Lesson 6: Volcanoes and Volcanic Eruptions Flashcards

1
Q

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

A

a’a (ah-ah)

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2
Q

Tephra comes in three sizes; ___ is the smallest

A

ash

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3
Q

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

A

Pyroclastic flows

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4
Q

The most abundant volcanic gas is ____.

A

Water vabor

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5
Q

A _____ is a Volcanic mudflow/debris flow

A

lahar

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6
Q

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

A

Property damage

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7
Q

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

A

d. Megathrust earthquakes

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8
Q

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

A

False

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9
Q

_____ eruptions are typically associated with shield volcanoes.

A

effusive

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10
Q

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

A

Block/bomb

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11
Q

Compare explosive and effusive eruptions.

A

Explosive: high viscosity
Effusive: low viscosity

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12
Q

What are the controlling factors of explosive eruptions

A

intermediate and felsic
higher viscosity
Usually violent vent eruptions

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13
Q

What are the controlling factors of effusive eruptions? (2)

A

Low viscosity
Fluid, gentle flowing magma

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14
Q

Compare fissure eruptions and vent eruptions

A

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

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15
Q

Explain Mafic lava eruptions’ characterization. (3)

A

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

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16
Q

What are pillow lavas?

A

bulbous structures that occur at fissure Eruptions due to being underwater

17
Q

What is ropy lava (pahoehoe)?

A

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

18
Q

What is Blocky lava (‘a’a)?

A

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

19
Q

What are shield volcanoes

A

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

Low in viscosity and volatile content
Gently flowing with effusive eruptions

20
Q

What are cinder cones? (2)

A

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

Associated with mafic (basaltic) eruptions

21
Q

How are Felsic and intermediate lavas characterized?

A

Usually causes violent vent eruptions

Pyroclastic deposits that fall back to earth

22
Q

What is tephra? (3)

A
  1. volcanic ash - <2 mm
  2. Lapilli - 2-64 mm
  3. Volcanic bombs/blocks -64mm+
23
Q

How are tephra classified?

A
  1. volcanic ash - <2 mm
  2. Lapilli - 2-64 mm
  3. Volcanic bombs/blocks -64mm+
24
Q

What are stratovolcanoes?

A

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

25
Q

What are lava domes? (5)

A

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

26
Q

What are continental calderas

A

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

27
Q

What are the common volcanic hazards? (5)

A

Lava Flows
Tephra
Release of volcanic gasses
pyroclastic flows
lahars

28
Q

Explain and characterize pyroclastic flow.

A

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

29
Q

Explain and characterize lahars.

A

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)