Topic 5 Geohazard I - Volcanoes & Earthquakes

Question 1

Where are volcanoes found?

Answer 1

All volcanoes are found where the mantle is melted into magma

Question 2

What are the four types of Volcanoes?

Answer 2

Shield Volcanoes; Stratovolcanoes; Cinder Cones; Lava domes

Question 3

Shield Volcano

Answer 3

a broad volcano form from innumerable layers of fluid basaltic lava laid down over yens to hundreds of thousands of years

Largest volcanoes on Earth

Slowly built

Question 4

Stratavolcano

Answer 4

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

smaller, steeper sided, and composed of lava and volcanic ash

Question 5

Lava Dome

Answer 5

Dome-shaped volcanoes that form when thick lava cannot easily flow piles around a volcanic vent and solidifiers into a domed structure

Far smaller than stratovolvanoes, typically only a few hundred meters high

May form on the flank of shield volcanoes and stratovolcanoes, or cap shield volcanoes and stratovolcanoes summit craters

Question 6

Cinder Cone

Answer 6

Small, cone-shaped volcanoes consisting of pyroclasts

Generally smaller than 400m

symmetrical, settling at the angle of repose (steepest angle at which loose sediment can settle)

erupt for a few years or decades and them become extinct

Question 7

Lava types

Answer 7

Mafic: Hottest, low viscosity, flows easily, Basaltic rocks

intermediate: Medium heat, medium viscosity, flows less easily, andesite rocks

felsic: lowest heat, High viscosity, does not flow easily, rhyolitic rocks

Question 8

Volcanic Gases

Answer 8

~8% of most magma is gas

Consists of water vapor, carbon dioxide, sulfur dioxide, and hydrogen sulfide

Question 9

Caldera

Answer 9

A large depression that forms when a volcano’s magma chamber empties and collapses after the volcano erupts

simplified: deflates into a crater

Question 10

What are the two types of erruptions

Answer 10

Effusive eruption: nonexplosive erruption that produces mostly lava and lava flows. commonly at shield volcanoes associated with mafic lava

Explosive eruption: an eruption that sends rock, ash, and volcanic gases high into the troposphere (high in the air). commonly at stratovolcanoes associated with intermediate or felsic lava

Question 11

Volcanic Explosivity Index (VEI)

Answer 11

ranks volcanic eruption magnitude based on the amount of material a volcano ejects during an eruption

ranges from 0 to 8 on a logarithmic scale (each whole number increase represents 10 times more material erupted).

Question 12

Lahar

Answer 12

A thick slurry of mud, ash, and other debris that moves rapidly down the volcano’s flank

Generated by:
Snow melting due to volcanic eruption heat

dome collapse

heavy rain on erupted ash

catastrophic crater lake drainage

Question 13

Pyroclastic flows

Answer 13

a quick-moving avalanche of gas and ash
speeds up to 700km/h
originate from collapse of eruption columns or landsliding of entire sectors of volcano

Question 14

3 fault types

Answer 14

Normal fault: tensional force pulls two pieces of earth’s crust apart, called fault blocks

Reverse Fault: compressional forces pushes two blcoks together and upward in relation to another block

Strike-slip Fault: one block moves horizontally in relation to another block as a result of shearing (lateral) force

Question 15

How do faults generate Earthquakes?

Answer 15

Earthquakes occur when stress exceeds friction.
crust breaks, and the blocks move.
Built-up stress energy is released and travels through the crust as seismic waves (earthquakes)

Question 16

focus (Earthquake Terminology)

Answer 16

The location of initial movement along a fault during an earthquake

Question 17

Epicenter (Earthquake Terminology)

Answer 17

the location on the ground’s surface immediately above the focus of an earthquake, where earthquake intensity is usually greatest

Question 18

Foreshock (Earthquake Terminology)

Answer 18

A small earthquake that sometimes follows a larger Earthquake

Question 19

Aftershock (Earthquake Terminology)

Answer 19

A small Earthquake that follows the main Earthquake

Question 20

Seismic waves: Body Waves

Answer 20

Two types of body waves:
Primary waves: compression waves that travel through Earth’s interior
Secondary waves: shear waves that travel through Earth’s interior

Question 21

Seismic waves: Surface waves

Answer 21

Two types of Surface Waves:
R waves: compression waves that travel through the crust’s surface, creating vertical, up-and-down crust movement
L waves: shear waves that travel through the crust’s surface, creating horizontal, side-to-side crust movement

Question 22

What is a seismograph?

Answer 22

an instrument used to detect, measure, and record ground shaking

Question 23

Modified Mercalli Intensity Scale

Answer 23

system used to rank the intensity of shaking during an earthquake

Categories:
I-III: slight
IV-VI: moderate to strong
VII-IX: very strong to violent
X-XII: intense to cataclysmic

Question 24

Liquefaction

Answer 24

Transformation of solid sediments into an unstable slurry by ground shaking