
eruptions
b. Form a small
cone of volcanic
material from
tephra

16. 3. Composite volcanoes – made of alternating layers of lava and tephra
Steep-sided mountains
Form where Earth’s plates are colliding and being forced underneath each other, or subduction zones.
Mt Ranier in Washington

18. 4. Fissure eruptions – magma that is very fluid
Oozes from cracks in the Earth’s surface.
Magma flows freely across the land, as flood basalts.
Most of Earth’s crust beneath the ocean is flood basalts.