✅HAZARDS 3.1.5.3 - Volcanic Hazards

Question 1

What are the characteristics of shield volcanoes?

Answer 1

Gentle slopes, wide base
Frequent eruptions, basic lava
High speed and low viscosity basaltic lava
Non-violent eruptions

Question 2

Where are shield volcanoes found?

Answer 2

Constructive boundaries

Question 3

What are the characteristics of composite volcanoes?

Answer 3

Steep sides, cone shape
High with narrow base
Explosive eruptions
Layers of alternating ash and lava
Secondary/parasitic cones

Question 4

Where are composite volcanoes found?

Answer 4

Destructive boundaries

Question 5

What type of lava is rich in silica?

Answer 5

Slow flowing, viscous lava

Question 6

What is generally erupted from volcanoes at destructive margins?

Answer 6

Lava bombs, ash, dust

Question 7

What are primary effects?

Answer 7

Occur immediately along with the event, as a result of it

Question 8

What are secondary effects?

Answer 8

Direct consequence of the event but not immediate

Question 9

What are lava flows?

Answer 9

Streams of molten rock that pour or ooze from an erupting vent

Question 10

What are the two types of lava?

Answer 10

Pahoehoe and A’a

Question 11

What are the characteristics of pahoehoe lava?

Answer 11

Smooth, billowy surface, relatively thin

Question 12

What are the characteristics of A’a lava?

Answer 12

Rough, jagged surface and thick lava

Question 13

When lava solidifies, what does it form?

Answer 13

Igneous rock

Question 14

How are gases released from magma?

Answer 14

As it rises to the surface and pressure decreases, gases are given off from the liquid portion

Question 15

What are the main gases that lead to acid rain?

Answer 15

Carbon Dioxide and Sulphur Dioxide

Question 16

How can acid raid impact the environment?

Answer 16

Polluting waterways and soil, killing plants and trees, dissolving rock

Question 17

What is ash made up of?

Answer 17

Fragments of pulverised rock, minerals and volcanic glass

Question 18

How is ash formed?

Answer 18

When dissolved gases in magma expand and escape violently into the atmosphere in explosive eruptions

Question 19

What impacts can ash have?

Answer 19

It can disrupt aviation, critical infrastructure eg electric power supply, and impact health

Question 20

What is a pyroclastic flow?

Answer 20

A high density mix of hot lava blocks, pumice, ash and volcanic gas

Question 21

How fast can pyroclastic flows move?

Answer 21

700km/h

Question 22

How do pyroclastic flows form?

Answer 22

Form collapse of an eruption column, colapse of lava domes, or ‘boiling over’

Question 23

Why are pyroclastic flows considered the most dangerous of volcanic hazards?

Answer 23

Their speed makes them inescapable, and due to high temperatures, it is impossible to survive one

Question 24

What is a lahar?

Answer 24

A moving mass of soils or mud made fluid by rain or snow moving down a steep slope

Question 25

What are lahars triggered by?

Answer 25

Heavy rain or large amounts of ground water flowing through rocks as it causes the top layer of soil to be removed

Question 26

What are tephras?

Answer 26

Rock fragments and particles thrown into the air by volcanic eruptions

Question 27

How can tephra lead to a pyroclastic flow?

Answer 27

If the rock fragments are hot enough to fuse together

Question 28

How can tephra cause a temperature drop?

Answer 28

If they reflect light and heat from the sun while in the atmosphere

Question 29

What are nuees ardentes?

Answer 29

Clouds of gas ash and lava fragments ejected from the volcano

Question 30

What can form part of a nuees ardentes?

Answer 30

Pyroclastic flow

Question 31

What are the main volcanic gases?

Answer 31

Sulphur Dioxide, Carbon Dioxide, Hydrogen Flouride, Hydrogen Chloride, water vapour

Question 32

How can volcanic gases have an impact?

Answer 32

Sulphur dioxide can cause acid rain and global cooling, Carbon Dioxide can cause global warming and Flourides can be lethal to animals

Question 33

What attempted control was used on Mauna Loa in 1935?

