Lesson 6: Volcanoes and Volcanic Eruptions Flashcards
A lava flows whose surface is broken into rough angular fragments is
a’a (ah-ah)
Tephra comes in three sizes; ___ is the smallest
ash
_______ are avalanches of hot ash, rock, volcanic glass fragments, and gas that move rapidly down the sides of the volcano during eruption.
Pyroclastic flows
The most abundant volcanic gas is ____.
Water vabor
A _____ is a Volcanic mudflow/debris flow
lahar
_____ is the most common risk to humans from lava flows.
Property damage
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
d. Megathrust earthquakes
T/F: Lahars are only triggered by volcanic eruptions.
False
_____ eruptions are typically associated with shield volcanoes.
effusive
A ______ is a solid rock fragment greater than 64mm in diameter that was ejected from a volcano during an explosive eruption.
Block/bomb
Compare explosive and effusive eruptions.
Explosive: high viscosity
Effusive: low viscosity
What are the controlling factors of explosive eruptions
intermediate and felsic
higher viscosity
Usually violent vent eruptions
What are the controlling factors of effusive eruptions? (2)
Low viscosity
Fluid, gentle flowing magma
Compare fissure eruptions and vent eruptions
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
Explain Mafic lava eruptions’ characterization. (3)
Less viscous
Flow easily
Occurs mostly on the ocean floor
Ropy lava
Blocky lava
Sheild volcanoes
Cinder Cones
What are pillow lavas?
bulbous structures that occur at fissure Eruptions due to being underwater
What is ropy lava (pahoehoe)?
When lava flow develops wrinkles resembling irregular folds in cloth as molten lava moves beneath it
What is Blocky lava (‘a’a)?
Surface may break up into very sharp, jagged blocks as the molten interior continues to advance
What are shield volcanoes
the largest volcanoes with gentile slopes, often associated with mafic magma.
Low in viscosity and volatile content
Gently flowing with effusive eruptions
What are cinder cones? (2)
small, cone-shaped, built from an accumulation of tephra
Associated with mafic (basaltic) eruptions
How are Felsic and intermediate lavas characterized?
Usually causes violent vent eruptions
Pyroclastic deposits that fall back to earth
What is tephra? (3)
- volcanic ash - <2 mm
- Lapilli - 2-64 mm
- Volcanic bombs/blocks -64mm+
How are tephra classified?
- volcanic ash - <2 mm
- Lapilli - 2-64 mm
- Volcanic bombs/blocks -64mm+
What are stratovolcanoes?
The result of Intermediate and Felsic Lavas
Very explosive
Produce combination of pyroclastic deposits and felsic/intermediate lava flows
Common in “Ring of Fire”
What are lava domes? (5)
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
What are continental calderas
Large summit depression
Eruption of felsic magmas/lavas
Violent explosions; supervolcanoes
Ultra-Plinian eruption extrudes a lot of pyroclastic debris
Very rare
What are the common volcanic hazards? (5)
Lava Flows
Tephra
Release of volcanic gasses
pyroclastic flows
lahars
Explain and characterize pyroclastic flow.
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
Explain and characterize lahars.
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)
