ArcVolcano

Question 1

Where do arc volacnoes form?

Answer 1

Above subduction zones

Question 2

What is an example of a continental arc?

Answer 2

Cascades

Question 3

How is magma created at a subduction zone?

Answer 3

Water is added to hot mantle which reduces the temp of the rock at high pressures

Question 4

Because water is involved, this magma has a high _____ content

Answer 4

volatile

Question 5

Where does melting take place?

Answer 5

in the mantle above the subducting plate

Question 6

What releases H2O?

Answer 6

Metamorphism at ~100 km depth

Question 7

When does the composition of the magma change?

Answer 7

When it interacts with the overlying crust

Question 8

Why doesn’t magma from island arcs change much chemically?

Answer 8

It rises through low silica ocean crust on the way to the surface

Question 9

What does island arc lava start as?

Answer 9

Basalt

Question 10

When does fractional crystallization occur?

Answer 10

When magma has a harder time going through new, thick crust

Question 11

What happens to magma during fractional crystallization?

Answer 11

It becomes more silicic

Question 12

What type of lava occurs from fractional crystallization?

Answer 12

Andesite lava

Question 13

The crystals tend to be ____ in composition

Answer 13

mafic

Question 14

What is the main difference between continental and island arcs?

Answer 14

Magma must work through crust of silicic composition to get to surface

Question 15

How does going through silicic composed crust change magma?

Answer 15

Through assimilation and secondary melting

Question 16

What is the crust of high silicia called that continental arc magma must go through?

Answer 16

granitic

Question 17

What melts at a lower temperature - granite or basalt?

Answer 17

Granite

Question 18

Assimilation

Answer 18

Magma melts through existing rock on its way up

Question 19

Where can secondary melting occur?

Answer 19

An overheated piece of lower continental crust

Question 20

Continental arc lavas have silica percentages from ____ to ___

Answer 20

50% (basalt) to 75% (Rhyolite)

Question 21

What rises with magma during hydration melting at subduction zones

Answer 21

Water

Question 22

Why are arc lavas more explosive than rift lavas?

Answer 22

It has water and other gases

Question 23

What types of hazards are more common with arc volcanoes?

Answer 23

Lahars and pyroclastic flows

Question 24

What is a Phreatomagmatic eruption?

Answer 24

A steam and ash eruption

Question 25

When can a Phreatomagmatic eruption occur?

Answer 25

When any volcano comes in contact with ground water

Question 26

What do Phreatomagmatic eruptions make?

Answer 26

Maars - low-relief volcanic craters with a lake in the middle