Volcanoes

Question 1

What is a volcano?

Answer 1

• Any landform (on land or beneath the ocean) that releases lava, gas, or ashes, or has done so in the past
• Most occur at divergent or convergent plate boundaries
• Anomalous volcanism can sometimes occur in the middle of a plate (intraplate volcanism)
• Anomalous volcanoes may be the result of: hot magma rising from the core-mantle boundary or asteroid impacts

Question 2

Good evidence that Hawaii is situated over a:

Answer 2

hotspot (islands in a row b/c plate is moving making holes as it moves = islands, tells us plate motion)

Question 3

Magma (and lava) can be:

Answer 3

felsic, intermediate, or mafic

Question 4

How does magma chemistry influence the nature of volcanic eruptions?

Answer 4

• Fewer covalent bonds between tetrahedra = thin, runny magma (mafic, low silica)
• More covalent bonds b/w tetrahedra = thick magma (felsic, high silica)

Question 5

Mafic (basaltic) lava flows easily and erupts gently

Answer 5

• Low silica content
• Low viscosity (good at off-gassing (releasing gas) due to low viscosity)
• Low gas

Question 6

Mafic (basaltic) lava flows easily and erupts gently

Answer 6

• Low silica content
• Low viscosity (good at off-gassing (releasing gas) due to low viscosity)
• Low gas

Question 7

Mafic lava textures

Answer 7

Aa - rough, fragmented lava blocked called “clinker”

Pahoehoe - smooth, shiny, and ropy surface

Question 8

Felsic magma tends to erupt catastrophically

Answer 8

• High silica content
• More viscous (resistant to flowing)
• High gas content (trapped between silica tetrahedra/crystals)
• Expanding gases fragment magma and rock, producing pyroclastic debris or tephra

Question 9

Intermediate magma eruptions are less

Answer 9

explosive

Question 10

Types of pyroclastic debris

Answer 10

• Ash
• Lapilli (tiny pieces of rock)
• Volcanic bombs (rocks size of fist)
• Volcanic block (house/car size)
• Welded tuff (compacted tiny rocks into rock)
• Pumice (vesicular)

Question 11

H2O, CO2, SO2 are the most

Answer 11

abundant gases released during an explosion

Question 12

What happens to the SO2 gas released during an explosion?

Answer 12

Sulphuric acid = acid rain

Question 13

Volcanoes can be classified into 2 groups:

Answer 13

1. Central vent volcanoes: central vent, summit crater

2. Large-scale volcanic terrains: no central vent, network of source material, extend over a large area

Question 14

Types of central vent volcanoes

Answer 14

• Shield Volcanoes
• Stratovolcanoes
• Rhyolite Caldera Complexes

Question 15

What is a shield volcano?

Answer 15

low silica, low gas magma originates in mantle, low viscosity creates broad gentle slopes

Question 16

What is a stratovolcano?

Answer 16

Alternating layers of mafic to intermediate lava flows with layers of intermediate to felsic explosively ejected pyroclastic fragments, explosive eruptions are common due to buildup of gases

Question 17

What is a Rhyolite Caldera Complex volcano?

Answer 17

High silica, high gas magmas, massive explosions (most explosive of all types), withdrawal of magma from the magma chamber causes collapse, produces an “inverse volcano” or caldera

Question 18

Large-scale volcanic terrains

Answer 18

• Mid-ocean ridges develop at divergent boundaries, basaltic flow creates a global network of interconnected seafloor ridges

Question 19

Volcanoes are highly variable in terms of:

Answer 19

size

Question 20

Volcano type is related to:

Answer 20

kind of magma

Question 21

Divergent boundary: mafic

Answer 21

lava flows

Question 22

Oceanic hot spot:

Answer 22

mafic lava flows, shield volcanoes

Question 23

Continental hotspot:

Answer 23

felsic to mafic lava flows, can be any type

Question 24

Oceanic-continental subduction zones:

Answer 24

felsic to mafic

Question 25

Ocean-oceanic:

Answer 25

intermediate to mafic lava flow, shield or stratovolcanoes, volcanoes form an island arc