Lesson 6: Volcanoes and Volcanic Eruptions

Question 1

A lava flows whose surface is broken into rough angular fragments is

Answer 1

a’a (ah-ah)

Question 2

Tephra comes in three sizes; ___ is the smallest

Answer 2

ash

Question 3

_______ are avalanches of hot ash, rock, volcanic glass fragments, and gas that move rapidly down the sides of the volcano during eruption.

Answer 3

Pyroclastic flows

Question 4

The most abundant volcanic gas is ____.

Answer 4

Water vabor

Question 5

A _____ is a Volcanic mudflow/debris flow

Answer 5

lahar

Question 6

_____ is the most common risk to humans from lava flows.

Answer 6

Property damage

Question 7

Which of the following is NOT a common cause of pyroclastic flows?

a. Boiling over from eruptive vent
b. Collapse of eruption column
c. Collapse of lava domes or flows
d. Megathrust earthquakes

Answer 7

d. Megathrust earthquakes

Question 8

T/F: Lahars are only triggered by volcanic eruptions.

Answer 8

False

Question 9

_____ eruptions are typically associated with shield volcanoes.

Answer 9

effusive

Question 10

A ______ is a solid rock fragment greater than 64mm in diameter that was ejected from a volcano during an explosive eruption.

Answer 10

Block/bomb

Question 11

Compare explosive and effusive eruptions.

Answer 11

Explosive: high viscosity
Effusive: low viscosity

Question 12

What are the controlling factors of explosive eruptions

Answer 12

intermediate and felsic
higher viscosity
Usually violent vent eruptions

Question 13

What are the controlling factors of effusive eruptions?

Answer 13

Low viscosity
Magma is relatively fluid
Flows easily
Gentle flow

Question 14

Compare fissure eruptions and vent eruptions

Answer 14

Fissure:
- common where the crust is undergoing extension and
where magma is relatively fluid (low viscosity)
- Are the dominant style of eruption
- Convergent and divergent plate boundaries
- pillow lavas
Vent:
- occur where lava is extruded at a central vent.
- Low viscosity
- Low volatile content

Question 15

Explain Mafic lava eruptions’ characterization.

Answer 15

Less viscous
Flow easily
Occurs mostly on the ocean floor
Ropy lava
Blocky lava
Sheild volcanoes
Cinder Cones

Question 16

What are pillow lavas?

Answer 16

bulbous structures that occur at fissure Eruptions due to being underwater

Question 17

What is ropy lava (pahoehoe)?

Answer 17

When lava flow develops wrinkles resembling irregular folds in cloth as molten lava moves beneath it

Question 18

What is Blocky lava (‘a’a)?

Answer 18

Surface may break up into very sharp, jagged blocks as the molten interior continues to advance

Question 19

What are shield volcanoes

Answer 19

the largest volcanoes with gentile slopes, often associated with mafic magma.

Low in viscosity and volatile content
Gently flowing with effusive eruptions

Question 20

What are cinder cones?

Answer 20

small, cone-shaped, built from an accumulation of tephra

Associated with mafic (basaltic) eruptions

Low to intermediate explosivity

Common on larger volcanoes, normal faults, or along cracks/fissures

Question 21

How are Felsic and intermediate lavas characterized?

Answer 21

Usually causes violent vent eruptions

Pyroclastic deposits that fall back to earth

Question 22

What is tephra? (3)

Answer 22

1. volcanic ash - <2 mm
2. Lapilli - 2-64 mm
3. Volcanic bombs/blocks -64mm+

Question 23

How are tephra classified?

Answer 23

1. volcanic ash - <2 mm
2. Lapilli - 2-64 mm
3. Volcanic bombs/blocks -64mm+

Question 24

What are stratovolcanoes?

Answer 24

The result of Intermediate and Felsic Lavas
Very explosive
Produce combination of pyroclastic deposits and felsic/intermediate lava flows
Common in “Ring of Fire”

Question 25

What are lava domes? (5)

Answer 25

The result of Intermediate and Felsicc Lavas
Steeo-sided mass of viscous and often blocky lava extruded from a vent
Rounded top
Can be isolated or have other lobes or flows from same vent
Can generate deadly pyroclastic flows

Question 26

What are continental calderas

Answer 26

Large summit depression
Eruption of felsic magmas/lavas
Violent explosions; supervolcanoes
Ultra-Plinian eruption extrudes a lot of pyroclastic debris
Very rare

Question 27

What are the common volcanic hazards?

Answer 27

Lava Flows
Tephra
Release of volcanic gasses
pyroclastic flows
lahars

Question 28

Explain and characterize pyroclastic flow.

Answer 28

High-density of hot, dry rock fragments and gases
Can result from
- explosive eruption of molten/solid rock fragments/both
- nonexplosive eruption of lava when parts of the dome/thick lava flow collapse down a steep slope

Question 29

Explain and characterize lahars.

Answer 29

A hot/cold mixture of water and sediment that flows down the slopes of a volcano and usually enters a river valley

Carry particles ranging from clay (mud flows) to boulders (debris flows)