Chapter 18: Volcanic Activity

Question 1

explain how magma forms. 3 factors

Answer 1

• temperature hot enough to melt the rocks (800 to 1200)
• pressure (temperature needed to melt increases with pressure)
• water (rocks with water will melt at higher temperatures)

Question 2

Basaltic Magma

Answer 2

when rocks in the mantle melt

Question 3

Andestic Magma

Answer 3

continental margins where oceanic crust is subducted into the Earth’s mantle

Question 4

Rhyolitic Magma

Answer 4

molten material that rises and mixes with overlying silica and water rich continental crust

Question 5

pluton

Answer 5

intrusive igneous rock bodies made from minerals mixing

Question 6

baolith

Answer 6

the largest plutons

Question 7

laccolith

Answer 7

mushroom shaped pluton with round top and a flat bottom

Question 8

sill

Answer 8

pluton that forms when magma intrudes paralell layers of rock

Question 9

Dike

Answer 9

pluton that cuts across preexisting rocks

Question 10

stocks

Answer 10

small-irregular shaped plutons

Question 11

calderas

Answer 11

large volcanic depressions

Question 12

shield volcano

Answer 12

mountain with broad, gently sloping sides and a nearly circular base.
ex. Hawaii Mauna Loa

Question 13

Cinder Cone Volcanoes

Answer 13

small with steep sides. (no more than 500m)

ex. Izalco in El Salvador

Question 14

Composite volcanoes

Answer 14

very large, lots of explosions, dangerous

ex. Mt St Helens

Question 15

tephra

Answer 15

rock fragments thrown into the air during a volcanic eruption

Question 16

pyroclastic flow

Answer 16

gas, ash, and other tephra flowing down a slope at incredibly high speeds. May contain hot, poisonous gasses.

Question 17

where do volcanoes form

Answer 17

plate boundaries (80 percent at convergent boundaries)

Question 18

convergent volcanism

Answer 18

convergence of oceanic plate creates seduction zones, places where slabs of oceanic crust descend into the mantle and eventually melt. The magma generated is forced upward through the overlying plate and forms volcanoes when it reaches the surface

Question 19

divergent volcanism

Answer 19

two plates move apart, magma is forced up through the fractures and faults that form as the plates separate

Question 20

hot spots

Answer 20

unusally hot regions of Earth’s mantle where high-temperature plumes of mantle material rise to the surface