Chapter 5

Question 1

Lava flows

Answer 1

molten rock that flows across the ground

Question 2

Pyroclastic debris

Answer 2

solid fragments ejected during eruptions (ash, pumice, volcanic bombs)

Question 3

Volcanic gases

Answer 3

gases such as water vapor, CO₂, and sulfur compounds released from magma.

Question 4

pyroclastic flow

Answer 4

fast-moving avalanche of hot ash, gas, and volcanic material

Question 5

lahar

Answer 5

a volcanic mudflow composed of water and volcanic ash/debris that moves down volcanic slopes, often triggered by heavy rain or melting snow.

Question 6

Shield volcanoes

Answer 6

have broad, gentle slopes from low-viscosity basaltic lava flows

Question 7

Stratovolcanoes

Answer 7

are steep and layered due to alternating lava flows and pyroclastic eruptions, often from more viscous andesitic or rhyolitic lava.

Question 8

Cinder cones

Answer 8

small, steep hills of pyroclastic fragments, formed from gas-rich basaltic lava that erupts explosively.

Question 9

Why do some volcanic eruptions consist mostly of lava flows, while others are explosive and do not produce flows?

Answer 9

Eruptions depend on magma viscosity and gas content. Low-viscosity, gas-poor basaltic magma results in gentle lava flows, while high-viscosity, gas-rich magma traps gas and pressure, leading to explosive eruptions with pyroclastic material.

Question 10

What processes may lead to hot-spot eruptions?

Answer 10

Hot-spot eruptions are caused by mantle plumes, which are columns of hot material rising from deep within the mantle. These plumes create melting in the lithosphere as they reach shallow depths, leading to volcanic activity independent of tectonic boundaries.

Question 11

How do continental-rift eruptions form flood basalts?

Answer 11

In continental rift settings, decompression melting of the mantle produces large volumes of basaltic magma. This magma can erupt through fissures, spreading out as vast, flat lava flows, forming extensive flood basalts.

Question 12

island arc

Answer 12

a chain of volcanic islands formed above a subducting oceanic plate at an ocean-ocean convergent boundary

Question 13

continental arc

Answer 13

forms along the edge of a continent above a subducting oceanic plate at an ocean-continent convergent boundary.

Question 14

Identify some of the major volcanic hazards, and explain how they develop.

Answer 14

Lava flows can destroy property; pyroclastic flows and ash falls pose severe hazards to life, air quality, and buildings; lahars can bury settlements; volcanic gases can cause respiratory problems; volcanic tsunamis may occur if an eruption disturbs bodies of water.

Question 15

How do geologists predict volcanic eruptions?

Answer 15

Geologists monitor earthquakes, gas emissions, ground deformation, and temperature changes around a volcano. Increased seismic activity or gas release often precedes eruptions, helping predict potential activity.

Question 16

Explain how steps can be taken to protect people from the effects of eruptions.

Answer 16

Evacuation plans, hazard mapping, early warning systems, and exclusion zones around volcanoes can minimize risk. Public education and communication also ensure people know evacuation procedures and danger areas.

Question 17

Accretionary Lapilli

Answer 17

Small, spherical pellets of volcanic ash that form when wet ash particles clump together as they fall during an eruption.

Question 18

Active Volcano

Answer 18

A volcano that is currently erupting, showing signs of erupting soon, or has erupted in recent history.

Question 19

Ash

Answer 19

Fine-grained volcanic material, smaller than 2 mm, expelled during explosive eruptions that can travel great distances.

Question 20

Block

Answer 20

Large, angular fragments of solid rock ejected during a volcanic eruption, often originating from the volcano’s vent or walls.

Question 21

Blocky Lava

Answer 21

Lava with a rough, jagged surface, formed when highly viscous lava cools and breaks into angular blocks as it flows.

Question 22

Bomb

Answer 22

Large, rounded fragments of lava ejected during an explosive eruption, which cool in flight and take on aerodynamic shapes.

Question 23

Caldera

Answer 23

A large, depression formed when a volcano’s summit collapses following an explosive eruption that empties the underlying magma chamber

Question 24

Cinder Cone

Answer 24

A small, steep-sided volcanic cone made up of pyroclastic fragments such as cinders, formed by gas-rich, basaltic lava eruptions.

Question 25

Columnar Jointing

Answer 25

A pattern of fractures that form during the cooling and contraction of lava, resulting in hexagonal columns.

Question 26

Crater

Answer 26

A circular depression at the summit of a volcano, formed around the central vent by explosive eruptions or collapse.

