2: Volcanoes

Question 1

Magma composition (mineral/melt)

Answer 1

Mineral: silca tetrahedra structure
Melt: broken up

Question 2

Basaltic Flow

Answer 2

Low Viscosity
Low Silicon Dioxide
Thin flow – travels far

Question 3

Andesitic Flow

Answer 3

Medium Viscosity
Medium Silicon Dioxide
Thicker than Basaltic Flow
Doesn’t travel as far

Question 4

Rhyolitic Dome

Answer 4

High Viscosity
High Silicon Dioxide
Very thick
Doesn’t travel – just builds up to form a dome shape above the center

Question 5

How does Dry Magma erupt?

Answer 5

Dry Magmas usually erupt fairly passively

Question 6

How does/can Wet Magma erupt?

Answer 6

Wet Magmas have the potential to erupt more explosively than dry magmas.

Question 7

Gas bubbles usually form in magma from…

Answer 7

…drop in pressure and rapidly expands in volume until it explodes

Question 8

Lava Flows: Pahoehoe

Answer 8

Type of basalt flow
Higher Temperature: 1100-1200 C
Lower Viscosity; flows easily
Some volatiles
Ropy Texture

Question 9

Lava Flows: Aa

Answer 9

Type of basalt flow
Higher viscosity; slower moving
Lower Volatiles
Breaks up into blocks that roll down the advancing front
Originate from cooled and dried-out pahoehoe

Question 10

Pyroclastic fragments

Answer 10

Variety of grain sizes (ash, cinders, bombs/blocks)

Deposited by airfall or downhill flow

Question 11

Shield Volcano

Answer 11

Largest type of volcano
Dominated by basaltic lava flows
Ex: Eilauea (Hawaii) - most active on Earth
Ex: Mauna Loa (Hawaii) - largest on Earth until recently
Ex: Olympus Mons (Mars) - largest volcano in solar system

Question 12

Cinder Cone Volcano

Answer 12

Smallest type of volcano
Mostly basaltic
Not terribly dangerous
Cone edifice is built of pyroclastic material
But lava flows may originate from the same vent

Question 13

Composite cone/stratovolcano

Answer 13

Cone-shaped, but much larger than cinder cone
Most andesitic flow
Composed of interbedded lava flows and pyroclastics
Explosive eruptions common - this is the most dangerous volcano type
Ex: Mount St. Helens, Mt. Rainier, Mt. Fuji, Mt. Vesuvius

Question 14

Dome Volcano

Answer 14

Smaller than shield and composite, but larger than cinder cone
Steep-sided slopes
Andesite to rhyolite flow
Explosive eruptions possible
Can occur on larger volcanoes

Question 15

Caldera

Answer 15

Form by collapse of a magma chamber after it is drained by an eruption
Small to large
Large ones are associated with extremely violent eruptions and large ash deposits
May later fill with water to form crater lakes

Question 16

Mid-ocean ridges

Answer 16

Basaltic lavas erupted on to the seafloor

Question 17

Mid-ocean ridges: Origin of Magma

Answer 17

Partial melting of mantle peridotite carried upward in convection currents (pressure drop causes melting)

Question 18

Subduction Zones

Answer 18

Most of the world’s volcanoes (on land)

Mostly andesite flow stratovolcanoes

Question 19

Subduction Zones: Origin of magma

Answer 19

NOT from friction, and the magmas do NOT come from melting of oceanic plate, rather…
wet ocean floor carried down sub zone heats up and loses its water; this water rises into overriding plate lowering the melting point of the rocks there.

Question 20

Hotspot volcanoes

Answer 20

Unrelated to Plate Boundaries

Are associated with the largest volcanoes on Earth (shield volcanoes, large calderas)

Question 21

Hotspot volcanoes: origin of magma

Answer 21

Upwelling mantle plumes, some from core-mantle boundary