Volcanoes

Question 1

What causes Volcanoes

Answer 1

Ocean-ocean, ocean-continent, subduction zone, mantle plumes, rift zones

Question 2

Magma

Answer 2

is melted rock material beneath the surface.

Question 3

Lava

Answer 3

melted rock material when it erupts at the surface.

Question 4

Active Volcano

Answer 4

has erupted in historic times (or at least within the last 10,000 years.)

Question 5

Dormant Volcano

Answer 5

has not erupted recently but geologically is likely to do so again.

Question 6

Extinct Volcano

Answer 6

is geologically is unlikely to erupt again.

Question 7

Plutonic Igneous Rock

Answer 7

cool slowly below the surface

Question 8

Volcanic Igneous Rock

Answer 8

cool quickly at/near the surface.

Question 9

Silica Tetahedra

Answer 9

Sio4

Question 10

Each mineral has a…

Answer 10

Crystallization point

Question 11

Igneous vs Magma

Answer 11

Magma mixing, melting of surrounding, partial melting, fractional crystallization.

Question 12

Why does magma have different composition?

Answer 12

Different minerals at different temperature.

Question 13

Magma mixing and melting of surrounding rock bodies…

Answer 13

are two reasons magma vary in composition.

Question 14

Fractional Crystallization

Answer 14

another reason magmas vary.
- As magma cools, high temperature minerals form first, if they settle out of the magma, the magma now has a different composition.

Question 15

At what setting do we find Volcanoes?

Answer 15

80% of volcanic activity is at a divergent plate boundary: 10% is at a subduction zone, and remaining 10% is at mantle plumes.

Question 16

Subduction Zone carries

Answer 16

water rich oceanic plate into the mantle where the water causes it to partially melt; it may mix with continental crust as it rises upward.

Question 17

Magma at mid-ocean ridges…

Answer 17

forms from partial melting of the mantle due to lowered pressure from spreading.
* the same process also happens during continental rifting and may eventually cause a mid-ocean ridge to form.

Question 18

Mantle plumes

Answer 18

can generate magma by partially melting the upper mantle or overriding plate (continental or oceanic)

Question 19

What happens when a volcano erupts?

Answer 19

When a volcano erupts it produces combinations of lava, pyroclastic debris, and volcanic gas.
- lots of silica makes a magma viscous because silica tetrahedra like to link together.

Question 20

Three types of lava

Answer 20

Rhyolitic, andesitic, and basaltic

Question 21

Basaltic lava

Answer 21

has the highest temperature and lowest SiO2 content so has a low viscosity

Question 22

Andesitic and Rhyolitic

Answer 22

magmas have lower temperatures and higher Sio2 content, so are more viscous.

Question 23

Basaltic Magma

Answer 23

has the lowest gas content and tends to erupt peacefully

Question 24

Rhyolitic Magma

Answer 24

has the highest gas content and tends to erupt explosively.

Question 25

Basaltic Eruptions

Answer 25

basaltic lava is hot, with a low viscosity, low siox, and low gas content
-lava tubes are common features of basatlic eruptions.

Question 26

Lava Tubes

Answer 26

form as the surface cools, but lava continues to flow beneath the surface.
-Columnar jointing often results as basaltic lava flows cools and contract.
-Pillow basalts form as the lava oozes out and a thin skin cools in cold seawater.

Question 27

Andesitic/Rhyolitic Eruption

Answer 27

lava is cooler with a higher viscosity, higher Siox content and higher gas content

Question 28

Andesitic/Rhyolitic Eruption

Answer 28

lava is cooler with a higher viscosity, higher Siox content and higher gas content
- This type of lava flows more slowly and usually not as far. Tends to be explosive
- Pyroclastic debris is common feature.
- Tuff/Tephra is a common product of andesitic/rhyolitic eruptions to form the rock tuff.
- Lahars occur when tephra mixes with water causing deadly flows.

Question 29

The 3 V’s of Eruption Styles

Answer 29

Viscosity controls lava flow
Volatile abundance controls explosiveness
Volume influences severity eruptions (small or large)

Question 30

Characteristics of Eruption Style

Answer 30

-Flood basalts are low viscosity, low volatiles, and very large volume
-Icelandic- type eruption are very peaceful eruptions from fissures than build up nearly horizontal layers
-Hawaiian- type eruptions produce higher lava fountains and low cones and may last for years as lava slowly flows downhill
-Shield Volcanoes form from low viscosity, low volatiles, and large volume basaltic lava flows
-Strombolian- type eruption short-lived explosive outburst of pasty lava ejected 10s-100m into the air.

Question 31

Lava Domes

Answer 31

high viscosity, low volatiles and small volume eruptions that happen after volcano/Plinan eruptions.

Question 32

Calderas

Answer 32

result from very high viscosity, high volatiles, and very large volume. Small summit of volcanoes.

Question 33

Where does Mantle Plume magma come from?

Answer 33

Magma erupting at a mantle plume volcano did NOT come all the way from the core/mantle boundary.

Question 34

How do mantle plumes change through time?

Answer 34

The basalt flows are called the Columbia River Plateau basalts because the river has eroded down through them in many places. Early mantle plume spreads out and is very hot; later it cools down and affects a smaller area.

Question 35

Movement of Magma

Answer 35

frequent shallow earthquakes

Question 36

Mantle Plumes are…

Answer 36

most easily studied using seismic waves.

Question 37

Pyroclastic Flows

Answer 37

can happen because of eruption column collapse.
-Volcanoes put many sizes of pyroclastic debris into the air, the heavier particles fall back and then rush down the side of the volcano.

Question 38

Lahars

Answer 38

following existing river valleys and quickly fill them with ash deposits. Pre-existing drainage patterns so their path is somewhat predictable.