Chapter 15 - Geohazard: Earthquakes and Volcanoes

Question 1

magma

Answer 1

melted rock below the surface of the crust

Question 2

active volcanoes

Answer 2

volcanoes that have erupted in the past 10,000 years and could erupt again

Question 3

extinct volcano

Answer 3

volcanoes that have not erupted for tens of thousands of years and will never erupt again

Question 4

lava

Answer 4

magma that spills into the surface of Earth’s crust

Question 5

shield volcano

Answer 5

a broad, domed volcano formed from innumerable layers of fluid basaltic lava laid down over tens to hundreds of thousands of years

Question 6

magma chamber

Answer 6

reservoir of magma beneath a volcano

Question 7

volcanic vent

Answer 7

the conduit through which magma moves and reaches the surface

Question 8

volcanic crater

Answer 8

bowl-shaped volcanic depression

Question 9

flank eruptions

Answer 9

happens where lava pours out the sides of a volcano through side vents, playing an important role in building shield volcanoes

Question 10

stratovolcano

Answer 10

a large, potentially explosive, cone-shaped volcano composed of alternating layers of lava and pyroclasts; also called composite volcano

Question 11

pyroclasts

Answer 11

encompasses any fragmented rock material that is ejected from a volcano; fire clasts or pyroclastic materials

Question 12

ash

Answer 12

pulverized rock particles and solidified droplets of lava that form a fine powder

Question 13

lava domes

Answer 13

dome-shaped volcanoes that form when thick lava that cannot easily flow piles up around a volcanic vent and solidifies into a domed structure; also called plug domes or volcanic domes

Question 14

cinder cones

Answer 14

small, cone-shaped volcanoes consisting of pyroclasts that settle at the angle of repose

Question 15

angle of repose

Answer 15

the steepest angle at with loose sediments can settle, usually ranging between 25 and 35 degrees

Question 16

mafic lava

Answer 16

lava with a temperature of 1,000-1,200 degrees C and a silica content of 50% or less, resulting in a high viscosity (easy-flowing)

Question 17

intermediate lava

Answer 17

lava with a temperature of 800-1,000 degrees C and a silica content between 50% and 70%, resulting in a medium viscosity

Question 18

felsic lava

Answer 18

lava with a temperature of 650-800 degrees C and a silica content of 70% or higher, resulting in a low viscosity (difficult-flowing)

Question 19

lapilli

Answer 19

rounded marble-to-golf ball-sized fragments of lava that solidify while airborne

Question 20

pumice

Answer 20

a lightweight, porous rock with at least 50% air content

Question 21

lava bomb

Answer 21

a streamlined or spherical fragment of lava ejected from a volcano that cools and hardens as it is moving through the air

Question 22

volcanic block

Answer 22

a fragment of rock that is torn from the volcano’s cone and ejected during an explosive eruption

Question 23

joints

Answer 23

cracks and weak planes in the rock

Question 24

columnar jointing

Answer 24

a geometric pattern formed when angular columns result from joint formation in the lava during cooling

Question 25

large igneous provinces (LIPs)

Answer 25

accumulations of basaltic lava that cover extensive geographic areas

Question 26

caldera

Answer 26

a large circular depression caused by the collapse of an emptied magma chamber after a volcanic eruption

Question 27

effusive eruptions

Answer 27

nonexplosive eruptions

Question 28

explosive eruptions

Answer 28

large volcanic eruptions

Question 29

volcanic explosivity index (VEI)

Answer 29

system that ranks volcanic eruption magnitude based on the amount of material a volcano ejects during an eruption (scale of 1-8)

Question 30

lahar

Answer 30

a mudflow that results when a snow-capped stratovolcano erupts, moving a thick slurry of mud, ash, and other debris rapidly down the volcano’s flank

Question 31

pyroclastic flows

Answer 31

quick-moving avalanches of gas and ash

Question 32

normal fault

Answer 32

a result of tensional force (extension) as two pieces of Earth’s crust are pulled apart

Question 33

reverse fault

Answer 33

a result of compressional force that pushes on block upward in relation to another block

Question 34

fault scarp

Answer 34

a result of the vertical movement of the fault blocks; also called cliff face

Question 35

focus

Answer 35

hypocenter; the location of initial crust movement along a fault during an earthquake

Question 36

epicenter

Answer 36

the location on the ground’s surface immediately above the focus and is usually the area of greatest shaking

Question 37

foreshock

Answer 37

a small earthquake that precedes a larger, main earthquake

Question 38

aftershocks

Answer 38

small earthquake that follows the shock of a large one

Question 39

seismographs

Answer 39

instruments used to detect, measure, and record ground shaking; also called seismometers

Question 40

modified mercalli intensity (MMI) scale

Answer 40

a scale that subjectively ranks the intensity of an earthquake based on structural damage (scale of I to XII)

Question 41

liquefaction

Answer 41

the transformation of solid sediments into an unstable slurry by ground shaking

Question 42

moment magnitude scale

Answer 42

an earthquake-ranking system based on the amount of ground movement produced