Answer 33

Bombing lava tubes

Question 34

How was Eldfell's lava controlled on Heimay in 1973?

Answer 34

It was blasted with freezing sea water to cool it rapidly

Question 35

How was Mount Etna controlled in 1983?

Answer 35

Barriers of rock and ash were constructed to divert the lava

Question 36

How can volcanoes be monitored using geological observations?

Answer 36

A tiltmeter can be used to measure slope angle and bulges, and GPS to measure horizontal movements caused y expansion before an eruption

Question 37

How can volcanoes be monitored using seismic activity?

Answer 37

Seismographs measure earthquakes around a volcano as it prepares to erupt

Question 38

How can gas emissions be used to monitor volcanic activity?

Answer 38

As magma nears the surface and pressure decreases, gases escape. Sulphur dioxide is released as large amounts reach the surface, and concentrations can be measured

Question 39

What is the main disadvantage of monitoring volcanoes using seismic activity?

Answer 39

Most volcanoes are on plate boundaries, so it can be difficult to distinguish between volcanic earthquakes and routine tremors

Question 40

Magma type: Basaltic

Answer 40

Silica content: less than 50% (low viscosity/ very runny) Forms Basalt

Question 41

Magma Type: Andesitic

Answer 41

Silica: 50-70% (medium viscosity) Forms Granite

Question 42

Magma type: Rhyolitic

Answer 42

Silica: over 70% (high viscosity, not runny) Forms Granite

Question 43

Plinian/ Vesuvian Eruption Features, example

Answer 43

Mt. St. Helens 1980 High silica content (makes eruptions long, up to days, and less frequent) Rhyolitic Explosive Big plume Fast Lava

Question 44

Vulcanian Eruption Features

Answer 44

All types of magma Violent gas explosions Very viscous lava Clearing of a blocked vent, releases lots of ash Katmai, Alaska

Question 45

Icelandic/ Fissure Eruption Features

Answer 45

Lots of basaltic, from a fissure At constructive boundaries Such as Deccan Plateaux, India

Question 46

Hawaiian Eruption Features

Answer 46

Basaltic, Lava very runny. Can form shield volcanoes when solidifies Constructive Generally not explosive

Question 47

Strombolian Eruption Features

Answer 47

Basaltic magma But viscous lava due to silica Short bursts of thick lava Constructive Mt Etna (used to have vulcanian but change in pressure makes them strombolian now)

Question 48

Stratovolcano (composite) Volcano features

Answer 48

Made of layers of ash and andesitic lava Destructive margins Explosive

Question 49

Basic Shield Volcano

Answer 49

Gently sloping cone of basaltic Lava constructive margins Gentle Eruptions Mauna Loa, Hawaii

Question 50

Acid Dome Volcano

Answer 50

Steep- sided cone formed from Rhyolitic lava which can't travel far solidifies in vents making explosive unpredictable eruptions Destructive margins Mt Pelee

Question 51

Caldera volcano

Answer 51

Cauldron-shaped summit, can fill with water. E.g., Lake Nyos, Cameroon Formed by gases built up beneath blocked vent Big eruptions Destructive margins

Question 52

Fissure Volcano

Answer 52

Elongated spit Basaltic Lava Constructive margins, ocean ridges Creates lots of plateaus due to fast flowing lava solidifying Heimaey, Iceland

Question 53

Active Volcano definition

Answer 53

Has had an Eruption in the last 10,000 years Could still be dormant

Question 54

Extinct Volcano definition

Answer 54

Hasn't erupted in the last 10,000 years & isn't expected to in comparable time scale

Question 55

Features of Block lava flow

Answer 55

High acidity so doesn't flow well. Forms block shapes

Question 56

Features of A'a lava flows

Answer 56

More basaltic than block lava flows, so not as rough Slow Irregular

Question 57

Features of Pahoehoe lava flows

Answer 57

Lower viscosity, flows further Can form lava tubes/ caves due to far distance When cools down becomes more viscous, can become A'a

Question 58

Pillow Lava flows

Answer 58

Flows under water that have become solid rock, spherical shape.