Question 27

Dormant Volcano

Answer 27

A volcano that hasn’t erupted in a long time but could become active again in the future.

Question 28

Effusive Eruption

Answer 28

A type of eruption where low-viscosity lava flows steadily from a vent, resulting in gentle lava flows rather than explosions.

Question 29

Eruptive Style

Answer 29

The characteristic behavior of a volcano’s eruption, influenced by magma composition, gas content, and eruptive dynamics (e.g., explosive or effusive).

Question 30

Extinct Volcano

Answer 30

A volcano that geologists consider unlikely to erupt again, often due to its isolation from a magma source.

Question 31

Fissure

Answer 31

A linear crack or fracture in the ground through which lava erupts, often leading to extensive lava flows.

Question 32

Flood Basalt

Answer 32

Vast lava flows that cover large areas, produced by high-volume eruptions from fissures, often associated with large igneous provinces.

Question 33

Ignimbrite

Answer 33

A rock formed from the deposition of pyroclastic flows, typically composed of compacted ash, pumice, and volcanic fragments.

Question 34

Lahar

Answer 34

A volcanic mudflow composed of water and volcanic ash/debris that flows down the slopes of a volcano, often triggered by rainfall or melting ice.

Question 35

Lapilli

Answer 35

Small fragments of pyroclastic debris, between 2 mm and 64 mm, that are ejected during an eruption.

Question 36

Large Igneous Province (LIP)

Answer 36

A region with extensive igneous rock deposits, often created by massive volcanic eruptions over a relatively short geological timeframe.

Question 37

Lava Tube

Answer 37

A tunnel-like passage within a lava flow, formed as the surface of the flow cools and solidifies while molten lava continues to flow beneath.

Question 38

Magma Chamber

Answer 38

A subterranean reservoir of molten rock beneath a volcano, which supplies magma for eruptions.

Question 39

Pahoehoe

Answer 39

A type of basaltic lava flow with a smooth, ropy surface, formed by the movement of very fluid lava.

Question 40

Pumice Lapilli

Answer 40

Small, light, frothy volcanic fragments formed from gas-rich magma that cools rapidly, often found in pyroclastic deposits.

Question 41

Pyroclastic Debris

Answer 41

Fragments of volcanic rock, ash, and pumice produced by explosive volcanic eruptions.

Question 42

Pyroclastic Flow

Answer 42

A fast-moving avalanche of hot gas, ash, and volcanic fragments that moves rapidly down a volcano during explosive eruptions.

Question 43

Scoria Cone

Answer 43

Another term for a cinder cone; a small, steep-sided volcano built primarily of pyroclastic fragments from gas-rich basaltic magma.

Question 44

Shield Volcano

Answer 44

A broad, gently sloping volcano formed by low-viscosity basaltic lava flows, creating a shield-like profile.

Question 45

Stratovolcano

Answer 45

A large, steep-sided volcano built by alternating layers of lava flows, ash, and pyroclastic material, often associated with explosive eruptions.

Question 46

Tephra

Answer 46

General term for any type of volcanic material ejected during an eruption, including ash, lapilli, and volcanic bombs.

Question 47

Tuff

Answer 47

Rock formed from compacted volcanic ash and other pyroclastic materials, often found in layers from past eruptions.

Question 48

Vesicle

Answer 48

A small cavity within volcanic rock that was formed by trapped gas bubbles during solidification.

Question 49

Volcanic Debris Flow

Answer 49

A dense mixture of water, volcanic rock, and mud that moves downslope from a volcano, usually triggered by heavy rain or melting snow.

Question 50

Volcaniclastic Deposit

Answer 50

Any deposit of volcanic material, including ash, lapilli, and pyroclastic rock fragments, which can be produced by eruptions or volcanic weathering.

Question 51

Volcano

Answer 51

A geological structure formed when magma from within the Earth reaches the surface, leading to eruptions of lava, ash, and gases.

Question 52

Effusive Eruptions

Answer 52

lava pours out of a vent or fissure

Question 53

Explosive Eruptions

Answer 53

Volcanic products are erupted into the air due to the gas in the magma

Question 54

Tectonic Setting of Stratovolcanoes

Answer 54

Subduction zones: high water content with more felsic magmas

Question 55

Phreatomagmatic Eruptions

Answer 55

the lava lake begins to drain out the center of a crater, drops below water, steam pressure builds and volcano erupts

Question 56

Flood Basalts

Answer 56

eruptions of massive volumes of basaltic magma and has been attributed to the arrival of a new plume

Question 57

Volcanic Hazards

Answer 57

gravity driven lateral flow of gas, pumice, and ash